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MG MG Y Type - Rumble/vibration

Hello everyone! Please give me some help diagnosing a strong vibration in my 50 YA. It comes on at about 40 mph indicated and on up. It feels like a typical U-joint vibration but I just had them replaced and no help. What next?
Paul Briggs

Paul; find a long straight hill if you can in Kansas. Coast the car down the hill at 40+, if the vibration is there it has to come from the tires, wheelrims, driveshaft or alignment. My guess is that it is caused by bent rims.I went through all of it and the upshot was that my wheelrims suffered from what is called "run on" ie they are bent. They can be straigtened and it was the single greatest improvement I ever made in terms enjoyable driving at 45-60 MPH. The rims are, I am told by the repairer, made of fairly soft steel and are bent by the machines used to change tires. Either use the new style machines made for mag wheels which do not touch the rims or do it by hand with the tire irons. Terry
Terry O'Brien

Hi Paul

At the risk of sounding silly, after I replaced the half shaft (prop down, diff out and stick it all back together again) I had a hell of a vibe from the shaft.

Did you
a) put the prop back on right - right end forward, and was it aligned as you took it off as the shaft is balanced? I am sure you would have marked up the shaft flange and diff/g'box flange so that you mated it back correctly. However, this was not my problem!
b) My problem was I had not tightened up the nyloc nuts sufficiently - so check all 8 nuts and bolts.

When I did this, the car ran beautifully! I felt a right prat when my friend Jack Murray suggested it to me, but he was absolutely spot on!

Good luck

Paul
Paul Barrow

Another comment from a Paul, went through this early on with my YA. Shaft had been removed by someone prior to my getting the car and it had not been refitted properly. Just went through it again with my Jeep, wherein the tech at the dealer had dropped the shaft and not marked, or ignored the marks and fitted it up wrong. Same vibration probs with both. Same correction for both. Best of luck.

Paul
Paul Gaynor

Thanks a bunch, I will investigate all of the possibilities. The previous owners did put on new tires so I will check the run-out. I have never had an MG where the driveshaft was position sensitive (the Y is my seventh MG and I have been through several U-joint replacements before) but I will definitely try moving it. I did notice that someone had tcked some misc. material on the shaft, probably in an attenmp to balance it, definitely not a factory looking job. Results later.
Paul Briggs

Eureka! I have found it! (Eureka is a small town about an hour drive east of here, by the way):) I found one of the nuts at the front end of the drive shaft working loose. Checked all the rest and took a test drive: vibration gone. Checked the run-out on the wheels too. Not the straightest in the world but OK for low to moderate speeds. Thanks alot for the advice everyone. Next thing is to get a new set of hardware for both ends so I don't have to worry about it again.
Paul Briggs

The propeller shaft may still require balancing, this occurs if the person who fitted the new UJ's 'rotated' the shaft before assembling the ends back onto it, so they can be 180 degrees out. You can try fitting a jubilee clip onto the shaft, at one end at a time, and rotating it 10 degrees until the vibration reduces. This is not a perfect way to cure it.

You may have fitted modern greased-for-life UJ's with no grease tube fitted. This will upset the original balance as well.

Check the cups in the UJ's are hard up against the circlip, or the shaft will rotate off-centre. A sharp tap with a hide mallet will usually re-seat them. A good guide is if you can move the circlips in situ, if they move round, the cup is not seated properly.

Are identical bolts & nuts used on the diff and gearbox connection? Did you mark the diff connection, and the gearbox connection before removal, then ensure it all went back in the same 'plane'?

Is the splined joint worn? This can permit the shaft to run out of true. Has it been stripped down, and assembled in its original position? If not the balance will be out, requiring the shaft to be re-balanced.

Remember, the shaft needs balancing as a complete unit, including the gearbox-ends grease nipple on the splines.

Is the nose-bearing of the diff worn? This will let the shaft run out of true.

Is the gearbox tail-shaft bearing worn? Again this will let the shaft run out of true.

Neil.
Neil Cairns

Neil, all good ideas. As I noted ealier, there is a lot of washers, etc. tack welded onto the shaft; obviously from an earlier attempted balance job. I will find a balance shop and have it done properly since there is no indication of where any baseline location would be. The u-joints were the standard Hardy Spicer greasable units.
Paul Briggs

This thread was discussed between 09/03/2002 and 13/03/2002

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