Home away from home
From Melbourne Australia (and likely under the car)
You may not have done any damage to the diff carrier bearings (hard to say, but I'd probably lean toward the idea that they made it ok) - but there is one thing often overlooked on a welded diff. On LSD diffs there's always the allowance of just a little bit of difference between the rpm of each axle, so they make it through corners etc without wheel hopping.
But a welded or spool diff, there's no give whatsoever. Now if you take that, and add to it (I'm just throwing this out there as an outside chance) the possibility that the rear tyres have an uneven rolling circumference (which is a slightly different to the 'static' circumference if you wrapped a cloth tape around the tyres to measure each one)- anyhoo, if there is a difference in that circumference, well one wheel will be 'trying' to turn a little bit faster or slower than the other, because for each metre travelled, one tyre might have 2 full rotations, but the other 2.05 or so.
So it'll then 'shudder' as it tries to cope (think of it as the straight line version of the 'wheel hop' you would get if you ran a locked diff and tried to turn it into a tight parking space at the local supermarket.
the damage/issue on the gearbox mount area - it's possible that the unis are seized or on their way there in the tailshaft. This would also cause a vibration/sound, and left long enough could damage the extension housing/bush o even the rear gearbox mount/rubber/crossmember.
However, given that you mention a welded diff, I'm going to take a gamble here and ask if you do a lot of hard starts, burnouts and or compression lockups (dunno what they are called elsewhere, but basically selecting a lower gear at higher road speed, and idle rpms, so it shakes the car and hops about on decel.,
I'm absolutely not judging you by asking the question, but what I _am_ saying is that if you happened to do a fair few burnouts etc, this could account for the gearbox mount damage/issues all by itself.
but first things first - I'd run a cloth tape around both rear wheels and measure the tyre's circumference on each (whilst in the air) It's not as accurate as a true rolling radius measurement, but it will work good enough to identify an issue. If you find that there's more than about 10mm (and some might say half that, but if it was 20mm, then look no further!) then that's the first thing to change.
you don't have to get new tyres, I'm pretty sure you could measure all 4 and find 2 that are very close, and swap those 2 onto the rears for the re-test.
It's also worth noting that if the welded diff centre is a recent addition, then presumably the car has done a number of burnouts, and with a stock diff they were 'single leg' burnouts - the right rear lifts a bit and that's the one that spins 9 times out of 10. SO that would then be 'grinding' away more tread on the right rear than the left, potentially increasing any size mis-match just prior to the swap to the welded diff centre.
Posted on: 2012/6/30 11:27