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Speedy's CR-01 Build Thread

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Metal. Lots of it. When I see a Tamiya kit with lots of metal in it, like a SRB, High-Lift, Bruiser, TXT-1, or TRF801XT, I get this taste in my mouth and memories of the Erector Set I had as a kid come back to me. I was 10, maybe 11 years old at the time, and I had a daily paper route serving about 90-100 customers every morning. One of the older ladies, I think a widow, lived by herself as her children had moved out and started their own families. As she got to know me better and learned about my interests in all things mechanical and electrical, she offered me an old Erector Set that her kids had played with a long time ago. I'm pretty certain my parents talked with her before allowing me to accept it, but it wasn't long before I had it and was really exploring it. This isn't a photo of my actual set; it's an image I found with Google from another site, but it's accurate in that my set was truly an AC Gilbert 8-1/2 Ferris Wheel set with red metal box, AC motor, pulleys, plates, etc.

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In fact, I still have this set today. It's in my son's closet in his room. It's still intact except for a few girders my dad has borrowed for a bridge in his AC Gilbert American Flyer train set. He has his trains, I have my RC cars...

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I have so many great memories playing with this stuff. The feel of the metal in my hands, using a screwdriver and a wrench to assemble plates and girders, the smell of the electric motors as they ran, the light on the front of the engine and the smoke coming out of the smokestack... It really captured my imagination and fueled my interest in engineering.

Fast forward 30+ years...

About two years ago I bought a CR-01 Unimog kit and stashed it in my closet for a future build. The metal chassis rails, lifted ride height, cantilever damper setup, and bead lock wheels really grabbed my attention. It didn't hurt that it was a Unimog, either. In real life these are amazing vehicles with portal axles, torque tube / coil spring suspension, lots of gear reduction, PTOs for accessories, etc. They are truly multipurpose vehicles used for agriculture, fire departments, moving railroad cars, plowing, transporting, etc. Browsing the instruction manual, I was really excited to see that almost the entire vehicle is assembled with screws and nuts just like an Erector Set. This really encourages tinkering and modifying after building it, as there aren't many screw holes in plastic to wear out and strip. It's that combination of metal content, Erector-like construction, subject vehicle, and unique Tamiya design that sucked me in.

Read more about the Unimog design here: http://www.unimogcentre.com/unimogprinc.html

The CR-01 doesn't fit into a standard RC vehicle class that easily. One could look at it as a crawler, something you use to climb rocks, but it's not quite at the level of a true competition crawler. The standard wheelbase is kind of short. The center of gravity is maybe a little high. The prop shaft drivetain might be at a disadvantage compared to MOA (motor on axle) designs. What about considering it a scaler, something that looks authentic and is used to drive trails? The suspension isn't necessarily accurate to real 1:1 vehicles with the cantilever damper setup, four link arrangement, and lack of panhard rod. Nothing stops anyone from making a CR-01 into one of these vehicles, but out of the box it tends to be more of a lifted/aggressively modifed scaler with some degree of crawling capability.

A few factors are causing me to dig this kit out of the closet and do a build thread on it.

- I bumped into some really cool CNC machined aluminum wheels recently: http://www.gearheadrc.com/22wheels.htm

- One of my coworkers asked for advice about crawlers and scalers for his son: http://www.tamiyaclub.com/forum/index.php?showtopic=72254

- Tamiya is releasing a new kit, the 58592 Rock Crawler Truck. I'm very happy to see Tamiya is continuing to offer this platform: http://www.tamiyausa.com/items/radio-control-kits-30/trucks-36500/rc-rock-crawler-truck-58592

- I couldn't find any CR-01 build threads on Tamiyaclub.

It feels like the right time to dig into this. With it being winter, and with my workload temporarily reduced at the office, I have a window of opportunity to enjoy some wrenching and dwell on some old memories. So subscribe to the thread, sit back, and enjoy the build pics!

Here's the CR-01 Unimog kit box. The box actually has an illustration on it, not a photograph, and I like it that way very much. In fact, I really do like kit box art that is drawn instead of photographed. When someone takes the time to actually create the box art, it tends to convey extra meaning. It's a minds-eye perspective of what the model represents. When I look at the box art I see these really cool bead lock wheels, big tires, metal chassis rails, cantilever dampers, bright orange Unimog body and chrome accents. It just looks like it means business to me.

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The box weighs a little more than the average kit. Opening it up shows this:

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Unpacking it all shows the following kit contents. Going from left to right, top to bottom:

- Chassis rails

- Box of metal bags and small plastic parts

- Tires

- Gearbox and lower deck parts

- Suspension parts and side plates

- Body set

- Axle parts, servo beds, and more suspension parts

- Battery tray and mechanism decks

- Manual, stickers, and antenna tube

- Bead lock rings and wheels

- Linkage connectors and steering knuckles

- Bumper and body post parts

- More linkage connectors and steering knuckles

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Have I been duped? Are only the chassis rails metal? Fortunately the metal parts bags do have some good content in them.

- Bag A has a large number of ball bearings, metal pinion/ring/diff gears, metal drive shafts, torsion springs, machine screw hardware, lock nuts, and ball connectors

- Bag B has threaded rods, ball connectors, machine screws, lock nuts, and servo saver springs

- Bag C has springs, suspension links, damper parts, and damper oil

- Bag D has a motor plate, large bearings, shims, shafts, cross pins, body clips, machine screws, lock nuts, servo tape, and wire ties

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Getting my work space ready...

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I have to be honest up front... This won't be a box stock build. I've been accumulating hop ups over time planning what I want to do with this kit. Here's a teaser of some of the things I have planned...

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More to come soon...

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I'm looking forward to this as well! On a side note Speedy, I'm originally from N.C. myself.

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davela72, I moved to NC from PA! I guess the states just traded headcount! LOL.

All right, time to start this build...

Step 1 involves building the cantilevers and upper spring perches. The arms and the perches are normally plastic (parts C3, C5, and C6), but for this step I'm using the following:

- Kit shafts, e-clips, and bearings.

- GPM spring perches. I prefer these over the 3Racing parts because the 3Racing parts require screwing the springs into them, whereas the GPM parts still have the side clip like the original plastic parts.

- 3Racing linkage arms. I like these more than the GPM parts because there is an extra hole in the fat arms for an intermediate setting.

- Kit ball connectors.

- RC Screwz stainless button head screws. Almost all of the steel Philips screws will be replaced with stainless hex hardware in this build.

Parts laid out...

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Finished assemblies...

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Step 2 has the completed spring perches as well as the side chassis plates mounted to the main metal chassis rails. In this step I replaced the kit parts with the following:

- The main chassis rails are replaced with Tamiya 54049 Luster Silver Ladder Frame parts. These are extra shiny compared ot the kit ladder frame rails.

- The plastic side frames, C7, are replaced with Tamiya 54087 Aluminum Side Frames. This hopup includes spacers to set the position of the side frames correctly relative to the original parts. I replaced the hopup fasteners with stainless hardware again (is that a hopup for the hopup??).

- All other hardware replaced with stainless hex hardware.

Parts...

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Built up...

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Step 3 is for building the battery tray and mechanism deck. The battery tray and battery strap pins are kit stock, but the rear mechanism deck parts (E1 and E3) have been replaced with Tamiya 54111 Carbon Mechanism Deck. Again, the hopup fasteners were replaced with stainless hex fasteners.

Parts...

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Finished subassembly...

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Step 4 combines the chassis sides and the center battery tray/mechanism deck into one larger assembly. The stabilizer springs are installed between the cantilever shafts.

Parts...

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Built...

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That's about all I'm going to do tonight. So far everything is going together well. My only complaint at the moment is the cantilever arms are just a tiny bit loose on the shafts; I tried both 3Racing and GPM parts and they were about the same. I did not try the plastic parts. This is something I might look into later.

Tomorrow I'll start working on the axles...

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The plastic arms also have some play. You'll have to run a tiny zip tie between the two arms to cinch them up or you'll lose a lot of effective suspension movement there. What it will look like is the body bobbing around when you traverse rough terrain. Once I zipped mine together the cantilevers worked so much better and the truck had better composure without the body/chassis swaying

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Although I don't particularly like the look of the finished CR-01, it does look like an interesting chassis to build with lots of adjustability* built in.

(* I'm not completely sure that's actually a word)

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Speedy, small world, lol! The build is looking great so far.....I see new wheels, are you using different tires with this?

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I'll start with the stock tires and see how they fit and run for now...

Last night I went back to the cantilevers for a little while and tried a few things to reduce the slop. I'm still thinking about this issue.

Continuing with the axles...

Step 5 is preparing the axle shafts for installation in the axle housings. Tamiya has 54108 Reinforced Drive Shaft & Diff Lock sets available, but these only make sense if you plan to run the diffs locked on extra challenging terrain. The hopup shafts have two flats ground into the ends such that they mate only with the diff locks; these cannot be used with the splined gears in the kit stock diffs. In this step all the kit stock parts are being used.

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Finished shafts...

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Step 6 is building the differentials. Since I'm using the kit axle shafts, I'm also building the differentials stock. Parts...

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Everything greased... I'm using the same Mobil 1 synthetic grease I used in my TRF801XT build. All the parts are metal, so there shouldn't be any issues with this lube. Note the diffs are not sealed with O-rings or gaskets, so actual grease is needed and not silicone oil.

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Finished diffs...

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Step 7 is installing the diffs and axle shafts into the axle housings. Parts B1 and B2, the plastic axle housings, have been replaced with parts from 3Racing. The fit between the main housing and the diff cover is almost perfect; there's virtually no slop between these parts.

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Assembly is not quite as straightforward as using the plastic parts. Pinion installation is the same, but installing the diffs and axle shafts requires undoing the inner E-clips, bearings, and shims so the shafts can be installed in the main housing. These go in part of the way, then the bearings and shims are installed, then the diffs are dropped into place. The shafts are pushed into the diffs, then the inner E-clips are reinstalled. With the plastic parts everything drops into one half housing all at the same time. 3Racing includes extra shims for the shorter shaft to get the pinion and ring gear mesh set correctly.

Installed parts... Note the small holes in front of the ring gears. It's possible to install a screw pin in these holes and lock the diffs. This is accessible from outside the axle housings as there is a larger hole sealed with a grub screw to provide access.

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Grease applied, and finished assemblies... The grub screw for providing access to the diff lock pins doesn't bottom out on anything, so it's possible to install the grub screw too far. Thread lock doesn't work well unless the screw is tight. My solution was to stretch a parts bag over the grub screw, install it, then peel back the extra bag material. This is like wrapping tape on a pipe joint.

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More to come soon...

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I do like those axle housings :wub: - this is a super build with some really choice metal hop-ups.

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Those axles are killer, nicely done!

BTW, here is the common cantilever fix on mine. If you're not going for shelf status its the easiest fix and virtually invisible on the stock black plastic arms. Your alloy arms would be a different story though. You could epoxy the arms to the hub to eliminate the play but that's pretty permanent.

DSC_4895_zps3d2a7ad1.jpg

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Wow, so much beauty...I really wanted one of these but went with an SCX10 cause it was cheaper :D

Keep the pictures coming dude!

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Really like the look of these chassis. Look fantastic when finished and as you say the box art is a plus point.

Ah I recognise that Mobil 1 grease, we use it at work all the time although we get it in 50 gallon drums for all greasing purposes on the buses.

James

:)

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You are doing a superb job on the writing and photography! You're right, we haven't seen much CR01 build love on here.

Love the hop ups you've chosen, and can't wait to see how this turns out.

Make sure and give the body as much love as the chassis! I'll be watching!
Cheers,

Skottoman

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Thanks guys for all the comments!

Skottoman -- Don't worry, I've been giving the body a lot of thought and plan to push myself to do something more involved. :)

The big accomplishment for the day was stripping and polishing some non-silver aluminum parts so they have a bright natural finish. I need these for the next assembly steps as well as later in the manual. Most of what I have is "correct" to start, but a few parts I couldn't avoid buying in color and just resigned myself to having to strip and polish them. I found some tutorials and information about how to do this on the web.

Here are the parts in their as-shipped state...

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Stripping the parts down to the base aluminum involves dunking them in Greased Lightning, a concentrated cleaner found in some home improvement stores. There are likely other cleaners with the same active chemicals; this was recommended and convenient to get for me. Once the parts are in the cleaner, agitating the container, moving the parts around, and lightly scrubbing them with a toothbrush causes the color dye to leach out of the part. The liquid turns the color of the dye first, then as the cleaner makes its way to the base metal the liquid turns cloudy. A good time to dump and refill is when almost all of the color has come out of the parts, but just a tiny bit is left. The second fill is used to get the rest of the color out. Then the final fill is used to get all the way to the base metal, and that when the cleaner gets cloudy. I found it usually took 3 fills/dumps to completely eliminate the dye and get to the metal. The overall process for a batch of parts probably takes about 10-20 minutes; although the C-hubs gave up their dye within the first minute.

This reminds me of a good practice I learned in chemistry class in university; it has some application to stripping parts. Basically, to conserve a cleaning rinse like deionized water, you use multiple small rinses instead of one large rinse. The math actually makes sense for this. Pretend you have 1 mL of contamination in a beaker and you want to reduce its concentration by 1000x. One approach would be to fill the beaker with 999 mL of deionized water and get a 1 part in 1000 mixture of contamination to water. Then you pour the beaker out, and the remaining residue has that concentration.

The other approach they taught us, and the more economical one, is to use three 9 mL rinses instead. Start with 1 mL of contamination. Add 9 mL. There's a 1 part in 10 contamination. Dump the beaker. Assume 1 mL left in the beaker again. Add another 9 mL, but now what you have is a 1/10 contamination mixed with 9 mL of water, so the contamination is now 1 part in 100. Dump the beaker. Assume 1 mL left in the beaker for the last time. Add another 9 mL, but with a 1/100 contamination mixed with another 9 mL of water, you now have contamination that is 1 part in 1000.

Instead of using 999 mL of deionized water, we only used 27 mL. When you're buying deionized water for a chemistry lab, it saves money.

Or, when you are stripping anodized parts, using a small container and dumping/refilling multiple times is more cost effective than stripping parts in a large bucket filled with a gallon of cleaner. That's really the point of the story.

Here are the parts stripped to the metal. They look pretty flat.

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Now that the parts are in a natural state, the last step is to polish and protect the aluminum. The same set of instructions recommended Mother's Mag & Aluminum Polish, again something easy to get at the local auto parts store. It was plenty easy to strip the parts, but it took a fair amount of rubbing and buffing to get a shiny finish. I think I invested about 2 hours stripping 5 batches of parts with multiple refills, and another 8-9 hours polishing each part by hand.

Buy your hopups in the right color to start!!!! In my case I wanted these specific parts, but they only come in blue, so I had to accept a diversion from the main build and prep them... Here is the end result.

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More to come...

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Made some more progress on the axles today...

Step 8 is attaching suspension mounts to the axles. D1, D8, and D9 are replaced with 3Racing parts. The nuts normally needed for the plastic parts aren't needed as the aluminum parts are already tapped. Kit ball connectors and stainless hardware are used.

Parts laid out...

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Mounts installed. Some of these parts come from the dunk and polish process from above; they seem to match up with the rest of the parts pretty well...

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Step 9 adds the lower spring perches to the suspension mounts. B4 and B5 parts are replaced with aluminum GPM parts.

Parts...

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Assembled...

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Steps 10 and 11 install the axles, steering knuckles (D10), and C-hubs (J1/J2) to the axle housings. All plastic is replaced with stripped and polished 3Racing aluminum parts, the king pins are upgraded to Tamiya 54102 CR-01 Reinforced King Pins, and the wheel axles and bearings are kit stock.

Parts...

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The C-hubs have different letter designations. J1 is A, and J2 is B. If the front axle is considered the reference assembly, then it has A on the right side and B on the left side. This sets 15 degrees of caster. The rear axle has the C-hubs swapped with A on the left side and B on the right side. This sets 25 degrees of caster for the rear axle. The reason why the caster is not symmetrical is because the slots cut into the hubs are not symmetrical; this will become clearer later when the axles are mated to the main chassis.

Finished assemblies...

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wow you sure didn't have a budget to work with. nothing but the best/metal will do. what will be the final weight vs the stocked weight? look fwd to the completed work.

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Hi Tamiya1/10, I have no idea what the stock weight is as I don't have one stock to compare...

Continuing with the build...

Step 12 is plugging all the electronics together to center the servos and install servo savers. I'm going for 4WS right off the bat. I'm using Turnigy TGY-4409MD metal gear servos with roughly 9 kg-cm torque and 0.12 s transit time. I had bought a few of these with the intention of testing them in a touring car because I like the speed, but when I checked them I found a little more gear lash than desired for an onroad car. These should work fine for a truck like this; I'm not as worried about super precise steering for a slow speed off road vehicle.

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Step 13 is preparing the servo, servo bed, and steering linkages for installation in step 14. The kit servo mounts and servo bed are replaced with Tamiya 54104 Aluminum Servo Mounts and Tamiya 54047 CR01 Aluminum Servo Bed. The kit steering linkages are replaced with Tamiya 54206 Turnbuckle Tie Rod Set.

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Step 14 is installation of the servo bed, servo, linkages, and bumpers to the front axle assembly.

Parts...

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Assembly...

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Rear shot of the front axle...

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Step 15 is fundamentally the same as step 14 for the rear axle. Normally the steering in the rear is locked; the instructions also call out optional 4WS. For the rear axle, the same parts substitutions apply and the construction is about the same with the exceptions of no bumpers and different spacers used on the linkages due to the different axle angles.

Parts...

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Both finished axles...

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Step 16 is the construction and installation of all the suspension links. Other than the stainless fasteners and some aluminum spacers, the parts are kit stock. Since the chassis side plates are aluminum instead of plastic, the hopup instructions show different spacer requirements for the links for the same mounting locations. I was able to repurpose unused aluminum spacers from the servo mounts and steering knuckles and avoid using plastic D6/D7 spacers.

Parts...

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Finished links...

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Links in the chassis...

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Axles installed... The cantilever links are holding the chassis up in this picture. It's starting to look like something now!

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More eye candy...

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Couldn't resist one more picture...

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I skipped steps 17 and 18 (building dampers) and jumped to step 19 right away to install some springs. I didn't want the axles flopping around on their own, so getting some springs installed right away was the top priority. The kit springs have been replaced with Tamiya 54085 Short Barrel Spring Set, and the spring retainers have been replaced with GPM parts.

Parts...

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Springs installed...

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Circling back... Steps 17 and 18 are for building dampers. I replaced the kit dampers with Gmade Team Zero 104mm dampers. The damper body and the top eyelet are all one piece; to build these you have to assemble a lower cartridge first, fill the damper body upside down, then install with the piston fully extended while screwing the lower cartridge into the damper body. Tighten slightly with a wrench, cycle the shaft in and out once, and the dampers will tend to rebound to the center of the shaft.

The damper kit includes threaded adjusters, springs, and aluminum lower spring retainers, so these dampers could be used in a normal coilover application instead of an inverted cantilever setup like the CR01.

Kit contents...

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Parts used in my setup...

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Step 20 is attaching the turnbuckle links and dampers to the cantilever arms. The stock turbuckles are replaced with 3x32 mm Yeah Racing silver turnbuckles.

Everything installed in the chassis...

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Another view...

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Before getting into Bag D and step 21, I think I have an idea for how to eliminate the slop in the cantilever arms. The path I'm going to explore is using some leftover ball connectors and threaded rod from a TB03 kit. Normally these ball connectors and rods are used for installing roll bars, but I think these parts could work to maintain a fixed relationship between the two cantilever arms.

More to come soon...

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