E36 Driveshaft for Increased Torque

[wrs 120]

Ever since upgrading my engine I've had driveshaft problems.

I'm making 343Nm peak torque x the 1st gear ratio gives around 1650Nm on the driveshaft worst case.

I have a stock E36 medium case diff style driveshaft with the first section modified for thre S6S420G gearbox. The diff is a 3.46 LSD built by KBM.

The universal at the diff end is always the one that fails. It goes stiff and locks up causing a lot of vibration and rumble. Because the driveshaft in the E36 has a straight alignment the roller bearings don't get to move and share the load.

I get between 2-6 weeks on a rebuilt driveshaft before it starts to vibrate. I don't know what's killing the universals but want to find a solution. Turbo engine would make far more torque than I am, what is done for the increase on a turbo? Is anyone else having driveshaft problems with the diff uni failing?

 

Edited January 15, 2023 by wrs

[Funkyflynz 151]

Strange, ive had zero issues with my 450+ V8 using the stock E36 medium case driveshaft and diff.  My concern is breakage (drifting on a 265 tyre) but so far its been fine, same driveshaft for over 12 track days with a 4.1:1 ratio gearset and 120-130kph wheel speeds.

Is your centre hanger bearing ok?

How about the bushings in the subframe and diff?  

The front bolt in the meduim case diff is weak and prone to breaking, have you checked that?

[wrs 120]

Thanks for the input. I rebuilt the subframe and replaced every bush and the diff bolt just to be sure prior to fitting the LSD and 2nd driveshaft. The third driveshaft was fully rebuilt and balanced by Driveshaft NZ, both UJ's and centrer hanger.

After failure of the third driveshaft and after making this thread I talked to KBM and it's possible I have a phasing issue or misalignment problem.

I'm going to give this a go to see if it improves things: replace the diff input flange with a 6 bolt from a 5 series. Rebuild the driveshaft with the M3 CV at the diff end. While I have it all apart I'll check the driveshaft angles and phasing to see if it's too flat. It would good to find the potential cause. If there is a phasing or alignment issue the CV will help hide it. It should be an easy job to just cut the driveshaft and fit the CV, re-balance an refit.

If there is an alignment problem I might be able to pack the center hanger mount and/or tilt the diff angle a bit.

KBM also commented they've done a lot of cars running much higher torque on standard driveshafts with no problems. I have to have some issue causing the UJ's to seize after a very short time.

[Funkyflynz 151]

Kaynes a knowledgeable dude, question on replacing the universal with the M3 CV,  where did you source an M3 rear half driveshaft? 

[jon dee 500]

On 1/15/2023 at 4:20 PM, wrs said:

The universal at the diff end is always the one that fails. It goes stiff and locks up causing a lot of vibration and rumble.

When you take the failed bearing out is it full of red "rust" ?

[wrs 120]

Got the rear section from KBM. Also a 5 series input flange to fit to the med-case diff + gasket, grease and locking collar.

No red rust - grease all good too. The bearing is just seized, likely due to being too straight - I doubt it's phasing. Happened to 3 rebuilt driveshafts in a row - bearing seizes at the center position after 2-6 weeks. It can be moved with a lot of force but is very tight and clicks back into the center position.

I think I'll need to fix the angle/alignment first as using a CV from a M3 won't help at all if there's no angle to create movement of the bearing surfaces.

[jon dee 500]

1 hour ago, wrs said:

No red rust - grease all good too. The bearing is just seized, likely due to being too straight - I doubt it's phasing. 

Do you see brinelling on the surface of the cross stubs ? Are any of the needles broken or flattened ? Are you still using the rubber donut coupling at the gearbox end ? If you have had three universals fail in similar fashion you may have something pretty unusual going on like a torsional vibration. More likely if you have eliminated the rubber donut. Closer examination of the bearing failure mode could provide some clues.

[rexila 4]

Hey mate I'm a Heavy Vehicle Certifier. We spec custom drivelines all the time. Easy to get premature failures if you haven't checked the numbers. If you want I can check it for free. Send me your email and I'll give you a list of what we'll need 

FYI trucks often come OEM with the diff UJ outside of what we would allow in NZ. We don't know why they set it up like that, but they work. Second we change something - it doesn't work. Sounds like what's happened with your car...