Gearbox assembly - pictures

(RIP) maverick

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UKGSer Subscriber
Feb 21, 2002
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Prince Albert, South-Africa
Ok here is some piccies when I rebuilt my gearbox recently. Sorry this took so long but been out on the bike as much as possible. It is not very complete and will try and answer any questions to my technical knowledge and appreciate if any previous "gearbox" rebuilders would comment on this devious task.

Firstly the output shaft flange seal.

1. Clean the Flange and have it completely degreased.
2. The new seal if original should be put on a special tool of some sort to shape to the flange face. I did not have the tool so decided to use the flange face for this job.
3. Boiled some water and placed the seal in the warm water for +- 10 minutes.
4. Tape the threaded part of the flange with a thin layer of insulation tape. This is to prevent any damage when pushing the seal on.
Last bit

5. Push the seal on with the inside facing the threaded part of the flange. Make sure the make and model requires this type of installation as my bike is a R100GS 1989 model.
6. When pushing the seal on be careful as it goes on extremely tight and could break if forced on skew.
7. Leave oil seal to shape for the duration off the assembly of the bearings and rest of the gearbox. If you are only replacing the seal the manual advise 2 hours at least. Would reckon it was on there for about 3-4 hours while I assembled the rest of the gearbox.
8. Carefully remove the seal trying not to disturb the shape of the seal lip.
9. Once the output cover is replaced and torque, press seal in position taking care not to damage or break it.
10. Degrease flange and refit carefully on shaft and in seal taking care once again not to damage the seal face.
Sorry about the quality on this picture..


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Main parts - Shafts

Ok, these are the buggers that can do your head in when you do not have the right tools.

On the left - Output shaft
Middle - Input shaft
On the right - Layshaft


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Output shaft

The output shaft bearings can easily be pulled using a bearing puller as shown. To refit them heat I heated up some oil(motor oil/gearbox oil) placing the bearings inside for 2-3 minutes on my camping stove and while hot quickly pressed them back on the shaft using the old bearing placed on top of them and a fairsize hammer to tap them into place the last few milimeters. Be carefull with the hot oil and bearings. Handling them with workers gloves or a pair of decent pliers is advised! The fumes of the oil is also dangerous and should be done in a well ventilated area.


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The layshaft was a bit troublesome for me as it requires a special puller to reach under the bearings or they can be pressed out if you have access to a decent vice. I decided to save myself the trouble and had the bearings pulled and replaced at Bracken for a few £££. Dropped the layshaft and input shaft off on the Friday and collected the Saturday morning. Please do note that this is a solid cast shaft and the gears can not be pulled as described with the output shaft, if it is badly damaged then you need to replace the whole shaft or find something decent 2nd hand!!


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Input shaft

Your main problem with the input shaft is the spring that needs to be compressed to remove the circlip holding the lot in place. Personally would not take the chance without a decent decompressor and can be fatal if the spring comes off and hits yourself or someone around you. So do take care if you take this off. There might be hardly any tension on the spring which should be fine but accidents usually happens with stuff like this.
The reason for stripping the input shaft would be the thrust bearing inner race(shown on the far left side of this picture) which is pressed on and can only come off from same side as the bigger bearing. Normally these bearings do not wear that much but mine was shattered after 60000 miles. This task was also given to Bracken with the layshaft. The bearing on the right is easily removed but do take care not to damage the shim plate behind it.
There is also a very tiny oil seal which is pressed in the shaft on the right which is advisable to replace.


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Bearing numbers

I have promised to give you guys the bearing numbers which was used and unfortunenatly misplaced them at home. Will go on search this weekend and post the details. This is all photo's that came out and wish I had taken more when stripping and reassembling the gearbox cover etc.
I used very simple tools like my camping stove to reheat the gearbox cover in order to pull it off and also the casing when replacing the shafts.
The output, layshaft and input shaft with the 1st gear selector should be dropped back in the casing the same time unlike the instructions in the haynes manual. The selector springs is easily replaced and all you need is a decent circlip plier.

Things I have replaced:
All the bearings
All the gearbox seals
All the selector springs
New gasket
New driveshaft bolts

Tools required:
Bearing puller/pullers
Flange removal plate
Thin walled socket to undo and redo the swingarm
10mm ringspanner for the driveshaft bolts
Heat gun or blow torch to heat the gearbox up
Various size sockets, spanners to undo and redo bolts
Torque wrench

Total cost for the spares, extra tools and labour

Done 800 miles since and not a drop of oil or problems so far.

Any questions let me know and will try and point you in the right direction.

Bearing numbers

Ok found bearings and here is the replacement numbers:

All these bearings is manufactured by FAG but would think that SKF or any other manufacturer with the same type bearings should be sufficient.

Output Shaft
Flange side: 6304RSR
Housing side: 6403.C3

Layshaft: 2 X 6304.C3

Input Shaft:6304.C3

The thrust bearing and inner race do not have numbers on anymore. But it is a special bearing and might be worth while to pay the tenner and get the right part.

The output seal was replaced with the original as the input shaft seal. I believe you could probably use Viton oil seals which should do the trick fine and can stand serious heat and costs hardly anything. Some items personally prefer to stick to the original and oil seals is one of those things.

Something else forgot to mention is that I went on the assumption because the original shafts and new gasket was used again it should be very close to what it used to be. Box is better than what it was and did not expierence any lockups or false neutrals. If you do replace items like the layshaft would recommend measuring and shimming the box as described in the manuals.
Did measure mine and they seemed to be in limits.

I think that about covers it and hope it was usefull at all.


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