Application: Porsche® 928, as follows:

1985-90 5-speeds and Automatics w/o LSD that want to add an 8-disk LSD
1985-90 5-speeds and Automatics with 4-disk LSD that want 8-Disk LSD
1990-95 PSD-equipped cars that want to change to 8-disk LSD


BACKGROUND: Most 928 owners know about the improvements to the 5- speed transaxle that exists in cars from 1985 and up. Dubbed the “G28” transaxle, and sometimes referred to as the “Borg Warner” transmission, the G28 has stronger synchro rings, more certain shifting, and the ability to handle more torque without damage (an important attribute for racers and hot rodders).

But, for all the benefits the G28 transaxle brought, the Limited Slip Differential (LSD) took a step back. The earlier transmissions had 8 friction plates in the LSD, 4 on each side for each of the rear tires. The G28, however, had only 4 friction plates total, 2 on each side, and as a result, a lower locking rate. The engineers had tried to compensate for the loss of half the clutch discs in the LSD by increasing the spring pressure on the plates, but it did not work. You just can’t beat a higher stack count of friction discs when the pedal hits the metal.


EXAMPLES: Facing facts, there are a great many 928 owners that would never experience the need or want for a better limited-slip differential, and for them, this upgrade is not necessary.

But, if you have ever throttled hard out of a 90-degree corner and found the inside-rear tire spinning wildly until you either lifted off the throttle or the tire finally hooked up – you have just experienced a loss through your LSD.

In that real-world example, if the LSD had been more effective, more of the engine’s torque would have reached the non-spinning outer wheel and your launch out of that corner would have been quicker. Critical for racers trying to carry exit speed down the following straight.

Another test: jack up one rear tire and apply a simple torque wrench to the center axle nut of the airborne rear wheel. With the other rear tire fixed on the ground, it will only take 15 ft pounds of force on the torque wrench to turn the tire against the late-model LSD, and 45 ft pounds of force to turn the tire on the early units. This simple and repeatable test demonstrates a 3-fold improvement in torque-holding ability.


CONCLUSION: the late-model G28 transmission is a definite improvement in drive-ability and durability, but its differential cannot hold as much torque as the previous model. The hot setup, therefore, is the late model transaxle equipped with the early LSD. The 928 owners who benefit from this upgrade are: performance drivers, DE drivers, those who have installed wider rear tires, supercharged cars, and racers.

Includes:
Custom 928MS case spacer
Custom 928MS bearing spacer
Custom 928MS bearing hub (used, remanufactured)
New Porsche® bearing seal
Fully Illustrated Instructions

I have the complete kit priced at $227 (provide your own LSD) or, for $600 more, I will provide you with a good used 8-disk LSD.

Our webpage is here:
http://www.928motorsports.com/parts/...ip_adapter.php

 

$600 seems like a great price for a good used 8-disk LSD.

 

Clever! There should be quite a few unused 78-82 posi's sitting around.

LSD makes a 928 much more fun to drive around town if you have a heavy foot. I already have a M220, but as I keep upping the power, I could use the upgrade.

I'm glad I kept my early LSD unit. Ha! (Tom M. )

 

Seven 30-minute races. We posted, as a result of changing the LSD, our best laptimes at BHF ever, on street tires. We had an improvement of 1.5 seconds per lap over our previous best at this road race course on Hoosier slicks. We were very happy with the results. Because we were able to accelerate out of corner 7 faster ( a sharp 90 degree right) with much less wheel spin, we noticed our top speed on the main straight was almost 10 MPH faster.

 

What oil do you use in your tranny?

I use 75W90NS, and I do not get any inside wheel spin with my car on street tires. 295/35 KDW2s I have to be careful on the throttle as it can break both free and give me a wag. (on track)

 

I think Carl has just a wee bit more horsepower then you do

 

Oh I know Erik,

 

Hi Carl,

I have a late 4disk LSD in my gearbox . Is it possible to change the parts inside against new ones from the early 8disk LSD ? Or is it necessary to use an original 8disk LSD ?

BTW I didn't know about this until today after reading your announcement.... All the time I was wondering about the limp locking rate of my LSD , even after renewal of all 4 friction disks two years ago :-(

Another product from your store that will make it under my x-mas tree :-)

 

Thommy, your not the first to try to "fix" the limp late model LSD with a rebuild. Honestly, I got my race car (which has a full roll cage) stuck in the driveway when one wheel lifted into the air. The late LSD is so bad the car would hardly move and we had to assist it with a shove. After the swap, expecting the same trouble, I goosed it (which had become the norm) and I nearly hit the garage door with the car.

Answer: no, the construction of the differential carrier is different and you cannot put the internals of the one into the other.

 

Carl,

Does this eliminate the need for the PSD pump system on 90 Plus cars where you would simply run the car as a standard LSD? Or does the 90 version work in concert with the original PSD pump and that entire system is left intact?

This could be a great alternative to those (like me) that currently have a non operational PSD pump.

 

Hi Carl,

thx for your clarifiying answer. Can you pls specify what gearbox types are "early" ? Or until which model years the early gearbox was built in.
600$ is really a great price, but if I add the german import taxes ~20% , its better for me to check in germany for an early 8-disk LSD .

 

Hi Carl

How long would it take (hours etc) to put this kit into a non LSD car like my UK 86 S2 ??

Can it be done in situ or does the whole of the rear end tranny need removing first ?

All the best Brett

 

I have been using red-line synthetic 75w/90 with friction additive and liked it.

This last time, I used 75w/90 Shockproof Heavy gear oil (Summit # RED-58204 ) and liked it even better in the race car.

 

Any transaxle before 1985 is "early". When in doubt, look straight up at the bottom backend of the transaxle. You will find the transaxle type stamped into the bottom of a reinforcing rib. It starts with "G28/xx" If G28/10 or higher, it is equipped with the Borg Warner synchros, 2nd casing design, and if it has LSD, it will be the post '85 4-disk style.

If it is lower than G28/10, its an early-style transaxle.

footnote: I hear that SOME late 83's and 84's have the 4-disk LSD in the early case. No logic to it from what I am told.

 

Yes. If you have a non-working PSD and want to replace it with this setup rather than fix it, you can.