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Fri Jul 25, 2025 9:39 am

how about some differential info? maybe there is a thread on this but I couldn't find it. I know theres the transmissions for dummies thread but I dont think it covers the diffs themselves ?

I was wondering if all IRS ( T1 ) used the same differential or if they changed with different years?
same with SA, did they change them?

and while were at it any other info would be great too. or a link to a thread that covers this if there is one.

Fri Jul 25, 2025 2:19 pm

a differential is just the means of transferring power to wheels. They typically consist of the carrier and the gears. The ratio used depends a lot on use and weight of the vehicle and power available. Limited slip use depends on where and how the differential will be used. The primary reason not to use a limited slip is control. Someone who has a heavy foot can find themselves looking at the spot in the road they were coming from when both tires break free at the same time. Someone in a 4-whd vehicle often uses a limited slip in the back and a standard in the front. This keeps at least one tire as an anchor if say climbing a hill and all 4 start slipping at the same time. I know that the bus technical section goes into the transmission and differential gearing ratios on different years and engine buses. There are also models geared for mountainous regions vs someone who just wants to drive on the freeway. I would imagine that type 1, and type 3 might have some specs published in the technical sections also.

Fri Jul 25, 2025 6:51 pm

Heh heh, i didnt think we’d start at ground level,” diff’s 101”. thought we’d be more specific to just VW, but that works!

Sat Jul 26, 2025 3:20 am

BFB wrote: I was wondering if all IRS ( T1 ) used the same differential or if they changed with different years?
same with SA, did they change them?

The very earliest IRS diff castings were slightly different from later ones. But those early ones are quite rare, suggesting the change happened soon after the introduction of IRS.
Then in 73, VW changed the tooth counts of all the gears inside the diff. Early was 11/17 spider/side gears. Late is 10/15.

The earliest swing axle diff castings were also different from later ones. Obviously, later is better. Swing axle diffs were machined for 6 bolt ring gears at the beginning, then around 67, they went to 8 bolt ring gears. The same gear tooth changes I noted above also happened to swing axle spider/side gears at the same time.

All IRS diffs were made for 8 bolt ring gears.

Sat Jul 26, 2025 6:00 am

Every now and then someone references a factory limited slip diff. Did VW ever offer that option or are all limited slips aftermarket?

Sat Jul 26, 2025 6:44 am

My understanding is that some Type 181 had a limited slip, but rare.

Sat Jul 26, 2025 7:36 am

Glenn wrote: My understanding is that some Type 181 had a limited slip, but rare.

I just finished going through the 1200+ pages of the off road photo gallery and i swear in there somewhere was something about that , or even that it was a type of locker? I dunno i think it might have been a shwimwagon ? ( I probably spelled that wrong but you know what I mean )
Some photos lead to threads and others dont but some do have lengthy descriptions and this might have been one of those.

Sat Jul 26, 2025 1:36 pm

oprn wrote: Every now and then someone references a factory limited slip diff. Did VW ever offer that option or are all limited slips aftermarket?
M220 was the option code.

The OEM supplier to VW was ZF:

Here is the family of limited slip differentials used in VWs. On the left is for swing axle. Next is IRS Type 1. Then 002 Bus. Finally 091/094 Bus

If you think you're going to remember all these diffs, then hunt the swap meets to find a ZF, forget it. VW never offered the limited slip differential option in North America, so you will never find one.
The overwhelming majority of ZFs went into Type 181 Thing transmissions. In Europe, the Type 181 was used by the German military, and all of those had a ZF in them. By the 1980s, all of the Type 181s had been retired from military use.