B2 90Q rear gearbox seal

David42U856 · 22-06-21, 11:26 AM

Having removed the propshaft to change the centre support on my 1985 90Q, I've noticed oil leaking from the gearbox rear seal. After a bit of investigation it seems that, of the three socket head cap screws holding the output shaft assembly in place, one was loose, one is rounded and the other missing completely. I'd like to replace the seal but not sure if it's possible with the box still in the car. Can anyone shed light on this? Looking at exploded views from various manuals, it looks like the rear flange with it's bearing and housing can be removed once the three securing bolts are removed (that's all the parts in the lower view of the attached exploded view). If I engage the centre diff lock, is there a good change that shift hub will stay in place? If not, is it possible to reassemble those parts through the opening in the back of the case? Looking for some guidance from someone who's done this before.
Another option is to fit all three screws and see if the leak stops. I'd rather do it properly though since it's up on stands and the prop is off.

mikes2 · 22-06-21, 02:04 PM

The 3 bolts attach to the U shaped item which is a balance weight. They don't hold the flange.

How do you propose to remove the flange ? Looks like it's an interference fit with no central bolt to hold it in place.

I think a puller would work or you could use long bolts and a support behind it to release it.

You've then got the challenge of extracting the seal. I'm not seeing any dimensions for the seal.

Groundhog · 22-06-21, 02:35 PM

This was a common fault back in the day, either you could not shift the bolts at all or they fell out. Almost certainly the leak is because of the bolt problem. 8 times out of 10 dealing with the bolt issue( i.e replacing them) cured the leak. If you want to go ahead then yes the back hosing can be drawn off on its own, the diff lock ring may drop. There is an ‘O’ ring around the housing and a seal where the flange enters. To get to that seal you will have to remove the circlip and press the shaft/flange off the gear and out. The seal can then be replaced. A word of caution, of the hundreds of quattro gearboxes I overhauled I damaged/broke/chipped a couple of gears when pressing the shaft through-they are guide delicate. When re-assembling the diff lock dog can be propped on the inside gear while you carefully remount the tail hosing ( considerably easier with the box out) Don’t forget when you re-assemble the cap head bolts need lock tight on them

PS yes the bolts do hold the damper and the housing.

David42U856 · 22-06-21, 03:04 PM

Thanks for the reply. On mine the balance weight (thanks for educating me on what it is!) has deep counter-bores and the screws seem to go straight through to the casing. It looks like it's 'C' shaped so will come off easily once I get the screws out. Not as straightforward as it might be since I'll probably have to drill the head off the one that rounded. If I can get to that stage I'll try to use bolts through the flange against some support to release it as you suggest. Is it just a wire 'C' spring in a groove on the output shaft holding it in? If that doesn't work I guess we're into slide-hammer territory - I'd like to avoid that!
I'm thinking I'll just try bolting it back up properly to see if that solves the leak.

David42U856 · 22-06-21, 03:13 PM

Thanks for the clarification Groundhog and the words of warning! I think I'll just bolt it up with new screws to see if that solves the leak ... that's if I can get the rounded one out. The one that I've released doesn't quite pass the flange OD which is going to be another challenge. If I had all three loose I guess there would be some wiggle room to get them in and out. If you happen to know the size and particularly the length of the screws that would be most useful. At least I can order them in advance.

Groundhog · 22-06-21, 03:20 PM

Cap head bolts are usually harder than standard bolts so make sure you have a keen drill and bit. If you have one a number 8 multi splined sockets ( used on drive shaft bolts) it can be hammered into the cap head....has always worked for me 99% of the time.

mikes2 · 22-06-21, 03:36 PM

They're M8x30

Groundhog · 22-06-21, 04:54 PM

Quote:

Originally Posted by David42U856

Thanks for the clarification Groundhog and the words of warning! I think I'll just bolt it up with new screws to see if that solves the leak ... that's if I can get the rounded one out. The one that I've released doesn't quite pass the flange OD which is going to be another challenge. If I had all three loose I guess there would be some wiggle room to get them in and out. If you happen to know the size and particularly the length of the screws that would be most useful. At least I can order them in advance.

The idea is that, in normal circumstances, one would back the bolts out as far as possible so they are clear of the housing and then drop the damper block with the bolts still in. To replace put the bolts into the damper block position same into place and then screw bolts into housing.

David42U856 · 23-06-21, 12:44 AM

Quote:

Originally Posted by mikes2

They're M8x30

Thanks - much appreciated.

David42U856 · 23-06-21, 12:48 AM

Quote:

Originally Posted by Groundhog

Cap head bolts are usually harder than standard bolts so make sure you have a keen drill and bit. If you have one a number 8 multi splined sockets ( used on drive shaft bolts) it can be hammered into the cap head....has always worked for me 99% of the time.

I have a set of multi splined sockets which are long enough to reach. I'll try this before I get the drill out. Hopefully this isn't one of the 1% cars!

22-06-21, 02:04 PM	#2
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	The 3 bolts attach to the U shaped item which is a balance weight. They don't hold the flange. How do you propose to remove the flange ? Looks like it's an interference fit with no central bolt to hold it in place. I think a puller would work or you could use long bolts and a support behind it to release it. You've then got the challenge of extracting the seal. I'm not seeing any dimensions for the seal. __________________ 1991 90 quattro 20v sport 1991 90 quattro

22-06-21, 03:36 PM	#7
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	They're M8x30 __________________ 1991 90 quattro 20v sport 1991 90 quattro

22-06-21, 02:35 PM	#3
Groundhog Grown up member Join Date: Nov 2009 Posts: 143	This was a common fault back in the day, either you could not shift the bolts at all or they fell out. Almost certainly the leak is because of the bolt problem. 8 times out of 10 dealing with the bolt issue( i.e replacing them) cured the leak. If you want to go ahead then yes the back hosing can be drawn off on its own, the diff lock ring may drop. There is an ‘O’ ring around the housing and a seal where the flange enters. To get to that seal you will have to remove the circlip and press the shaft/flange off the gear and out. The seal can then be replaced. A word of caution, of the hundreds of quattro gearboxes I overhauled I damaged/broke/chipped a couple of gears when pressing the shaft through-they are guide delicate. When re-assembling the diff lock dog can be propped on the inside gear while you carefully remount the tail hosing ( considerably easier with the box out) Don’t forget when you re-assemble the cap head bolts need lock tight on them PS yes the bolts do hold the damper and the housing.

22-06-21, 03:04 PM	#4
David42U856 Newbie! Classic Audi Club Member Join Date: Aug 2015 Posts: 17	Thanks for the reply. On mine the balance weight (thanks for educating me on what it is!) has deep counter-bores and the screws seem to go straight through to the casing. It looks like it's 'C' shaped so will come off easily once I get the screws out. Not as straightforward as it might be since I'll probably have to drill the head off the one that rounded. If I can get to that stage I'll try to use bolts through the flange against some support to release it as you suggest. Is it just a wire 'C' spring in a groove on the output shaft holding it in? If that doesn't work I guess we're into slide-hammer territory - I'd like to avoid that! I'm thinking I'll just try bolting it back up properly to see if that solves the leak.

22-06-21, 03:13 PM	#5
David42U856 Newbie! Classic Audi Club Member Join Date: Aug 2015 Posts: 17	Thanks for the clarification Groundhog and the words of warning! I think I'll just bolt it up with new screws to see if that solves the leak ... that's if I can get the rounded one out. The one that I've released doesn't quite pass the flange OD which is going to be another challenge. If I had all three loose I guess there would be some wiggle room to get them in and out. If you happen to know the size and particularly the length of the screws that would be most useful. At least I can order them in advance.

22-06-21, 03:20 PM	#6
Groundhog Grown up member Join Date: Nov 2009 Posts: 143	Cap head bolts are usually harder than standard bolts so make sure you have a keen drill and bit. If you have one a number 8 multi splined sockets ( used on drive shaft bolts) it can be hammered into the cap head....has always worked for me 99% of the time.