Speedy's TB04 PRO Build Thread

[speedy_w_beans 4272]

Let's build a TB04 PRO! This is the first version, not the PRO II, so it has the short reversible suspension and JIS screws instead of the TRF418-style suspension and hex screws.

The big features for the TB04 include transverse motor orientation, LiPo-compatible chassis tub, transponder mount location molded into the tub, gear differentials, 6 degree caster front C-hubs, and short dampers. As a "PRO" kit and not a "R" or "TRF" kit, there are a few things missing from the hop ups such as double cardan joints, aluminum suspension blocks, and aluminum/carbon steering parts, but that's just fine. Most of the good stuff is included, and the price was attractive for what came with the kit.

The box...

The contents...

Since this kit's release Tamiya has issued an errata/update to the manual to change the sequence of assembly; this is supposed to help with some binding in the drivetrain some of the early customers experienced. The PRO II manual has this sequence in it, so I may bounce between the PRO and PRO II manuals as I work through the assembly steps.

Time to get started...

[speedy_w_beans 4272]

Bag A is for steps 1-5; the rear suspension arms, center and rear gearboxes, gear diffs, rear gearbox input shaft, and spur layshaft are all constructed here.

Step 1 is buildling the rear suspension arms. These are the same arms as used on base-level TB03, TA05V2, and FF03 kits. Carbon-reinforced versions of these arms are used on the TRF416, TRF417, and TB EVO V as well as some of the "R" spec kits. Tamiya includes metal suspension balls, which are a nice upgrade from the plastic parts normally clipped from the "A" parts tree. The blue aluminum ball connectors look nice, too!

Two comments right away. First, the droop screw holes are supposed to be drilled to half depth with a 3mm drill to increase the hole diameter. Half the hole should still be left undrilled to insure the droop screws engage the material. This isn't in the step itself; it's shown in the sidebar next to the assembly step, so it pays to read the whole page while assembling the car and not get too focused on just the instructions in the step box. Second, the spacers that go on each end of the hinge pin seem to be reversed from what is normal. Normally the thinner spacer goes towards the center of the chassis, and the longer spacer goes towards the end of the chassis. I can't decide if this is intentional or an error on the part of Tamiya...

Step 2 is installing the rear suspension arms to the chassis. The assembled arms mate with suspension blocks, and these blocks are secured to the chassis tub. I compared the TB04 chassis tub to a new TB03 chassis tub, and the mounting holes for the gear cases and suspension blocks are in the exact same locations. Given this, I swapped the hinge pin spacers to make the wheelbases the same since I plan to rotate bodies between the chassis.

[speedy_w_beans 4272]

Assembling the rear suspension was a little disappointing. Right away I discovered that my chassis was badly tweaked. Holding the rear of the chassis down and pressing the front showed a good few millimeters of movement; it basically was rocking back and forth on a diagonal line from front to rear. I had read about this issue on another forum and was hoping I wouldn't get stung by it as well, but no such luck. In the end I took the chassis to work with me, clamped it a flat metal table, and heated it with a heat gun for a half hour to try to make it conform to a flatter shape. I probably fixed half the tweak, and the little that remains doesn't resist flattening as much as it did before. I'm hoping installing the gearboxes and front/rear stiffeners will remove the remaining tweak, but we'll see.

Also, when installing the suspension blocks I discoverd the rear-rear 1D block doesn't quite fit easily in the tub. For the TB03 there's a 1mm spacer under each suspension block; for the TB04 there are no such spacers dictated in the instructions. I found I had to apply continuous pressure to the 1D block while inserting screws from below the chassis to overcome the ears at the rear edge of the chassis. The rear-front 1XA block didn't have this interference issue.

So, step 2 and I've reheated the chassis, pressed in the 1D block, and swapped the hinge pin spacers... Also, I installed 0.3 mm shims between the rear hinge pin spacers and the suspension balls to take most of the fore-aft slop out of the suspension arms.

Step 3 in the TB04 PRO manual is installing the rear gearbox and center gearbox to the chassis. The rear gearbox is the same part as what's used on the TB03; the center gearbox is new. It requires installing the motor mount plate before attaching it all to the chassis.

Here the errata/update kicks in, and it's reflected in the TB04 PRO II manual. Step 3 only installs the rear gearbox; the center gearbox is saved for step 6 in that manual. In my case I've decided to assemble the center gearbox and then lay both it and the rear gearbox aside until later. I'd rather assemble the gearboxes as separate modules and then worry about how they're attached to the chassis later.

The updated procedure requires thread locker for the screws holding the motor mount in place. I've used blue Permatex in the past and it works fine, but when I built my TRF801XT the kit included a small amount of anaerobic gel. The gel worked well for me, and I like how little mess it creates while handling fasteners. For hex screws it's really nice to have the fastener on the tip of the driver, and just lightly swab the threads through the gel before installation. Even though the stuff from the automotive store is less expensive, I just like how easy it is to handle the gel.

Here's the assembled center gearbox; note the cutout for the spur holder.

Here's the rear gearbox and the chassis screws for the rear and center gearboxes.

[speedy_w_beans 4272]

The gear diffs are built in step 4, and the rear gearbox pilot shaft and center gearbox main shaft are built in step 5. Plenty of parts below. Originally the kit included bushings to support the outdrives in the diff cases, but I swapped them for some 850 ball bearings.

Assembling the gear diff halves is pretty straightforward; only a little bit of care is required. An 850 ball bearing and long outdrive are inserted into the diff case first, then the O-ring is wetted with diff oil and slipped down the outdrive shaft until it seats in the case. Two shims are dropped on top of the O-ring, then a cross pin is installed, and finally the bevel gear drops on top of the cross pin. The same procedure happens with the diff case cap, only a shorter outdrive is installed. At this point it's worth mentioning the kit includes black O-rings; some people have experienced leaking in their diffs. There is a set of orange TRF O-rings available and some people have had good success with them. Some people have also used Associated green slime to help seal their diffs. I opted to use the kit black O-rings, skip the green slime, and see what happens. I can always replace the O-rings or use green slime later if I discover leaking.

The diff case cap gets a gasket installed in it, and the diff case itself gets the spider gears and cross shaft installed. I opted to use the plastic parts instead of the hopup steel gears and steel cross pins because a few people have reported good durability with 17.5T and 13.5T brushless systems; I'm not looking to run crazy power in this car, so again I'll just try the stock parts and see what happens.

While assembling the spider gears onto the cross shafts I noticed a bit of friction and discovered a small amount of flashing on the cross pins. I lightly scraped a hobby knife against all exposed flash three times and then reinstalled the gears; most of the friction was gone then. Installing the gears in the diff case and test fitting the whole assembly, the gears moved relatively smoothly with only a hint of notchiness. It was difficult to tell if the spider gears were meshing with the bevel gears properly because there is some lash between the bevel gears and the cross pins in the outdrives. I thought I would try adding 0.1mm shims to the spider gears to see if they would start binding at all, but they didn't. As a result, I installed 0.1mm shims for all spider gears in both diffs. The idea is to keep the mesh as tight as possible without binding, and also provide a smooth surface for the gears to rotate against (instead of letting the relatively rough plastic gears rotate against the relatively rough inner diff case directly). The little bit of notchiness in the spider gears should go away after running a few packs through the car, giving the gears a chance to bed some.

Per the instructions I filled the diff cases up to the cross pins. To help the oil settle faster I rotated the outdrive while holding the cross pin in place with a hex driver. This circulated the oil and brought out most of the air bubbles. it took a few cycles of spinning the gears, letting the oil settle, and then adding a drop or two more oil to get the right fill level in the diffs. For the rear diff I'm using Associated 1000 cst oil; for the front I'm using Associated 20,000 cst oil. The rear diff is set loose for stability; the front diff is stiffer to help with powering out of turns. I know some people run thicker oils, like 500,000 cst or even 1,000,000 cst to get a pseudo-spool effect for racing, but I didn't have any on hand. Plus, I found driving in the street even a moderately stiffer front diff provides a good amount of extra power while steering.

The diff halves went together nicely. The cap dropped into place and the gasket fitted in place with no issues. All holes lined up and there was no issue installing the screws. Tamiya supplies four M2x8 machine screws per diff to hold the halves together. Invest in a dedicated 1.5mm hex driver to install these screws; it's well worth it compared to using the small hex key included in the kit.

The ring gears are separate from the diff cases; on one hand this is great because worn gears can be replaced without opening the diff. On the other hand this adds some extra weight to the diff with extra screws and more plastic material. Again, four M2x8 machine screws hold the ring gears in place and a hex driver is beneficial to make installation go more smoothly. The shims and bearings install without drama, and I like how the bearings are just a little tight on the plastic to hold them in place. Right now I'm happy with how these went together, and I'm happy with how they feel.

[JeepnMike 150]

Finally! So far it looks like a fun build. That was also great advice getting a 1.5MM hex driver for the gear diff screws.. that is next to impossible with the hex wrench.

[speedy_w_beans 4272]

Tonight I managed to get through most of step 5 and part of step 6. These two steps involve building the rear gearbox pilot shaft, the center gearbox main shaft, and the center gearbox transmission shaft. I was expecting to spend a fair amount of time shimming out gaps between gears, bearings, and e-clips, and this kit certainly provided those challenges to work through.

The rear gearbox pilot shaft starts out pretty straightforward. The shaft itself has a regular 1050 ball bearing installed, a spacer from the "T" parts tree, a 1050 thin ball bearing (3mm thickness), 0.3mm of shims, a cross pin, bevel pinion gear, and e-clip.

Since I had the gear diffs completed, this was a good time to install the rear gear diff and the pilot shaft into the gearbox halves and check mesh. What I discovered was that the pilot shaft had about 0.3 mm of slop in it, and this allowed the bearings, shims, and bevel pinion to move around a fair amount. Not good. The goal is to get the teeth faces on both the pinion and the ring gear in perfect alignment, so this requires setting the pinion depth relative to a fixed gear case feature while not binding up the bearings. That reference feature is the ridge between the two bearings. In the end what I did was add an extra 0.2mm of shims (total of 0.5mm) between the thin bearing and cross pin, and I added a 0.1mm shim between the pilot shaft cup and the thicker bearing. This brought the two bearings closer together to engage the gear case ridge more tightly, and it set a definite depth of the pinion relative to the thin bearing. With the upper gear case half in position, I could then rotate the pilot shaft and assess the pinion/ring mesh. There was just a small amount of notchiness between the two gears, so I moved the 0.1mm shim from the ring gear side of the diff to the other side. Instead of the diff located with 0.2mm on one side and 0.1mm on the other side, my diff just has 0.3 mm on the side opposite the ring gear.

The center gearbox main shaft is easy to build as well. Install the cross pin for the bevel gear, the bevel gear, and the e-clip. Slide on two 0.1mm shims, a flanged 840 bearing, and two more 0.1mm shims. Slide on the spur holder, insert the cross pin, and attach the spur gear to the holder. Slide on a standard 840 bearing and install an e-clip. Easy peasy.

Just like the pilot shaft, this was a good time to assess the main shaft and see what sort of shimming or correction it might need. Installing it into the center gearbox by itself, I found the bevel gear could move 0.7-0.8mm between the e-clip and shims/flanged bearing -- not good. The flanged bearing wasn't guaranteed to be perfectly located on the motor mount because there were no shims between the regular 840 bearing and its e-clip; there's at least 0.3 mm of movement and it allows the spur holder to grind against the motor mount in the extreme case. The spur holder itself is a little loose on the shaft, so the attached spur actually rocks from side to side some. This is a criticism I've seen thrown at the Hong Nor/OFNA JL10e spur holder, but it's not a problem with the TB03, so this is somewhat of a letdown. The final issue I found was that the 840 bearings were clicking on every rotation and weren't smooth like the other bearings in the build (so far). Talk about a mess to deal with!

I figured it would be a good idea to build the transmission shaft from step 6 and install it with the main shaft in the center gearbox to get a total read on the situation. This shaft gets built with a 950 bearing, bevel gear, cross pin, two 0.1mm shims, an 1150 bearing, a cross pin, and a grub screw. The last cross pin and grub screw drive the cup on the rear gearbox pilot shaft, while the cup on the front of the transmission shaft drives the prop shaft running to the front gearbox.

In the errata/update and the latest TB04 PRO II manual the grub screw is supposed to be installed with thread locker so it doesn't back out on its own, allowing the pin to fall out and cause damage. While using thread locker and torquing down the screw is good, the cross pin could still slide out with the slightest of screw movement because there is no locating feature on it. The best thing to do in this case is use a rotary tool to grind a flat in the pin so the grub screw actually engages something; even if the screw backs out 1 degree, the flat prevents the pin from sliding out. This is good practice for older (pre-TRF417) CVD assemblies and every drivetrain cross pin on the TRF801 series; newer chassis use a circular retaining clip to prevent the pin from sliding out, and the grub screw is eliminated.

[speedy_w_beans 4272]

To get the perfect alignment between the bevel gears on the transmission shaft and the main shaft, I had to add shims on the transmission shaft. One extra 0.1mm shim was installed between the cross pin and 1150 bearing on the transmission shaft for a total of 0.3mm of shims. For me this aligned the gear teeth faces almost perfectly. To move the cross pin deeper into the bevel gear and prevent the transmission shaft from moving back and forth, I added 0.6mm of shims between the transmission drive cup and the 950 bearing.

For the main shaft I started with the bevel gear and worked my way across it. With the flanged bearing located against the motor mount properly, the bevel gear is actually located very well with just the specified shims in the instructions. I didn't care for the dead space between the face of the gear and the e-clip, so I installed 0.8mm of shims to take out all the slop. On the other side of the flanged bearing I removed everything and worked on the spur holder first. I tried a thin strip of Scotch tape to take up the gap between the shaft and the holder's bore, but the tape was too thick. Then I discovered a tapped hole in the spur holder and realized a 3mm grub screw could be installed to take out all the slop. The instructions don't say anything about installing a grub screw, but the feature is there to use. I found a standard 3mm grub screw was a little too long; it protruded out the side of the spur holder and I had to grind the tip of it off with a rotary tool to make it seat deeper in the holder. Using both the cross pin and the short grub screw worked perfectly; the spur is perfectly rigid on the shaft now, and there's almost no additional circular runout at the gear teeth. The last item I needed to address was shimming between the regular 840 bearing and the e-clip, but I don't have any 4mm shims -- just 3mm and 5mm. So, I'm going to place an order for some 840 bearings and 4mm shims, and finish this gearbox later.

Here's a quick look at the center and rear gearboxes on the chassis tub. They're not fastened to the tub at this time; I just wanted to see the drivetrain parts all together and feel how they work together. Everything seems smooth and slop-free.

I'll probably move forward with more suspension, front gearbox, steering, uprights, shocks, etc. as subassemblies, and then combine the subassemblies later -- I want to replace the bearings on the main shaft and finish shimming there before bolting in the gearboxes, chassis stiffeners, and damper stays. The bearings and 4mm shims are a small setback, but TQ and Avid have always been good shipping little parts like these.

[JeepnMike 150]

That is a lot of shimming! Question.. Are any of the gears metal?

[speedy_w_beans 4272]

That is a lot of shimming! Question.. Are any of the gears metal?

Absolutely. The pinion gear is metal!

I'm sure that's not the answer you're looking for. The standard kit uses plastic for all gears except the pinion (of course). There are options available for metal diff gears and cross shafts, and some people have used DB02 metal bevel gears in the center gearbox.

There are also options for a ball diff with aluminum outdrives and a front one-way. The one-way can be locked with cross pins to act like a spool as well. Some people have used TB03 ball diffs, one-ways, and spools to save some weight over the TB04 gear diffs.

I'm just building this stock at the moment to experience it as designed. All the fussing over details is a quest to get the best result possible out of the stock kit.

[Backlash 481]

Ummmmm... How do you put a motor in it?

The pinion gear needs to be behind the mounting face of the motor??

[Cplus 94]

Couple of comments.

If you installed the gasket dry, it will definitely leak. You need to add some slime here or at the very least some of the thickest diff oil you have.

Using a 850 bearing instead of the bushing is not a good move. The bushing is designed to sit flush with the o ring and provide mild pressure to help it seal. The bearing won't do that as you are relying on the bearing seal sitting against the oring which it can't to the sme tolerance as the flush bushing.

The plastic spacers on the arms are best replaced with alloy ones. They are very cheap. These are used to change the wheelbase as you've said. It's a tunjng tool. I guess if just bashing you won't notice much.

Just a tid bit, most TRF cars call for 3mm inboard as standard FYI.

[Cplus 94]

Ummmmm... How do you put a motor in it?The pinion gear needs to be behind the mounting face of the motor??

There is another part to go on yet. He motor doesn't mount direct to that alloy plate.

[speedy_w_beans 4272]

Couple of comments.

If you installed the gasket dry, it will definitely leak. You need to add some slime here or at the very least some of the thickest diff oil you have.

Using a 850 bearing instead of the bushing is not a good move. The bushing is designed to sit flush with the o ring and provide mild pressure to help it seal. The bearing won't do that as you are relying on the bearing seal sitting against the oring which it can't to the sme tolerance as the flush bushing.

The plastic spacers on the arms are best replaced with alloy ones. They are very cheap. These are used to change the wheelbase as you've said. It's a tunjng tool. I guess if just bashing you won't notice much.

Just a tid bit, most TRF cars call for 3mm inboard as standard FYI.

Cplus, thanks for the comments. I think you have some valid points.

My diffs have been sitting on the desk for the past few days and I'm seeing just a touch of seeping around the gasket. I can't decide if this is some oil that was on the gasket squeezed out during assembly, or if the diffs are actively leaking there. I'll keep an eye on it some more. I do have some spare gaskets and I can always add some sealant if necessary.

If you look at the picture of the diff parts in post #4, you can see how the O-rings seat against the diff case plastic, not the bushings. Substituting bearings for bushings should have no effect as I measured the thickness of both, and they were identical. This means the outdrive cup is in the same position for either option relative to the diff case, and that results in the same cross pin position on top of the shim stack and the O-ring. There is a plastic wall between the bushing/bearing and the O-ring, so there's no dependency on the bushing edge or the bearing shield. The only thing I could possibly see happening is the inner race of the bearing shifting inward relative to the outer race, and that would relieve some of the pressure on the O-ring and might allow leaking. The same thing will happen as the bushing starts to wear. Right now the seeping I see is only around the main gasket. I'll keep an eye on this as well.

I agree the alloy spacers are nice; they wear longer and aren't expensive. I have a few packs of them and have them earmarked for another build in the future. I'll use a few of them when the plastic ones start to wear on this car.

Thanks again.

[speedy_w_beans 4272]

This past Saturday I built some more of the TB04 PRO kit and took pictures, but I was feeling kind of lazy with respect to posting in the build thread... Tonight's posts are mainly to catch up and take stock of where we're at.

Bag B is for steps 6-14; these steps include the rear and center gearboxes, rear stiffeners, rear suspension, front suspension arms, and front gearbox.

I had already broken into bag B earlier to build the transmission shaft and check mesh in the center gearbox, so step 6 was partially complete. I still don't have the gearboxes mounted to the chassis, nor do I have the gearbox covers installed, and that's just fine as I'll explain later.

Step 7 installs the center gearbox cover; I'm skipping that for now as I still need to replace the 840 bearings and do a little more shimming.

Step 8 installs the rear stiffeners to the rear gearbox, but there's no point in doing that until I close the rear gearbox and attach it to the chassis tub. I'm not closing the rear gearbox until I rebuild the diff; Cplus called it and it looks like I'll be rebuilding the diff with better gasket sealing. The O-rings in the diffs are still ok, but the gaskets are no bueno right now. I have a picture of this later.

Step 9 is building the rear uprights and turnbuckles.

No suprises here. Everything goes together per the instructions easily. There is a small hole at the bottom of the upright that needs to be drilled with a 2.5mm drill for a grub screw; later this grub screw will capture the hinge pin that goes through the upright. The instructions for the turnbuckles actually call for lengths to the nearest 0.1mm, so calipers are needed if you want to set the lengths to kit spec properly.

Step 10 is finishing the rear suspension; this involves attaching the uprights to the rear suspension arms with the hinge pins, spacers, and grub screws; installing the dogbones; and attaching the turnbuckles. In the TB04 PRO II kit the dogbones are replaced with lightweight swing shafts.

[speedy_w_beans 4272]

In the previous step black O-rings are installed in the axle stubs; in this step red urethane sponges are installed in the outdrive cups. The O-rings and sponges prevent the dogbones from moving from side to side.

This is just a test fit of the rear end to see how it is coming together.

Step 11 is installing the front-rear 1A suspension block. This is the block immediately in front of the steering rack. The instructions call for removing some material from the corners of the block facing the steering rack; this is for clearance with the steering turnbuckles. I used a file on each end of the block.

Front-rear block installed...

Step 12 is building the front suspension arms.

[speedy_w_beans 4272]

Like the rear suspension arms, the droop screw holes are drilled to half depth with a 3mm drill. The droop screws are set to 2mm protruding under the arms, both front and rear. The spacers are set to their normal positions. The 1A blocks do not accept suspension balls; the hinge pins fit in these blocks directly.

Step 13 installs the front-front 1A suspension block, capturing the front suspension arms.

Step 14 installs the front lower gearbox to the chassis tub; I'm skipping this step for now.

Bag C is for steps 15-21, including the front steering rack, pilot shaft/gearbox, stiffener, C-hubs/knuckles/CVD axles, turnbuckles, and center prop shaft.

Step 15 is building the steering rack. I got a little excited and started building it, then realized I should probably get a picture of the parts before it all goes together.

[speedy_w_beans 4272]

This steering rack is an improvement over the TB03 steering rack for two big reasons. The first reason is the bridge is designed for ball bearings; these are much more precise than the flange tubes a base TB03 uses. The second reason is the tie rods connect to the center steering bridge instead of the bellcranks; this reduces the number of tolerances from knuckle to knuckle and tightens the steering in general. I believe the orientation of the ball connectors provides more opportunity for tuning Ackerman as well. The TB03 steering can be improved by drilling the plastic steering bridge to accept 630 ball bearings instead of flange tubes, but with the TB04 the bearings are now standard. Overall the TB04 is a much better setup.

Step 16 is installing the steering in the chassis tub. This involves two hinge pins and four 630 ball bearings.

Step 17 is building the pilot shaft for the front gearbox.

[speedy_w_beans 4272]

I built the pilot shaft and installed it in the front gearbox to test the mesh with the front diff. In the end I shimmed the pilot shaft the same way as the rear pilot shaft -- one extra 0.1mm shim between the drive cup and the thick bearing, and two extra 0.1mm shims between the thin bearing and the cross pin. The front diff didn't require moving its shims; the gear mesh was good already (versus the rear diff that required moving one of the 0.1mm shims to the other side).

In theory the front gearbox cover should be installed, but I'm waiting for now.

Step 18 is installing the front chassis stiffener, but that's waiting until all gearboxes are sealed and installed. For now here's a picture of the complete drivetrain resting on top of the chassis tub.

A few days have passed since I worked on this chassis, and I left the gear differentials sitting in their gearboxes to see if the seeping I had witnessed earlier was limited, or if the diffs were actually leaking. When I checked them this morning I found the bottom of both diffs had a sizeable amount of oil near the gasket. I was expecting to find a drop of oil in each gearbox when I came home from work today, but it looks like the oil has dispersed across the plastic of the diff case itself. Here you can see at least one diff looks a little wet.

So, here's the list of items to be resolved at this time:

- Center gearbox: Replace 840 bearings and shim one end of the main shaft. Bearings and shims are in the mail and coming from TQ.

- Rear gearbox: Rebuild the gear diff to seal the gasket better. I have extra gear diff cases and gaskets on hand already. I'm going to use a little bit of black silicone RTV to seal the diff better and stay with 1k diff oil.

- Front gearbox: Rebuild the gear diff to seal the gasket better. Same as the rear diff, I have extra cases and gaskets on hand and will use black silicone RTV. I did place an order for Associated 60k and 100k diff oil to replace the 20k I used earlier; these oils are in the mail and should arrive from Tower tomorrow.

- Rear suspension spacers: I'm dithering and thinking about moving the hinge pin spacers back to the positions stated in the instructions. There's probably a good reason why those positions are recommended as a starting point.

- Gear lubrication: I need to lube all the plastic gears before closing the gear cases; I have some chain lube that applies wet and dries leaving a Teflon coating behind.

- Chassis tweak: This is a TBD still; this needs to be assessed again after the chassis stiffeners are installed.

[speedy_w_beans 4272]

The short answer is I'm setting everything by eyeball and by feel. I use a flashlight and a magnifying glass to inspect the alignment of tooth toe on both gears visually, and I assemble the gearboxes and check backlash by feel. Sometimes it takes a few assembly/disassembly/shim cycles to get good tooth alignment while minimizing the backlash. This is not something explained in the instruction manual, but it has to be done to get the best performance and wear life out of the gears possible.

The long answer is I'm using some guiding principles and iteratively checking alignment and mesh until it only takes a single shim to be on the edge between free running and just slightly notchy/binding.

The principles are found on the first 2-3 pages of this article on setting bevel gear mesh, "How to Design and Install Bevel Gears for Optimum Performance: Lessons Learned."

http://www.geartechnology.com/issues/0613x/bevel-gear-installation.pdf

The two key issues are alignment and backlash. Because these are bevel gears both conditions have to be considered at the same time while shimming. Because the gearbox covers are already designed and don't have any offset or angle adjustments, the only parameters we have to work with are pinion position/preload and ring gear position/preload. Since the pinion gear has a higher angle/longer cone associated with it, it gets shimmed first because final backlash adjustments with the ring gear have less of an effect on tooth alignment. I need to check tooth alignment visually with the gearbox covers open, but I need to feel the backlash with the covers closed so the bearings are fully captured and maintain position.

So while building the front and rear TB04 gearboxes I did the following:

- Build the pilot shafts and gear diffs per instructions.

- Install these assemblies in the lower gearbox halves.

- Visually inspect tooth toe alignment between the pinion and ring gears.

- Shim between the pinion gear and thin bearing to achieve alignment, assuming this equates to the pinion's cone apex aligning with the ring gear's rotational axis.

- Shim between the pilot shaft's drive cup and the thick bearing to remove most of the remaining axial play; this locates the bearings against the gearbox features and prevents the pinion from moving axially much.

- Confirm the diff assembly doesn't have any axial play.

- Install the upper gearbox half to capture all bearings firmly.

- Hold the outdrives and gearbox firmly and rotate the pilot shaft back and forth to assess backlash. There's some backlash between the cross pin and the pinion gear in addition to the backlash between the pinion gear and ring gear.

- Also hold the gearbox firmly and rotate the pilot shaft while letting the outdrives rotate freely. This is done for several revolutions of both gears to assess if there is any notchiness or binding.

- Remove the upper gearbox half.

- If there is no notchiness/binding, move one shim from one side of the gear diff to the other side of the gear diff to bring the ring gear closer to the pinion. If there is a little bit of notchiness/binding, move one shim from the ring gear side to the other side to space the ring gear away from the pinion.

- Check tooth toe alignment again visually.

- Reassemble and check backlash again by feel.

- If all good, done. If there are alignment issues or binding/lash issues again, adjust some more and test again.

With the center gearbox I didn't give any priority to either main shaft bevel gear or the transmission shaft bevel gear because both gears have the same angle. I installed those shafts and visually inspected tooth alignment, and then shimmed the gear that seemed farthest from correct position first. The same cycle of visual inspection with the gearbox cover removed and checking backlash with the gearbox cover installed applies.

While doing all this shimming I was also considering if there would be any interference between the transmission shaft and the rear pilot shaft, and I was considering how the center prop shaft is spring loaded in the front pilot shaft. This is why I added some shims between the transmission shaft's drive cup and 950 bearing and pulled the cross pin a little deeper into the bevel gear's engagement feature. So, with the TB04 each gearbox has to be right, but it's also good to be mindful of the connections between the gearboxes.

That's about the best I could do with what I know and what I have to work with... If the gearboxes still grenade then at least I have a reference point for how it all went together and can make adjustments to procedure from there...

[speedy_w_beans 4272]

I worked on the front and rear gear diffs tonight, transplanting the moving parts into new cases with new gaskets, and using black RTV to help the paper gaskets do their jobs.

I'm hoping my parts for the center gearbox arrive tomorrow, but package tracking isn't looking good at the moment. If not tomorrow, maybe the parts will arrive Saturday. In the meantime I worked on steps 19-26.

Step 19 is building the front C-hubs, knuckles, CVDs, and turnbuckles.

The CVDs are nice because they use clips to hold the cross pins in place instead of grub screws. This saves me from having to grind flats in the cross pins, and it makes future maintenance easier. The turnbuckles went together as expected; no surprises there. The C-hubs needed 2.5mm holes drilled in them to accept grub screws; these will capture hinge pins later when attaching the assemblies to the front lower suspension arms. This is similar to how the rear uprights capture the hinge pins. The only modification I made to the assembly is I added a 0.3mm shim below each upper flange tube and above each steering knuckle on each side. Without the 0.3mm shims the knuckles would float up and down within the bounds of the C-hubs; this translates into a little bit of undamped motion. The 0.3mm shims took up most of the slack without binding the steering.

Step 20 is attaching the front C-hub assemblies to the front lower suspension arms. All it takes are a few hinge pins and grub screws.

[speedy_w_beans 4272]

Attached...

Step 21 is installing the center prop shaft, but that won't be done until I finish the gearboxes and attach them to the chassis. This step is easy enough; the prop shaft is spring loaded and just pops into place.

Bag D is for building the dampers and damper stays, and mounting the motor to the center gearbox.

Steps 22, 23, and 24 show how to build the dampers. One modification I made is I lightly coated the spring retainer O-rings with damper oil to make them move more smoothly over the threaded bodies; this isn't in the instructions, but it is in the instructions for several off-road models (DB01R, TRF801XT). The other modification is I added a 0.1mm shim under each damper piston to remove all the float between the two e-clips on each damper shaft. This reduces the amount of undamped motion each time the suspension moves.

[speedy_w_beans 4272]

Step 25 is building the rear damper stay and attaching the rear dampers. I'm only going so far as to build the stay now; the dampers will go on later. The instructions show sealing the edges of the carbon fiber stays with CA glue, but since these parts aren't close to the ground I'm not going to worry about it. I'd sand and seal the carbon fiber if it was a bottom deck, but top decks, damper stays, and bumper covers don't see the same abrasion as the lower deck. One modification I made to the instructions is I added washers under the heads of the damper post screws; this is to minimize deforming the positioning holes.

Step 26 is building the front damper stay and attaching the front dampers. All the same comments as step 25 apply to this step as well.

Once the center gearbox is updated and all bevel gears are lubricated, major subassemblies will start coming together in preparation for Bag E.

[ChrisRx718 4470]

Looks....expensive!

Love all the blue bits.

[speedy_w_beans 4272]

Time to wrap this up... A small envelope with bearings and shims showed up yesterday, so I went to work finishing the chassis.

New 840 bearings and three 0.3mm shims finished the center gearbox.

I lubed all the gears with PTFE; it goes on wet and dries to a super-slippery finish.

Hallelujah, the gearboxes are now 100% built!

Center gearbox attached to the chassis. No issues experienced.

[speedy_w_beans 4272]

Front and rear gearboxes attached. I experienced a little bit of binding between the center and rear gearboxes, but installing the chassis stiffeners seemed to fix it.

Front and rear stiffeners installed.

Rear dogbones, axles, turnbuckles, damper stay, and dampers installed.

Front CVDs, turnbuckles, damper stay, and dampers installed.