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MG MG Y Type - YA gearbox bearings.

It seems I need to replace one or both of the gearbox bearings in which spin the first motion shaft and mainshaft, and possibly the bearing in the rear casing. Not sure yet (until the gearbox is extracted) whether any associated bearing guards, circlips etc will need replacing - hopefully not, as I don't know if they're available new. Can anyone advise the dimensions of the 3 ball- bearings, and are they common to TC or TD? Sourcing them might be easier if they are common to other variants, as I suspect. Armed with the specifications, I may even be able to order them through bearing suppliers here in Aus.
PS - Willy, if you're here - yes, the propshaft uj's are fine, the gear teeth seem to mesh ok, so if I'm lucky, it might "just" be 1 or more collapsed gearbox ballbearings. Hope springs eternal etc.
Thanks again. John.
J P Hall

Cheers John. so I take it you still have the rumble running the gearbox without the tailshaft connected---?
William Revit

Oh yes, sorry - that's the first thing I checked this morning, still the same rumble, albeit not quite so loud without the load. If anything, sounds more like the rear mainshaft bearing of the two, but I'm thinking it would be good practice to renew both? John.
J P Hall

Interesting, it's a wonder it's not noisy through the gears but then the rear bearing doesn't speed up much until the car gets up some pace.
if it were the front bearing you'd hear it whirr up in neutral with a rev then in 1st then whirr up again in 2nd then 3rd then quiet in 4th so yeah most likely the rear bearing has failed out of the two---or the cluster bearings but then they'd whirr up through the gears--just depends how deep you want to get into it and what you find with the rear bearing I guess-
The gearbox/bearings are the same as tc/td/tf so will be readily available at a bearing shop I'd think-
William Revit

These gearboxes are pretty tough, but the needle rollers in the laygear(cluster) are the weakest link. Once the case hardening wears from the layshaft, the needles rapidly deteriorate causing a pronounced rumble as the gear meshing gets worse.

The large bearing in the gearbox is very expensive. I last did a gearbox about 5 years ago, and all the bearings were available in Australia (eventually), but not cheap.

The hard-to-get bearings were supplied by Premier Bearings in Albion (Brisbane), while the more common from CBC Bearings.

I have the mortal remains of several extinct gearboxes here in Black Mountain, so if you need the odd circlip or lockbolt I can likely help.

The workshop manual is quite good for stripping and rebuilding the gearbox.

Good Luck

Tony Slattery
The Classic Workshop
A L SLATTERY

Thanks Willy & Tony.
A couple of updates:
(1) With the propshaft taken out of the equation, I don't seem to be getting the <obvious> grinding noise first experienced the other day, even at fairly high revs (gauge indicating 50mph). There is (possibly normal?) gearbox noise across all gears, which perhaps persuaded me yesterday that with propshaft unbolted the problem was still there. Like phantom pain??
(2) So today I'll repeat testing, both with and without the propshaft fitted. Willy's original comments ring true - I need to consider bearings in the diff area and even wheel bearings as possible culprits, even if the rear gearbox bearing is partly at fault.

I do thank Willy & Tony for chipping in with advice - two gurus always willing to help.

John.

J P Hall

Testing continued: nut checked on diff /tailshaft flange, tailshaft refitted, halfshafts and drums refitted. Question: with gears engaged, only the nearside wheel is currently "driven" - is this a feature of the YA diff of which I am not aware? I expected both wheels to be driven once a gear was selected. Still not able to reproduce the graunchy/whirry noise of the other day, but not yet game to put the wheels back on the ground! John.
J P Hall

Just a thought - check the propshaft for any marks near the handbrake mounting and check your rebound mount on the gearbox.

If the rebound mount fails, the gearbox can lift just enough for the propshaft to contact the captive nuts/bolts for the handbrake mount.

And yes, your diff is working if only one wheel turns with both wheels off the ground.

Good Luck - keep looking for clues. You need to be sure it's a gearbox issue before removing it.

Cheers

Tony
A L SLATTERY

Tony - You make a good point "if the rebound mount fails ..." : What about if I'd put the radiused washer in upside down under the rebound rubber? The rubber itself looks to be located correctly, though I'll be double checking when I get the car up on my old Repco hoist. In the meantime,washer inserted correctly now and everything else buttoned up ready for road testing tomorrow. There is in fact some scoring on the propshaft exactly where you described, but hard to tell whether it's new or old.
Considering I initially thought it was gearbox noise, the outcome of this will be interesting. I should maybe change the heading for future reference. Don't know how to do that.
John.
J P Hall

Noises are always interesting to diagnose, specially over the 'net. One persons idea of a vibration can be another's deep rumble. With the floor out you'll always hear 'some' gearbox noise but very unusual as said before to have gearbox noise in 4th gear only. Much more likely to be something other than the box itself. Gearbox mountings are probably fairly high on the look at list or tailshaft u joints, they can feel good but be bound up then check again and be slogged out,have a real good look there but usually they clunk on/off the throttle and vibrate at speed, if it's a really slow deep rumble then maybe wheel bearings -but they don't usually fail just like that ,they tend to gradually fail over several miles. you can check them by swerving on the road while it's noisy the noise should change on/off as you swerve side to side unloading the bearing
William Revit

Yep, thanks for your patience Willy - my son Ben ( Ben Hall, would have to be a bushranger), the only proper mechanic in the family, suggested exactly the same as you & Tony - turn corners, speed up & down, keep road testing to see if the noise repeats. If not, quoth the true mechanic, you've fixed it, dad!
The gearbox mount setup will be checked when up on the hoist - that and the propshaft look like the most likely causes. John.
J P Hall

Well I wish I knew how to edit the original heading to this discussion. Originally I was pretty sure the sudden onset of rattle/vibration/graunch in 4th gear was gearbox related. Even the stethoscope suggested so, when applied to gearbox casing, rear wheels in the air. After following sage advice above, the culprit appears to be: loose rear propshaft flange bolts. All four.
This was only revealed when, as suggested, I revisited gearbox and propshaft mounts - the propshaft bolts were all present, nuts in place, but ALL had worked just loose enough to enable vibration once the speed built up. Unbelievable.
This car has been driven several times a week for the last 3 years - so to my shame, presumably I failed to torque up the bolts originally, and they have gradually worked loose.
New bolts with locknuts (Nylock?) this weekend.
Another lesson learned.
John.
J P Hall

This thread was discussed between 02/06/2025 and 13/06/2025

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