A-frame vibration at speed

[adam quantrill]

Another annoying thing, over the past month or so the 400SX has started vibrating at speed at the rear, I noticed a small amount of vibration after I bought it but it seems to have got worse. Unlike the usual XJ diff vibrarion this comes on at around 80 or 85 and steadily gets worse, it's still present at 100 to 120.

I have just been underneath the car and all the UJ's seem fine, no loose driveshaft nuts etc.

I have to get some new tyres all round anyway so that should cater for any possibility of wheel imbalance.

Any other ideas? The car has only covered 10k miles so I don't think the usual component wear problems should kick in just yet...

[chassis 33]

Bushes decaying perhaps?

Regards
Iain

[jchase]

Yes, I reckon the two vertical bushes on the Diff carrier are worn. The angle of the diff to the drive shaft is set by these, see if the nose of the diff is pointing too far down - I just took my carrier off, and that was the case. The trailing arm tasmin I had the diff nose was inline to the cardan shaft. You might be able to compensate by loosening the four 16mm headed bolts on the intermediate flanges (oo-er) to get yer pecker pointing right. Or maybe shim the rear carrier to chassis to get the nose up a bit on the diff.

-Jim

[wedg1e]

Lost a balance weight off one of the driveshafts or propshaft?

[number 7]

Is it more significant when lifting off and re-applying throttle? If so, could point to something in the diff. Worth checking that the large nut behind the prop flange on the diff has not slackened itself. All you need to do is remove the four nuts and bolts securing the prop flange to the diff flange and swing it out of the way. If the big nut is loose it means that the preload on the pinion bearing has been lost. Strictly speaking its then a diff out and re-assemble with a new crush washer to properly set the pre-load.

7.

[adam quantrill]

No, it's pretty much throttle independent, it's just related to overall speed.

[grahamw48]

Can't comment.

Never go into 3 figures as it messes my hair up.

[leorest]

wedg1e said:

Lost a balance weight off one of the driveshafts or propshaft?

Do drive shafts need balancing? Mine show no evidence of being balanced. I had asumed that the lower rpm due to the final drive ratio put it below where vibes started to be a problem.
Leo