- Schumacher Cougar SV -
Words & Pictures: Arn0

Transmission

Only for the second time, Schumacher does not use a belt transmission on his two wheel drive buggy, the previous one being the Cougar 2000. So the SV owns a brand new transmission with four gears plus the usual spur-pinion, without taking in consideration the differential spur. At the end of the day, that makes five gears, impressive for a two wheel drive.

To get it done, seven bags need to be opened!! Here are the components of this transmission:

• 3 pins
• 6 bearing
• 2 seals
• 2 eccentrics
• 4 gears
• 2 housings
• 1 motor plate
• 3 screws
• 3 shafts
• 3 spacers
• 4 washers
• 2 nuts
• 1 spring
• 2 slipper plate
• 2 slipper pad
• 1 machined spur

That makes a total of forty one items. There are this many components because this transmission is adjustable in different ways. Let’s have a quick overview of the four major assemblies detailed below:

1 - the transfer shaft with the slipper clutch already seen on the Cat SX

2 - the layshaft with it’s gear

3 - the height-adjustable idle gear

4 - the differential

By default, the internal ratio is 2.6:1, kind of a magic number in 2wd, and it is defined as 'medium internal ratio'. 'Medium internal ratio', that means there is a 'high internal ratio' and a 'low internal ratio'. This can be achieved but replacing a set of pinions: the ones on the outside of the gearbox. Per kit, you have a 23 tooth and a 33 tooth, but you may switch for 22/34 to get the 'high internal ratio' for hi rev motors. 'Low internal ratio'  is established by combining a 24 tooth gear with a 32 tooth one which is a better fit for low rev motors such as those dedicated to the stock class. In every case, fine tuning of the final drive ratio is still achieved with the inseparable spur-pinion.

It is possible to set the transmission height, a setting that appeared some years back but is very useful to increase or reduce traction of the rear end. In the present case, the casing will always stay in the same position, meaning some eccentrics located around the differential will allow the adjustment of this parameter. But to do so, one gear - and consequently a shaft - needs to move up or down, which is done by the eccentrics inside the gearbox.

Before pushing forward, let’s have a better view of the layshaft gear inside the gearbox. This gear is mounted on a shaft with two pins; these two pins are held on by two o-rings. Fresh mounted, that looks good. But projecting ourselves into the future, the o-ring may dry, the pins may push on those o-rings and at one moment, one of the pins might escape and have a nice and devastating journey inside the casing. You get the point: bye-bye internal gears. So, while mounting this gear, you can either replace the pins by roll pins or use a tiny drop of glue to avoid any pin movement. Of course, some other alternative solutions may appear.

Done with the rotational parts, let’s have a look at the fixed parts. The motor mount is a one-sided chamfered purple anodized 4mm aluminum plate, a nice look piece to cool down the motor. The two others fixed parts are the housings. Complex molded items with a lot of recesses and details, the twins may have cost Schumacher some effort. The internal shape is well made, no play between gears, shaft distances are good with the provided external gears and no doubt will work great with the optional ones described above. But strangely enough, there is no lip all around one of the housings to provide sealing. Look deeply at the shape, it is impossible to get this lip done as the casings are almost symmetrical and molding processes do not allow the fabrication of this lip. To get it in place, the housing should have been asymmetrical or with an additional piece, but would probably be even more complex to produce. Here, only the design team gets the answer and the final decision was a compromise between various parameters, as always in engineering.

The assembly is in fact pretty straight forward. Be sure to install one eccentric on each housing and in the same position. As recommended, the differential will be set low to get the highest traction possible so the idle gear must be positioned low, otherwise you won't have mesh contact and consequent motion while accelerating.

As standard equipment, the transmission is loaded with a slipper, the basic system designed years back. The components are the same as the ones from the Cat SX, so no surprise. And as the 4wd, the setting will be realized from the other side of the spur location.

Once together, the whole transmission runs smoo... almost smooth, there is one spot where you can feel some resistance, a hard spot most probably due to a tiny something on the nylon gear located before the metal one. That will disappear after a little break-in.

One advice that will be useful while putting the transmission into place, do not tighten the three screws holding the motor plate and so, do not install the spur and the related items.

Differential

To get the transmission fully done, the differential is the next step.

First point to note, an additional sheet giving some advice on a specific point of this part of the car's assembly; the mounting of a circlip with dedicated pliers, provides advice for this procedure.

The design is the same as the one for the Cat SX, just to note a thrust bearing and four Belleville type disc springs are fitted on a fully threaded screw. The use of a fully threaded screw is weird as one of the thrust bearing washers will come in contact with the thread at one point. In the first instance, it’s worth the try as is works fine on the 4wd but switching for a partly threaded screw would be a good idea. This assembly sits inside one output once installed from the inside of the differential and not from the outside.

Others designs are based on the use of a spring and nut, both located on the opposite output where the thrust bearing is located. The Schumacher design makes the screw tightening directly on the opposite output, meaning no nut, and a headless screw secures the whole package.

The assembly is pretty straight forward. The thrust bearing discs are not the same thickness, the difference is minimal so be careful. Also be patient while putting on the circlip, it can be twisted slightly to avoid any freedom and take care how you insert it as the additional sheet is very clear about that. You may add a spot of glue to make sure this circlip won’t move. The differential will be adjusted once the car is done, tightened enough to be borderline loose.