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MG MGA - differential noise

Hi,

Had the first maiden-drive today after 4 years of work. Went pretty smooth. All gears shift nicely. The engine still need a bit of tuning. But ok for now.

Just (why else this new thread)...
If I take my foot of the accelerator to slow down, with the gear still engaged, I hear a screaming noise, which it seems come from the diff. The minute I decouple, it is gone. If I press the accelerator again, it is gone. The diff looked fine when I had it in my hands. I must say that was the only part I did not take apart. THe oil was clean when I first took it out and the pignon and crown wheel looked fine. I have new 80w90 oil in it. Checked the level and it is ok. In forward there is no noise and all seems fine.

With the hand brake applied I can turn the propeller shaft about 5mm measured on the outer edge of the flange. Do some backlash, but not excessive.
Drive shaft itself has new universal joints. At 80kmph there is no vibration in the car indicating unbalance in the shaft.

Note that the noise is certainly not the whining noise some differentials make. It sounds more like a screem, much like a brake with a worn brake pad.

Any suggestions? If needed I can try to record it and upload it.

-- Paul
Paul van Adrichem

Here's an old old mechanics remedy....its unorthodox by any measure but may help you in this instance. If the backlash is worn out and the rear end is actually howling... a couple of bananas stuffed into the diff is supposed to give enough bind to get rid of the howl.

It goes in there with the 90 weight.

I would only use this to diagnose if I all ready changed the copper washers on the sun gears first and still had the noise.

Its a little tricky to do as you need to slide those sun gears in perfect to get the axles to slide back into there required position. Still a back yard mechanic can do it with some patients.

Its not a permanent fix but something I would do as a very last resort. Better to remove the pumpkin and have a specialist take a look. If you are in a bind its an option. (But not a great one)

Good luck and report back what you find!
Steven Devine

Reminds me of the old story of putting sawdust in the gearbox!
J H Cole

Paul, Presumably this problem wasn't there when you started the restoration 4 years ago so what work did you carry out on the axle during the 4 year spell? The 5mm backlash doesn't sound too much but if it's all due to wear or whatever in the crown wheel and pinion it could be enough to cause the noise. My back lash was around 3-4 mm and about of this went when I replaced the differential thrust washers. Looking back I don't think I needed to take the axle apart as there was no noise or clunking...........Mike
m.j. moore

Did a test drive with the battery cover removed. The noise is clearly coming from the diff. In acceleration there is no noise. In decceleration you can see the diff tilt a bit. I'm not sure if that has anything to do with it. I did not pull the bearings of the pinion. The oil that came out before the work was clean (that is not particles).
Mike, unfortunately I got the car in a non-driveable state, so I don;t know how it was before the work. And all I did to the rear axle is: cleaning, new bearings and seals and brakes.


-- Paul
Paul van Adrichem

In my last post I meant to say that only about a third of my backlash went after replacing the diff. thrust washers and it didn't seem worth the effort especially as I had to replace bronze washers with fibre ones.
Paul, I think I would look around for a professional axle repairer or, if you feel brave and have the special tools and gauges, try the setting up procedure for the wheel and pinion outlined in detail in the Workshop Manual plus what to do after replacing pinion bearings................Mike
m.j. moore

Mike, I'll. give it a try myself first. first drain the oil looking for particles and wear scratches. Checked the workbook manual. I do have a gauge. Just there is a special tool that is no more than a block of steel with a specific thickness tob let the pinion protrude beyond the bearing races. Anyone knows this value?
-- Paul
Paul van Adrichem

One thing you could check before going to all the trouble of removing the axle again is the torque on the end pinion nut which is (it's in the WM) I think 140 lb.ft. ................Mike
m.j. moore

Paul, I had a similar problem with my TC, it turned out to be the carrier bearings. Someone who did the diff. up before I got the car put the carrier bearings in back to front. OK driving but screaming on the over-run.
Regards, Don TF 4887 TC XPAG 7730
D J Walker

Hi,

Mike: you had it right. The nut of the flange on the pinion was not thightened. I did take out the diff while I was at it. Could see the markings Thrust on the outer side of the cage bearings. will put it back in tomorrow.

Paul
Paul van Adrichem

Paul

With the diff on the bench it is quite a task to get the required torque on the nut in question. I made up a 'pinion stay' that worked very well. Someone on this BBS told me about it a number of years ago. I cannot remember who it was.

Steve

Steve Gyles

Nice tool!
Art Pearse

Paul, It will be nice to know if your backlash measurement has changed after the axle has gone back.

Steve, I seem to recall making up something similar, but less professional looking, when I did mine...................Mike
m.j. moore

Yes, my tool was just a long flat piece of steel with a hole in it to bolt to one of the flange holes. I just stood on it while I slackened and tightened the nut.
Neil MG

Hi, I did the same as you guys did: took a long flat piece of steel, and drilled a hole in it to bolt it to the flange. I grabbed the flange into the vice, put my foot on the long piece of steel and pushed to get to the right torque.
After that I checked the backlash and the preload. THe backlask was about 0.25-0.3mm and the preload about 1 Nm (difficult to measure).
Put everything back and new oil in (EP 90): Perfect! No sounds, even with the battery cover removed: Nice and smooth, not vibrations. Life it good!
So the root cause was clearly the bolt of the flange!

-- Paul
Paul van Adrichem

Btw. The backlash I now measured on the crown wheel, not on the input flange. I could still check that if one is interested!

-- Paul
Paul van Adrichem

Paul, If it's no trouble I wouldn't mind knowing the input backlash now the axle is good. When I did mine there was about 4 degrees of backlash on the prop. shaft. I estimated that just less than a third of this was due to backlash between the crown wheel/pinion.........................mike
m.j. moore

Paul van Adrichem,
Glad you didn't have to go banana's to get that fixed....nice job! :-)
Steven Devine

This thread was discussed between 11/07/2014 and 23/07/2014

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