BMW R51/2 trasmission

[Goro F]

hello all
i noticed that round about 70/80km/h the trasmission becomes noisy. My mechanic told me that the first thing to check is the hardy disk in the drive shaft group. Than we have to look into the final drive. The drive shaft can move a little and maybe should not, even if a little clearance is allowed I assume

thx in advance if you have some reccomendation or if some other parts should be checked based on you experience (enclosed a screenshot of exploded views)

[Darryl.Richman]

Have you greased the U joint (#2 in drawing) under the dome cover (that has left handed threads!) on the nose of the final drive? There's a zirc fitting you can grease with a needle tipped grease gun. If not routinely serviced, it can sieze and fail spectacularly.

[jwonder]

There are many things that can make noise since there are a ton of rotating and meshing components in the gearbox as well as the final drive.

You state "noisy", is it a whine, growl, clunk or some other noise? That would certainly help us debug a bit more.

In which direction is your driveshaft moving? If you push it forward and back does it move in that direction? Hence, pushing the driveshaft "into" and out of the final drive does it move? Or, does it move radially, like when you simply grab it and push and pull on it? This would be two totally different problems/adjustments.

Darryl so aptly mentions greasing the u-joint, and I would further ask what oil you use in the various components?

[Goro F]

hello thx for your replies

i need to check to provide further information you need to support me

what I can say is:
- for the propeller shaft I told my mechanic to use Mobile GX 90 OR Shell Spirax 90 because those are the indications I found in the Lubricating Plan of user's manual. I hope that he did..
- personally i did not grease the U joint. I downloaded the lubricating plan and yes, it's reccomended
- for sure there is radial movement by pushing it down or pulling it up. Forward and back I don't know..I need to check.

I will come back with more informations, sorry for this.. i'm not expert and i'm trying to learn as much as I can. Also because a couple of years ago I entrusted my motorbike to a mechanic who did a lot of bad work

Mosè

[Goro F]

hello
we disassembly the trasmission

- there are distorsions and deformation on hardly disk visible
- we notice radial movement in one of the two direction of U joint
- bearings of U joint look good and greased

we measure the distance between the two seegers which keep in the position the U Joint and the U joint, and there is some tenths to be recoverd (44.7 mm vs 45/45.2). It sounds strange to me since I see that a new U Joint should be 48 mm while the one that is mounted is 44.7 and the space between seeger 45 / 45.5. How it is possible? If I buy newone of 48mm it will not fit..

The mechanic told me that we can try to recover the clearance clamping a little bit on U Joing until the clearance is almost zero.

the type of noise when i run over the 60/70km/h is like a "TRRRRRRRRRR" but not metallic. It sounds like vibrations

enclosed some pictures to better explain
Mosè

[Goro F]

I did some research and so far I understood that there are two types of U Joints:

the one that is mounted on BMW R50/2 R51/2 R50-R69S should be 48mm X 19mm
the one used for BMW R50/2 R51/2 R50-R69S is 44mm X 14mm

saying that, i cannot explain myself how can have on my BMW R51/2 a U Joint 44.7mm X 19mm. Unless this comes out of mixed parts put together to make a "Frankestein" or it's a reworked part, but then also the shaft should have been reworked accordingly

anybody have any experience or other opinions?

[jwonder]

Does your driveshaft have a bulb in it to hold the dust seal? If so it is a later driveshaft. If not then it’s a R 51/2 shaft. The R 51/2 also had a smaller seal and no bump in the driveshaft.

[jwonder]

I also just measured some u-joints I have here and they indeed measure 19mm x 48mm. I believe this is what is in my R 51/2 but I did not change my u-joint as it was fine.

I suggest you try to get your current one to run straight and if it’s still smooth put it back. I do not think the u-joint is your noise.

I would be looking at the following for a noise like you describe:

1) your final drive does not have the correct pinion depth or preload.
2) your final drive gear is wearing or has abnormal wear.
3) your gears in your gearbox have wear and/or are no meshing correctly.
4) your tires are old, noisy by design, or your inflation pressures are not correct. Try 5 lbs more and see if the speed changes at which the noise occurs.

I have typically found speed related noises to be caused by rotational parts and not small ones like the driveshaft. Further, for you to hear it at that speed means it’s either really loud or is also be transmitted through the frame. Gears will certainly do that. Tires will whine as well. The driveshaft might do it but it would be low on my list.

[jwonder]

I also just noticed you have snap rings on yours. I have never seen that on an original driveshaft. Anyone correct me if I am wrong, but mine are all staked. Yours have been upgraded. Not bad, just not the original ones. I would question if the length is incorrect and might be putting undue pressure on the hardy disc.

The Barrington manual and likely the shop manual on our site have the correct spacing for the driveshaft.

[Darryl.Richman]

I also just noticed you have snap rings on yours. I have never seen that on an original driveshaft. Anyone correct me if I am wrong, but mine are all staked. Yours have been upgraded. Not bad, just not the original ones. I would question if the length is incorrect and might be putting undue pressure on the hardy disc.

The Barrington manual and likely the shop manual on our site have the correct spacing for the driveshaft.

Don't the prewar plungers... and the R51/2... have snap rings? Just looked at the parts book for the prewar bikes, and they definitely have snap rings. I think the R51/2 is the same thing. The "/3" bikes have staked crosses.