Bilal928S4

On my 89 5speed, I put the car on jack stands put the transmission in neutral. Rotated the driver side rear wheel by hand and the passenger side does not rotate. I tried rotating in both directions but the other wheel does not move.
So I a non-LSD differential?
Thanks

Kevin in Atlanta

Non-LSD

dr bob

If there'sd brake drag, for instance, on one rear wheel, turning the opposite wheel won't turn the dragging wheel LSD or not. With LSD, the torque required to move that dragging wheel needs to be less than the breakaway torque of the clutch pack. That can be anywhere from maybe 20 lbs/ft (per GB) down to none if the clutches are worn or the wrong lube is used.

The definitive test is to look for the "220" on the gearbox itself and on the options label. Lots of folks 'have' a limited-slip diff that's reverted to unlimited-slip over time, so the wheel test you did may not be effective.

The "test" for limited-slip breakaway torque is easy if you have a torque wrench and a wheel lug socket. Car out of gear and brakes off, raise one rear wheel, chock the opposite front wheel. Using the torque wrench, determine the torque needed to just barely rotate the raised wheel. Get a reading with the torque wrench pointing out from the center of the wheel, another reading with the wrench pointing the opposite direction, and average the two readings. This pretty much eliminates the bolt spacing from goofing your numbers. Numbers any higher than 25 lbs-feet will likely chatter in slow turns, so should probably be reserved for track applications. The LSD in my '89 is still pretty tight, enough that I couldn't use the foot brake while moving in or out of my previous garage with epoxy floors; car would just go straight, especially backing up. With tender parking brake use, I could generally get the car to turn some if needed. As much as I liked the look and the easy care with the sealer over epoxy, it was slippery when first applied. Front tires scuffed it in pretty quickly though...

Bilal928S4

The reason I was confused was that on the 89 WSM that I have on volume 2 page 30-0201 (I think) they have a listing of the manual transmissions for different years. On G28/55 there is an * and at the bottom the asterisk states that all 88/89 came with 40% LSD.
Maybe as usual I am missing something. The vin check does not show a 220 option.

Bilal928S4

Hi dr bob,
Can you elaborate where on the transmission I should look for the 220 option.
Thanks

wpgshark

Options code, manual or by the spare, but that doesn't guarantee it, my 88 has a 220 option code, but the tranny had been changed for a non LSD version.

If you do have a 220 code and want to be sure the tranny will have a number on the bottom, that can be cross referenced. Even then an LSD could have been added so the only way to be absolutely sure is to scope it.

DougM

Jack up the rear of the car and remove the upper fill plug. Nothing will spill out. Look in the hole with a flashlight and you will be able to see if you have it.

The Fixer

If you use the old torque wrench / lug nut method, whatever value you see required to turn the rear wheel, you add a % for the lug nut being offset of center of the wheel (advantage).

(I figure this percentage by measuring the length of my T wrench & lug - center of wheel dimension)

so if I see 20 lbs it's really about 22.5 lbs required.

Bmw635

Another quick easy option is to drive it hard in turn, LSD should kick in.

Hilton

Its part of the transmission type/serial number code, on the bottom of the rear-most-rib (just under the back panel).

For an 89 S4, it'll be:

G 2812 1K xxxxx (open diff)
G 2812 2K xxxxx (LSD)

Your confusion from the manual is that all G28.55 have LSD (they're the 89 GT and clubsport gearbox).

Of course its still possible someone changed the diff in your car - so the only really sure way to tell (in the absence of proper LSD function when turning wheels) is to open the back. You might be able to get a good enough macro shot with a compact camera through the fill hole to see which diff is in there.

Bilal928S4

Hilton,
Thank you for the clarification. I just checked and it is an open diff with the 1K marking.

Bilal928S4

Does anybody know what size Allen is required for the 3 plugs? Are the three plugs the same size?
I am in the process of changing the fluid in my transmission. I will be using the redline NS 75W90.

Hilton

Its a 10mm allen on the S4 boxes. 17mm on the earlier cars (up to '84 from memory).

Bilal928S4

Thanks. It's an 89 S4.

z driver 88t

After a number of owners it's anybodoy's guess. My '84 has a used '85 trans that was originally non-LSD but the previous owner had 928 INTL put in an LSD when he bought it from them. Confirmed it when I had the transmission apart earlier this year replacing the shift centering spring. Best way to know is to test it.