atb

Bill,
I think 100% NS in the diff may be an issue?
Is anyone else running their LSD with straight NS? I know when I serviced my stock LSD unit, I reduced it some with standard gear oil, maybe 1/3? No problem leaving double black stripes set up like this.

GregBBRD

Bill:

The limited slip should have resistance to slipping, without a chatter or shudder. I get these cars in, frequently, with limited slips that have had the incorrect gear oil used. They will chatter/shudder. Sometimes a gear oil change fixes them, sometimes it is too late and they are damaged. A "late" limited slip that "kills" the friction discs will also "kill" the large internal pressure rings for the spider gears. These are expensive. An "early" limited slip (that is still stock) that "kills" the friction discs only damages the outer lamina. They are cheap. Note that if you "separate" the friction discs in an "early" limited slip to improve the amount of "torque" it takes to turn the limited slip, the friction discs will then be touching the inner pressure rings, not just the outer lamina. I always make sure that the friction discs that touch the inner pressure rings are in very good condition, so that they don't "smear" (from wearing out) and ruin these inner pressure rings.

The friction discs are like designed to wear and be replaced. They are not "forever" pieces, but a "stardard" replacement part. Think of them as a "clutch disc"....which is actually what they are....

I don't use Redline, so I can't tell you much about how it works or how long it takes to get into the limited slip and "do its thing".

I normally change the gear oil to Mobil 1 LS 75/90. Auto Zone has it. I then take the car out and spend 15 minutes or so just turning corners, in my parking lot....in both directions. If there is an improvement, I will then tell the customer to drive the car for a week or so and see if the chatter/shutter goes away, completely. If there is no improvement, I take them out and repair them.

Frequently, the friction discs will have "smeared" the surface and there will be metal transfer to the outer lamina, when the improper gear oil has been used. Once they have "smeared" the moly surface, there is no chance of them getting better/working correctly.

Good luck.

Bill Ball

Well, here goes...
Sure, that's certainly possible. Quite a bit of metal wore off. The wear on the gears is very even and no area looks fresh. Wouldn't I have heard noisy gears?

OK, so the grey stuff in solution could be aluminum. Where from? AFAIK, nothing in the diff rubs on anything aluminum. The disc holding the magnets is aluminum, but it looked unscathed when I had the cover off. I had an awful lot of gray steel on the magnet.

Mine is late despite Carl indicating that the early ones went through 84.
I note quite a bit of metal shavings on the little magnets on the magnetic disc in that thread!

I have no idea. I suppose I could flush with some new fluid. I did reinfuse the drained fluid as it was so fresh, despite the gray color.

This is where I've been getting various opinions. Making it slip by adding standard gear oil sounds counter to the purpose of a limited slip. Greg seems to like Mobil 1 LS, straight, I believe. Maybe I'll drain the Redline and put that it.

atb

I disagree with this. Chattering and shuddering around corners is very much the way an LSD set up for drag racing reacts. If you do this in a car with a spool rear end, where there is no give at all, the inner wheel will actually chirp as it spins in place trying to keep up with the outer wheel. There needs to be a little bit of give in order for the LSD to work in the corners. I don't know if its just the NS gear oil, the possible condition of your LSD unit like Greg is mentioning, or a combination of both, but for the street the LSD needs to have the proper oil to allow it to slip in the corners.

I haven't heard of anyone who has run 100% NS in their 928, I'd be curious to see if anyone has and whether or not there have been any complications. I don't know if there is anything to these designations, or if its just branding, but it is interesting that the Mobile product that Greg suggests is branded as as an "LS" - limited slip, gear lube, not an "NS" or non-slip gear lube.

Swap it out and report back. Let's hope its an easy fix.

Speedtoys

Well, mine does this as well, since swapping in the 2.54LSD from my 2.2LSD.

The 2.2 didnt clunk away out back, my RX8 doesnt (Measures 38lbs in the pack) the supra neeever ever did and two had a torsen, one normal plates, and my 65lbs 83 rx7 (custom beer can shims) wasnt clunky this much in the paddock either.

Bill Ball

Ok, well, I may try the M1, although it's not cheaper than Redline as I thought Greg had said. Also, look at this...

http://www.mobiloil.com/usa-english/...e_Changed.aspx

fraggle

Is there a guide out there for LSD work?
I have an older diff than I plan on putting in my later box with Carl's adaptor kit, but I'd like to make sure it's in top shape before it goes in, so anything I can inspect, set or rebuild beforehand would be a plus.

Carl Fausett

The WSM has a fair exploded view and info on how to stack the plates and replace them.

And we have our guide for how to install the early-into-late LSD kit. You have that, right?

Carl

Carl Fausett

I forgot to mention, we do sell all the friction disks and plates to rebuild the early LSD.

Here is a link: http://www.928motorsports.com/parts/...lip_plates.php

Bill Ball

Here, the thread by Ducman82 and Greg Brown has relevant info.
https://rennlist.com/forums/928-foru...-question.html

fraggle

Thanks guys, I'll be studying a bit there.

jheis

Here is what Redline recommends for a 5 speed with LSD

"Thank you for contacting Red Line Oil, some time ago we used a fluid blend in the Porsche transaxles to closely match the original. The 75W90NS now contains a slight amount of friction modifier, for improved shiftability not for chatter control.
In your 928 transaxle the 75W90NS is recommended, if chatter is present from the clutch type limited slip when making a slow/tight turn a slight amount of Friction Modifier can be added, being aware that excess will adversely affect shiftability. Typically Porsche limited slip differentials don’t chatter, if chatter occurs 1 to 1½ % would be a good starting point. The 75W90 contains 5% friction modifier too slippery for the synchros so not recommended for use in a manual transmission/transaxle.

Regards, Dave
Red Line Oil"

I'm running NS in my '89 5 speed and the "chatter" is almost completely gone. Sounds like straight 75W90 may be the way to go for an automatic where you're not worried about synchros.

James

Speedtoys

James: Good Email there.


I suggested a SF Bay Area tech-talk and drive up to RL a few weeks ago, the only response was someone attempting to suggested RL busted his gearbox. Im keeping the field trip on more a private list since the thread went zero miles. You interested in this on some Saturday in the future?

jheis

Sure

Bill Ball

James: OK, that's good. I've seen others mix in 25% 75W90 which would approximate the friction modifier percentage they are recommending. I hope I find no more metal. [LATE EDIT: This appears to be wrong. We should be using 75/90 without the NS designation.]