I may have changed the wrong diff :-)

Hi again, sorry, this is my last new thread today I promise (bloody newbies

When I recently bought my latest beast (1992 RR classic 3.9 auto) it was making a strange drivetrain-related grinding noise above about 35mph when throttled off / coasting. The noise stops if you throttle back on, OR if you brake, and comes back again if you coast again.

So I asked a few people who I thought should know, and they sucked in air and said, "Ooooh that'll be your diff" and when I spoke to the seller he said he thought it was the rear diff. It was difficult to identify exactly where the noise was coming from.

Being not a terribly proficient mechanic, I wondered whether to get someone to do the work, like I usually do, or try and do it myself. Feeling brave, I chose the second route, so I sourced a rear diff, read up about how to do it and all that, and did it. It all went really smoothly - I was dead chuffed!

Until I took it for a test run.

The noise is still happening, exactly the same.

Do the symptoms I've described sound like a diff? I.e. the damn front diff!

Or if it could be something else, what else?

I am slightly loathe to try and change the front diff because it looks a whole shedload more difficult than the rear, mainly because freeing the half shafts to pull them out a tad looks way complicated. Unless folk hereabouts can persuade me otherwise..

Thanks again in advance.
Ron

Check the universal joints on the props.

I'm just fixing a similar problem on mine. Mine sounded like a series or squeaks though, and a massive clunk when you put the power back on. Not really a grinding noise. One of the uj has disintegrated.

I'd also check the wheel bearings. Jack up one wheel at a time, grab it one hand on each side and try to rock it, then do the same holding top and bottom of the wheel. Any play, change the bearing.


And look at the brakes to see if they are grinding or scoring in any way.

mundungus said:

Check the universal joints on the props.

I'm just fixing a similar problem on mine. Mine sounded like a series or squeaks though, and a massive clunk when you put the power back on. Not really a grinding noise. One of the uj has disintegrated.

I'd also check the wheel bearings. Jack up one wheel at a time, grab it one hand on each side and try to rock it, then do the same holding top and bottom of the wheel. Any play, change the bearing.


And look at the brakes to see if they are grinding or scoring in any way.

Click to expand...

Not so much a clunk, definitely an ongoing grinding. The props are all brand new and appear ok. I will go and check the wheels and brakes now.

Thanks..

you could have removed one prop at time to isolate front back wont hurt t/box for a test run,also jack up one wheel and it should turn stiffly with bar on wheel nut if wont turn viscous seized and will damage diffs or next weakest point,front diff would have been first choice, if you can undo 14 x 14mm 9/16 bihex bolts on chrome ball to axle you can save alot of work by pulling shafts out far enough to let diff out without disturbing brakes

mine done that and it turned out to be the transfer box

Final drive worn out.Rebuild gearbox and transfer.

thats a bit drastic to start with,noise on over run is usualy diff

My pet fettler is picking the beast up tomorrow... he listened today as we stonked down the A3, and he made various 'hmm' noises, wouldn't be drawn on any definite diagnosis yet though! We shall see.

--

Quick update in case it's of interest to anyone.

Turned out to need a double-cardan prop.

Simple as that. No more grinding!