Gearbox rear extension distance piece.

[Colin Lindsay]

Morning all.... been out already in the garage fighting with a 1200 gearbox (actually a FD-prefix Spitfire Mk3 gearbox) on which I have been replacing the bearings.

The biggest problem has been what should be the easiest - the rear extension bearing right at the end. I removed the old bearing and cleaned up the housing then replaced the new bearing, and on removal originally there was a 'distance piece' washer on which the bearing sat. Once I replaced the housing it sat proud of the gearbox by the exact depth of the distance piece and would only tighten very reluctantly, and being worried about causing damage to any of the internals I removed it all again.

If I seat the bearing right to the bottom of the housing - as I would do for example with wheel bearings - the unit won't fit. The workshop manual says to drive the ball race into the bore, fit the oil seal, fit the distance washer and using a hollow drift drive the entire housing down over the shaft until it reaches the gearbox. If I do this, once just short of the final position it takes considerable force which actually starts to push the entire shaft out of the front of the gearbox, and there's a 1- 2 mm gap between box and extension that I don't want to force closed.

Does it mean that I should use a hollow drift and drive the housing down - and by doing so the bearing will be pressed back by the distance washer up to the correct distance? Could I therefore half-fit the bearing and when the housing is seated, drive it down to the correct position? As you can see from the photo, when seated the bearing looks to be where it should be, but there's a lot of room for the oil seal. Any thoughts? I remember having the same trouble with the last one I did just last year, but can't remember how I overcame it...

 

 

[johny]

doesnt it all sort itself out when the drive flange nut is tightened as this actually forces the flange up against the bearing inner race? 

[Colin Lindsay]

It's not as far as the flange yet; the actual extension will not meet the gearbox case but leaves a large gap; the bearing inside the housing is against the distance washer and cannot move any closer. What I'm wondering is: if I tighten the extension then it will move down, and the bearing will slide back out of the extension slightly, maybe only 1mm or so. I just want confirmation that doing so won't cause any problems once driving. Once I have the extension casing in place I can add the oil seal and tighten the flange on to the proper torque, but at present if I tighten the extension with the fully seated bearing it exerts so much pressure that it pops the split ring off the rearmost main bearing and slides the entire shaft through the gearbox and out of the front - which can't be good!

 

[johny]

I cant see how it can force the front out as the casing rear bearing has circlips that should keep it positioned both relative to the case and the mainshaft so something is definitely wrong if your able to push the mainshaft through too far.

My WSM drawing of the Vitesse/GT6 box shows the tail bearing with a gap to the rear housing but the bearing shouldnt protrude enough that it will prevent the rear seal going in right up to shoulder in the housing....

[Colin Lindsay]

21 minutes ago, johny said:

I cant see how it can force the front out as the casing rear bearing has circlips that should keep it positioned both relative to the case and the mainshaft so something is definitely wrong

Which is what I'm saying: Once I start to tighten the extension into the 2mm gap it's exerting so much pressure that it pops the rearmost circlip off and pushes the entire shaft forwards. I have to remove the rear housing, recentralise the two main bearings, reattach the circlips, and try again... but still a 2mm gap with the extension bearing in place, but none if I remove it and fit the housing with no bearing. My WSM just says: "drive the ballrace into its' bore" which I assume means fully seated.

BUT: got it sorted a few minutes ago; fitted the extension cover without bearing and tightened it against the gasket, dropped the distance washer over the shaft and then drove the bearing in, and it's gone in flush with the housing. I'm happy that it's where it should be. No idea why it won't fit as per the WSM method but it's now in and that's that. I hope!

[johny]

I wonder if your circlip is weak as normally the tail bearing moves quite easily in the rear housing so should just get pushed out slightly as you do up the fixing bolts...

[Colin Lindsay]

I've replaced it anyway, just in case... and the whole unit is now assembled so I can leave it until it's time to fit.

Once fitted I'll be worrying that something in the internals has been disturbed, leading to increased wear or noise... I'm just a born worrier!