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Author Topic: Final drive input bearing  (Read 232 times)

Offline dogshome

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Final drive input bearing
« on: January 01, 2022, 10:32:51 AM »
I have the final drive. It's a finned type. Uninspiring use of bathroom sealant on the flange and a stripped driveshaft filler tapped 9/16 UNC with a metric taper hydraulic fitting jammed into it. Splines show some wear, maybe 20% but OK. New seals fitted in the big bit by my friend, I have the seals and big torque wrench for the input side. Plus the tool he made. We put a 9/16 tap through and I've cut a suitable bolt with copper washer for the filler.

Much cleaning and slooshing with solvent and nothing unusual came out. Bit of metal dust very fine and on the magnetic plug. Normal. 

The only bit that is bugging me is the very slight rust on the outer (inner race) due to it not being on the unit for a few years. Cleaned with scotchbrite, but not convinced.

Not planning to take the main cover off, although now un-decided about that too! But it looks like the input bearing can be pulled out with the pinion by heating the case and does not need any other special tools. Just 2 big screwdrivers behind the input spline/nut. The bearing is about 40. I don't fancy that one failing on the motorway. SO. The question is, if I just heat the case (leaving bevel etc intact) can i just pull the pinion out and replace that bearing?


肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline Tony Smith

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Re: Final drive input bearing
« Reply #1 on: January 01, 2022, 06:15:05 PM »
Yes, but you should not unless you really need to.

I would be inclined to run it a few miles and then listen for noise. Also of that bearing is unhappy the local heat will give it away.

Bear in mind that of you change that bearing you will need to completely check the shims setting the contact patch of the crown and pinon.

Chances are the existing ones will be close enough, but of they are not you are on a world of hurt.

However, if you do proceed and change the input pinion bearing, do also change the small inner bearing as it is usually this one that wears out
 Be warned they can be a right bastard to get out - use heat.

However I I would run the FD and look/listen for sounds of distress.
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline dogshome

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Re: Final drive input bearing
« Reply #2 on: January 02, 2022, 08:17:12 AM »
You are right. If it needs a full rebuild later, then so be it. I don't know if the gears are shot or not so a run will find anything there too.

A bit more elbow grease and happier. On the basis of a micron more wear vs skidding / vibrating ball race turning at 6000RPM. Pic below. I can't imagine anyone ever having this particular problem before, it's only because the inner race has been off the bike and the thing half stripped for the past ??? years. The rest of it had a good coating of oily filth  :thumbsup:

(why do pics always make things look worse than they are!)
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline georgesgiralt

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Re: Final drive input bearing
« Reply #3 on: January 02, 2022, 09:42:35 AM »
Hello Lads and Gals,
When I studied mechanic, a teacher told us that regarding bearing, if you see something on the race the bearing is shot. If you feel something on the bearing race when running a nail on it, the bearing is double shot.
So IMHO your bearing is just good for the bin.
As per it's replacement and setting the pinion position, carefully measuring the position the pinion has with the shot bearing and setting that measure once the new bearing in place is IMHO sufficient.
Do not forget to change all slip seals on the drive unit.To remove the bearing in the body (to change the seal witch it conceal) put the housing upside down on the bench, and heat the drive unit evenly. When the proper temperature is reached, the bearing will fall with a noise on the bench. To install it, cool the bearing and heat the drive housing. Not that difficult except cleaning the old gasket.... (of course you have a beer can cut properly to protect the big lip seal when assembly time comes from the splines.... )

Offline dogshome

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Re: Final drive input bearing
« Reply #4 on: January 02, 2022, 09:45:42 AM »
 ;D


肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline dogshome

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Re: Final drive input bearing
« Reply #5 on: January 02, 2022, 10:25:25 AM »
 :engel017:
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline Tony Smith

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Re: Final drive input bearing
« Reply #6 on: January 02, 2022, 03:56:24 PM »
Hang on here. Which bearing are we actually talking about?

The initial discussion in my mind was about the input shaft bearing behind the bell coupler that connects the driveshaft to the final drive.

But the photos are of the "big bearing" that supports the output side of the "ring" gear.

Now here is the thing.

The big bearing works for a living and whilst it can have a long and happy life (coming up 50 years for some) it needs to be in perfect condition.

It's opposite number in the early final drives is a sleeve needle roller bearing which unlike the tapered roller fitted to later final drives will never know what hard work is and unless it shows signs of physical damage can be safely left alone.

The OP says it is a "finned" case final drive so I am assuming late model.

In any event replace the big bearing and the tapered roller. Then shim the damn thing properly. Ignore those that say "just bung in new bearings, put the old shims back in and just ride it" they do not know what they are talking about.

The problem is that sometimes given the precision nature of bearings if you change out the same brand of bearing you will be pretty close, possibly 50 percent of the time. That is not odds I like.

Remember I said that this bearing works of a living? It needs everything going for it.

My original comments related to the input bearing behind the bell coupler. In contrast this bearing will never know what hard work is. The same size bearing is fitted in the differentials behind BMW V12s. For the miniscule power of an airhead it is grossly over spec. Hence my "run it and see how it goes" suggestion.

Combined with the knowledge that setting up new input pinion bearings adds a further dimension of complexity to the shimming process. In other words, not trivial.

It also occurs that your photo is of a disassembled bearing. In my experience by the time a ball bearing has worn sufficiently for you to reverse the manufacturing process it is stuffed, never mind the corrosion on the race.

1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline dogshome

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Re: Final drive input bearing
« Reply #7 on: January 02, 2022, 04:28:32 PM »
It's the small dual angular input ball bearing supporting the pinion. I do not intend touching the needle rollers or large bearing on the bevel gear.

The bevel gear looks good, the pinion has some wear as do the splines, but serviceable.

I plan to replace the split ball bearing with a single piece modern equivalent. 3305-BD-XL-TVH. That is the one that had rust on one of the split inner races (it was on a shelf for years).

肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline dogshome

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Re: Final drive input bearing
« Reply #8 on: January 07, 2022, 07:12:22 AM »
For reference, the breather plug can be exchanged for a much more cost effective M18 x 1.5 Hydraulic breather.
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline dogshome

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Re: Final drive input bearing
« Reply #9 on: January 07, 2022, 10:20:16 AM »
New bearing.
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline dogshome

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Re: Final drive input bearing
« Reply #10 on: January 08, 2022, 01:44:40 PM »
All back together, but missing the pipe that carries the brake arm through the final drive. Part number is 33112301760. Can't see it listed in the UK, so before I start making calls, anybody got one or is it a standard bit of tube I can buy? i.e. 16mm or 5/8 etc.
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline dogshome

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Re: Final drive input bearing
« Reply #11 on: January 09, 2022, 07:51:29 AM »
Hole is 15.86mm. Shaft is 13.85 with 14mm OD of installed O Rings.

5/8" 20 SWG ube is 15.88 OD and 14.052 ID. So will try a bit of that with loctite and/or heat as required.
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline dogshome

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Re: Final drive input bearing
« Reply #12 on: January 14, 2022, 09:52:24 AM »
OD is a good press fit  8)
ID needs a bit of grinding to get pivot through  :D

Note worn but usable splines. Gears are in better but obviously 'used' condition. I'll see what the ones fitted look like soon. Couldn't get back wheel out before now due to huge tyre, only squinted at splines for smear of moly on them.
« Last Edit: January 14, 2022, 09:55:29 AM by dogshome »
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline dogshome

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Re: Final drive input bearing
« Reply #13 on: January 16, 2022, 02:18:57 PM »
Just for information:

1. 5/8" 22 SWG would be a perfect size for the tube if you lose one. Needs a little sanding on the OD or heat to install.
2. My mate owes me a beer after knocking main seal in too far and managing to twang the spring out whilst doing it  :dizzy2:  They must be flush with the housing or the seal rides on the bearing carrier. Not quite sure how the spring came off, but the seal was replaced without lifting the cover using the correct BMW anti-nick tool on the splines. I found it by putting some oil in and leaving it on the bench (what with all the repaired threads and DIY brake tube). Wasn't expecting this bit to be a gusher!
3. Seal is an 85x65x10mm SC metric seal with single lip. A TC twin seal is available and offered by some as an upgrade - the second seal is only a dust seal (not sprung) and in this case won't contact anything anyway. I will check once I have one from Ebay in my grubby mitts.



« Last Edit: January 16, 2022, 02:21:10 PM by dogshome »
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline dogshome

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Re: Final drive input bearing
« Reply #14 on: January 19, 2022, 12:29:06 PM »
I couldn't find a BMW branded can, so had to slum it. This actually worked very well indeed  :tekst-toppie:

Sitting on bench full of oil overnight......

No, the second seal does nothing. It might detract dust a little.
« Last Edit: January 20, 2022, 01:16:53 PM by dogshome »
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O