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MG MGA - Driveline spline wear

Greetings from the Pacific NW,

Besides chasing pin-hole leaks in my rust bucket of a gas tank (epoxy is slowly getting the upper hand), I am trying to sort out a shimmy that shows up at about 5,000+ RPM. I cannot tell you what the exact speed is since the speedo is in the shop. The shimmy is most likely in the front end or an out of balance wheel it is a whole body shake through the steering wheel.

In an effort to eliminate other suspects, and give her a grease job, I jacked her up to take a closer look at the drive shaft. The UJs appear to be tight, but there is slight but noticeable play in the driveline spline.

I pulled the driveline to take a closer look. Moving the spline in reduces the play to zero. The UJs are properly aligned. In searching the archives I was unable to find any detailed reference to worn driveline splines. Any thoughts on spline wear tolerances? Now that we are some 50 years on, I would expect that most used parts would have the same issue. Does anyone rebuild or replace the splines?

A secondary issue is that both the transmission output seal and the differential input seals are leaking. Can either or both of the seals be replaced without removal of the transmission and/or differential? The transmission was rebuilt at some point as the syncro in second works.

I have a 59 Roadster, March birthday, so I have the third variation of drive shafts with flanges at both ends and a spline connection at the rear. She already has new rear dampers, and the fronts have been topped off (but still need a rebuild). Frontend components look to be way past due for a rebuild, I have ordered the parts and plan to do the work later this later this summer. The tires are older, but serviceable 155-R15 radials with disk wheels.

I do not believe that the driveshaft is the cause of the shimmy, but given the amount of play I would not entirely rule out the possibility. Of greater concern is what the driveline play may be doing to the transmission output bearing & seal, as well as that of the differential seal.

BTW Had a chance to meet David Breneman at the PNW All British car show this past weekend, always nice to put a face to a regular contributor.

Thanks, John
jjb Backman

The seals can be replace without removing the trans or dif. A good drive shaft shop should be able to replace both sides of the spline joint for you.
J Heisenfeldt

If I understand you correctly you have the sliding joint at the rear - on the diff. end of the shaft? I thought that the spline joint should always on the transmission side of the shaft. The spline joint was obviously built into the tranny in the early cars. I assume they would keep the spline on the same end of the driveshaft when they changed to the later style.

David Ahrendt

One of the first things other MGA owners comment about driving my car is how taught it is - the result of a front end that is in tip-top condition and all aligned and balanced. If your front end is worn out, then the shimmy could well come from anywhere in there. The rebuild can be done in a few hours (and it's usually VERY dirty work), so should be the first step. Only then can you be sure that you have a wheel balance problem or not. It will be a revelation when you have replaced all the tired and perished seals and bushings, and had the wheel alignement checked out.

The propshaft should be switched so the spline is at the front end, though it may be hard or impossible to get it out with the gearbox in the car. It can be done by removing the hadbrake support brackets at the tunnel, but that is also a pig of a job. Last time I just moved removd the axle U bolts and slid the axle back along the springs (but I have a 1500 propshaft without the centre spline, so you may have a chance with yours).

While you do that, change the seals in the rear of the gbx and the front of the diff - as Mr Heisenfeldt says, this is easy enough if you can get under the car (make sure it is properly suported when you are tugging the old seals out.), just get a stout screwdriver under them and butcher away till it comes out, you won't break anything else in the process. Use a large socket as a drift to install the new ones, making sure they are square.

dominic clancy

I would not bother changing the spline from the rear to the front, unless you need to take the driveshaft out for another reason.
There is no operational difference with the spline at the front or rear. The MG factory put the spline at the front, but the Triumph factory put it at the rear.

I do not believe that play in the spline would cause your "shimmy". Wear in the U joints certainly could. Also, spline wear would not damage the seals.

The probable culprits are the wheel balance, wheel alignment, and general front suspension condition.


Mick Anderson

Worn splines can cause quite a vibration as the drive shaft can start to swing like a jump rope, quite common on pickup trucks. It would not however be related to engine RPM, only the speed of the car.
J Heisenfeldt

John Backman writes:

> BTW Had a chance to meet David Breneman at the PNW All British car show this past weekend, always nice to put a face to a regular contributor.

But I'm sure you could have picked a better face. :-)

Still, it was very nice talking to you, John. Hope we meet up again!

David Breneman

This thread was discussed between 29/07/2008 and 31/07/2008

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