Driveshaft pressure is normal?

[IanMc]

Hi all - just about finished (famous last words) recommissioning a 1988 r65 mono and doing local shakedown rides before I set off on anything more adventurous.  When I changed the drive shaft oil, there was hardly any it in (cold).   I dropped in 150ml and went for a run then got a bit paranoid about overfilling (as in more oil in the drive than I thought due to cold), so thought I would just check it hot.   There was some distinct pressure in the shaft when I took out the drain plug, to the extent it blew a fair bit of oil out and onto the tire.  I refilled and went round the block and just opened the filler a bit - a distinct hiss.    Out of interest I swapped the filler with a valve breather type (0.5bar) to be rewarded with oil all over the tyre within 10 miles.   I can't really see why it would build up pressure within the driveshaft, but it definitely does!  Where else could it come from?   The breather in the final drive it clear.   Or am I overthinking this and some pressure is normal?   There don't seem to be any leaks anywhere.   Any thoughts or advice from the community?  Thanks

[Bob_Roller]

The driveshaft should be vented to the transmission . There is a small vent hole in the just above the drive shaft area .
The transmission is vented by the bolt that secured the drive cable for the speedometer.
All of the pre-owned bikes that I have had the wrong bolt installed no drilled passage way in the bolt .

[IanMc]

Aha - thank you, that makes sense in that there is a shared breather essentially.   I have checked the bolt and it is fact the right one with a hole and not blocked (can blow through it).   Given the amount of pressure (I am assuming it is high), there is no oil residue around the bolt.  I took the speedo drive out and it all looks fairly clean inside - no corrosion/gunk but also no oil residue.  So I am wondering whether the link between the driveshaft and gearbox is blocked.   Can you get at it by just removing the boot and have a bit of a dig around with a wire?   Alternatively, and back to my original post, maybe a certain 'hiss' when changing the oil is normal and I am over thinking it?   Given my test with a pressure release valve, it is at least 0.5bar.

I'll pop out for a quick ride and see if I get a hiss from the gearbox by pulling out the speedo drive.   If not, and the driveshaft still hisses, I think it has to be the link between the two.

[georgesgiralt]

Hello,
The driveshaft tube is sealed at the final drive because these is a strong leap seal where the nut adjusting the bearing pressure lies.
So the pressure must go out at the transmission end.
The rubber boot should be perfectly tight and sealed, so the pressure should go into the gearbox.
But if I'm not mistaken, the GS gearboxes have the leap seal assembled differently in order to make the box sealed from the swing arm. *
So either you had a gearbox swapped and/or assembled wrongly.
As I do not won a post 1984 R65 nor a GS, take my words with a pinch of salt.

* : If I'm right, some driveshaft were not oiled so one must prevent gearbox oil to leak into the swing arm.