Differential noise? - help appreciated

[nfm]

Dropping my car in to the local specialist for its annual next week. Over the last year I have noticed a gradually loudening noise from the rear best described as mechanical/rotational rather than a more constant wheel bearing hum. Coasting in neutral sees noise unchanged. Noisiest at 35/40 just now, above that goes away/drowned out.

Suspicion is it is the rear differential. Anyone heard of this and if so can the diff be adjusted or rebuilt or is it a replacement job. 50k on the car but vigorous exiting of bends a frequent pleasure so may have contributed - alternatively has been roller mot'd which it is suggested elsewhere is not helpful.

Any insights in lieu of my mechanic diagnosing would be much appreciated.

Cheers

 

[mjheathcote]

Can't really help but don't forget its not a traditional differential back there....its a transaxle, combined gearbox/differential.

 

[wink]

IMHO would expect the noise to change on/off load if it's the diff. A constant noise might be wheel bearing?

 

[nfm]

Tks guys. Just had a wheel bearing go in the Alfa and like past cars it was a constant Hum. This sound is quite different and much more geary /rotational. Assume not gearbox as no change if declutch or neutral. I had a diff go in a 131 Sport many moons ago and feels similar but stretching the memory.

Will do the on off load thing tomorrow and report back.

 

[allandwf]

Handbrake shoes?

 

[GeoffCapes]

I had a funny rattle on my 4200 that only occurred at certain speeds. Turned out to be a couple of exhaust hangers had broken and rattled at those same speeds.

 

[nfm]

Handbrake shoes is an interesting one. Were changed about 10k ago but are prone to failure. Handbrake does work ok but will pull lever on the move to see if it changes the noise and revert.

It isn't a rattle, it is a very distinct rotational sound so doubt it is exhaust related, but Tks

Cheers

 

[nfm]

Ok, just back in and no noise change either when applying handbrake or when putting car under load. Car just passed mot and handbrake performed well, so pretty sure we can rule that out.

Anyway, other thoughts welcomed and if all quiet will update next week when service guy has a poke and prod.

Cheers

 

[redsonnylee]

Have a good check underneath I had a sort of rubbing/scraping sound, although it was handbrake shoes we also discovered the propshaft lost a bolt and the others were loose also one of the rotorflex bolts had fallen out.

 

[nfm]

Tks, hope it is something simple like that. Will find out next week.

Fingers crossed.

 

[philw696]

Hope it's not the torque tube falling out !!!!

 

[nfm]

Hope not, doesn't sound cataclysmic yet but needs sorted now. Guy knows his stuff like your self Phil so with luck will get it diagnosed soon.

Cheers

 

[nfm]

Update, just to close off this thread and provide answer for anyone with a similar issue. Didn't resolve locally so took it to Autoshield and confirmed diff bearing. Replaced and reset and now fine. Bill a tad wallet lightening but had a new clutch fitted at same time, as old one was ending life, so at least labour costs spread over the two jobs.

Marios confirmed he has seen this before.

Happy to have the car back sorted and bill still less than years depreciation on Ronny repmobile (at least that's how I justify the man maths!).

Cheers

 

[conaero]

On the subject of differential noise, I had moaning coming from my diff (2006 GS with 44k miles).

I had it when I did not use the car for a while and pulled off my drive hard left. Now to understand this, when pulling away hard left with a car that has been stood for weeks, the oil is all in the bottom and cold and the hard left turn (or right) loads the most strain on the planetary gears of the limited slip diff has the most work to do with the near side and offside rear wheels.

So first I dropped the diff/gearbox oil and replaced with something from Eurospares...no change.

Spoke to Opie Oils and they advised me to not bother with cheap ES oil and sold me this:

Motul Gear 300 75W-90 Fully Synthetic Racing Car Gearbox & Diff Oil -3 x 1 Litres for £55 delivered.

I also purchased an oil filler which is basically a big turkey baster/syringe. The gearbox and diff should hold about 2.7 litres of oil but could only get about 1.9L in before it came flooding out.

Drove the car and it still did the same so I use a drop of oil LSD modifying as recommended by Opie:

http://www.opieoils.co.uk/p-6320-re...tial-friction-modifier-break-in-additive.aspx

When putting it in the gearbox I noticed that the remaining oil would now fit in.

Finished up and tested....quiet as a church mouse. Go easy with the oil modifier you will find that the smallest recommend initial amount is enough....or the fact the gearbox took the final near litre of oil...too much and you will knacker the LSD clutches.

Gear Oil syringe:

https://www.bodyshop-tools-supplies.co.uk/product_view.php?id=19300&gclid=CPqkw9SDodACFWgq0wodIzwIrQ

 

[mjheathcote]

I would tend to think getting the correct volume in made the difference, you were 30% short after all!
Assuming the volume was correct when you drained out the original oil, I would guess the new oil alone at correct volume made the difference.

 

[conaero]

I would tend to think getting the correct volume in made the difference, you were 30% short after all!

I am not inclined to disagree.

 

[mjheathcote]

Interestingly Miller Oils based near me do an oil analysis service for engine and gearbox oil.
As I am due an oil change I am tempted to use this service. They can analyse the oil for any contamination, wear metals, and check the viscosity. Even the silicone content that would indicate the air filter needs replacing!
Might be worth doing before....Might indicate all okay and no need to change the oil! Each oil sample test 25 quid or 2 samples over 6 months 40 quid to map a trend with usage.
Sounds interesting to me!

 

[nfm]

All good extra info and helpful to all, Tks. To be clear, by the time I dropped mine off for repair it was a really painful rotational clunking - it was mechanically knackered by then and upsetting to drive if you had any mechanical sympathy. Two different issues with two different solutions methinks.

Cheers

 

[voicey]

The reason you couldn't get more in than you got out is because there is only a very small oilway between the gearbox and the diff. When you fill up the first time you are only filling half the box. You must wait about 30 minutes before re-filling for a second time to give the oil a chance to flow into the other side of the box. The same goes for draining - just let it sit with the drain plug open for ages in order to get it all out..

 

[conaero]

The reason you couldn't get more in than you got out is because there is only a very small oilway between the gearbox and the diff. When you fill up the first time you are only filling half the box. You must wait about 30 minutes before re-filling for a second time to give the oil a chance to flow into the other side of the box. The same goes for draining - just let it sit with the drain plug open for ages in order to get it all out..

I did suspect as much, I assumed I had either not drained it fully or had an air lock. A little half mile drive, return, refill and it was all good.