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Whiny rear diff - advice needed

Posted: Tue Jul 23, 2019 9:56 am
by pauluspaolo
Hi all,
I took my SS1 out a couple of days ago (my wife & I went to a classic car show at Newby Hall near Ripon - only saw 2 Reliants there & they were 3 wheelers :( ) & the rear diff is very whiny at any sort of reasonable speed. Is this normal - they all do that sir! - or does it indicate that I need a new/reconditioned one?

I have to say that the diff has always been like this & doesn't seem to have got any worse over the years that I've owned the car (10 this year I think). What has got worse is the oil leak from the diff. It's not like the diff is completely draining of oil overnight but it's bad enough that the MOT tester mentioned it & it's certainly becoming noticeable on the garage floor (not that this is a massive concern)! I regularly check the level of the diff oil & top up if needed but it never seems that low to me despite the leak.

Anyone got any advice??

Many thanks :)

Whiny rear diff - advice needed

Posted: Tue Jul 23, 2019 10:34 am
by peter freeman
Try Molyslip - cannot do any harm even if it does not reduce the noise.

Whiny rear diff - advice needed

Posted: Tue Jul 23, 2019 11:35 am
by scimjim
They’re fairly bulletproof and under stressed in the small sports and don’t generally make any noises. You can rebuild them, buy a reconditioned item, or just fit a replacement s/h one?

With the zetec you have, I’d go for a 3.62 ratio? I have plenty of s/h 3.92 but think I sold my last 3.62 to Nick Keyser recently.

Whiny rear diff - advice needed

Posted: Tue Jul 23, 2019 1:27 pm
by reliant-reviver
Mine sings a bit at speed and I live with it. It's more noticeable with the hardtop on as this seems to amplify cabin noise.

Any noise from the diff is very apparent in an SS1 due to it being sat just behind the occupants. Later cars / Sabres did feature additional insulation underneath the fuel tank to try and quieten things down.

If the diff whine is really that bad you may as well change it for a good secondhand unit although it's a bit of a faff. However the presence of a whine does not likely mean there is any impending doom. They are strong units and don't really fail.

Whiny rear diff - advice needed

Posted: Tue Jul 23, 2019 1:56 pm
by Corky
I’ve got two 3:62 here if you’re looking to buy one.

Correction, I've got two 3:92 here :oops:

Whiny rear diff - advice needed

Posted: Tue Jul 23, 2019 9:50 pm
by CNHSS1
Check the diff mount bushes and moutings to chassis. If they are damaged or the chassis plates cracked the diff cradle can actually touch the chassis and it rings like a bell! Changing the diff will not improve things

Whiny rear diff - advice needed

Posted: Wed Jul 24, 2019 10:45 am
by pauluspaolo
Sorry if it's a dumb question but what would the difference be between a 3.62 diff when compared to the normal (3.92?) diff?

Many thanks :)

Whiny rear diff - advice needed

Posted: Wed Jul 24, 2019 11:02 am
by philhoward
Simple maths - about 7.5% "taller" in each gear. As a result, 5th gear become 22.5mph/1000rpm instead of 21mph/1000rpm, so 70mph is now about 3100rpm instead of about 3350rpm

Whiny rear diff - advice needed

Posted: Wed Jul 24, 2019 11:03 am
by scimjim
Lower rpm when cruising, more useful first gear.

Whiny rear diff - advice needed

Posted: Wed Jul 24, 2019 11:04 am
by peter freeman
We never use 1st gear

Whiny rear diff - advice needed

Posted: Wed Jul 24, 2019 2:00 pm
by pauluspaolo
Ta for that & it's food for thought as whilst I do use 1st gear it is pretty much redundant.

Just out of interest Jim how much would you want for a standard 3.92 diff?

Thanks again :)