Questions on early style LSD
03-10-2011, 09:24 PM
#1
Rennlist Member
Thread Starter
Questions on early style LSD
I need an LSD for my OB track car, so if anyone has one available, please let me know.
Are there only two versions of the LSD diff?, and if so, what year is the change point?
I was looking through the PET, and the exploded diagram for MY '79 only shows two friction plates per side, I thought the older cars eight plates total. Is this just a mistake? It looks like the exact same diagram that they show for the S4.
Are there only two versions of the LSD diff?, and if so, what year is the change point?
I was looking through the PET, and the exploded diagram for MY '79 only shows two friction plates per side, I thought the older cars eight plates total. Is this just a mistake? It looks like the exact same diagram that they show for the S4.
03-10-2011, 10:08 PM
#3
Nordschleife Master
Afaik Brian is correct. Change was 1984/85.
I have an old style kicking around waiting to go into my track car (87 box). But iirc Porken has one he wants to sell to....
I have an old style kicking around waiting to go into my track car (87 box). But iirc Porken has one he wants to sell to....
03-10-2011, 11:04 PM
#4
Inventor
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The 8-disc are like crisps, you can't have just one. 
I have two again. I would sell one. I have one of Carl's kits to put one of them in my '85 (although really I'd be happy to just throw in a 4-disc w/o the adapter).
I'm still confused by the different LSD bodies. The differential housing length changed in '83 with the 4-speed auto. The 4-disc starts '85 with the LSD body with large openings. So a '83-84 LSD 8-disc may fit '85-up?
I have two again. I would sell one. I have one of Carl's kits to put one of them in my '85 (although really I'd be happy to just throw in a 4-disc w/o the adapter).
I'm still confused by the different LSD bodies. The differential housing length changed in '83 with the 4-speed auto. The 4-disc starts '85 with the LSD body with large openings. So a '83-84 LSD 8-disc may fit '85-up?
03-11-2011, 01:09 AM
#5
Inventor
Rennlist Member
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More info on the '85-up LSD that I've been meaning to scan from the '85 Service Bulletin. Note the note.
They didn't change the part number (928 332 511 20) from '83-'86, even with the change to 4-disc?
Oh, and BTW, why don't LSD units have 928 part numbers on them?
They didn't change the part number (928 332 511 20) from '83-'86, even with the change to 4-disc?
Oh, and BTW, why don't LSD units have 928 part numbers on them?
03-11-2011, 02:34 AM
#7
Former Sponsor
For clarity....
There are 4 "friction discs" in the early limited slips...2 on each side.
In the early limited slips, 2 of these "friction discs" are touching each other on each side.
That leaves 4 total "friction discs" making resistance to slip.
There are 2 "friction discs" in the late limited slips...1 on each side.
That makes 4 total "friction discs" making resistance to slip.
Notice that this sentence about the late limited slip is the same as the sentence for the early limited slip. I've highlighted them, so that it can be easily seen.
So what is the difference? Nothing, in stock form! People that change a stock early limited slip for a stock late limited slip are....foolish. They would be better off buying softer toilet paper....
The difference is purely about the "potential" to change the amount of friction. It is possible to separate the two "friction discs", on the early limited slip, that touch each other on each side and end up with:
8 total friction surfaces making resistance to slip!
The advantage of having more friction surfaces is that one can increase the life of the limited slip (more friction surface area to wear), increase the break-away torque (improve limited slip action), and make the limited slip more predicable (increased resistance to change, because of the increased friction surface).
One must carefully measure the break-away torque, when this is done and change the "outer discs" (which come in 3 different thicknesses) in order to end up with a limited slip that is not pure "evil"!! You can easily completely ruin the handling of a vehicle by making the break-away torque too high!!
Also note that increased friction surface also will significantly increase transmission temperatures. All limited slips modified to use 8 friction surfaces, with increase break-away torque need transmission coolers!
There are 4 "friction discs" in the early limited slips...2 on each side.
In the early limited slips, 2 of these "friction discs" are touching each other on each side.
That leaves 4 total "friction discs" making resistance to slip.
There are 2 "friction discs" in the late limited slips...1 on each side.
That makes 4 total "friction discs" making resistance to slip.
Notice that this sentence about the late limited slip is the same as the sentence for the early limited slip. I've highlighted them, so that it can be easily seen.
So what is the difference? Nothing, in stock form! People that change a stock early limited slip for a stock late limited slip are....foolish. They would be better off buying softer toilet paper....
The difference is purely about the "potential" to change the amount of friction. It is possible to separate the two "friction discs", on the early limited slip, that touch each other on each side and end up with:
8 total friction surfaces making resistance to slip!
The advantage of having more friction surfaces is that one can increase the life of the limited slip (more friction surface area to wear), increase the break-away torque (improve limited slip action), and make the limited slip more predicable (increased resistance to change, because of the increased friction surface).
One must carefully measure the break-away torque, when this is done and change the "outer discs" (which come in 3 different thicknesses) in order to end up with a limited slip that is not pure "evil"!! You can easily completely ruin the handling of a vehicle by making the break-away torque too high!!
Also note that increased friction surface also will significantly increase transmission temperatures. All limited slips modified to use 8 friction surfaces, with increase break-away torque need transmission coolers!
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03-11-2011, 10:24 AM
#8
Rennlist Member
Just to get some clarification on this - CAN the early LSD be installed in the later transaxles? (e.g. my '89 S4)? IF so, is there any modification that needs to be made, or additional parts that must be obtained to make the install work well?
THANKS for clarification.
Gary Knox
THANKS for clarification.
Gary Knox
03-11-2011, 12:41 PM
#9
Inventor
Rennlist Member
Rennlist Member
$400, including shipping? (Email me.)
Yes.
With a '78-'82 unit, you'll need an (adapter from Carl). You also need to machine a bevel on your (or a spare) magnet wheel to clear the ring gear. (Per install manual.)
I *think* that one from '83-'84 may bolt right in. Unfortunately, there are no 928 part numbers on the LSD bodies, just what looks like serial numbers, so you have to go by the housing length, AFAIK. IIRC, the '83-up housings are 5mm longer/shorter of the earlier. (There is a thread somewhere that covered this.)
With a '78-'82 unit, you'll need an (adapter from Carl). You also need to machine a bevel on your (or a spare) magnet wheel to clear the ring gear. (Per install manual.)
I *think* that one from '83-'84 may bolt right in. Unfortunately, there are no 928 part numbers on the LSD bodies, just what looks like serial numbers, so you have to go by the housing length, AFAIK. IIRC, the '83-up housings are 5mm longer/shorter of the earlier. (There is a thread somewhere that covered this.)
03-11-2011, 04:24 PM
#11
Rennlist Member
Thread Starter
Gary,
Here's a kit sold by 928MS to allow installation of the early LSD into a later tranny. I don't know if the carrier was narrower on the early models, or if the tranny cases were narrower, but in either case it appears the early diffs need an adapter plate to fit in the later model tranny cases.
http://www.928motorsports.com/parts/...ip_adapter.php
Here's a kit sold by 928MS to allow installation of the early LSD into a later tranny. I don't know if the carrier was narrower on the early models, or if the tranny cases were narrower, but in either case it appears the early diffs need an adapter plate to fit in the later model tranny cases.
http://www.928motorsports.com/parts/...ip_adapter.php
Just to get some clarification on this - CAN the early LSD be installed in the later transaxles? (e.g. my '89 S4)? IF so, is there any modification that needs to be made, or additional parts that must be obtained to make the install work well?
THANKS for clarification.
Gary Knox
THANKS for clarification.
Gary Knox
03-17-2011, 11:58 AM
#13
Drifting
KEN, great price man!
Greg - I really appreciate your input. I am about to rebuild an early LSD for my race car and, after disassembling and inspecting, was wondering if it is possible to reconfigure the disks. I also intend to install a tranny cooler as well--we were having issues downshifting on hot days with an open diff; I would hate to think what it would be like with the LSD.
Greg - I really appreciate your input. I am about to rebuild an early LSD for my race car and, after disassembling and inspecting, was wondering if it is possible to reconfigure the disks. I also intend to install a tranny cooler as well--we were having issues downshifting on hot days with an open diff; I would hate to think what it would be like with the LSD.