Diff rebuild

[charlie_pank]

I've got a 3.14 quaife ATB and want to convert it to 3.92. Am I right in thinking I can get any 3.92 crown-wheel and pinion (like this) and get someone who knows what they're doing to put them in my existing diff?

[Klunk]

If you're buying the complete 3.92 diff then it's a simple job (for someone who knows what they are doing!) to take out the ATB from the 3.14 and fit it into the 3.92.

 

However if you're just buying the actual crownwheel and pinion without the case, then I think you have to be careful as the back plates to the diffs are different depths due the crownwheels being slightly different diameters. So although the C&P will fit, the back plate won't clear the crownwheel. I had this problem on one but can't remember which size I was going from and to.

 

Regards,

 

Giles

 

Edited by - Klunk on 3 Jun 2012 13:46:47

[charlie_pank]

Hi Giles, I'm quite good at doing stuff myself, what's involved in taking out the ATB? and putting it in the other diff?

 

 

Charlie

[Klunk]

Hi Charlie,

 

Assuming you're buying a secondhand complete diff:

 

In short, undoing the castellated bearing holders either side means the crownwheel and diff will come out and then unbolt the crownwheel from the open diff. Bolt the crownwheel to the new LSD, swap over the bearings and put back into position in the diff and replace the bearing holders. Make sure the backlash is set up correctly. There should be no need to touch the pinion so setting the backlash is a question of moving the crownwheel and LSD left and right by winding the bearing carriers in and out.

 

If you're swapping a crownwheel and pinion into your diff housing then that's a lot more complex as you have to set the depth of the pinion against the crownwheel using shims and a crush washer to ensure it meshes in the correct position. Then you have to set the position of the crownwheel left and right as before.

 

If you're going to do it yourself I would do it with a complete 3.92 and swap in your LSD. However you will need a dial gauge to set up the backlash correctly and possibly a bearing press to swap the bearings over.

 

Somewhere I have a Haynes manual for a Sierra which details how to do it in full. Will look for it later and let you know.

 

Regards,

 

Giles

[mav]

Diff overhaul PDF on the Scorpio website here

[charlie_pank]

Hmm, it looks like the sort of thing I COULD do, but I'm not sure I can be bothered! I'll get some quotes for doing the swap/rebuild tomorrow...

 

 

[Klunk]

Those were precisely my thoughts! 😬 Got a diff stripped, shotblasted and rebuilt by local mechanic. Cost me the princely sum of £100

 

Regards,

 

Giles

[Mankee]

This sort of tool is handy for undoing and setting the diff bearing retainers: here. If you are fitting your ATB to a fully working and silent diff, then you could mark the positions of the retainers and refit them in exactly the same place. But if you are only going to use the bearing tool only once, you might as well pay someone to do it properly once in the first place! And maybe chuck new bearings and seals in there too: here.

[The Pikey]

Getting the pinion preload right without the right tools and crush washers is an almost impossible so I would get a complete 3.92 diff with a decent pinion preload and put your current LSD in it. Also you will have to decide if you are using new bearings, if you don't then will also need the castalated nuts off the old diff as well because they will have the matching shells for the roller bearings on the LSD (don't get the left and right mixed up!) Another reason not change pinions from there original cases is because they are all have various shims to set the pinion height to take machining tolerances into account. Your 3.14 is worth somewhere between 300 and 800 quid on ebay by the way.

 

Jason

 

Edited by - Jason Fletcher on 4 Jun 2012 16:31:09

[johnnyseven]

Any idea how much it should cost to have a 3.92 ap sure track overhauled? Got a quote of 350+vat including new bearings,does that sound about right?