Bob thanks for info,interested if there is anyone near me who could rebuild a box for me unless it would be worth getting tools what would I need as am in engineering?
Things you will need . . .
1. A means of locking the output drive flange while you are undoing / tightening the nut. I made a locking bar out of a length of flat steel, about 24" long. It needs to be bored to allow a 24mm socket to reach the nut.
A flat bar will also need a spacing disc underneath it as the output flange is sunk below the surface of the alloy housing that the rubber gaitor fits around.
There is a special tool available which is very nice, but quite pricy. I really must get one
.
2. Having got the nut off (its torqued to 163.5 lbs/ft) you have to draw the output flange off the taper on the shaft. These can be tight.
I made a heavy steel plate that bolts to the flange which is itself threaded to take the legs of a hydraulic bearing splitter.
Again, the special tool does this with less faffing about. My solution does work though.
3. Remove the nine 6mm socket-head bolts holding the end cover and then heat the cover to release the three bearings which are an interference fit.
I use a propane torch (carefully) or a 2Kw hot air gun. Carefully heat the whole cover evenly to just short of the boiling point of oil.
With the end cover removed, this is what you see, there will be shims on the end of the bearings:
I won't go through the whole re-build process - this is about tools - but here is a useful link:
http://jhau.maliwi.de/mot/gearbox.html
4. The selector cams come out as a single unit (two bolts through the front of the box). There are three springs and an indexing roller that can be replaced.
5. The two selector forks that operate on the output shaft are then removed by drawing their spindle shaft out of the box.
Remove the long, thin, oil baffle from above the output shaft (small cross-head machine screw on the top of the box).
The front face of the box then has to be heated to release the output and intermediate shafts and the input shaft front bearing.
The Selector fork that operates on the Intermediate Shaft has to be drawn off its spindle shaft as the gear shafts are removed - its spindle is fixed in the box.
6. You will need some form of puller to get the bearings off the gear shafts. I find a bearing splitter to be best (I now have a set of smaller ones than this
):
A three-claw puller can also be made to work, but the claws are often too thick to get between the back of the bearing and the adjacent gear.
7. On re-assembly, the gear shafts have to be shimmed to give a clearance of 0.05mm (
). This is where the technical stuff begins.
First, re-assemble the whole mechanism in the main gearbox case (heat the case to settle the front bearings). Then fit a new cover gasket.
You need to determine how far each bearing protrudes above the rear face of the gearbox case. To do this effectively you will need a "Shimming Plate". I bought mine from Mat Beekers at BMW Boxer Supplies:
http://www.bmwboxersupplies.com/product_info.php?currency=GBP&cPath=2&products_id=68&osCsid=a7794b0f5f8476e4e62316f6ca082d67
I drilled mine so that it could be bolted down on the gasket. It looks like this:
Then determine the thickness of the Shimming Plate. You will require a micrometer gauge for this:
Then you will need a "Depth Micrometer" to measure the height of each bearing's outer track above the Shimming Plate. They will all be different and you will get different readings as you work your way around each bearing
.
Next, you need to measure the depth of each bearing housing in the cover plate. Again, there will be different readings at different points around each housing.
Then do your sums. Pick the most representative values for the height of bearing and depth of housing for each bearing. The calculation goes:
Shim thickness required = depth of housing - ((thickness of shimming plate + height of bearing) - 0.05mm).
Shims are available in four gauges - 0.2mm, 0.28mm, 0.38mm & 0.5mm. Check the actual thickness of each group with the micrometer as there will be variations (i.e. don't just take the thickness from the packet !).
Remember that there is an oil baffle on the end of the Intermediate Shaft - measure it and treat is as a shim (its 0.5mm if you want to know
).
I lightly grease the shims to get them to stick to the shaft bearings and then put four 6mm studs into the case to locate the (hot) end cover as it is re-attached.
8. With the case re-attached, check that the gears work before you bolt up the output flange
The output flange is torqued-up to 163.5 lbs/ft. I use a 'certified' 50-300 lbs/ft 3/4" drive wrench.
And that just about sums up the tools you will need - without getting into details as to how the gears and selectors go together, or how you replace the springs & seals.
Any questions - just ask Rob Farmer
(Seriously, PM me if I can help).
Bob.
).
the reality was that it was impossible to change gear without forcing the gear lever back to the centre position.
he may, however, just have been taking the piss 
).
).
.
