Overhauling Rear Drive

These notes cover all rear drives after chassis number 65186, but the procedures for the overhaul are similar. Before starting this job, do some diagnostic work to determine the extent of repairs and replacement parts needed. Jack up the car and make it secure and remove the wheel and brake drum to reveal the brake linings. You should plan to replace these anyway as most of the work you do in dismantling the rear drive must be repeated if the rear brakes are to be replaced. If the brake shoes are covered in oil then the rear seal must be replaced. Take off the rear chain cover, taking care not to damage the synthetic rubber gasket that is normally re-usable. If there is corrosion present, you should plan to replace the chain and the rear axle bearings. Remove the small oblong cover at the front end of the chain case again taking care with the synthetic rubber gasket. Check for corrosion around the small chain wheel and pinion, if none is present, it is usually safe to assume the front bearings are in good condition. If you are not sure, it is better to remove the complete rear drive from the rear frame by releasing the eight bolts from the rear suspension rubbers. Once you have dismantled the rear drive the car is not moveable and if this is important to you, then plan to have all the parts and tools available to complete the overhaul.

Minimum parts requirements are as follows:-

2 Rear Axle bearing 6205 Partsmart 1767 1 Rear oil seal Partsmart 1769 Pair brake linings Partsmart 1348

Tools

A two or three leg puller is required to remove the chain wheel after the taking off the retaining nut. The workshop manual shows a large and complicated extractor for removing the rear axle. However, the axle usually moves very easily after a few blows from a large hammer. Of course the shaft must be protected if this method is used and a soft metal drift is normally used for this kind of work. Failure to protect the shaft end will result in extensive damage to the axle and may even make it unusable.

In many cases the rear axle will be removed leaving the inner bearing and seal in position on the shaft. When this happens, a really special puller is required. The problem is that there is no available surface for a conventional puller to grip and the bearing is often so tight that it cannot be removed even after destroying the seal to allow the puller to fit behind it. In this case a special shaft bearing puller is required. A suitable one is marketed by the Sykes-Pickavant company in the U.K. and consists of two curved jaws that are bolted together under the bearing face. A conventional puller is then attached to this and will pull off even the most stubborn bearing. It is possible to make a similar device by grinding steel angle sections to grip the bearing face and bolting them together. If you do not have access to extensive workshop facilities, do not attempt this job. Bearing removal can take many hours and you may end up grinding the bearing off the shaft with consequent risk of damage.

If you remove the rear axle bearing housing (by removing the four hex head bolts inside the chaincase), remember to apply sealant to the faces on re-assembly. Failure to do this will allow oil to leak through to the brake linings. The brake cam is also a source of oil leaks and you should ensure the ‘O’ ring (available from Partsmart) is in good condition.

Replacing the front drive pinion bearings

Be sure to complete the above-mentioned diagnostic work before starting, as this job is difficult and time consuming. These bearings rarely fail and it is not normally worthwhile dismantling and replacing the bearings unless corrosion is present It is assumed you have removed the entire rear suspension form the car to do this job although the engine can remain in place. Before removing the chain completely following the diagnostic checks, re-attach it to the large chain wheel. This will allow you to prevent the shaft turning while you remove the left hand thread nut on the carden shaft drive pinion. If the nut is very tight, put the rear wheel on the studs to help prevent the shaft rotating. The bearing housing can now be removed, (after removing the screws), by gently tapping the suspension rubber and the bearing will remain on the shaft. A special puller is needed to remove the carden shaft pinion – the Sachs puller for the corresponding carden shaft pinion on the engine is too big. Try to borrow an early MOC puller made from a carden shaft. (Do not cut up an old carden shaft to make one as these parts are now rare and valuable). If the above puller is not available, use a proprietary thin jaw puller. When the pinion is removed, the shaft can be gently tapped through the bearing, taking care not to damage the thread. Take care with the speedometer drive as this is easily bent when fitting the new bearings. Assembly is simple but remember to coat the housing faces with sealant to prevent oil leaks. The oil seal 1757 (available from Partsmart) used to seal the shaft on the drive end sprocket shaft, (located behind the Cardan shaft drive sprocket), should be replaced before re-assembly.

Partsmart now offers the following new parts for the rear drive unit:-
1755 Nilos ring ? 0.95 this is the cover fitted over the 6205 bearing behind the chainwheel. The purpose of this ring is to retain grease in the bearing and to prevent dirt entering.
1754 Nilos ring ? 0.95 this is the cover fitted over the 6304 bearing on the drive end sprocket (speedometer cable side) . The purpose of this ring is to retain grease in the bearing and to prevent dirt entering.
1757 Oil Seal ? 2.75 used to seal the shaft on the drive end sprocket shaft. Located behind the Cardan shaft drive sprocket. Replacing this seal normally requires the drive end bearing housing to be removed.
1433a Gasket for small chain cover plate ? 1.95 . This plate is often removed to allow access to the chain during replacement in case of breakage or if it accidentally comes off the sprocket during repairs or replacement of the chain.

The above parts are suitable for use on all KR200’s from chassis number 65186. Owners of early cars built from 1955 to 1957 use the earlier type rear drive. This uses 6204 type bearings in both the rear axle and front pinion drive shaft – Partsmart does not stock parts for this early type. However, if any parts are required for this early type drive, please contact Helga and we will try to locate them. With a rear axle of only 20mm diameter as compared to 25mm for later type, this unit is obviously weaker than the later one.

Partsmart offers the FMR spare parts book (Part No, 1804 at ?3) that identifies all the parts for both types and includes diagrams showing how the various parts are assembled. If you need other components for the rear drive, used parts are available from Derek Cole.