IRS Superdiff setup questions

Discuss VW transaxles and transmissions. Gearheads wanted!

Moderator: Henryhoehandle

Post Reply
lowvolks
Posts: 7
Joined: Thu Dec 28, 2006 5:58 pm

IRS Superdiff setup questions

Post by lowvolks » Tue Apr 03, 2018 1:43 am

Hi,
I'm installing a superdiff in a late T1 IRS trans, and was wondering what everyone does to set the sidegear endplay? I have a Weddle superdiff that uses the 10/15 tooth gears. Are there different thicknesses of sidegear thrust washers besides the originals? I've tried assembling with one thrust washer, which gives about .022" endplay. This seems like too much since the factory spec is .000" to .005", but I also tried using two washers and that didn't allow enough clearance. Also, this superdiff doesn't have any provisions for a center block spacer between the side gears like the original. Is the center block spacer typically not needed with this type of differential?

I've searched on this, but haven't found any clear instructions for how to set the clearances on these - which makes me wonder if I'm overthinking it... it just seems odd to me to have such loose tolerances in a part that's theoretically an upgrade over stock.

Thanks in advance, any suggestions are appreciated.

User avatar
Pablo2
Posts: 408
Joined: Sat Jun 25, 2011 7:37 pm

Re: IRS Superdiff setup questions

Post by Pablo2 » Wed Apr 04, 2018 12:39 am

I don't blame you for being leery of this much play. If I were you, I'd install a 2nd thrust washer that's been surface-ground to size.
aka Pablo, gears, Geary
9.36 @ 146 in '86

lowvolks
Posts: 7
Joined: Thu Dec 28, 2006 5:58 pm

Re: IRS Superdiff setup questions

Post by lowvolks » Wed Apr 04, 2018 1:32 am

Thanks for the confirmation - that's what I'll do. I think I'll grind the thrust washers to target .002-3 play in the side gears.

Another related question, are there any tricks to getting equal backlash on all 4 spider gears? I have 3 spiders that are very close, and one that has a quite a bit more backlash than the others. I'm not aware of any adjustment for this? At the moment I'm using old spider gears from 2 different factory differentials which can't possibly have equal amounts of wear. Would you recommend buying a new set of 4 spider gears to minimize the inconsistencies between gears?

Do the IRS superdiffs have the same oil supply issues that the swing axle superdiffs are known to have? Are there any oil holes I should drill or enlarge while it's apart on the bench?

Thanks

Casting Timmy
Posts: 115
Joined: Sun Nov 17, 2013 9:42 pm

Re: IRS Superdiff setup questions

Post by Casting Timmy » Wed Apr 04, 2018 7:16 am

The IRS diffs have a 1/4" hole or so through the side with the long side gear, this is all that's needed. The IRS doesn't have the oiling issues of the Swing diffs, it gets lots of oil in through the diff cover.

I like to do the 2 shim method, but based on my tooling and methods I find it easier to remove material from the diff cover with my lathe. I wish I had a good method of thinning the shims down, but I just modify the diff covers right now. You will also find that the bearing preload will make the clearance disappear on the short gear side a little. Hopefully my theory of the gears all breaking into each other and bearings setting in is correct, in that this clearance will quickly come back once it's driven a little.

User avatar
Pablo2
Posts: 408
Joined: Sat Jun 25, 2011 7:37 pm

Re: IRS Superdiff setup questions

Post by Pablo2 » Wed Apr 04, 2018 12:23 pm

I've yet to find a low dollar super diff providing equal backlash to all 4 spiders. One spider's typically just "along for the ride".
aka Pablo, gears, Geary
9.36 @ 146 in '86

Bruce2
Posts: 6850
Joined: Sat Oct 13, 2001 3:01 am

Re: IRS Superdiff setup questions

Post by Bruce2 » Wed Apr 04, 2018 12:28 pm

Instead of trying to grind a shim thinner, make a new one from shim stock.

Bruce2
Posts: 6850
Joined: Sat Oct 13, 2001 3:01 am

Re: IRS Superdiff setup questions

Post by Bruce2 » Wed Apr 04, 2018 12:30 pm

lowvolks wrote:
Wed Apr 04, 2018 1:32 am
Would you recommend buying a new set of 4 spider gears to minimize the inconsistencies between gears?
I don't think NOS 10 tooth spider gears are available. All the new ones you will find will be 11 tooth.

lowvolks
Posts: 7
Joined: Thu Dec 28, 2006 5:58 pm

Re: IRS Superdiff setup questions

Post by lowvolks » Wed Apr 04, 2018 6:07 pm

Thanks, good to know I shouldn't have any oiling issues.

I did consider cutting new washers from shim stock. I noticed that the original washers aren't perfectly flat, so by the time I get them trued up on the surface grinder they might be getting to the point of being too thin for the endplay I'm targeting. I might try the originals and see how much material needs to be taken off to get them flat again. I haven't got to setting up the bearing preload yet, I'll make a note to check the endplay when I get to that point.

Weddle lists new genuine VW 10 tooth spider gears on their site. If these would help equalize the backlash I'd give them a try.
https://weddleindustries.com/products/1000161/1006267

I do have a couple other factory diffs with used spider gears. I think before I buy new ones I'll experiment with mixing and matching the used spiders and see if I can determine whether the inconsistency is coming from wear in the spider gears or the way the diff is machined. I'll post back if I find any obvious results.

Thanks all for the help.

Post Reply