MG T-ABC

Sometime in the past the PO replaced the pinion cap on the diff with a Moss version using a lip seal. After apparently many years the lip seal began to leak. In replacing the seal I dutifully marked the rear flanges with red paint dots so that I could reassemble them with proper orientation. I also wanted to inspect the pinion gear, bearings, etc. while I was at it. In the heat of battle the red dot on the pinion flange disappeared. I cannot vouch for its orientation, that of the pinion housing, nor that of the pinion gear. I reassembled but now have noise from the previously quiet trans when compression braking. Does someone have a strategy the restore the proper orientation? Which parts are orientation critical? I suppose I could try each of the four orientations of the pinion flange and go with the quietest. What are the downsides with this? Some group wisdom would be appreciated. Thanks.


Jim Davis
1949 MGTC 7225
Houston

Jim...check the flanges for punch marks...that is the way they're normally marked before disassembly. If you're lucky someone has taken it apart before you and punched them.

Would changing the orientation cause such a noise? I was always under the impression that marking the flange was only for balancing purposes. And I've always wondered how much (if any) difference that could make.

I would agree with Steve, the orientation of the flange seems unlikely to be the cause. Checking the front pinion bearing offers little in the way of guaranteeing a clean bill of health. This bearing has been the source of many a ruined differential and it seems prudent to follow Roger Furneaux's advice and fit tapered roller bearings which are more robust. Contact Roger for his note on fitting such bearings. As for your present problem, how much backlash can be observed when jiggling the pinion flange?

Check that the u-joints are in phase. Be sure that the yolks are aligned correctly.

Eric - There is very little backlash observed, in my opinion.

Dave - Please go into more detail on yoke alignment and assuring the u joints are in phase, although the u joints and the yokes were not disturbed. They are in the original orientation with each other, being on the same side of the flanges which were disconnected.

I can't tell from your original post if you removed the driveshaft using the flanges at each end or just at the rear end. If you didn't disconnect the driveshaft using the sliding joint then whatever phasing you had should still be intact. Do you have the sliding joint at the front of the driveshaft? When I first got my TC the driveshaft was in backwards and did some funny things.

To check u-joint phasing look at the attached image. The yolks should be perfectly aligned with each other as shown in the top picture. Even a few degrees off can make a big difference.
Edited to add I'm not sure why the attachment ended up here twice.

Thanks for getting back to me on this. I disconnected only the rear flange connection and didn't disconnect at the sliding sleeve front end. It looks like the alignment and phasing should be ok. I'll check it out further using your attachment. I guess I'll try the flange in the other positions and pick he best one. I'll also give the trans a going over. Thanks for the help

When I had the new 4.625 crown and pinion fitted to my rear axle, the shop chose to fit the flange from my spare diff unit to the one I was using in the car. I installed the diff unit in the car (driveshaft previously straightened and balanced), and was disappointed with vibration when the driveshaft rpm exceeded about 3300 rpm. This vibration could have been perceived as noise, as well.

After trying to figure this out, I swapped the flange from the other diff unit over, and the vibration disappeared. Upon examination, it was determined that the pinion flange that I removed was slightly bent, probably from mishandling during storage and moving. I'd suggest removing the driveshaft and rotating the flange, checking for any distortion.