final drive complete strip

[monkeyboy]

Just an opinion, having just replaced an input shaft taper roller bearing on a BMW car diff, taper roller bearings like any other kind are made to be EXACTLY the same size including the assembled height. Unless you are changing the input shaft and pinion, or the crown gear itself, or there is very significant wear on either gear, if I can't you should not need to reshim.

If that were the case then why would there be shims on them when new? Same with the crown gear - shouldn't they all be exactly the same size? Then we would only need shims after they've worn surely. I'm absolutely not starting an arguement here You can't tell how much something has worn without measuring it. OK - so the bearing is the same size as the one that came out - so has the taper bearing worn down to mean there is more gap at the crown than there should be? You can't tell without measuring. I only say this as a warning as I changed my crown bearing about 1k ago - simple process - no problem and replaced with the same shims. My taper looked quite slack and worn. I had a new one but didn't fit as I couldnt accurately measure the gaps (I'm a crap mechanic - even though I bought the tools to measure I wasn't confident as the slightest movement of my bench setup wasn't allowing me to do it properly!) So I put it all back together - the old bearing felt a bit worn...

I'm going on a BIG trip - took the gearbox out to get it rebuilt last weekend - some oil came out the diff when I was disassembling. It was grey and quite metalic - not good news - so I sent it away with the gearbox to have it done properly including the taper bearing. Mine has done over 100k so maybe that's a factor too though

 

[buellzebub]

I believe the bearings are all manufactured to near as damn it exactly the same size, I therefore believe the shims are there to compensate for inaccuracies in the FD housings. I don't believe it would be financially viable for BMW to invest in the equipment, tooling, machining etc required to manufacture high accuracy castings for each and every model throughout their range, whereas a bearing manufacturer specializes solely in accurately made bearings.

Mick

livin' the dream

 

[monkeyboy]

I believe the bearings are all manufactured to near as damn it exactly the same size, I therefore believe the shims are there to compensate for inaccuracies in the FD housings. I don't believe it would be financially viable for BMW to invest in the equipment, tooling, machining etc required to manufacture high accuracy castings for each and every model throughout their range, whereas a bearing manufacturer specializes solely in accurately made bearings.

Mick

livin' the dream

Understood - but that doesn't stop the taper bearing wearing significantly over time, and that will certainly effect the distance at the crown.

 

[buellzebub]

Understood - but that doesn't stop the taper bearing wearing significantly over time, and that will certainly effect the distance at the crown.

Yes, you're absolutely right. Maybe that is also, or possibly the main, reason for reshimming, it certainly makes sense.

Mick

livin' the dream

 

[Grizzly]

Bearings Still Have a Manufacturing Tolerance

Bearings may seem very accurate items to us - but they still have a tolerance on every dimension ie a high limit and a low limit.

Cheers.......................Grizzly

 

[Ian J Hartley]

Shims

The shim on the input shaft (pinion) is to position the teeth of the input shaft centrally on the teeth of the final drive (crown). This is so the wear is even across the teeth where they mesh together. Because the teeth are helical cut the position of the mesh is critical to even out the wear.

The shim on the small crown bearing is to adjust the backlash between the input (pinion) and output (crown) drives. Raises or lowers slightly the output drive teeth so that they mesh correctly to minimise backlash and wear.

The large shim on the final drive large bearing is to preload the bearing when the whole thing is assembled. Basically compresses the whole final drive assembly so they will handle the dynamic loads from the wheel.

If the rotation motion was all in one direction, then the shimming might not be that critical, but there is a 90 degree change of motion on the final drive. That requires accurate shimming. If you don't get it right, then the wear rate will be high. A crown pinion set cost over £300.

 

[Nick591]

Totally agree Ian. My point was only that if replacing bearings and assuming other parts (gears) are not worn the bearings will be identical dimensions to the original so original shims can be reused. Shim set up is needed when FD first built at factory to accommodate slight variations in machining tolerances of gears and casings. If you are not changing the gears you should not need to change the shimming. I was amazed that on my BMW 118d diff the main diff assembly runs on angle contact ball bearings held in place by large circlips - not a shim in sight. BMW must have really got their machining sorted out or use selective assembly of components to get the set up right when new.

 

[biker/trucker]

hey. still having hassle with this, pulling my hair out at this stage, ive shimmed up the tapered bearing, and the large output bearing, all 100% had the bike back together every thing seemed perfect zero play in the rear wheel, rode bike for a mile checked the wheel still fine, did about 20miles checked again and ive loads of play again, changed the oil when I got home and ive fileings on the magnetic bung, when the bike cooled down couldn't feele any play in the wheel again, any ideas?

 

[Packer]

If it has play warm and not cold I would start by checking if the pre-load is correct, the alloy case will expand more than the steel gears/shafts.

As for filings did you have the FD off the bike and clean it out thoroughly? Is it possible that there were still iron filings inside from the previous bearing failure?

Have you inspected the input shaft bearings?

I believe the specification in the manual allows for some movement at the wheel rim, you'll need to check as I can't remember what it is. Any measurable rocking movement at the rim is going to be about 200 times greater than the movement at the shaft. This assumes you holding the wheel say at the 9 and 3 o'clock position and trying to move it.

Have you seen this thread on Advrider ?

 

[biker/trucker]

Thanks for that, will take it appart tomorrow and see, both bearings are new, I did think the alloy casing was
hotter than it should be tho, generally it used to be warm but was really hot today, that would make sense if I
had it preloaded too much, can't think what else it could be really, I'll update tomorrow when I have a look at it.

 

[biker/trucker]

i seem to have this problem pretty much sorted , not having any more fillings, and the alloy casing its getting nearly as hot, I still have a little bit of play in the wheel but im going to keep riding it and keep an eye on the FD oil for further fillings, just haven't got the money at the minute to go and buy reconditioned FD or get it professionally done, will see what happens thanks for the advice!!