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MG Midget and Sprite Technical - educate me

hi could someone educate me on diffs. the car iv just bought has a noisy diff and at this point dont know whether to get it repaired or get exchange unit. first i know there are different ratios but what should i have in my 78 midge and how can i tell what it is. also what ratio is recommended for just road use.
regards bob.
trebor

Quoting Terry Horler's book, the diff was changed in 8/1977 from 3.9:1 to 3.7:1
This should give 17.9 mph/1000 rpm.
The ratio is usually stamped on the diff casing. I think there is a relatively recent thread (archived by now) which indicates where the stamping can be found but I guess someone will have a picture.
I would not have thought checking the road speed/rpm would be accurate enough to differentiate as the difference amounts to less than 1 mph.

G Williams (Graeme)

Diff ratio is stamped on the top of the casing. Not easy to see from underneath.

There is an easy way to check.

Jack up the car, lock one rear wheel, turn the other wheel two complete revolutions and count the number of turns of the diff flange/propshaft.

Dave O'Neill2

noisey diff will be because the thrust washers have disintigrated leaving a degree of slop... I think they are fibre washers in the later axles so the wrong oil will destroy them (that and just age)... why not take it apart and fit new washers.
C L Carter

Worn thrust washers tend to give a clunk when going on/off the power.

Whine is caused by worn crownwheel and pinion, or bad meshing due to bearing slop.
Dave O'Neill2

the diff is soaking wet in oil. probably been run with low or no oil. ill know when not so cold and drain it to see whats in there.
trebor

Dave O'N,

Would this method work if a LSD is fitted? If not, how do I check what diff is fitted to my car?

Thanks,

Doug
Doug Plumb

I think that would depend on the type of LSD.

If a plate type, just rotating the wheel once should give the right result...and don't lock the other wheel.
Dave O'Neill2

"I think that would depend on the type of LSD."

The regular stuff that Timothy Leary advocated. :)
Lawrence Slater

Where on the diff is the oil? I believe the banjo casings are susceptible to rust and can pinole. The pinion seal can also be the culprit. Oh joy... collapsible spacers!
Cue Lawrence, scaffold pole, 18" string and an ex-GPO diff.
G Williams (Graeme)

havnt done close inspection yet. only knelt down and looked under rear of car and it looks covered everywhere. will jack up ane have a good look when weather gets a bit better.
bob.
trebor

"Would this method work if a LSD is fitted?"
If Dave's first method doesn't work because the wheel won't turn with the car out of gear, then you have the type of LSD which requires both wheels off the ground and only 1 revolution.
Paul Walbran

back to the noisy diff.on inspection today found diff to be about half empty.filled up and went for drive. still the same noise only on acceleration.come off throttle or coast out of gear, no noise.no clonks on and off throttle. does this sound like diff or poss gearbox. i am lead to believe box had been reconed.
thanks bob
trebor

This thread was discussed between 17/01/2013 and 21/01/2013

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