Final drive TOOTH ENGAGEMENT QUESTION

[gtgt_bangbang]

Final drive TOOTH CONTACT / BACKLASH QUESTION

Does anyone know ;

HOW FAR DOES THE PINION GEAR -to- CROWN WHEEL TOOTH CONTACT SPOT MOVES, FOR EVERY SHIM INCREMENT ?

This is for the shim under the drive pinion bearing, which controls the PINION INSERTION DEPTH INTO THE HOUSING,
which controls the pinon to crown tooth patch.

I'd like to move the center of the contact patch a couple mm to center.

These shims come from 1.5 to 2.5mm in 0.05 increments.

Does any body have a stash of these shims , used, to sell swap or share ?
I'd prefer to get an answer and nail it, but I'd generate the useful data if I could get an assortment of shims .



fuller story -
The 'math' marked on my case & pinion indicate a 2.24mm shim required under the drive pinion bearing,
( +20 scribed on the crown wheel & 46 stamped on the case ,ie 77.70 - 75.46 = 2.24mm)

This unit had a 2.19mm shim (as measured, call it a 2.2) under it the pinion gear bearing upon tear-down,
I reassembled it with the same shim.

This part is actually called a (for instance) 33 12 1 231 239 COMPRESSION RING - 2,1MM

Reading the contact point with gear marking wax indicates an " thinner shim / deeper pinion required" error in the contact patch.

I'd like to move the contact patches centers , up to a couple mm
TYI to anybody with experience adjusting their Final Drive tooth patch..




BACK LASH ADJUSTMENT - CROWN WHEEL SHIM

I dont have the measurement jig to put a true number on back lash but its easy to see & feel this sort of movement.
I'd estimate the original backlash in this drive would have been easily over .010", if jig measured.

Clymer says the back lash should be "nil',
and the BMW manual says the backlash should be .004 to .006" ,

There was 2.09mm shim in there.
This shim is actually called a 33 12 1 231 239 COMPRESSION RING in max.

I got a nil+ backlash by substituting a ~1.93mm shim stack.

"stack" ?
I picked up a set of thin-stock shim washers to stack up / test / determine changes for set up.
You can search ebay for dimension ( 37mm x 47mm) pops up a number of english vendors
moakes-trading had the lowest shipping & total cost. Ran about $20 all in and mail was fast.
I bought their minimum (10x count) in each .1, .3, .5mm thickness, in order to make up a pretty comprehensive set of set up shims.
The shim stock isnt dead on those numbers but nothing majic about the exact numbers
FWIW, almost every shim I got from bmw has been off by a bit, but in the window. Good nuf for tractors like these.

I'll probably just use the stack of set up shims to run, but that brings up the next issue- bronze or steel ?
cos Im guessing some of the popular/low stock COMPRESSION RINGS are getting pretty spendy ,
and probably euro supply delays.


CROWN WHEEL SHIM MATERIAL ? Steel or bronze ?

these crown wheel shims for back lash adjustment are bronze at least according to Max catalogs
for instance ( 33 12 1 231 239 COMPRESSION RING, ) ,

The shim coming out of my bike was steel.
This is a sliding contact point and the bearing flanges/ shim were of course polished but not overly worn or not all destroyed.
I also see some of these shims in BMW packages elsewhere that appear to be steel.

Anybody know if BMW substitute material bronze vs steel ?



I could see why either material is acceptable, as the only load directly ON this back lash adjusting shim is

a) due to gear interactions & thrust reactions ( mainly the gears want to climb apart when loaded)
This means when the "climb apart" force is highest, the needle bearing shim is UNLoaded...
and
b) the combined effect of this shim and the large OD shim , ( for instance 33 12 1 230 540 SHIM - 90 X 99,8 X 0,750MM
This is the large shim between the 07 11 9 981 760 GROOVED BALL BEARING , and the inner cover.)



SO NOTE - Dont overlook; if you change the BACKLASH by swaping needle bearing shims as described above ,
you should also change that large, 99.8 OD shim to compensate, otherwise you'll be side loading the large ball bearing more than intended
This whole crown wheel assembly is one solid stack from needle bearing to ball bearing .

For example , reducing back lash requires a THINNER needle bearing shim ,
which then requires a THICKER ball bearing shim , to keep the ballbearing properly loaded.






The excess backlash in my FD may account for why the only bearing in my drive that felt sketchy was this bigass ball bearing.
Its rough, probably very noisy and I'm going to replace mine.

Boxer2valve shows how to take that bearing off with an large $$ puller,
but notice that the crown wheel has a set of holes intended to drive off the bearing ( the manuals agree) .
Hoping that some heat , a drift and a zealous hammer will allow removal. Would not be risky to cut if off, either.
Install of that bearing is a simple " heat it up / install on cold crown wheel" job

 

[gtgt_bangbang]

To beat dead horse lol,
The contact spot moves on the order ~3mm for every .1mm of spacer change.

I flat lapped a 2.19mm pinion shim (in there at tear down) to 2.1 then 2.05,
assembled drive at each step for contact patch check.

The 2.1 was probably enough and 2.05 still looked good , particularly on the drive side.
but there was some minor galled spots on one edge of the coast side , which might have affected coast results.
Looked like some debris got in there in the past , spots had mostly self polished ,
but I gave a touch up of dremel / emory then polished with tripoli to try tease them out a bit more.
Ddint do that until after tests & noticing issue

Let the new wear commence.


My drive was marked for 2.24mm from the factory but contact patch was relatively off center. Maybe pics later but revealing photos hard to obtain
and I'll probably reduce the new 2.1mm shim coming , by a few .01 for hopefully last assembly & build it for good if it passes check.

assembling drive with out green or gummy seal saves those parts when doing checks and wont affect results.
IN fact I left the whole pinion assembled with all the washers , hub & nut , just inserted the whole assembly in the heated case.

It took 90~100C ( via cheapy IR gun) to slip the bearing in. I was using mapp and a propane torch , and wanted to get on with it without overheat / warp,
so panned the flames a lot all over .
Some temperature sensing ink would be a good buy if planning ahead.
other ways of course.., oven thermometer, a thermocouple, might even find a metal cup that fits in the bore and wait for it to boil water
.
heres a for instance for the ink, no experience with these, but https://spotsee.io/temperature/heat-mark-indicator-inks-pigments-coatings, exists.

Dont try insert it when housing too cold ! if the assembly cocks / hangs on the way in, its a powerful thermal sink and grabs tight.
then theres a lot of heating to do to get the whole thin back to temp.
But with the bore aimed vertical, assembly drops in & sits in place until cool.

The case must throughly cool before checking, thermal expansion could certainly alter results.


New angular bearing installed after measuring so have to check one more time but the dimensions of the assembled pinion were identical , not expecting a problem.

 

[Lendog]

I hope you are capable of doing what you want, if that diff locks up you’re in a bind too, you may end up with a whining diff,
diff lube can be used to identify the contact area, if the contact pattern is not beautiful the diff will be noisy

 

[AntonLargiader]

I've built a lot of FDs and in nearly all cases the BMW math works out great, so it's very very rare that I need to change that shim and check results. However, I do have one such FD on the bench right now. It's from a Hexhead and the contact shows that the shim needs to be thinner. I think the math says 1.83 and it had a 1.85 in there. I've changed for a 1.80 but have yet to see the results. The contact was really on the tips; I have no explanation for why it was so wrong.