Offroad-Express

Have just put a 50mm EFS lift in my SWB GU, and at the back have ended up with about a 70mm lift after settling from about 1,000 k's on teh road.

Have come across a small problem though which I have nailed down to being a vibration in the rear driveshaft spline. There is a very very slight 'traditional' vibration when taking off and the drive train is under load, but that is not the main problem at the moment. Once things have warmed up I get a noise, rather than a vibration, but is still a vibration of sorts when the drive trian is under freeload, prominent mostly at around 90kph. So as you go into a corner at say 100 and back of and the rear spline goes from being under load from the engine, to being under load from the rear wheels driving you get a short Brrrrrrrrr. Go down a big hill, put it into neutral and you get a constant Brrrrrrrrrrr. We have just replaced the rear UJ's and no change. Last night after 3 hours of experimenting I am now 99.9% sure it is the rear spline, as with more people in the truck it doesn't do it - more weight, the back sits down, and the spline is pushed up into the shaft more. Greasing the spline removed about 80% of the problem until the grease is worked out of the system.

So what can I do now? Packer on the back diff where the driveshaft bolts to to shorten back up the driveshaft, but this will increase the UJ angles more. Extendable top arms.....?


Arrrggghhhh

Thats normal rear driveshaft vibe you get from a lifted shorty GQ / GU. Extend the lower arms or shorten the uppers.

buy or make some longer lower arms,normal that fix's most vibs with 2" lifts

I have a set of longer lower arms from the guy on TM that sells them, no problem with them, and they seem to be a good price.


Dave

GQTROL wrote:Thats normal rear driveshaft vibe you get from a lifted shorty GQ / GU. Extend the lower arms or shorten the uppers.

There is 2 causes of vibration: universals have reached max angle; and universal angles are not close enough to being the same.
The usual approach to both scenarios is to space the gearbox support cross member down and (as above) change the diff pinion angle. The preferred method is usually to move top or bottom (most common) side of the diff back. Moving back is preferred to increase distances, some have moved the axle back nearly 300mm .

Or you can get a CV driveshaft made.

Or you can just live with it as a lot of these problem go away with a bit more time.

My choice would be to give it a few more K's before you do anything. I'd then look at a different driveshaft as a 50mm lift shouldn't have driveshaft problems and shouldn't need spacers, arms or anything else to work. I say 'shouldn't' as most of the trucks you see around have nothing done at all and work fine.

Forgot to mention the 3rd cause of vibration, universals not lined up. Caused by the driveshaft being pulled apart and not put back in the same orientation. Worth a check as we've seen this numerous times.