Differential Bearings Failing? - S2 Cab

[cdickinson]

In a similar context to my previous thread (inlet cam) I need advice / comments on the following please...

I asked my indie to investigate what I had guessed was a failing rear wheel bearing. I have had such a failure on 2 previous cars (205 Gti & Mk1 Golf Gti) and thought the sound was very similar hence my assumption.
However, my indie has diagnosed failing diff bearings! (plus still potentially the n/s rear wheel bearing). They have had the car up on ramps at 50mph in top gear to help them with the diagnosis and are 90% sure that the diff is the cause. They cannot be any more certain without performing a strip down.
They have quoted a bill well over 1k which includes 20 hours labour.

I do hold high regard for my Indie but am just concerned that my car has only covered 54k. (S2 Cab, pamepered, full docuemented history and proven mileage)

Has anyone experienced anything similar with their diff bearings or could it be something else that is more common to failure that I can run past my indie?

Many thanks,
Chris.
(going to plant some money trees in the back garden!)

 

[sawood12]

Failing diff bearings are a rare failure I believe - it's not something you hear about alot. The only instance where i've heard of a failing diff is my work collegue who rallies a MK1 Escort and in his turbo he liked to drift it round roundabouts so there is no surprise his diff packed up.

Anyway he's not moved over to the states and he gave me his old gearbox with knackered diff and a decent 2nd hand diff that he bought off ebay. You are welcome to any parts you might need as they are cluttering up my garage and I can't be bothered to sell them. I had some rediculous notion of getting an LSD or TorSen diff and building it into his old gearbox so the diff is surplus to requirements.

 

[knightma]

Noisy diff bearings are quite common on high mileage 924/944's and make a bearing rumble proportional to road speed. However they will run for many thousands of miles without seeming to get much worse. My old 924 developed noisy diff bearings at about 120 000 miles. I'd covered in excess of a further 30 000 miles before I decided to get them replaced as they were getting noisier but they still hadn't failed. There are two methods that I know of for determining whether the noise is diff bearings or rear wheel bearings. The first, does the noise level change when cornering. If so, it is likely to be a wheel bearing, if it gets noisier going right, it will be the left wheel bearing and vice versa. The other method is to remove the half shafts and tow the car down the road. If the noise disappears the problem could be the diff bearings. There is another candidate though and that is the gearbox output shaft bearings. As the output shaft is always meshing with the diff, it will always turn at a speed proportional to the rear wheels so will also make a noise proportional to road speed.

Once a gearbox or diff bearing gets quite noisy I would recommend they are replaced. The noise is caused by the rollers and/or races pitting due to metal fatigue. Small pieces of the surface metal break away. These get in the oil and will accelerate wear on all other mating components in the gearbox/diff such as other bearings and the gear teeth.

Edited to add: 54k miles does seem quite low but not impossible for diff bearings. The reason being that they are opposed taper roller bearings. This means they are pre-loaded towards each other by adjustment shims. This pre-load is very sensitive to the shim adjustment and no 2 diffs will have identical pre-loads. If yours was set too tight on factory build it would cause a premature failure.

I had my 924 bearings replaced by the the former OPC in Stourbridge, Swintons in the early 90's. To save money I took the gearbox out myself and delivered it to them. When I collected it, I couldn't turn the 2 output flanges by hand. They said it was due to the diff bearing pre-load and that it would loosen up with time. I accepted their word and fitted it back in the car. The noise was gone but the fuel consumption increased noticably and the car would hold without the hand brake on all but steep gradients. Sure enough within about 5 thousand miles (less that a year) the noise was back. Unfortunately for me, Swintons had by now gone out of business but after a couple of visits to the then new OPC at Little Aston, Porsche Cars GB agreed to honour the guarantee and the bearings were replaced again. This time they were fine but it does show that these bearings will begin to break down quite quickly if the pre-load shims are not set correctly.

 

[cdickinson]

Scott, many thanks for the kind offer for parts. I'll speak to my Indie and come back to you if we think anything can help reduce the cost. (I think we use the same guys over in Carlton...)

Mark, thanks for the tip to work out if it is a bearing by listening whilst cornering - it is not something I had considered and will give it a try. However, it is definately a rumble which grows with road speed (proportionally as you suggest) and therefore the diff bearings may well be on their way out. I spoke to my Indie in detail about this and they expressed the difficulty in doing this job due to needing the correct tools, and that the bearings may simply have never been setup correctly in the first place hence premature wear - they did say this is a common problem in 968's and is suggested to have been created by poor setup in production which only manifests several years / many miles later!??

I only do 2-3k a year so can hopefully save for a while and closely monitor the changes in noise before taking it further.

It's all a bit of a pain really because I had plans to spend a little contingency cash on basic performance mods to help freshen her up a bit (induction kit, chip and de-cat), but that's all now obviously on hold - she certainly needs to be running correctly first.

Cheers,
Chris.

 

[Tom]

Hi Chris,

I've just had my S2's gearbox rebuilt following a sudden increase in noise - see my thread "Transmission noise and speedo wonky" http://www.porscheclubgbforum.com/tm.asp?m=290658&mpage=1&key=񆽢 for a detailed description of the symptoms. In my case the car had covered 101k and the diff and output shaft bearings were badly worn.

Hope this helps.

Tom

 

[cdickinson]

Hi Tom,

Great descriprion of symptoms in your thread. I need to go out and try a few of your hints for confiming the cause but I think I have the same problem - certainly from your description anyway.

I see you eventually opted for a gearbox rebuild. Can I ask what you ended up paying and how much warranty they have offered?

Also, do you of anyone else know what constitutes a full gearbox rebuild compared to just replacing diff bearings? I have been quoted for the replacement of both(?) diff bearings only. Whilst they have the unit out (geabox incl diff = transaxle?), should I be looking at getting other parts refreshed?

Thanks,
Chris.

 

[Tom]

Hi Chris,

I spoke to quite a few people before deciding on the best way forward - I think everyone who offered a rebuild said that they wouldn't give a warrenty on the box unless they replaced all the synchros etc in addition to the bearings.

In the end, a friend of a friend who owns a performance car garage sorted the rebuild out for me - he took the box out and refitted it himself and sub-contracted the rebuild to an ex-colleague who races 944s, so I probably got a very good price overall. In total I paid just under a grand: £100 for removing and refitting the box, about £400 for parts and £500 for labour. I got a full 12 month warranty on the box.

Tom

 

[cdickinson]

Many thanks Tom, looks like you did well to hunt around and were fortunate to know the right people.
I've been quoted more than your total costs just for the diff bearings to be replaced.

Chris.

 

[xenon]

Did you get your jumping out of gear problem sorted yet, Tom?

 

[sawood12]

ORIGINAL: cdickinson

Scott, many thanks for the kind offer for parts. I'll speak to my Indie and come back to you if we think anything can help reduce the cost. (I think we use the same guys over in Carlton...)

Mark, thanks for the tip to work out if it is a bearing by listening whilst cornering - it is not something I had considered and will give it a try. However, it is definately a rumble which grows with road speed (proportionally as you suggest) and therefore the diff bearings may well be on their way out. I spoke to my Indie in detail about this and they expressed the difficulty in doing this job due to needing the correct tools, and that the bearings may simply have never been setup correctly in the first place hence premature wear - they did say this is a common problem in 968's and is suggested to have been created by poor setup in production which only manifests several years / many miles later!??

I only do 2-3k a year so can hopefully save for a while and closely monitor the changes in noise before taking it further.

It's all a bit of a pain really because I had plans to spend a little contingency cash on basic performance mods to help freshen her up a bit (induction kit, chip and de-cat), but that's all now obviously on hold - she certainly needs to be running correctly first.

Cheers,
Chris.

No probs on the parts - they are just clutering up my garage at the moment and i've got no real plans to do anything with them.

Yes, I do use Zentrum, Mike and the gang will sort you out no probs. I'd use him more often but getting through to and from Carlton is a real pain the neck from Derby. They might be moving soon so hopefully he is moving to the Derby side of Nottingham as I find it a real pain in the neck to get to no matter what time of the day I travel.

I'd expect a gearbox rebuilder to at least warrant the work they do. If all he does is replace bearings then why wont he at least warrant your bearings and exclude your syncro's?

 

[Tom]

Hi Ian,

Regarding the "jumping out of 3rd" problem - not fixed yet but I've got it booked in for Thursday for diagnosis. The hope is that the linkage needs adjusting - the theory being that it isn't so much jumping out as not quite going in. For the past week I've tried to switch off my auto-pilot and make sure that whenever I change in to 3rd, it's well and truly in. So far, so good...

 

[xenon]

Good luck!