final drive question...

[Deleted User 61]

The largiader site has a link to a pictorial that might help.

That's a good link and will be useful to monolever owners.

Whilst there are some useful bits of info in there, I wish there was a site that was specific to twin shocks.

Yeah, Duane has a little bit on the subject: http://w6rec.com/duane/bmw/finaldrive/

But even he says "10. An incorrect pattern can only be fixed by someone with experience, shims and tools."

[SteveD]

Yeah, Duane has a little bit on the subject: http://w6rec.com/duane/bmw/finaldrive/
But even he says "10. An incorrect pattern can only be fixed by someone with experience, shims and tools."

Yep, that's the sort of comment that seems to replace a description of the job.

I expect the job is tedious and may need some trial and error with shimming, and assessment and reassessment via colour markings on the ring/pinion interface to check for correct shimming.

eg, on a twin shock, do you just put it all together and turn it on the bench, then open and inspect the colour wear pattern? Repeat as necessary. A few sacrificial gaskets, a couple of shims and it's done?

Are there any tricks to checking correct alignment without opening everything up repeatedly? Can the same cover gasket be used each time the cover comes off, until finally replacing with new when happy with the shimming?

[Deleted User 61]

Paging Dr. Duane, on the white courtesy phone...

[Garnet]

http://www.bmwra.org/otl/finaldrive/

That is a nice explantion of what is inside a monolever drive and what may go wrong.

What he did not cover is what the cause of the "wheel play" over time.

I remeber Doug saying that he has developed play in his drive which is felt by the wheel moveing back and forth. I can't remeber weather it was hot or cold, but it goes away at the opposite temp. So, the case changes shape with temp and afects the bearing prelaod. That I asume is what you are going in to do Doug.

But what has changed over the years? Has the case changed shape? Or have the bearings worn that much?

[dougie]

Garnet - thanks for that.
I have just taken a break from figuring out how to shim this thing and it seems I am on the right path.
Measuring crown/pinion clearance is difficult as you can't fit feeler gauges in anywhere. I have Plastigage, modeling clay, a dial indicator, and .004" aluminium shim stock (better known as a Tuborg beer can).

The original problem was that axial play was increasing at the rear wheel, i.e. I could grab the wheel and feel noticeable play even after a long ride.
I have also found that I have greater than .010" crown/pinion clearance.

The plan -
Determine the inboard shim size to correct crown/pinion clearance. I am testing by stacking thin shims that I cut out of plastic sheet. That should be close enough to avoid buying more than a couple of real ones.
Then I have to figure out the outboard shim.
I wish they had used something like Hylomar rather than a gasket.
I will replace the huge bearing ($$$ ) and seal.
This could take a while, especially if these shims are a typical "back order" part.

[Major Softie]

I wish they had used something like Hylomar rather than a gasket.
.

As I recall, the K1100 I pulled apart was O-ring sealed. Way better.

[Duane Ausherman]

Paging Dr. Duane, on the white courtesy phone...

We actually had little need to shim a FD. That was because they are so reliable that a shop such as mine had at least a dozen or more laying around for spares. They had little value and so it was usually cheaper and faster to just swap them.

We did several of them over the years, but never did enough to get good and fast at it. If one did a few in short order then one would learn to "guess" fairly accurately. The many times of heating and cooling make it a time consuming job. None of it is brain surgery.

The concept is simple. One must move the two gears in and out until the contact is in the correct place. If the gears contact on the end, then they will chip away. One needs to start by having a few special tools, a way to hold it rigidly, a variety of shims and a good heat source.

About the time that you are finished, you probably won't be in a hurry to start another one any time soon, at least I wasn't. If a person did one FD a day, then probably the ability to guess from the play just what size shim to try first would emerge.

I think that I would want to make up a test fixture to hold a dial indicator to measure the play easily and reliably.

[dougie]

As I recall, the K1100 I pulled apart was O-ring sealed. Way better.

That must be a $10 o-ring

[dougie]

I think that I would want to make up a test fixture to hold a dial indicator to measure the play easily and reliably.

That's what I ended up doing.