torque arm mod, less driveshaft wear?

[scribbles]

i have searched the forum so sorry if this has already been covered.
the man who is doing my gearbox and putting a longer fifth gear on told me about a mod to the torque arm. my driveshaft is on the way out and i asked him about the various driveshaft repairs and upgrades that are around. he told me that if you machine the torque arm and make it adjustable in length. then, when the bike is high on the suspension you can shorten the torque arm to make the bevel drive line up perpendicular to the swing arm. then the idea is there is less wear on the lower universal joint because it isn't running at an angle. also as the swingarm moves up and down, the spline can move in and out easier because it is in line with the shaft and getting pushed at an angle. this means there is also less force being pushed up to the top UJ and making that wear.
then hopefully the shaft will last loads longer because isn't it the increased angle the r100gs shaft runs at that that wears shafts out?
anyway i thought it sounded convincing but would love to hear if anyone has tried it or knows more before i try it.

 

[nud1e]

replace the rear shock with the shorter unit from the R80/100R. This has the same effect as suggested.

 

[Beemerboff]

That spline at the rear of the shaft has to slide real freely, especially under load.

If they dont they will tend to lock up, which locks the the suspension too, and the UJs on the shaft get a hammering.

I found this out the hard way with the half shaft splines and UJs on a 2.5 PI Triumph , a long time ago.

The answer back then was to lube the splines with the special lube Renault sold for the CV joints in their front wheel drive cars.

This solved the problem on the Triumph with the locked suspension, and as a bonus the UJs lasted about five times as long too.

I dont think the BMW white lube cuts it in this situation - and I have lubed the splines on my paralever with CV joint grease.

Everyone who rides my bike comments on how well the suspension is set up - I believe the free sliding spline helps make it this way, though the Ohlins shock and HPN Magnum fork inserts help too.

And the shaft has 85,000 hard Ks on it and still feel good.

 

[scribbles]

85000 sounds pretty damn good from what ive gathered. the bevel does sit at quite a steep angle when the shock is jacked up. obviously its true if you drop the shock down it wont run at as much of angle but then you've got no ground clearance. my shock is crap on the road unless its done up tight aswell. i was wondering whether if you shorten the torque arm it would throw the whole lot out. is it not set out as a parallelagram and if you shorten the torque arm it will make the bevel move around more as the suspension moves?

 

[Beemerboff]

Problem with the paralever is that it was designed to be oil filled like the twin shock and monolevers, then they changed their mind and made it dry with grease filled joints.

The reason given is the cushion joint in the shaft, which doesnt tolerate being in oil very well.

So , if you could find a rubber boot to protect the joint, it would be possible to run the shaft in an oil bath, like the rest of the bikes.
It would be similar to a cv joint boot, without as many ribs.

This would solve all the problem easier than than mucking around with the suspension geometry.

The boss for the drain plug is already cast into the paralever, so you would just have to find somewhere for the filler.

 

[(RIP) pastyman]

Problem with the paralever is that it was designed to be oil filled like the twin shock and monolevers, then they changed their mind and made it dry with grease filled joints.

The reason given is the cushion joint in the shaft, which doesnt tolerate being in oil very well.

So , if you could find a rubber boot to protect the joint, it would be possible to run the shaft in an oil bath, like the rest of the bikes.
It would be similar to a cv joint boot, without as many ribs.

This would solve all the problem easier than than mucking around with the suspension geometry.

The boss for the drain plug is already cast into the paralever, so you would just have to find somewhere for the filler.

Sounds very interesting.. Has anyone ever tried this?

 

[scribbles]

had a thought about this. would it work if you got a thick rubber boot and strapped it to the bevel spline then pushed the driveshaft on and pulled the boot over and onto the drive shaft past the bottom universal joint, fill it with cv grease and then strap to the shaft. then do the same to the top universal joint. i believe the bearings on the universal joint also suffer from a lack of grease?
thought it sounded feasible unless with the gyroscopic effect at top speed it swells up and pops!! anyone know how fast the shaft spins at top speed?