Dear all
Following on from my CV joint saga (opened a new thread as it's now a different problem):
www.honestjohn.co.uk/forum/post/index.htm?t=71745
yorkiebar was right (unfortunately).
The play is all in the diff, at both ends (shame I didn't spot that in the N/S before!).
So, my question now is, will the 'box have to come out, or can the situation be saved in situ (I'm assuming the 'access plate' under the diff. allows you to do something)?
Many thanks.
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Have a look at the gearbox where the N/S driveshaft goes in. If you see a large casselated (sp?) nut, concentric with the driveshaft, then you should be able to remove the diff in-situ. Take out both driveshafts, take out the sump plate, and undo the large nut - it's held by a clamp plate which interlocks with the teeth of the nut.
There is a method to set the pre-load on the bearings when you put it back together - but, I've forgotten how to do that. I'll see if I can find it in my notes.
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Im guessing your going to strip the diff down and inspect everything like the gears and pinion,crown wheel etc?
When you rebuild it with new shims you will need to "blue the gears" with engineers blue to get the correct mesh pattern.
It's not hard just take your time get the haynes manual & you will need a dial gauge to set up the pre load too.
You may save some cash on the bearings by going direct to a company that supplies them rather than vauxhall themselves.
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I had mis-remembered (over 15 years since I last did one!) - you also need to remove the gears from the gearbox to allow clearance for the final drive gear and diff to come out.
It's not difficult, you need to take the remote housing off the top of the gearbox out, and the reverse light switch, and then take off the gearbox end cover, and the plate which holds the gearbox outer bearings. The end plate, bearings, shafts, and gears all then withdraw from the body of the gearbox.
The preload is something that you might find difficult to set - it's equivalent to about 1.5 Nm with the diff turning at 1 revolution per second. I would measure the radius of the diff cage, and tie some string round it, and use an appropriate weight to apply the torque, and then tighten the large casselated nut until it dropped steadily.
You don't need to worry about alignment, and setting up the mesh, as this is a helical gear pair, not a crown wheel and pinion like in a rear axle. There aren't any shimmed adjustments to make - just the preload.
However, if the gears have been running on worn bearings, it's likely that they won't mesh together again quielty.
It's also worth looking to see what caused the bearing failure to begin with.
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Why not just replace with 2nd hand box/diff? Lot easier, quicker and maybe cheaper?
Then you got original to play with/repair as you wish?
Fairly common problem and cure that way.
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>>Lot easier, quicker and maybe cheaper?
That depends. If the repair can be effected by fitting new bearings, then I disagree. If, however, new gears are needed, then, I agree.
Assuming bearings only;
>>Lot easier
No - getting the gears out of the 'box, and the diff out is not difficult at all, and changing the bearings over isn't difficult.
>>quicker
Possibly? - I don't think there's much in it either way.
>>maybe cheaper
2 bearings from a bearing factor, 2 oil seals, and some gaskets, and some oil. I don't think you'll buy a gearbox for that.
However, if you find you need to buy a gear pair, then, yes, I think you will be able to buy a S/H gearbox cheaper.
Edited by Number_Cruncher on 07/02/2009 at 18:20
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fair comment, but if you dont sort out the reason for the failure you will be doing the job again, and again.
So, therefore possibly faster cheaper and easier to use 2nd hand box
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>>but if you dont sort out the reason for the failure you will be doing the job again, and again.
Yes, but that depends upon what the reason is - with rolling element bearings, there isn't an external reason. Up to 10% will fail before their L10 (or B10) life is reached even if there are no external problems.
I suspect that perhaps this gearbox is a bit marginal for the engine, and you might very well be fitting a SH gearbox with the bearings just about to go bang!
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The information on this site might be helpful;
www.marineengineering.org.uk/tribear/triroller.htm
Disadvantage No 5 describes the early failures which are inevitable when rolling element bearings are specified.
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Dear All
Thank you to all the replies. Unfortunately it's a 'new' Haynes so gearbox rebuild pages are out. Now I have to tell you - I think I've got the diagnosis wrong again :-$
I took the sump plate off yesterday, after noticing the shafts moved indepedantly of each other (i.e. one didn't move when I rocked the other).
So third time lucky... it looks like the diff. gears are where the free play lies. Now, I'm thinking this isn't so bad - find some gears, replace all 4 along with the plastic carrier bearing in-situ, and put the sump cover back on. The diff itself seems solid (i.e. I don't think it's a bearing problem).
Is this practicable, or is it likely that worn bearings wore the gears out in some way?
Edited by mfarrow on 08/02/2009 at 09:33
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>>Is this practicable
It's quite easy to get the bevel gears out once the driveshafts are out.
If you remove the clips and withdraw the cross shaft, the bevel gears and plastic bearing should turn in the housing, and come out of the window in the diff housing.
I don't know what the prices are for these bevel gears, but, they shouldn't be too expensive, because they aren't particularly well finished - they don't need to be as well ground and the gears don't turn much in normal use.
Has someone been booting it a bit, and allowing one wheel to spn up in the snow and ice?
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Thanks NC.
Has someone been booting it a bit
I don't know about that - car was bought with 116k on the clock, now covered 122k.
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OK now I'm trying to work my way around a differential, and the way the shafts are supported in the housing.
I'm assuming that with all the free play, and the movement in the gears, that the majority of the bearing is in the differential gears themselves?? However logic would tell me there should be at least two bearing points on the shaft, i.e. the diff. carrier. This being so, is it more likely the diff. carrier has failed as well, or instead of, the gears? I'm assuming the shafts run plain in the carrier bore, is this correct?
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>>I'm assuming the shafts run plain in the carrier bore, is this correct?
Yes, and this is the bearing surface - the bevel gears splined to the inner CV joint effectively float. Ordinarily, there's very little relative motion between the driveshaft and carrier, and what motion there is is quite slow.
If you grasp the large helical gear, can you move the whole diff from side? You shouldn't be able to move it at all, as the bearings should be pre-loaded.
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Too late to look now as the cover is back on, but all the movement was in the shaft/gears when I shook them.
I assume that means the carrier is worn.
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>>I assume that means the carrier is worn.
And if that's the case, you're probably better sourcing a replacement gearbox. A new diff carrier will not be cheap.
Edited by Number_Cruncher on 08/02/2009 at 19:15
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Dear all
I've been and had it apart again today, and took the diff out.
Thanks NC for the removal method - I like the assurance of pictures so I bought a 'proper' Haynes for an eighties Astra/Belmont. Much better.
Anyway I confirmed my diagnosis that the diff carrier is worn. The bearings were tight and the gears OK. So it looks like I'll be getting a secondhand gearbox. Unfortunately I haven't got the lifting gear to replace the whole box... fortunately this means I can pick up any F17 transmission from a Vauxhall to rob the carrier out of, swap the final drive gear, fit new bearings and put back.
Now, this is where I need some technical advice. I'm worried that the driveshafts will have worn in the same way. There's some slight dulling of the surface of the shafts, though I can't feel any significant groove or pitting. Would the surface of the shaft be hardened, and the carrier not?
Thanks for any advice.
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All done and dusted.
A secondhand gearbox for £60, some new bearings, seals and oil were all required.
Some pointers:
The gearbox main casing doesn't have to be removed to take the diff out on these. However, it does have to come out to set the pre-load as otherwise you'd obviously spin the mainshaft.
The casing and shafts only came out so far as there isn't sufficient clearance to remove in situ without dropping the box down, however this is far enough for the pinion gear to clear the diff.
A carefully crafted house brick makes an excellent pre-load setting weight.
You'll need to buy or fabricate your own tool to remove the castellated nut, there isn't enough room to remove it on cars with subframes with a flat bar as mentioned in Haynes.
Oh, and remember to order the right gasket from Autovaux, otherwise you'll be playing about with gasketing silicone all afternoon!
Thanks to all, especially to GM designers who made the diff. so accessible.
Edited by mfarrow on 22/02/2009 at 21:33
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