Blueprinting a Blackfoot

[Saito2]

Though the term is tossed about too cavalierly in the car world, I have blueprinted and couple engines in my time. It felt much the same when I decided to build a re-release Blackfoot from scratch, incorporating as many fixes as I could to its flawed, but fun design. The Blackfoot is one of those vehicles that invites creativity in solving many of the issues Tamiya left the truck with. Many have made modifications and guides have been written. There are multiple solutions to the same problems which breeds unique takes on the old 'Foot and this is probably no different. I did try to take a whole system approach, looking at how the various problems interconnect to reach a decent comprise to all. Fortunately, the Blackfoot is a blast to drive, so having a reliable one is rewarding and I intend for this one to see decades of use.

Starting with the gearbox itself, I was never too happy with the sloppy fit of the B1 and B2 plastic counter gear shaft and bearing retainers in the stamped metal side plates. They slide around, both side to side and radially which I can't imagine being good for internal gear mesh. Furthermore, I found if the counter gear shaft was slide to the left (away from the motor) the drive train spun more freely. The fix was an adhesive like shoegoo (thanks for the tip @ruebiracer) and aluminum foil.

Glue alone would anchor the plastic parts but not center them nor take up the excessive diameter clearance. I placed aluminum foil over the B1 and B2 parts before inserting them, gradually adding layers until achieving a perfect fit before gluing. The excess was trimmed away with a hobby knife. Its important trim it away from the inner flange section of the B2 part as to not shim those pieces inward, putting pressure on the diff. It just for taking up the diameter difference. As a bonus, I was able to add more layers of foil to the right side B1 part to skew the counter gear to the left for less internal friction. Bearings. throughout are a must as always.

There are a great number of fixes for the problematic rear diff, which separates under power leading to the dreaded "clicking". I chose the "oldfrogshot" style mod, tying the stock diff cups/outdrives together internally.  I have reasoning behind this choice which leads into the drive axles which leads into the rear suspension, each system impacting the design as a whole. Its a hot mess, but one I worked through until I got it right (for me anyway). More to come...

[Frog Jumper]

I like this Mod. I’ll try it on my Spur shaft...

Terry

[Saito2]

We all know by now that the stock stamped metal sideplates do not keep the diff gears together under load. The teeth skip and click and eventually wear out. There are 3 basic fixes (I find shimming to be more of a band-aid, IMO) and most are variations on one of those three themes. Bracing the gearbox sideplates is one. I started down this road and have done it in the past on other ORV monsters. The only issue (again, astutely pointed out by @ruebiracer) is that while the gears can no longer spread, they still put direct thrust loads on the diff bearings. There's nothing inherently wrong with gearbox bracing techniques I just decided to go a different route this time. The second fix is the MIP diff. The diff is great. I am so happy MIP produced such a quality product. Unto itself, its likely flawless. The one failing is is was designed to work with the stock universal swing shafts Tamiya felt the need to include in the monster ORV version re-releases. The problem with these is evident in the next pic:

The right rear uni shaft is much closer to the edge of the drive cup/outdrive. With trailing arm flex and the increased leverage provided by the larger monster tires, that shaft can pop out. I never read about complaints from those who used the uni shafts with Frogs (the uni shafts were originally a hop-up for the re-re Frog) so perhaps the tires are much to blame. I tried everything to get them to work. Shimming the backside of the stub axle inward can only go so far before the pinned wheel adapter starts thrust loading the outer bearing  in the trailing arm. I wasn't content giving up shock travel either (shortening the shocks effective extended length will keep the axle deeper in the cup). The outdrives provided for use with the uni shafts are deeper than those that come with the standard re-re Frog dogbone set. If MIP modeled their ball diff after the deeper outdrives on the ORV monsters, this is likely why they aren't supposed to be used with the shallower Frog outdrives and their attendant dogbones. This situation leads me to the oldest of the three solutions, the "oldfogshot" mod.

I'm always curious what long-gone Tamiyaclub member oldfrogshot would think if he knew his mod was still being discussed all these years later. Either through drilling and tapping or simply using a nut and machine screw (after the drive cup/outdrive pin is knocked out), the oldfrogshot mod ties the two outdrives together. I did this mod (using a machine screw and nut in my case) on a complete set of re-re Frog parts, outdrives, dogbones and stub axles. The big issue still remaining was how to space them. Tamiya normally recommends o-rings in the drive cups. The crux of the matter is the extreme angles the axles operate at.  A classic RC10 can be set with it dogbones nearly level. Not so with the ORVs. As the trailing arm moves through its arc, the dogbones get tight (with o-rings stuffed in them) and then looser again. This wasn't acceptable for me. I wanted a smooth movement to the rear trailing arms (see how all this interconects? lol).  Without the oldfrogshot mod, the o-rings can't be removed. They are required to place inward pressure on the diff outdrives to keep them from working outward. The oldfrogshot mod negates the need for the o-rings and the dogbone can be spaced how the user chooses (which I imagine varies from vehicle to vehicle).

In my case, the left outdrive received a small piece of soft sponge foam to limit dogbone chatter but nothing more. The right side still faced the issue of the dogbone being closer to the edge of the cup so I wanted slight inward pressure to keep it engaged. the answer was a small bit of a pen spring inserted into the right stub axle:

 

Finally, fully traveling, bind-free rear suspension with a diff that won't disintegrate. I had the back of this truck apart over a dozen times to reach this point but it was worth it (and kept me busy, lol). More to come...

[Saito2]

On to the rear suspension. The various issues with the trailing arm suspension have been chronicled before as have the fixes I have utilized. While ditching it all together may be the most effective answer (one Tamiya did themselves in following versions of the Blackfoot) trailing arms and their functional nature are part of the original Blackfoot experience for me. 

The above shot shows some of those fixes. The front mount is very flexy so I made one from FRP. The rear mount is vulnerable and prone to splitting. The rear shock mount on the trailing arm is tapped out, and through-bolted with a machine screw and nut (every machine screw is tapped and every tapping screw is heated before insertion to reduce the chance of cracks in the plastics down the road). The rear mount is further braced with a strip of aluminum secured to the lower hole on the trailing arm. There's more hiding within however:

I was never happy with the inner trailing arm pivot riding purely on a hole punched in the sideplate. Wear-induced slop in this area certainly isn't good for dogbone retention either. A small section of nylon tube is cut and fitted in the hole between the side plates. It is carefully reamed to size and aids in supporting the inner pivot. CRP made something akin to this BITD. That purple stuff on the inner arm pivot seen in the last pic in the previous post is wax. I use wax as a lubricant for certain suspension pivots. It doesn't attract dirt and grit like typical grease does.

Wax is also used on the outer pivot (K7 and K3 in the re-re Monster Beetle manual). This is, unfortunately, a higher friction pivot point with a lot of surface area as the pivot is so big. I use the stock plastic pieces as opposed to the aluminum Frog pieces. The plastic version is retained with 3 screws vs the 2 for the Frog version and indexes the pivot on both its inner and outer diameters for more stability. Being covered rather than an open hole probably shields it from dirt better too. The one issue the plastic piece does have is the stress it puts on the small ear coming off the chassis for the lower screw hole: 

Its hard to make out but this old Blackfoot shows a white stress line on the lower ear of the ABS chassis. Whether this is from initial cold screw insertion (likely as there isn't a great deal of material there), stress from use or impact stress, I don't know. The ear doubles as a "stop" for the rear trailing arm. To preserve it I did the following:

I tapped the hole through and used a longer machine screw and nut for better retention. Its very hard to see, but the trailing arm no longer rest on the stop either. I laboriously measured and shimmed the shocks internally so they extend mere thousand's of an inch from contacting the stop. I wanted maximum suspension travel without quite slamming into the stop every time. Speaking of stops, Tamiya instructs you to use hard plastic stops to prevent the tires from hitting the body. These were replaced with rubber tubing to soften the impact forces on the chassis. Now the rear end is just about complete after much gremlin-chasing.

[Boomstick]

18 hours ago, Saito2 said:

On to the rear suspension. The various issues with the trailing arm suspension have been chronicled before as have the fixes I have utilized. While ditching it all together may be the most effective answer (one Tamiya did themselves in following versions of the Blackfoot) trailing arms and their functional nature are part of the original Blackfoot experience for me. 

The above shot shows some of those fixes. The front mount is very flexy so I made one from FRP. The rear mount is vulnerable and prone to splitting. The rear shock mount on the trailing arm is tapped out, and through-bolted with a machine screw and nut (every machine screw is tapped and every tapping screw is heated before insertion to reduce the chance of cracks in the plastics down the road). The rear mount is further braced with a strip of aluminum secured to the lower hole on the trailing arm. There's more hiding within however:

I was never happy with the inner trailing arm pivot riding purely on a hole punched in the sideplate. Wear-induced slop in this area certainly isn't good for dogbone retention either. A small section of nylon tube is cut and fitted in the hole between the side plates. It is carefully reamed to size and aids in supporting the inner pivot. CRP made something akin to this BITD. That purple stuff on the inner arm pivot seen in the last pic in the previous post is wax. I use wax as a lubricant for certain suspension pivots. It doesn't attract dirt and grit like typical grease does.

Wax is also used on the outer pivot (K7 and K3 in the re-re Monster Beetle manual). This is, unfortunately, a higher friction pivot point with a lot of surface area as the pivot is so big. I use the stock plastic pieces as opposed to the aluminum Frog pieces. The plastic version is retained with 3 screws vs the 2 for the Frog version and indexes the pivot on both its inner and outer diameters for more stability. Being covered rather than an open hole probably shields it from dirt better too. The one issue the plastic piece does have is the stress it puts on the small ear coming off the chassis for the lower screw hole: 

Its hard to make out but this old Blackfoot shows a white stress line on the lower ear of the ABS chassis. Whether this is from initial cold screw insertion (likely as there isn't a great deal of material there), stress from use or impact stress, I don't know. The ear doubles as a "stop" for the rear trailing arm. To preserve it I did the following:

I tapped the hole through and used a longer machine screw and nut for better retention. Its very hard to see, but the trailing arm no longer rest on the stop either. I laboriously measured and shimmed the shocks internally so they extend mere thousand's of an inch from contacting the stop. I wanted maximum suspension travel without quite slamming into the stop every time. Speaking of stops, Tamiya instructs you to use hard plastic stops to prevent the tires from hitting the body. These were replaced with rubber tubing to soften the impact forces on the chassis. Now the rear end is just about complete after much gremlin-chasing.

I had problems with the Flying Brick and the plastic swingarm retainers. I went with aluminum and drilled all 3 holes on both sides, epoxied the screws in from the back with washers on them and use nuts on the outside. I ended up swapping out the washer locknut on the bottom screw because it hits the swingarm so a lylok nut is now used. It's much stronger now. Unfortunate I cracked the chassis on the front during a 60+mph crash and have to replace it so I'm doing it all over again once the new chassis arrives.

[markbt73]

This is great stuff! I did a lot of similar things when I rebuilt my Blackfoot about ten years ago, including the same reinforcements to the rear arms. I did use the aluminum Frog-type outer suspension arm holders, though.

Curious to see what you come up with for the front end. Mine's still pretty floppy; I basically just used the tightest-fitting parts I could find and called it good.

[Saito2]

10 hours ago, markbt73 said:

Curious to see what you come up with for the front end. Mine's still pretty floppy; I basically just used the tightest-fitting parts I could find and called it good.

The front end's a bit of an open book. I don't think, by design, it will ever be super-tight and precise. I've seen rubber tubing used to replace the brass tube on the front radius arm mount. While it does tighten up the radius arm pivot, it also imparts resistance to suspension movement, so I skipped it. The nicest parts to use are the old brass bushed CRP front arms. I miss old CRP stuff. At one time, I would heat and press-fit brass tubing into the pivot points to tighten up clearances. I would heat the brass, because cold press-fits into PC/ABS plastic is a bad idea. Someone pointed out removing the material needed to press-fit the brass tubing would effectively weaken the stock PC plastic arm, however slight, so I quit doing that for now. The CRP pieces were made from reinforced plastic. I do plan on experimenting with polyethylene film inserted between the aluminum BA26 (re-re no.) arm mounts and the arms themselves to take up clearance and provide a slippery wear surface.

Above, I fitted the Frog front skid plate. I can only guess Tamiya replaced this nice piece with the tiny servo guard on the Blackfoot as a cost-cutting measure. The Frog version, besides offering more protection, strengthens the front of the chassis at its narrowest point and ties into the H1 part.

On the chassis top side I have a few things going on. I was never crazy about the mechanism lid being affixed with zip ties at the rear, especially as it doubles as a front shock tower support. Fortunately Tamiya fixed this in the later Blackfoots. Here, as others have done, I removed the re-re chassis brace tubes, BA 23 and installed the King Blackfoot B1 part and corresponding B10 mechanism lid. This affair is screwed together for more strength and greater precision. 

I wasn't done with one of those BA23 tubes yet though. @mongoose1983 showed us that one of these works great as a brace for the rear body mount ears on the chassis. That's topped with aftermarket reinforced rear body mounts (CRP, I'm guessing) as the stock pieces are vulnerable in roll overs. The front mount was replaced with some angle aluminum and a trimmed off piece from one of Tamiya's long, generic sized body mounts. These latter post are made from a much more rubbery plastic and resist damage. Depending on its diameter, it might need turned down to fit the Blackfoot body mount hole. That square piece of scrap ABS plastic sitting on the tire is installed on top of the mount, below the body. This spreads impact forces out across the hood to avoid the mount punching though the body as stockers sometimes do. The steering servo is centered with stronger treaded rod for steering arms. Washers shim the axles to take up the slop created by Tamiya using axles axles that are oddly slightly too long.

Once I'm able to get out again, I plan on getting a drill press. With said press, the creation of new steering blocks are in order (along with a dozen other projects). It looks like the old Parma blocks reduce bumpsteer by raising the pivot points. While this is possible to do with the stock blocks, I feel they're weak enough without adding the leverage of that stress in as well. I once saw steering blocks made from literal blocks of plastic. While not pretty they seemed quite stout so I will try to replicate them in the future. Once again, if CRP was still around...sigh.