Wedge Drive Shaft to Diff Bolts

[John042]

Hi does anyone know for sure the size of the bolts/nuts from drive shaft to diff size. A 18 mm socket seems to fit but the amount of force needed to move them I'd rather be sure than round the nuts off. However the first one I attack this evening has moved but I guess being a nut bolt arrangement will need a spanner to hold the bolt head between the diff flange and disc? I reckon it's going to be an angle grinder to release the drive shaft. Thanks for any info.

[adam quantrill]

I use a hex socket rather than 12-point, then there's no danger of rounding off.

As I have a wheel off I can check the size at half time.

[John042]

Thanks Adam. Just about to order a set of short impact sockets. J C.

[phillpot]

18mm is a bit of an oddball?

Are they imperial bolts, perhaps 11/16" AF ? Although that equates to 17mm near as damn it

[John042]

Thanks Mike, my suspicions, being a XJ6 Diff could indeed be imperial size, 18mm is odd. I'll wait out for any further info. J C.

[adam quantrill]

17mm was too tight, 18mm a bit loose but that was what iI used with a hex socket. My guess iis iit's imperial really

Edited by adam quantrill on Tuesday 10th July 21:03

[phillpot]

It's a Jag diff (4HU ?) in my Taimar, definitely imperial bolts.

7/16"unf from memory with 5/8" af nut size but that's only about 16mm ?

[John042]

Thanks all. I've just destroyed a 3/8 drive, 1/2" if I can get assess. 11/16" seems about right but they're so seized up that an impact gun isn't working. Are they special bolts, nuts before I get busy with an angle grinder? J C.

[adam quantrill]

Yeah the bolts are special and you don't want to cut them or the driveshaft end will have to come out of the diff and partially disassemble the bearing too, probably wrecking the oil seal. The nuts are special too but replaceable. You could drill them carefully if you avoid the bolt thread then use a cold chisel to split.

I used a 1/2" drive on an 18mm socket and a 3 foot breaker bar, I estimate the torque was around 100lbf before they shifted.

They can be very tight if they have been on there a long time.

[phillpot]

John042 said:

Are they special bolts, nuts before I get busy with an angle grinder?

Nuts are nothing special but if diff is like mine bolts cannot be replaced without stripping the diff down?

[John042]

Thanks Mike/Adam. 18 mm seems to be a good fit on a shallow socket, 1/2" drive. The one I've moved obviously is now turning the bolt, so a thin open ended spanner is needed. Judging from the calipers the bolts have never been moved. What fun I got to look forward to, not. J C.

[adam quantrill]

That's unlucky because the bolts are an interference fit in the flange and usually don't move.

I would crack the other 3 on that side first then see if the rotating one still rotates you never know if it goes on the cock slightly it might grip the shaft in the flange then you can get your nuts off. Phew!

[John042]

Thanks Adam. I didn't progress further last night as my deep 18mm socket wasn't that good a fit. A shallow one on order. Hopfully the bolt is not turning but I was using 2 x 1/2" extensions with a metre piece of pipe to start the nut turning. Maybe some heat might help? I supose the worst senerio could be cutting the bolts and dropping the diff. Not what I would be looking forward to. Thanks for the encouragement. J C.

[adam quantrill]

You won't have to drop the diff the side driveshaft bearings come off with 5 bolts on each side.

[John042]

Thanks Adam, hopefully it won't come to that. The nuts are ridiculously tight even using a breaker bar with an extension. The danger of course is damaging the nuts hence the query on their exact size. J C.

[SEvans]

Couple of things that haven't been covered.... The nuts are a special lock nut. Nyloc type lock nuts aren't any good due to the heat.
Heat usually does the trick when they are difficult to remove and you will probably get away with using some without damaging the seals in the diff, as the brake disk will act as a barrier. Need to be careful though as you have 2 petrol tanks above you plus pipework etc. If all else fails you could grind the side of the nut away with a Dremel.
There could be shims on both sides of the disk. The shims between disk and diff are used to center the disk in the caliper. The shims between disk and drive shaft are used to set the camber. Good luck. Hope you get it sorted. Steve

[phillpot]

SEvans said:

Couple of things that haven't been covered.... The nuts are a special lock nut. Nyloc type lock nuts aren't any good due to the heat.

Fair comment my Taimar has drum brakes, in the proper place, behind the wheels


Guess someone like these would do the job......... nuts

[adam quantrill]

I have seen nylocs used before even by TVR dealers. They are OK as long as corrosion sets in before the first track day ;^)

Yes the better ones have the little slits cut into them and self-lock.

[John042]

Thanks Adam/Mark. Success one disc removed. 18 mm socket, 3 x 12" extensions and a 1.5 metre breaker bar seemed the best option. Working in an HGV Engineering area replacing the nuts shouldn't present any problems. Quite surprised at the number of shims on the drive flange, 8 in total. At least when the discs arrive I can make sure they're the right size. Thanks for the encouragement chaps. J C.

[adam quantrill]

8 is that all I have 11 on one side 10 on the other!