SRB Superlight - vintage restomod

[Mad Ax 10826]

There's a lot of history to cover with this project, and I may have previously covered some of it already, although I can't find it right now.  Essentially, this is the story of how I came into possession of a vintage SRB chassis and parts, and how those parts came together to build a race car.

We begin back in 2012, at the Tamiyaclub 10th year anniversary swapmeet and bash, where I had the pleasure of meeting lots of like-minded Tamiya enthusiasts in person for the very first time, not least being Mr. Tamiyaclub himself, @netsmithUK.

At the time, I had owned my Buggy Champ Gold Edition for less than a year, and although I loved it, I was too precious with it to really enjoy driving it.  In fact at that time, it had only been carefully around the flat at home.  I had hoped to pick up a vintage SRB project for a more hands-on approach to SRB ownership, but I expected any donor chassis would be well above my price range.

It turns out, I was wrong!  Because Netsmith had his own swap table, and was trading all manner of vintage parts at knockdown prices.  Spying a bargain, I came away with a vintage chassis, complete with Scorcher roll hoop, complete transmission and front suspension, although it was missing the wheels and tyres, front body post and steering crank and links, radio box and rear cage.  I also bagged a set of Proline gold wheels, You-G front tyres, sand paddle rear tyres, and a new rear cage.  All for a bargain basement sum - I can't remember exactly what I paid for it all, but it was at the lower end of double figures.

Of course, it would be a good few years before I got around to doing anything with the old thing, and the first photo I have is from March 2014, when I collected the parts together for a build in what was then my studio and hobby room.

[Mad Ax 10826]

After that, there is no record of the buggy at all until 2017.  I'm fairly sure it never got ran, and just hung around gathering dust because I didn't have a suitable body for it.

Here it is sitting on my workbench on the 6th of April, 2017, ready for me to pull it apart and make it a runner for the Iconic bash at Broxtowe (possibly the last bash even that Iconic organised).

In this shot, I have opened the gearbox, for some reason

and in this one I've ground it out to fit a mod motor.  I think that's an old Yokomo 17 turn, but I could be wrong.

[Mad Ax 10826]

I had a problem with the steering hub balljoints popping out before I'd even got as far as the Iconic bash.  This is on the 11th April, when I was adding all new re-release ball cups to the vintage arms.  This necessitated some modification, as the OG cups are a straight cylinder down into the arm, and the re-re cups are tapered, so the arms had to be reamed out slightly.

modification is clear in this photo, although 5 years and 11 months later I would decide it wasn't quite enough and take out some more.

 

[Mad Ax 10826]

Finally, as in, one day later, I had everything ready to go back together

and also I'd finished my modifications to the gear case

things briefly went back together, but I didn't run the car much, as I was waiting for a ball diff to arrive...

[Mad Ax 10826]

Arrive it did, and two weeks later, just a few days before the Iconic event, I had the parts laid out in front of me on the workbench.  Apparently.  I can't really remember, my daughter was just over 2 months old at this point, but I took this picture of it, so it must have happened.

Pictures are sparse, but I recall having some trouble getting the re-re ball diff in the vintage transmission.  It seemed the gearbox halves were too narrow, possibly a problem in the casting, and if I screwed it together with the ball diff in place it would bind up.  In the even I assembled it with washers between the screws to space it out a little.  This means no beach running for the SRB Superlight, but I was only intending to run it on astro tracks.

Which are packed out with sand.  Which I didn't know at the time...

Anyhoo - it all went back together, and I even cut some braces between the roll hoop and the front shock towers, with an additional brace between said towers, to stiffen the whole thing up.  I guess I was worried that running without a radio box would add too much flex to the chassis and risk it breaking, but I don't think I understood how flex works and was trying to make it as rigid as possible.

Here it is, all ready to run, minus the body.  I think at this point I must have been using the Kamtec Baja body from my other SRB, because I wouldn't paint a body for this one until later in the year.

The car did get run at Broxtowe on the 30th April, but I don't think it went entirely well, the ball diff stopped working and I couldn't tighten it up.  Fearing I'd snapped the screw, I threw it in the back of the van to strip down at home, only to find the diff was fine and I just wasn't tightening it enough.

[Mad Ax 10826]

The Superlight would get another run later that year, at the 2017 Iconic Revival, but I recall having so many problems with it that I only ran it in one heat, then switched back to the re-re car for the rest of the day.  The main problem was the front arms coming loose and flying off, and general floppiness in the front end caused by bent swivel pins.  Still, it looked cool, with the body slung low and the arches cut for clearance.

2017 was the first time I saw a "proper" competition-modded SRB.  This beast was wider, longer, and ran low to the ground.  Pukka Parts had started making SRB performance parts, and my stock re-re and aging Superlight were no match for them, and I came home determined to make something better.

And now we must fast-forward to 2023, because the poor Superlight has been consigned to the storage box ever since Revival 2017 (I think, I don't remember taking it anywhere else).

Every year since then I've entered the SRB class as a backup option, but it wasn't until 2023 that I was accepted (or perhaps forced into) that class.  Which is where the next chapter begins.

[ploots 312]

Watching this with interest as I've got an original one to strip and make better and probably enough parts to build another one,so does the rere ball diff work in an original gearbox 

[Mad Ax 10826]

For the last few years, the SRB class has been split into two: standard SRB, and modified.  Modified covers the crazy Pukka Parts style conversions, which are streets ahead in terms of performance, and standard is, well, fairly restrictive.  Motors, shocks and tyres are open, but bodies are limited to those available in the day, and the car can't have any parts on it from later models, nor can it have any mods made that aren't in keeping with the spirit of the times.  i.e. if people weren't doing it in 1979, you can't do it now.

The body rule is strict enough to forbid modern repros - ergo, if I want to run this car at Revival this year, I have to park the lightweight Kamtec body and find a genuine Tamiya.

Fortunately, I have one.

I think I got this from someone on here, although I don't recall who or when.  I think I had a plan for it when I bought it, but I can't remember what it was.  It may have been that I wanted the body for this actual chassis, because it never had a body, but then decided it was too good to run.  Either way, it's spent the last few years in a box, and before that, it's obviously been exposed to arachnid excrement.

The light bar isn't needed for Revival (we once raced an SRB in the two-hour endurance race, where lights would have been a nice addition, but that isn't run any more) so it swiftly came off.  No, wait, actually, it didn't come off swiftly, it came off slowly, with a good deal of cursing and swearing about how hard it was to get the hex key in and the box wrench on and be able to turn everything without it falling off or dropping onto the floor.  But it did eventually come off.

Well, that's one step closer to a Revival car.

To be continued...

[Mad Ax 10826]

9 hours ago, ploots said:

Watching this with interest as I've got an original one to strip and make better and probably enough parts to build another one,so does the rere ball diff work in an original gearbox 

The short answer is yes - I had to space my gearbox halves with washers to make it fit, but I can't be sure if this applies to all vintage SRB cases or if there were differences or imperfections in the castings.

I'll be buying another ball diff later this year if I can find one, and fitting it in the re-re.  I've got another vintage SRB gearbox somewhere, if I've got time I'll try it in there to see how it fits.

[Mad Ax 10826]

This is the collection of bits literally as they came out of the box.  Note the rubber grommet around the front suspension pin - this was a vain attempt to increase the track width with minimal parts and tools when I was racing back in 2017, and it didn't work, it just made the arms fall off even more often.

Also note how badly bent the pins are.  I was able to straighten them just a little in the vice.

The next trick involved the drill press and a succession of drill bits to put in a 2.5mm hole

 

[Mad Ax 10826]

All cleaned up and ready to fit

Then the awkwardly-shaped suspension arm was carefully clamped and drilled, very carefully so as not to damage the fragile thread.  I had to do some of them with a hand drill as I couldn't clamp the arm on the right angle for the drill press.

Finished part, fitted with an Axial screw pin

[Mad Ax 10826]

Finished and repaired front end back together

and mounted:

I wanted to make some changes to the chassis, which meant taking off the servo.  I thought I'd used servo tape to attach it, but apparently I used the same stuff they use to attach the wings to airliners.  In the end I had to get medieval on it to get it off.  This would later require a heavy clean-up with Sticky Stuff Remover to get the servo case clean, but because the SSR is very thin and the servo wasn't waterproof, it all went inside the servo and I had to open up the case to clean it out inside.  Otherwise it continues to weep out over the next few years and constantly causes the servo to come unstuck off the tape.

[Mad Ax 10826]

For my next trick, I wanted to make an upper deck to hold the battery.  Not running the standard radio box is all well and good, but using straps around the bottom of the chassis isn't great, because they get hung up on the track, which makes them dirty and frayed and isn't helpful for landing smoothly off jumps.

The aim here is to remain "within the spirit of the era" - so, no carbon fibre or graphite or other exotic materials, and no full-length deck incorporating bell crank steering and servo mounts, because that wasn't really a thing in 1:10 in 1979.

The stock SRB might have had a plastic radio box, but the Super Champ had a second deck to help locate the battery and electronics, add lightness and possibly survive race conditions better than the standard plastic shatterbox.  So, as far as I'm concerned, I'm totally within the spirit of the era to make an upper deck to locate the battery, because that's exactly what the Super Champ had.

I used some 2mm GRP sheet.  It's black, but it isn't carbon.  I'd have used that yellowy-greeny natural GRP colour, but I only had that in 3mm, and that's overkill.  It would be nice to remake the main chassis plate in black to match, but we'll have to see about that.

[Mad Ax 10826]

I left a big overhang on the front of the plate to help electrical location, but I had to shorten it later to get the servo in.  I didn't want to use a low profile servo here, partly due to possible (unfounded) complaints about it not being period correct (technically, neither is a modern full-size servo, and even a basic servo is faster and stronger than a '79 servo ever was), also partly because I want the biggest possible mounting face for servo tape, since the original car never had servo posts.

Made some standoffs out of 4mm-ID alu tube from B&Q.  I desperately need more of this!  B&Q is only a 5 minute drive away but I'm too lazy to go there.

I had to use socket-head screws on this as I didn't have any button head that were long enough.  I'm tempted to try countersinking the stock chassis to really get some smoothness on the underneath.

and finally - an assembled chassis!

[Mad Ax 10826]

The final thing before I shut down for the day was to throw on some wheels and test-fit the body.  It's a genuine Tamiya body, no less, so it'll go right on with no problems, right?

Well, cool though it looks, no!

My first though was that I had the wrong roll hoop.  I vaguely remembered the Rough Rider having a lower hoop to the Sand Scorcher.  But in retrospect, I think that's wrong - all 3 of my SRBs have the same size hoop.  The difference is the front body post, which is longer on the Scorcher.  The difference that confused me here is that there's supposed to be some plastic standoffs from the driver parts tree between the roof and the rear body clip, and the front post is supposed to be mounted on top of the steering crank, which I don't have on this car.  Hence, this body is too low.

But, I actually think it looks seriously cool.

I need to allow space for bigger tyres - we're allowed to run modern rubber at Revival, so I'll have some 2.2s to accommodate.  The smoothies already catch the arch on full compression, so I've either got to trim the arches or lift the body.

I've contacted the Revival organisers to ask if trimming the body is allowed.  This body has already been trimmed by the previous owner, but I'm sure it's still well within the spirit of the times.  Slamming it like a chopped rod might not quite be in keeping with the spirit of the thing.  But, if I cut into the rear of the body where it touches the rear cage then I could set it sitting lower, in fact I'd tune it so it's about as low as it can go without the rear wheels touching the arches.  Then I'd level off the front end, and see if the arches need trimming, and take off just what I need to make it work.

Or, maybe, I'll just put it where Tamiya intended and get out on track to race, and stop worrying about how cool it looks.  Because earlier today I temporarily put in some spacers and lifted it up so everything clears, and it still looks fab.

[Mad Ax 10826]

Another update on this one from last weekend.  I was a bit concerned that the servo tape wasn't going to hold the servo, but as the stock SRBs never had servo posts, I didn't want to break from tradition and add them.  I'm sure it would be fine to install servo posts under Revival rules, but didn't want to drill the stock chassis.

Instead, I made another small plate to go over the top of the servo and clamp it down.

I then temporarily threw in some electrics and took it for a spin.

[Mad Ax 10826]

It drives OK for a vehicle that's as old as I am, at least on the concrete out the back of my workshop and on the patio slabs.  It's too small for the grass at the moment, I tried but it got bogged down.

The good news is that the front end held together, nothing came off and it's about as well mannered as one can expect from such a primitive design.  The shocks and springs haven't been properly set up yet, in fact I might need to revisit them later as they're only cheap units and I don't think I'm getting quite the travel I'll want, especially once I have modern rubber installed.

Still, that's a long way off yet.  Now I've proven the chassis concept, it's time to tidy it up.

Switch screwed into place

although this clearance issue is going to be a problem later

drilled holes for the zipties

installed a shorter battery strap from an Element kit, with the end trimmed off so it doesn't drag on the ground

[Mad Ax 10826]

And that's that, for now.  My next plan was to make a removable plate to go between the stock chassis plate and the transmission assembly, to make a rudimentary anti-squat.  When I took the chassis apart for this rebuild, I'd previously put some chunky washers in there - I don't recall doing it, but I can only think it was for anti-squat, or to change the suspension angles in some way.  The washers aren't a neat solution, but a flat plate of FR4 would be perfect.

Unfortunately I've got the top deck standoffs too short, so there isn't space to lift the transmission assembly.  This means I'll have to cut new standoffs and probably remove the smaller standoffs from the servo clamp plate.  That's not a big job, but at this point I was 99.9% certain I didn't have any more aluminium tube to make more standoffs from, so I aborted and did something else instead.  Later I found an entire new length of tube, so this is a quick job for the weekend, and then I'll be onto the body and interior.

The body pictured above didn't come with a driver figure, so I stopped off at Racecraft RC on my way home from the office and picked up a genuine Sand Scorcher re-re driver and nosecone set, which (I didn't realise) also comes with the stinger exhaust, so maybe this one will get a bit of cosmetic attention around the back, too

[simalarion 2552]

Your like a RC Offroad Sensei 

[Grumpy pants 5541]

On 3/29/2023 at 10:10 PM, ploots said:

Watching this with interest as I've got an original one to strip and make better and probably enough parts to build another one,so does the rere ball diff work in an original gearbox 

The vintage gearbox is cast differently to the Re-Re one.

I thought there were 2 types of the ball diff as well.

Can’t tell you much more than to be fair. 

[Grumpy pants 5541]

On 3/30/2023 at 8:12 AM, Mad Ax said:

All cleaned up and ready to fit

Then the awkwardly-shaped suspension arm was carefully clamped and drilled, very carefully so as not to damage the fragile thread.  I had to do some of them with a hand drill as I couldn't clamp the arm on the right angle for the drill press.

Finished part, fitted with an Axial screw pin

Is this a ‘belt and braces’ fix to stop the arms falling off? 

[Grumpy pants 5541]

Great thread, enjoyed it a lot!

Thank you 👍

[Mad Ax 10826]

1 hour ago, simalarion said:

Your like a RC Offroad Sensei 

You wouldn't say that if you'd ever seen me race off road   mostly I just make it up as I go along.

When I called in at Racecraft RC earlier today, Adie reminded me yet again of that time when he beat me around the track with a re-re Sand Scorcher with a Sport Tuned when I was driving a modified Blitzer Beetle with an Acto Pink...

39 minutes ago, Grumpy pants said:

The vintage gearbox is cast differently to the Re-Re one.

I thought there were 2 types of the ball diff as well.

Yes, the ball diff in the Superlight isn't a perfect fit, and I've had to space the gearbox halves apart with washers, so it isn't sealed any more (I'll probably seal it with gasket compound once I'm happy with it).  I think the diff in there is a Type II, I was chatting to Adie about it earlier today and he said the main difference between the original and the Type II is the Type II comes with threadlock on the shaft to stop it unscrewing.  I think I read somewhere recently that the Type II is adjustable with the wheels on too, by sliding a hex wrench into the cup to lock it up, then turning the other wheel to tighten it.  I may be wrong, though.  Adie advised fitting it backwards, so that the torque will have the effect of tightening it, not loosening, although I'll need to look at that in more detail.  In my experience, left hand wheelnuts come off more often than righthand ones, which means the braking torque actually puts more shock through the drivetrain than the acceleration torque.  That makes sense - even with a super hot motor, there's some lag in accelerating the drivetrain, but when you land from a jump with the wheels spinning, the sudden stall in the wheelspeed is much sharper.  Even spinning the wheels going over bumps in the track surface will put a lot of stalling torque through the drivetrain.

His other advice was that a newly-installed ball diff might slacken off a couple of times as it wears in (mostly the springs bedding in), but once it's been set, leave it alone - people tend to constantly fiddle with their diffs, which upsets them and makes them more prone to coming loose.

I picked up a new Type II diff today to go in the other SRB, which is a re-re, and will be my wet weather car because it still has its radio box.  Although I really just want to run this Superlight project, if I can.

[Mad Ax 10826]

45 minutes ago, Grumpy pants said:

Is this a ‘belt and braces’ fix to stop the arms falling off? 

Yes, exactly this.  I had so much trouble with the arms coming off last time I raced an SRB.  Also the UJs slackening off at the rear - not on the original but the re-re is terrible for it.  When I was racing it in a 2 hour enduro, we would have to pull off the track every 5 laps to tighten the UJs up again.  Even then, it was common for one of the UJs to come off and for our race car to be taking up half the track as one driveshaft made a steady bid for freedom.  That car had the spool in the back, so it would run well enough with only 1 driveshaft in to make it back to the pits.

Yeah, tightening up them damned UJs every 5 laps for 2 hours, in the dark and the rain.  That was a looong race...  We won our class, but in fairness that was only because all the other SRBs failed to finish.

[Grumpy pants 5541]

The funny thing about the arms falling off is Tamiyas’ fix BITD was to use cable ties on the Super Champ 🤦