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MG MGB Technical - Differential Play. How much is OK?

How much play should I have on my Diff please?
I had the diff worked on when the Quaife unit was fitted about 1 year ago and I was told it was in reasonable condition.
I have always had a small take-up clonk but I put this down to the box, whic has now been changed.
With the rear wheels on the ground and the prop shaft removed, I can rotate the rear flange about 1/16" or just more than 1mm. I hear a solid clonk but the fluid would have all drained down as the dif has been stationary for over 3 months.
Dave
D M Tetlow

1mm sounds fine, I can't recall where I read it on line but I read that 10mm is OK, 15 is too much and 20 needs the washers done. I took the source seriously.

Mine has about 4-5mm.

Liam
Liam H

Dave, that doesn't sound bad at all. There are several points in the rear axle/differential assembly where slack is present so unless you pull the rear cover it will be hard to determine where the clearance is. That much clearance in the pinion to ring gear fit would be bad, that much in the spider gears isn't a problem, in fact it's common because of wear on the thrust washers.
Bill Young

Thanks Gents.
Dave
D M Tetlow

The clunkectomy, replacing crush washers, is about a 2 hour job if you really dawdle, and can clear your conscience for years to come. Vic
vem myers

To change the thread a bit. Should you use "Special" bolts for the ends of the prop shafts, i.e. Hi spec Shoulder bolts or could I use any bolts I have that fit.
Dave
D M Tetlow

I wouldn't use anything that fits. I would think the OE bolts are grade 5 or better. YOu don't want the bolts to break while driving down the road a 70 mph.

Clifton
Clifton Gordon

"The clunkectomy, replacing crush washers"

The 'clunkectomy' involves replacing the *thrust* washers. The crushable washer is on the pinion shaft and not affected (unless you make a cock-up) by replacing the thrust washers.
Paul Hunt 2

Dave, I'd use the shoulder bolts unless a standard grade 8 fits the holes without any "slop" which would allow the flange to rotate slightly. The idea is to make sure the flanges don't move in relation to one another.
With the Quaife unit fitted, I don't think you need to worry about the usual thrust washer problem as the Quaife design is quite different.
Bill Young

I changed the oil in the diff on my 79 MGB today. Less than 1/2 pint drained out. This probably explains why the car was making a droning noise while driving. I refilled the diff with a fresh quart of 85/140 EP gear oil. I see no signs of seepage. For sure I will be checking for leaks. I just hope I did not ruin the rear on this car.

Anyone else have this happen?

cheers

Gary :>{D
79 MGB
gnhansen

Yes. When I first bought my roadster I checked the diff level and it was fine. As it didn't drop any on the garage floor I assumed it wasn't leaking, although it was a little damp around the cover. But while out one day it started whining really badly. I limped home and found it was empty. Took the cover off and cut a new gasket, refilled and checked very frequently after that but there was no further drop in level. Refilled it continued to whine a bit, more noticeable with the hood/top up, virtually unnoticeable with it down. Over many tens of thousands of miles after that it did seem to be getting very gradually quieter, but barely so. Eventually I replaced the axle, but as part of a conversion to wire wheels, not because of the whine. As long as they have enough oil they will whine for ever and not fail.
Paul Hunt 2

Paul: thanx for sharing your experience. Suffice to say Iwas rather concerned. Obviously this is an item I need to check on a regular basis.

I just came back from a short ride and yes it is much quieter. As I put the car in the garage, I checked for leakage - none.

To refelct your story, I do notice the cover gasket looks a bit damp. My first impression is that it tis due to overflow from the refilling. Again, I will keep it in check

thanx

cheers,
Gary :>{D
79 MGB
gnhansen

Gary-
The Salisbury tube-type axle is a grossly over-engineered piece of design work, originally intended for use in light trucks and vans. Usually, the only thing that damages it is letting the oil level drop too far. This often happens when the breather on the top of the tube on the passenger side (right above the horizontal bracket) gets plugged up with road crud. Air then is trapped inside the axle, the differential gets hot and causes the air trapped inside to expand, and then either the gasket or the pinion seal starts to leak as a result of the internal pressure. When the axle cools, air is drawn in through the leaking gasket. The process is repeated every time the car is run until the oil is gone, which usually takes a very, very long time. Once in a blue moon a dedicated garage mechanic will check the level and top it off, so outright failures are unusual. Cleaning the breather is a simple affair, but most DPOs do not even know that it is there on the top of the right side axle tube. Just clean around the top of the axle tube with cheap carburettor cleaner so that crud will not get into the threads, unscrew it, and spray it out with carburettor cleaner, carefully clean the threads with an old toothbrush, then put it back in after it dries. Simple.
Steve S.

Because later rubber bumper cars have a rear sway bar it places more load on the drive train when going on & off the throttle. This causes the pinion flange to shift minutely on the spline of the pinion as the load against the crushable spacer is not enough to stop it moving when going on and off the throttle which causes a 'ping' through the drive shaft.
To cure this annoying problem, remove the pinion flange and put a couple of drops of locktite on the spline and refit the flange. Allow about 1/2 hour before driving again.
Garth
Garth Bagnall

This thread was discussed between 04/09/2007 and 18/09/2007

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