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Propshaft and diff


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Hi Everyone,

My 1979 S1 Eclat vibrates at speed (70+), it's been the case since I got it 2 yrs ago. I've changed a bunch of things (tires,alignment, bearings, u/j, engine & gearbox mountings, bushes ..) without success.

I was so far leaning towards an incorrectly balanced propshaft, as the vibrations were clearly vehicle-speed related.

After changing the engine and gearbox mountings, the car now makes a loud (bearing?) noise coming from the back when I lift the throttle. Vibrations are worse.

I got my mechanic to lift the car, and I saw that the propshaft has a lot of play towards the differential end. 3 sec video here : 

https://youtube.com/shorts/PU7DujiBpNU?feature=share

 

So...clearly something's not right with the diff, but I don't know if:

- a poorly balanced propshaft could have destroyed the differential

- or the diff was just progressively deteriorating.

 

With this long intro, I have 2 questions: 

- can this great group advise on the most likely cause, what parts are most likely to fail?

- can the propshaft be removed without taking the engine+gearbox out, once the diff is removed?

 

I'm hesitating between:

- buying a bunch of internal diff parts (input bearings,seals, etc) and hoping that the damage doesn't extend to pinions and other internals...(cheap on parts, likely more expensive on labour)

- sourcing an entire diff (lotusbits has a newly rebuilt one, but it's not cheap, and I have to ship it to Singapore. But labour would probably be higher than with the first option)

 

To add some context, I'm not equipped nor qualified to takeout the diff and investigate, I would need to book time with the shop.

 

Happy to listen to your advice.

Thanks a lot!

Bernard

Edited by BernardSG
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If it's been like that for lots of miles there is enough play there for the pinion/crown wheel to be badly worn - even if you rebuild it it could still be noisy.  You could try buying a second hand one but I've dismantled several now and they've all been knackered!  If you want to get one rebuilt locally I think I'd still try to buy a known good crown wheel & pinion to replace yours.  The other part of the diff that wears badly is the casing itself - the crown wheel tapered roller bearings are held in place so poorly in a lot of these diffs that they fret and wear the surface to which they abut, meaning the case itself needs machining.  Lotusbits reconditioned diffs might seem expensive but there is a lot of work involved with rebuilding one and at least you know you'd be getting a good one.

If you have an under-slung spare wheel the prop shaft will come out after the diff has been removed.

Taking the diff out will also give you opportunity to sort out the handbrake linkage etc.

Pete

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To remove the diff crown wheel, you need to manufacture a tool to spread the casing. Its an easy enough task to a machine shop but using it is very risky. Spread the casing a little too much and the casing is rubbish.

Something else for the pro and con list when considering a reconditioned diff.

Also, viewing your video, I would be surprised if the pinion and crown wheel were in good condition. Drain your oil and examine it for metal. That will be a good indicator as to the condition of your diff. Metal in the oil = but reconditioned diff.

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It's the rear "open" end of the casing that gets over-stretched if not carefully done - not the pinion end.  It looks like an almost complete collapse of the pinion bearings - which is a surprise because they are substantial.  Maybe not had enough/suitable oil in the past probably - looks like quite a marked oil leak past the pinion oil seal.

Pete

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