Roof sorted - now on to the Diff Whine

[Chanceschmerr]

After a recent failure of my Z4's roof and a fruitless attempt to sort it ourselves, I had to take it in to a local shop on @True-Blue 's recommendation to get it sorted. They did so at a very reasonable cost, so I was impressed enough to have them tackle the next thing I wanted to look at - this diff whine I'm really noticing on accel/decel for lower gears.

Today I had them flush the brake fluid (we found water in it earlier this year with a sensor, so it seemed prudent to do), and flush/change the Transmission oil (no indication it's ever been done, manual transmission 2010 model), and flush/change the Diff oil (ditto, no evidence ever changed).

Thats done, and my shifting is markedly smoother, thankfully! Too short a drive home to really hear the diff yet, especially as I had top down for the drive.

That said - he did note that although the transmission oil he drained looked/seemed fine, the drained diff oil looked "a bit milky" and has actually a bit low on oil, even though he could find no leaks anywhere on the diff.

Should I be worried? To me, some emulsion with 16yr oil sounds plausible. But the fact the transmission oil was fine (not milky) poses a contrast that has me wondering.

Anyone else see low diff oil after so long on their Z4, without any evident leaks? I guess whether the whine has gone away will tell me for sure if I have an issue.

 

[Chanceschmerr]

Update. Taken it for a drive, after a few mins of driving, whine reappears as before.

&$*@*$.

I think next is to change the two rear tires. One is run flat and one is not - the other non-runflat got a puncture last year before I bought the car and was replaced with a run flat. I'm wondering if these two dissimilar tires (with different tread thicknesses) could be causing the whine.

Worth a shot. The non-run-flat is getting low on tread...

 

[matsmith749]

Tires could well be the culprit.

Should always be replaced in pairs (same axel).

But with your car having 1x run flat / 1x non run flat on the same axel, likely different wear profiles - they could easily have a slightly different rolling radius. As well as just being plain mental.

I would change them & see how you get on.

 

[enuff_zed]

Tires could well be the culprit.

Should always be replaced in pairs (same axel).

But with your car having 1x run flat / 1x non run flat on the same axel, likely different wear profiles - they could easily have a slightly different rolling radius. As well as just being plain mental.

I would change them & see how you get on.

I must admit that I always thought mixing a runflat and normal tyre across the same axle was illegal, or at least an MOT failure (which I suppose is more or less the same thing)?

 

[matsmith749]

I reckon you are a similar age to me & remembering radial / x-ply rules

But yeh, run flat + non run flat (who knows what the makes are) on the same axel seems very very wrong. The tyres react differently to road impacts, grip levels can't be the same.... I can only imagine on a semi-performance car this would feel terrible.

Driving like a granny in a 1.0 corsa or similar might not be so bad.

 

[Chippie]

When I bought my 35is it had different branded non run flats on the rear, when accelerating hard the rear was all over the place and a real handful to keep straight, fitting mps4s’s to a 4 corners made a huge difference, I can’t imagine how bad mixing run flats and none run flats would be.

 

[Chanceschmerr]

Tires could well be the culprit.

Should always be replaced in pairs (same axel).

But with your car having 1x run flat / 1x non run flat on the same axel, likely different wear profiles - they could easily have a slightly different rolling radius. As well as just being plain mental.

I would change them & see how you get on.

This is my thinking. I havnt noticed a performance impact, but then I dont have driving experience with a Z4 before this one.

I reckon you are a similar age to me & remembering radial / x-ply rules

But yeh, run flat + non run flat (who knows what the makes are) on the same axel seems very very wrong. The tyres react differently to road impacts, grip levels can't be the same.... I can only imagine on a semi-performance car this would feel terrible.

Driving like a granny in a 1.0 corsa or similar might not be so bad.

Once in my old Tiburon on a road trip in my college days, I blew a rear tire in the middle of nowhere, Colorado. Limped across the border to BFN, Kansas to the nearest repair shop. They had no tires to match my 195/55R15's, so they put a 195/60R15 that they did have. I drove the 1500+ miles back to Kingston, ON like that. The rear tires actually wore like two sideways wedges by the end - never seen anything like that. Aside from abnormal wear noise, no long term impact to the car or axel though. I put new tires on in Kingston and drove it for another 14 years after that.

But then, thats a Hyundai and a front wheel drive haha

 

[Chanceschmerr]

In any case, thanks for the advice. Going to change the tires in the next couple of weeks and see! The whirring noise is definitely still there - sounded almost like it was coming from the front left of the car when driving the other day. Can't make heads nor tails of it.