Schumacher CAT XL 2WD (T402) for vintage racing

[LurkingCAT]

Even though I’ve been lurking around with CATs since autumn 1986, I’ve not come around to post a build of one of my absolute favourite rc platforms on RC10talk – HIGH TIME!
Of course many threads on here from before, but here goes my own take on a CAT. Hopefully contributing to the information already on here.

The C-Car being very popular in Norway (1/12 track), we were already familiar with Schumacher back in 1986. When reading teasers in the British magazines of an off-roader it got to be my priority number one to get my claws in this beast. Preorder was in, and I got my T400 out of the first handful of cars shipped to Norway autumn 1986.

The T400 “Competition All Terrain” was later called the SWB (Standard Wheel Base – not Short Wheel Base).
Schumacher experimenting with longer chassis plates (10-25 mm) resulted in the XL conversion kit (+25 mm), available from spring ’87. This was the point the “Standard Wheel Base” was introduced as a term to distinguish it from the new long wheel base. Glyn Peglar won the Reedy Spring International at Romsey with the XL in April ’87, but most Schumacher drivers had the SWB all along to the IFMAR Worlds at Romsey in August – including Hirosaka. When he got the long wheelbase car from Cecil Schumacher at Romsey, he had the SWB in his suitcase.

In 1987 the XL also came as kit (T401 4WD and T402 2WD), and changed with upgrades along the way until the XLS was released in 1988. First still with the grey bumper and front spool with oneway bearings, later with the black bumper, front diff and other upgrades.

I followed this development closely as I had these three platforms through the XLS. After the XLS I jumped over to the Yokomo 870C.

Anyhow, now over to the XL 2WD build. Never drove 2WD Schumacher before the Topcat, but now I want to make a 402 for vintage racing on astro/carpet.
The starting point is the XL chassis in the picture:

The XL chassis share the “winged” front of the top deck with the SWB.

[1911Colt]

This is already my new favorite thread!

Even though the T402 was not considered a success in its time, I have wondered how it would do today. Mid-motor was a hindrance for a 2WD buggy on 1980s tracks. With the massive grip of modern tracks, all competitive 2WD buggies have evolved into a mid-motor configuration. It will be interesting to see how well it goes.

[LurkingCAT]

Yes indeed. Hardly saw the 2WD on tracks back in the eighties, but it will be interesting to see how it performs on tight high grip tracks. That’s why I wanted to take on this particular build, and there are some specific assets to the XL from the XLS I want to investigate on the track. I'll come to that later.

Must mention I watched a youtube channel where this guy is kicking around with vintage cars (no one mentioned). In an episode I saw a few days ago he was covering the XLS Masami build. He thought it was very strange that the battery clamp screws were fitted from below – it would make more sense if you could handle these screws from the top. And yes, it is a bit strange if you don’t know these were designed the C-Car (where they were a perfect fit) and put straight on to the CAT (#C058). The youtuber reamed two holes in the undertray to get access…

Including a picture of the battery clamps and the common solution many of us used back in the eighties. Cutting a slot at the bottom of the screws so one could tighten and loosen the battery from the top. BTW these clamps were some of the hard-to-find parts before the rerelease. On this car I think all parts will be original XL except for some obvious ones we will come to later on.

[LurkingCAT]

The side plates for the gearbox (T072 Cover plate and T073 Motor plate) are generation tell offs, and can also reveal the upgrade history of a CAT. However, the part numbers for the plates were the same for SWB, XL, XLS and Procat.

The holes inside the green markings are for mounting the upper rear suspension arms on the suspension pivot (T079) and is fixed to the fibreglass suspension bracket (T105) at the same vertical level.

There are three configurations of this hole pattern. The “high hole” seen in the picture (SWB/XL), the “two hole” (XLS), and the “low hole” (Procat). The second hole on the XLS shares the same position as the low hole on the Procat (red dot indicates the position of the lower hole).

Lowering the position of the upper arm was a popular mod to the rear suspension geometry of the SWB and XL. This gave more camber gain and in general better results on bumpy and loose tracks. To achieve this, one could drill out the lower hole and use the lowered fibreglass suspension bracket (T145), or much more commonly go for the full-blown rear suspension geometry modification kit (T646) both lowering the position of the upper arm and increasing traction width. The fibreglass suspension bracket in the T646 kit was the T154, and was later included in the XLS kit. Homemade and other third party solutions were also common.

For this build I’ll keep the original layout with the T105 suspension bracket to get a higher inner pivot position giving less camber gain.

Also worth mentioning are the eccentric bearing housings (T081) used as tensioners for the short rear belts. The eccentrics mounted on plates in the picture are the XL/XLS ones. The one with the knob is the later Procat/Cougar, still with the same part number. I've seen several of the new built SWB with the later knob eccentrics as many of these builds are the result of years of parts collecting. Something to keep in mind if you are aiming for a authentic and truthful CAT build.

To make things even more nitty gritty there are two versions of the eccentrics without the knob. One where the inner diameter allows the rear hub (T031), e.g. integrator outdrive go through, and one with smaller inner diameter found on the very early SWBs. On those the rear hubs had to be mounted from the outside.

[1911Colt]

Lowering the position of the upper arm was popular modification to the rear suspension geometry of the SWB and XL. This gave more camber gain

School is in session! So many good bits of info I didn't know any of it.

For the part I quoted, Shelby did this same trick for his Mustangs (except he did it on the front). It was actually a Ford engineer's idea (Klaus Arnung, I think?) but Shelby's name was on the car, so we know it as the "Shelby drop".

[LurkingCAT]

Good to hear!

Cool, never heard about the Shelby drop

[LurkingCAT]

If you are familiar wrenching both RC10 6 gear and early CATs, the kinship between the diffs on the layshaft are quite striking. Following the power route down to the outdrives things are a bit different, with gears vs belts and Schumachers integrator which was employed to enable a varying amount of drive to the front wheels. One of the most common mods to the CAT was to replace the integrator with a drum diff and solid layshaft, and was offered by several suppliers such as WASP and MMS.

Anyhow, for the 2WD the integrator offers and unintended but interesting asset on high grip tracks. Even if the integration of drive to the front wheels is not an issue on the 2WD, the integrator can be used to tune the resistance of the diff, just as changing viscosity in modern gear diffs. The diff itself is adjusted as loose possible with no slip. The effect on the diff from integrator adjustment is quite remarkable on the work bench. Will be interesting to see how it actually works. In my modern Schumacher 2WD I typically go to the heavier diff oil in the gear diff on high traction. Now I will see if the integrator serves me with this tuning option.

Gear box built as per XL/XLS spec.

[LurkingCAT]

The high hole transmission plates are accompanied with high hole inner transmission housing (T071). Later the housing came with two holes under #T293.
I've cut out a small inspection hatch for the belts and covered with a "swing around" polycarbonate plate.

[1911Colt]

Clever! My CAT may be getting one of those inspection panels.

[LurkingCAT]

The small and anonymous rear suspension pivot blocks (T077) are adding to the tuning possibilities of the CAT.

A simple and effective way for adjusting the rear anti-squat. There is an early version of this part with the same part number, but I think I will save the description for a SWB build thread...

Anyhow, the little block can be mounted with the square out, round out and flip it round the screw. This gives combinations for various degrees of anti-squat.

Some examples of different configurations.

[LurkingCAT]

Built a standard XL steering with the T116 fibreglass centre track rod.

To go along with the wide track mod, Schumacher made the T170 wide centre track rod.

On the original XLS the wide rear/front was part of the kit along with the wide steering rod. However, faithful to worlds setup, the release Masami XLS came with the narrow centre track rod.

This car will be built with narrow track width both front and rear.

[LurkingCAT]

There are some different drive shafts.

To the left original SWB/XL and a longer version to the right. I can’t get myself to drive with the early ones, so opting for the ones in the middle. They are the Schumacher mk3 found on Bosscat and other newer platforms. Just a tiny bit longer and a perfect fit.

If you want to build a genuine early car and wonder if you have the right narrow axles, you should look for NO outer sleeve (see photo 2) and the grooves at the end on photo 4 (to ensure is not a cut down longer one).

[LurkingCAT]

For me it was mind blowing to see the tuning possibilities of the CAT, and gave me a new understanding of the complexity of RC cars - everything from drivetrain to suspension geometry.

The front pivot bracket (T006) came with the SWB and XL kits (left on picture). It serves as top mount for the shocks, and the inner hinge pins for the front suspension arms. They are quite upright and gives a caster of ≈ 6°.

As you can see to the right, the XLS (also Procat) came with a new pivot bracket (T156), leaning more backward and giving you 15° at the hinge pin.

However, another tuning possibility with the CAT is to swap around the offset suspension arms. The same suspension arms are used front and rear, with an A and B lower arms and A and B upper arms.
In this set up I opt for the original pivot bracket along with upper and lower B arms to the left, and A arms to the right.

As you see in the last picture this gives a backward off set of the upper arm, adding to camber on the hub.

Swapping the lower arms gives vertical alignment of the upper and lower arms.
In addition, the lower front arms have two spacer O-rings allowing for additional fine tune.

[LurkingCAT]

At last able to get a bit of time at the workbench after too long a pause.

Chassis coming together.

Except for internal limiters and adding diaphragm I rebuilt a set of shocks to XL spec.
Springs from the Schumacher tuning set (medium and short).

Also replaced the T091 rod end on the shock piston with the T238/239 rose joint.

[1911Colt]

Classic Schuey tooling marks on the shocks