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MG MGB Technical - Driveline shudder 73 GT

I took the GT onto the pike today and at 70 I noticed a rythmic shudder. The shudder was subtle but rapid and the shuddering would come and go in a wave like rythm. On the way home on regular roads I noticed it much fainter in the 50 range. It was not from the front end. Misaligned driveshaft or rear end issue or something all together different?
FWIW, The we put in a black label OD into the car that did not have it before.
carl w french 1

I vote drive shaft/universal joint problem. Sounds like an inbalance..differentials groan and growl.

Did the O/D unit seem to operate properly throughout the rpm range?

rick ingram

The OD works great. The lockout switch is operational. I did notice the other day some leaking to the rear end on the passenger side of the diff ( I am more used to Banjos). I made a mental note (and forgot) to check and do a drain/refill). I was not underneath the car when we were hooking the engine tranny back to the car. My mechanic was doing the under the car stuff that day. I was thinking i should check under the car to see if the driveshaft was hooked up correctly. Rick, I cant remember what the marks are for lining up the correct bolt holes?
carl w french 1

Sounds like you need to get the uv joints rebuilt. I would just check for play in the driveshaft first. a pretty simple and cheap job to fix
Eric Willis

Carl. The first thing to do is to test some of the systems. Visually inspect the drive line to see that the bolts are tight and the U joints do not allow the driveshaft to have play in it. Check the U joints to see that the yokes are properly aligned. (Tom Sotomayer has an article on this, with illustrations, at on the MG section.)

If the prop shaft seems to be in good order, check tire balance. Front end shudder is felt through the steering wheel. Rear end related shudder is felt--well, through the rear end incontact with the seat.

One thing to check out, because no one ever mentions it, is the U joint on the steering column. It can also cause a shuddering feeling in the steering wheel, cannot be lubricated, is probably original and developes a funny wear pattern. (Something on the lines of the rocker arms having the needle bearings.)

Let us know what you find.

Les Bengtson

Thanks Les (and others). I will get under the car tomorrow and check those things out. The tires are of uncertain history are of two types (and sizes!) front and rear Bridgestone Potenzas 185/70/14 in the rear and Firestone FR680 175/65/14. I am planning on a new set of something soon. But I will get the rear tires balanced soon.
carl w french 1

Carl, you may also want to inspect your rear brakes. If you have an axle seal leaking in the back passenger side, the brakes can become contaminated with gear oil and swell, causing them to drag on the drums. I'm not sure where you noticed the leak, but this is a possibility.
Jeff Schlemmer

Carl, did you mark the flange joints before you disconnected them ? If not, disconnect the front flange & rotate the drive shaft 180 degs & then reconnect it. This sometimes works. Barrie E
Barrie Egerton

I had a similar problem that was from the wheels. If you are running wire's see if they are true. Also make sure your wheels are speed ballanced. Another issue might be wear on an inner hub. Sometime the bearings will wear the hub and they will have movement that at high speed gets magnified. If you pull on a wheel and it has some movement in and out you should check the innner hub.

Had something like this years ago on my old roadster, one of the rear tyres had a bulge in the tread. Had checked prop shaft etc, jacked the car, started the car in gear and looked at the tyres from behind the car and could see the tyre going up and down. Changed tyres and was OK.



Since a prop-shaft is balanced off-car it shouldn't make any difference how the gearbox and diff flanges are orientated. What *is* important is to check that the two yokes are in the same orientation, if the sliding joint has been apart at any time it might have been put back incorrectly. If the vibration started on its own it may have lost a balance weight as well as having a collapsed UJ (as mine did), but as a last resort if it was OK before and only started after you removed and replaced it you could try each combination of orientation of front and rear flanges, that should keep you busy for a bit! For much the same reason I mark the studs and holes on my V8 wheels, and locate them on the studs with tapered Rostyle nuts before tightening the shouldered V8 nuts.
Paul Hunt 2

This thread was discussed between 22/03/2006 and 23/03/2006

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