Cluning noise from rear end

[ham204]

Recently I have been hearing a 'clunk, clunk' noise from the rear end of my Sprint when I try to drive off. It usually happens when the car has been driven for some time and almost always when I drive off on an uphill gradient, the steeper the more 'clunkier' it becomes. By 'clunking' I mean a heavy metal on metal noise. Once I drive off, the car acts normally. Last Sunday it had a particularly bad case of 'clunking' and decided to keep it garaged until I sort out the problem. The car has new UJ's, rear suspension bushes all round plus GAZ adjustable shocks.

Is it a case of diff rebuild?

[dollyman]

The fact it has new uj's suggests one has failed, it wouldn't be the first time.....

Tony.

[yorkshire_spam]

Is it a single "clunk" on take-up or a repeated clunk-clunk at the frequency related to road speed?
A repeated clunk-clunk-clunk at road speed would suggest a rotating component like CV/UJ in the propshaft or maybe a knackered carrier bearing on the prop allowing the start-off torque of the prop to deflect it far beyond normal operation.
A single clunk - maybe diff, or even a very knackered bush in a suspension arm?

[ham204]

The fact it has new uj's suggests one has failed, it wouldn't be the first time.....

Tony.

Yes that's possible - will check over the weekend. Cheers

[ham204]

Is it a single "clunk" on take-up or a repeated clunk-clunk at the frequency related to road speed?
A repeated clunk-clunk-clunk at road speed would suggest a rotating component like CV/UJ in the propshaft or maybe a knackered carrier bearing on the prop allowing the start-off torque of the prop to deflect it far beyond normal operation.
A single clunk - maybe diff, or even a very knackered bush in a suspension arm?

More like a 'clunk - clunk' as I release the clutch to drive off and then it stops as I pick up speed. It does this only on an uphill road. On a level surface, it goes just fine. I will check the UJ's though

[cliftyhanger]

Yes, time to get it in the air and a couple of levers to check stuff. In fact everything that moves at the rear, plus the prop.

[ham204]

I had a good look today and nothing seems amiss. The UJ's needed a couple of squirts of grease. The propshaft turns a little before engaging the gear in the diff. I took a video but it's too large to upload. If it was a clock face, I would say the prop turns less than 5 minutes. Is this normal?

[Carledo]

30 degrees, (5 "minutes") is quite a lot of backlash, but your measurement is less than precise if you'll forgive me for saying.

I've run for years on about half that (12 degrees measured) and aside from a bit of a whine and the odd single clunk on slow takeoffs (don't do many of those) I haven't really had a problem. Nor has it got any worse, despite my blatant abuse.

I'm slightly fascinated by it being more prevalent on uphill starts. It's a bit akin to my brake line lock induced burnout loads, before I got my superhard red tie bar bushes, I used to get the axle tramping and bouncing the diff nose off the pinion snubber bush which made a horrid staccato thumping noise. Limiting the tramp stopped that.

I'd be looking hard at the tie bar bushes and the prop before condemning the diff.

Also, on the offchance, check the gearbox mount, if it's gone soggy, it could induce all sorts of noises.

Steve

[cliftyhanger]

Thinking about it, the hill start bit does make sense, in that cars often roll back a smidge. Certainly enough to open up the backlash on the diff?
That backlash is not too much of an issue, it is in the diff itself rather than the CWP (you have to carefully feel that backlash, it is really subtle and usually a degree or 2, and won't be obvious with the prop attached)

I would change the oil to something like Redline heavy shockproof, I am sure that is yellow metal safe (though not to be used in our gearboxes especially with OD) as it will do nothing but help.

[ham204]

Thinking about it, the hill start bit does make sense, in that cars often roll back a smidge. Certainly enough to open up the backlash on the diff?
That backlash is not too much of an issue, it is in the diff itself rather than the CWP (you have to carefully feel that backlash, it is really subtle and usually a degree or 2, and won't be obvious with the prop attached)

I would change the oil to something like Redline heavy shockproof, I am sure that is yellow metal safe (though not to be used in our gearboxes especially with OD) as it will do nothing but help.

What is the weight of Redline heavy shockproof?
I may not find that particular brand but something similar with the same weighting. Thanks.

[cliftyhanger]

What is the weight of Redline heavy shockproof?
I may not find that particular brand but something similar with the same weighting. Thanks.

It reckons it behaves like a 75-250, but the spec in 75-140 I believe. It doesn't thin anything like as much as normal oils.
Moss sell an 85-140 oil advertised as suitable for quietening diff a bit. That is GL5, but yellow metal safe.

I got my redline stuff off fleabay, delivered in a coupke of days, £22 all in. OK, expensive for gear oil, but it is good. And an extra tenner or so isn't a lot. (1 1/2pts of beer locally)

[ham204]

What is the weight of Redline heavy shockproof?
I may not find that particular brand but something similar with the same weighting. Thanks.

It reckons it behaves like a 75-250, but the spec in 75-140 I believe. It doesn't thin anything like as much as normal oils.
Moss sell an 85-140 oil advertised as suitable for quietening diff a bit. That is GL5, but yellow metal safe.

I got my redline stuff off fleabay, delivered in a coupke of days, £22 all in. OK, expensive for gear oil, but it is good. And an extra tenner or so isn't a lot. (1 1/2pts of beer locally)

Thank you! I reside in Malta and will look for it here. Cheers

[cliftyhanger]

Thank you! I reside in Malta and will look for it here. Cheers

Ah, that puts a different slant on it!

[Manta]

A good way to let people hear the symptoms is to upload the video clip to YouTube then put a link on here to your video,

[ham204]

A good way to let people hear the symptoms is to upload the video clip to YouTube then put a link on here to your video,

I posted the video to the FB page