HELP, Grinding noise from rear end of MU

[Pissy]

HI all,

I just recently got a 2” suspension lift and ever since then I get a grinding sound from the rear of the MU (diff or tail shaft). It occurs during a small phase when the car is under its momentum and the when the power first comes on or off, it’s kind of hard to explain?
Just image doing 100km and slowly release pressure off the accelerator until the car begins roll by itself, it is in between these two points that it grinds? At 60kms it hardly noticeable but at 100km it’s very loud.

Mechanic has gone over the whole rear end and everything is in good condition nothing loose or worn, so he tried to lower the cross member/gear box 5mm and then 15mm just in case it was a gear box and tail shaft angle problem, then he tried to offset the diff so that slightly angles up to the tail shaft but none of these 2 work.

Although it is not affecting the MU’s performance but one would have to assume that any noise out of the normal usually means TROUBLE!!

HELP!!
Any Suggestions

[PeterSchurms]

If the mech has checked it out this may be a waste of time, but anything is worth trying.

While the mu is safely on a hoist, dyno or similar get someone to take the truck up to 100 or so to when the noise is worst and while your under it take a large screw driver place the handle near your ear lobe and the end on the diff and or gearbox in a number of locations (obviously not near moving parts), if its diff/power train related you should hear be able to pinpoint the fault location. This is called the screwdriver or stethescope test.

When you changed the diff oil, did you use LSD oil and was there any metalic flakes in it?.

I would expect a 2" lift is not going to create a too greater angle for the diff to be lubricated effectively, but maybe you could consider an extra 300-500ml of oil. Others may have a little more insite here.

The noise may also be just coincidental and symptomatic of another problem.

Good luck

[justin]

Check the oil in diff, make sure there’s no water crap sucked in. Uni joints normally click at certain points of revolution when they're worn, (well mine did). And I don't think the lift would affect it as there is a lot of lifted Mu's here and I ain't heard it's an issue. The timing could just be a coincidence; did you cross any rivers after your lift? J

[geeves]

First thoughts are brake shoes, wheel bearings pinion bearing, diff inards. If it was the driveshaft there would be vibration as well but do the Mus use a center driveshaft bearing which might cause this. A long shot after the lift but worth checking is has the exhaust or tyres ended up close enought to touch somthing they shouldnt
Also try removing the rear drive shaft selecting 4wd (hubs locked) and driving the same test The car will act like fwd but should show the same rear dif symptoms

[Pissy]

Thanks Guys for the suggestions,
the lift is only 14 days old and I even have not had a chance to go off road yet or do any river crossings. I will do a proper service on it (not just oil and filter change) in months time which will include diff and gearbox fluids. To tell you guys the true I don't even know if it has an LSD (7/94 model), sometimes when I spin the wheels on the grass both go and other times one does, so i guess it be? Will jack it up and hand spin one of the rear wheels and see if other turns.
Pretty sure its not an angle problem as the mechanic told me that the SWB patrols have allot shorter tail shaft and therefore its angle far greater and most of them don't have problems.

Getting off the current topic, is there any simple inexpensive way to lift/push up the gear box, seeing that it the lowest point of the MU by 2-3inches?

[justin]

Mine is the same year and month and has a LSD on. But it does have a use LSD oil only sticker on the diff and a G80 code in the Vehicle ID plate.

As for the gearbox lift, if you find out let me know. I've had so much fun balancing the entire weight of my vehicle on the transfer box skid plate, eh Graham! ;D

[geeves]

Easy way to lift the gearbox/transfer case would be to put packers between the gearbox mount and rear cross member but I dont know anyone that has tryed this. Possible problems are clearans between the gearbox or bell housing and the floor, and driveshaft length and angles and clearances as they pass the other cross members. Some of this could be fixed with a body lift some might need a lot more thought and engineering. Its definatly worth a try and someones got to do it first Measure carfully and let us know how you get on. My tranfer case makes a very good plough and is very had to hammer back into shape arfter some of the harder trips

[Graham]

I can vouch for Justin's balancing skills. I'm sure that if he needs to work on his MU he could just stick a hi-lift jack under the 'log catcher' and he'd be fine! (Until the cat jumped on the bonnet)

I've been gentle with mine, I think I need to go on a trip somewhere.

G.

[Pissy]

For a person who only knows how to change tyres, the oil and filter, a project of the caliber is WAY out of my league and cash stores (or should I say cashless stores).
Only was wondered if anyone had done it or if it was as easy as getting a different cross member, but again proven wrong, this is why I am known as a "Novice", .
Well then, will go to plan "B", body lift and 33'' when off roading (Just hope that the extra size will not overload MUs diff and gearbox/transfer case?)

Cheers