Thread Tools
Feb 01, 2015, 06:41 PM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP

"Who let the Cats out?" - Rebuilding a couple of vintage Schumacher buggies


Though the Kyosho Optima Mid was my first competition grade RC car, and has since my youth become my favorite vintage 1/10 4WD RC, lately I've looked around for other cars from that era. One of the rivals of the "Mid" was the Schumacher CAT, a very capable competitor. Also with a nice oldskool shell design, making it even more tempting to try one out.

Eventually I gave in, and started looking for these cars, and found a couple, hopefully giving me enough parts to build one runner, and another for on the shelf. This topic will show the progress on rebuilding these "CATs".

As one car will be intended to be pretty on the shelf, aka be a "Shelf Queen", updates about that car will be posted in the 3rd message in this thread. The first and second message will deal with rebuilding the car that is intended to run, and will have electronics installed.

First Impressions:

Update 2 february 2015:

I intend to mainly focus on the runner, and in between waiting for parts etc, put some work on the shelf queen. The latter looks pretty clean already, and it may come to this that it will only be taken apart should I need parts from it for the runner. The shelf queen will be kept pretty much stock, with a repro body trying to depict the car that Masami had great successes with.

First a little explanation why CAT is written in capital letters, it's actually short for "Competition All Terrain", which does well describe the car's potential, as well as have a catchy name. Later Schumacher cars would continue to have feline inspired names for a while. Modern CAT designs have very little in common with the vintage CAT, just like with Kyosho, the Lazer ZX-R is very different from the Lazer ZX-5, despite almost identical name tags.

And now it's time for some pictures of the intended runner:

One thought that first hit me when seeing this type of car, was that it must be pretty fragile, considering the rubber bands at front. Especially when the stock black bands are no longer present, but another type is used:

This is actually a neat feature of the car. When you hit a track border or curbstone with one of the front wheels, this almost always causes damage, steering links unsnapping, breaking C-hubs, bent CVD shafts, etc... At least if the hit is with some speed. The CAT tried to solve this issue:

If you look at this picture more closely, you will notices a metal pin, with bent top end, right behind the shock mount. This is actually a vertically placed hinge. When the front wheels hit something on either side, the rubber band at front allows the entire suspension on that side to swivel backwards, absorbing the hit without damage, at least that's the idea. As you can see on the second picture, the front drive shafts are made from 2 parts, sliding in each other. This allows the front to swivel back, without popping a dogbone out of a drive cup, like would happen with a regular dogbone or cvd/U-joint. The key is, just like with a servo saver, to get the strength of the rubber band such that the front doesn't get too "floppy" and the "crash protection" is only active with a hard impact, not during regular driving.

This vid of the other car shows why the decision was made to make the one on the pictures above the runner, and the other one the shelf queen:

(0 min 28 sec)

Massive slop on the rear suspension, this is also the earlier type, that had the option to adjust rear toe-in with a tie-rod. As you can see the wheel has plenty of movement in 3 axis, not something you want on the rear end of a car. It's like uncontrolled rear steer, as can be found on a forklift...

Now on the 3rd picture, one may have spotted a small flathead screw, at the end of the upper A-arm. This can squeeze the ball cups, that are at the end of the A-arms, a little together, and reduce slop. A neat system, that allows to reduce slop for a while, until arm and pivot ball need replacing in the end, but on the posted vid, these screws are already fully tight. The pivot balls are worn such, that the silver coating is fully gone, and sourcing replacements is not an easy task. I'll later post pics with full dimensions, maybe someone has a suggestion for a replacement. This will not only pose a chance that the static shelf queen gets promoted to running shelf queen, but will also be handy to keep the main runner, well eh... running. Other parts on this car will show little wear, there is only one gear besides the pinion, as the rest is belt drive, and the wheels use oversized ball bearings, so wear will be pretty low there are well. These pivot balls seems to be the CAT's known weak point.

Update 3 february 2015:

Before moving on, some more study on how these cars are put together was needed. The Cat first started with an intricate drive system, similar to the RC10 6-gear transmission. The diff is located on the layshaft, but instead of using small gears, like the RC10, the drive of each diff-section is transferred with 2 belts. Somewhat complicated and this system also features a 32p spur.

The other car has the so called MMS layshaft, which relocates the diff-function to the rear axle, like on the Lazer ZX-R. This is less complicated, and should run more smooth. Also, a 48p gear can be fitted. Better for a runner.

Now, the MMS parts are on the car with the sloppy suspension, and the stock layshaft etc are on the car with the tight suspension. So, this is coming down to some swapping around of parts, to get the best, and partially upgraded parts installed on the runner, and the stock parts on the shelf queen. I was expecting only having to rebuild the runner, and only clean up the shelf queen, new repro body, etc. but it's going to be a little more work to get the desired results. But that's what a hobby is for, right?

Starting with the "Runner"

Update 4 february 2015:

With some help from other vintage fans, I've been able to identify some more parts, and decide what is best to use on the runner, and on the shelf car. For instance, the orange belt, that is visible on the pictures above, turned out to be an upgrade, with less stretching than the stock belt. So definitely a part for the runner. As well as the rear end of the same, which uses parts from a later Cat version:

Despite having the newer parts on the rear suspension, the gears are still stock on this car. After opening the rear gear box, the main components could be inspected. First, the so called "integrator":

This part connects the driven outer gears to the gear driving the belt to the front. The rest of the internal parts showed quite a bit of rust...

... and dust...

...which is now gone...

Here's an overview of the other drive components:

Not only the bearings were rusty:

After a good cleaning, things looked much better and some parts could be put back together:

Next, swapping parts between the 2 cars, so that the runner gets the updated parts, and the shelf queen the stock ones.

Update 5 february 2015:

Before being able to put some things together again, more cleaning was needed. Even though this car uses no gears inside the gearbox, it was pretty greasy inside. Here's a pic of the other car's gear box, with the MMS layshaft:

The layshaft may seem like made of black plastic, but this is the same part after cleaning up:

When a plastic part gets so dirty, it's no surprise that the rest could also use some cleaning:

Meanwhile I'm looking for a replacement spur for the runner, as the one that was installed on the MMS layshaft, has a series of deformed teeth.

Update 8 february 2015:

Bit of a slowdown in the rebuild progress. I did find a lot on Ebay containing a couple of spurs that would likely fit, and in convenient teeth count. Like 89T, as was fitted, and a little above and below. I still need to get to know what the drive ratio of the MMS layshaft is, so I can calculate total gear ratio.

When rebuilding the MMS diff, I kept having a little diff slip. The cause was simple, the metal plates had become unglued from the outdrives. So while the diff was tight, the plates could move over the outdrive surface. On some cars you can fix these with CA glue as well, but as the outdrives had a recessed part, and CA glue doesn't fill up that gap, there would be too little surface to glue. So it was decided to use the epoxy glue that the manual suggested. To ensure the plates would line up well, to get a smooth working diff, I decided to screw the diff together after the plates had been glued, and this glue was slowly starting to cure.

The first times the diff was put together, and some pressure was added, excess glue would seep out a little, so I had to take the diff apart again, to remove this glue, or the diff might be totally glued together eventually... After a few of those rebuilds, I couldn't tighten the diff. I feared for a stripped thread on the long screw going through the diff, but the cause was less severe, the lock nut had fallen from it's place. Yet some more rebuilds later, no excess glue was coming out when adding more pressure to the metal diff plates. One metal plate had moved a fraction out of center, with a flat blade screwdriver I could nudge it back to the middle. The diff felt more smooth afterwards, there was clearly more resistance than with a mildly greased gear diff. but the resistance was about the same when turning the diff outdrive manually. Time to let the glue set and focus on other things.

Meanwhile, part of the other car's rear gear box, with the diff on the layshaft, was pieced together again:

Btw, anyone who, like me, isn't familiar with the vintage Cats, will probably wonder what the reason is for the pointed part on the plastic ring with the holes. Because the car uses belts for transferring power from layshaft to rear axle, these belts need to be tensioned, to avoid slipping. The rings with the holes and small arrow point, are excentric bearing holders, in which the bearings of the rear diff or integrator, are held. With the 2 screws loosened, the rings can be rotated, and due to excentric shape of the rings, the rear diff gets moved a little to the rear or to the front. Thus resulting in more or less tension on the belt, depending on what direction the rings are rotated. The arrow point helps to set the left and rear the same. This even allows to tighten or reduce tension, without having to that the gearbox apart.

Update 10 february 2015:

While waiting for the epoxy on the diff outdrives to cure, the chassis was cleaned te remove some glue remains:

With the blunt rear end of a kitchen knife, the dried out glue remains could be scraped off without damaging the fiber chassis plate:

As the front diff was having lots of lateral play, as well as binding, this section was carefully taken apart:

It seems like more parts were changed on this car during it's "life", by the previous owner, as the front diff is not the standard one. This one has different, larger diameter, drive plates, with hex shaped sections to avoid the plate rotating on the outdrive, and more diff balls. This probably explains the lateral play, maybe some spacers are missing, or something else has been overlooked when replacing the stock diff. Time to do some research...

Update 12 february 2015:

The mystery of the slop on the front diff hasn't been solved yet, I'll probably just get a couple of 8 mm shims, as I will also need these for the rear gear box, on the layshaft, and remove the play on the front with those as well.

Meanwhile I did some work on the front suspension arms. As everything there is feeling smooth and with very little slop, I decided to just partially strip this section, and clean up the parts. This is definitely a special design:

This pic clearly shows how the hinge pin holder is attached to the plastic frame that sits on each side of the front transmission housing. The next pictures show the same part, but then seen from behind:

One thing that is very clear on these shots, is the metal pin with the L-shaped end, that is the vertical hinge for the system that prevents breaking front suspension arms.

The next pic shows a detail on the front suspension arm, a little flathead screw, that slightly pulls the ends of the suspension arm, where the pivot ball sits, together, to reduce slop:

I also received a couple of spur gears, and test fitted an 89T:

It took a while to center the gear, as it tends to slide away a little when tightening the screws, but it runs very true now. Once I get the 8mm shims, I can put the gearbox together, and make some more progress.

Update 24 february 2015:

I received a Pro Cat front diff housing, to try if that would solve the issue, but there was no real difference. With that in mind, and after some research and asking questions to vintage car fans that have more experience with these old "cats", it seems that the only way to solve the play on the front diff, is using shims. Those shims are here now, so I expect to be able to make some progress soon.

Update 26 february 2015:

I put back together the front diff, and needed 2 of those 0.3mm shims on each side off the diff to get the play to a very acceptable level. The diff now runs very lightly in the flanged bearings of the front transmission housing. During re-assembly of the diff, I discovered that the plastic casing of the thrust bearing of the ball diff, was starting to come apart. Turns out to be a common problem, which can be solved by fitting a metal thrust bearing. I could take the still intact bearing of the intended shelf car, and fit the damage one to that, but it would still be plastic. Original Schumacher metal thrust ball bearing sets are over 10 GBP, but from a site selling all kinds of bearings, I found a cheaper direct replacement, that should be just as good. These are on order now.

The rear gear box has been partially put back together now, with the rear belts installed. It feels very smooth when I rotate the spur, but I will need to take out the diff screw, when the metal thrust bearing arrive.

Update 15 july 2015:

Took some time to work on the runner again. I finally had enough parts to make two complete front shocks. These do still have a different shade of color than the rear ones, but all 4 are working smoothly enough. One shock did move much lighter than the other, despite having straight piston rods, and the same type of piston. Even swapping things over this difference stayed with the same shock absorber. I guess the o-rings on one of the shocks are a bit more narrow, maybe these have been replaced on one before I got the car these came on, and these need to be broken in a little. As temporary fix I put thinner shock oil in the tougher moving shock, so both now have the same feel when compressed.

Anyway, the rear and front transmission were put back on the chassis plate, and the front gear box temporarily fixed, as the new belt cover wasnt installed yet:

Between the U-joint and the steering assembly, you can see the 2 holes for the vertical hinge pin of the "kickback" mechanism:

Next up was cutting the repro belt cover to size, and fitting it to the top deck:

Still quite some things remain to be installed, like the wing mount, and suspension arms. But first there was the challenge of making the gear cover fit:

As you can see the cover not only covers the spur and pinion, but also the diff outdrives and the various mounting holes for the right suspension arm. That would mean a lot of different holes to be cut out, including a large one for the big black ring around the diff outdrives. I decided to try something different:

It doesn't give a 100% seal this way, but I doubt it would have, had the cuts been made differently. Anyway, back to the chassis, here it has the rear suspension arms installed again:

Then it was time to install the front suspension arms again. Especially the second picture will be interesting, as it shows the "kickback-system", that allows each of the front arms to swing back upon a hard impact. The third picture shows the two strong rubber bands installed, that hold both suspension arms tightly against the gearbox, so these can only swing back in a crash, but not during normal running. A very clever system, though it takes some getting used to.

That's it for today...
Last edited by SoloProFan; Jul 15, 2015 at 03:51 PM.
Sign up now
to remove ads between posts
Feb 01, 2015, 06:42 PM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP
(reserved for updates)
Latest blog entry: For the love of the hobby!
Feb 01, 2015, 06:46 PM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP
(also reserved for updates)

Shelf Queen version

To keep the build logs more apart, I will post the updates about the shelf queen car in this posting, and the first 2 postings will deal with the runner, rebuilding and running that.

Update 12 july 2015:

First I was going to get the other car, with the saddle pack chassis, rebuilt as shelf queen. However, this car was missing quite a few things, plus I wanted it to look close to a stock CAT XLS, which used a stickpack chassis. Rebuilding 2 cars, with 1 1/2 car and some loose parts, turned out to be near impossible, so another car had to be found. This wasn't easy, as there aren't the many XLS being for sale, but eventually found this one:

Pretty much complete, even can with the front stabilizer installed:

Except for the long vertical screws, the rear end also looks very much stock:

The undertray has some cracks, but overall looks pretty good for it's age:

The belt cover might seem like a seperate part, as it's clear, and the rest of the undertray isn't, but in fact, the cover is part of the undertray. You can see the little rough edges where the masking take was:

Update 13 july 2015:

As you can see, the car was in need of some cleaning...

First I started with the shocks, with some good results:

Next the front and rear suspension was partially taken apart, to be able to clean the dirt:

Here you can see the right side cleaned, and the excess part of the bolt, that holds the rear toe-in link, cut down so it doesn't stick out so much. The left side still needs to be done.

The wing that came with this car was far from original, so I had already ordered a couple of repro wings and a repor body, a while back. Here's the first wing cut to shape, along with a first attempt to make a new wing mount wire:

Then the new wing was painted black, and loosely placed upon the wing mount, to see how this would look:

The wing may look a bit out of place, without decals, but that will be fixed in the near future. Btw, the wing mount used here is another one than on the picture, as I want this car to look close to the car Masami ran, and he has the wing mounted lower than stock.

The new repro body was also cut out, as well as a second wing. Maybe I'll paint the second wing white, to see how that looks with the old body shell. Anyway, I took a few shots of the repro body mounted on the car, with the second, stil unpainted, wing. Those "see-through" shots have something special, I think:

More to follow soon...

Update 14 july 2015:

Some more shots of the shelf car, with new unpainted body. The second pic is my favorite.

Last edited by SoloProFan; Jul 14, 2015 at 10:24 AM.
Feb 04, 2015, 04:58 PM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP
Updated added, with some pics as well.
Latest blog entry: For the love of the hobby!
Feb 05, 2015, 10:20 AM
Time For Me To Fly!
fastmax's Avatar
Nice project, and a very interesting design. I have never owned or played with any of the CAT 4wd buggies. Back in 1990 I had a Top CAT which was a belt driven 2wd buggy with inboard front suspension. I loved that car. It was my first introduction to Schumacher, and showed me that they place a lot of focus on making their rigs highly tunable, and high quality.

Looking forward to seeing these rigs come together, and seeing some video of the runner in action!
Feb 05, 2015, 07:00 PM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP
Originally Posted by fastmax
Nice project, and a very interesting design.
Indeed, it's a bit like a discovery, working on such a different car.

Small update added.
Latest blog entry: For the love of the hobby!
Feb 06, 2015, 10:58 AM
Car Bashing
Jym73's Avatar
Feb 08, 2015, 02:11 PM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP
Small update added
Latest blog entry: For the love of the hobby!
Feb 08, 2015, 02:24 PM
dunc2504's Avatar
Nice project .
Looks like you have an XLS and a Procat there.Still some wishbones on ebay to help with the joint slop . I am gathering parts for a Procat build just now , prices are not as crazy as Xls parts (YET).
Feb 08, 2015, 02:39 PM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP
Originally Posted by dunc2504
Nice project .
Looks like you have an XLS and a Procat there.Still some wishbones on ebay to help with the joint slop . I am gathering parts for a Procat build just now , prices are not as crazy as Xls parts (YET).

I understand the reasoning, but both are XLS, except one has a Procat rear suspension added later. I understand quite a few of these cars were partially updated by their owners, as some improvements were cut in with later versions. You can see the chassic on the car with the ProCat suspension, is the stickpack chassis of the older cats. The ProCat came with a 7 cell saddlepack chassis.
Latest blog entry: For the love of the hobby!
Feb 10, 2015, 06:09 AM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP
Update added with some pics.
Latest blog entry: For the love of the hobby!
Feb 10, 2015, 03:40 PM
Time For Me To Fly!
fastmax's Avatar
Making some nice progress, and that chassis cleaned up very well.
Feb 10, 2015, 05:13 PM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP
Originally Posted by fastmax
...that chassis cleaned up very well.

Surprised me a little too. I was considering leaving the glue residue on, and just stick the ESC or receiver on top of it. But the glue was very brittle, and could be chipped off with a little pressure with the blunt metal blade.

Anyway, gotta get to study the manual again, it sure is a special design.
Last edited by SoloProFan; Feb 12, 2015 at 05:18 PM.
Feb 12, 2015, 05:18 PM
Fan of just about anything RC
SoloProFan's Avatar
Thread OP
Added some pics of the front suspension system and rear gear box.
Latest blog entry: For the love of the hobby!
Feb 25, 2015, 10:59 PM
Registered User
They are not much fun to work on are they. I rebuilt two a few years ago.
The red belt is an aftermarket one by wasp racing.
The CAT came with ugly white elastic bands from factory. The black O-rings were a common upgrade.

Don't know how they got so much dirt in the gear box. Never seen that before.

Picture of my blue runner and red/ orange shelf CAT's
Last edited by tekno23; Feb 25, 2015 at 11:13 PM.

Quick Reply

Thread Tools