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Posted by: r_towle Jun 14 2004, 04:01 PM

Hi,
In a previous thread, I asked which was the best LSD...
I have done some reading and now I am dangerously educated (not enough to know, but enough to have an opinion)

I think that what I need is a disk type true limited slip differential due to the fact that this is a dedicated autocross/track car.

Now, yesterday I had alot of fun testing my car and had some success and some surprises.

I bought the car with a "locked" differential. That means a welded differential with both drive axles going the same speed no matter what...
This made for some quick learning trying to negotiate some of the tight turns in our local autocross course...
Luckily I chose wisely and used the 10 plus year old racing slicks for my test day because alot of the rear tires still remains on the pavement....it was the only way to turn (not that theres anything wrong with that)

So....my question, what locking percentage would you recommend for an autocross car with circa 180-200 hp...? 1800 lbs

Rich

Posted by: TimT Jun 14 2004, 04:05 PM

go with 80/80. I think with the stock preload is something like 80/20

Is this a stock 901 LSD, or is a Guard unit?

Posted by: r_towle Jun 14 2004, 04:16 PM

seems that I will go with a guard unit.
Just got off the phone with Guard and he told me go with 40/60 for autocross and adjust up when I go to the track???

Experiences???

Posted by: TimT Jun 14 2004, 04:34 PM

We have guard set up the difs 80/80, these numbers are from very respected grand am, and ALMS crews (a mechanic at my friends shop is on his way back from Le Mans).

BUT!! these are not auto-x cars!! they are pure track cars GT3RSR's etc. I dont know much about auto-x set ups

I would however listen to Mr Guard, he knows a thing or two!!

Posted by: r_towle Jun 14 2004, 06:58 PM

thanx

rich

Posted by: SirAndy Jun 14 2004, 07:06 PM

warning, stupid question ahead:

for AX, where you have A LOT of tight corners in either direction, wouldn't a 50/50 split be the best ????

Andy

Posted by: seanery Jun 14 2004, 07:59 PM

accordiang to the GT page, for autocross a torque biasing diff is better than a limited slip. A limited slip is better for a track car.

Posted by: Brad Roberts Jun 14 2004, 08:09 PM

80% works fine when you have over 180hp in 1800#.

I do think that a Torque biasing diff would work better in a AutoX car than a plate style, but the torque biasing diff is a TANK compared to a plate style (which translates into engery spent on accelerating/stopping that weight)

Go with the 80/80 ramp and adjust your driving for track/AutoX.


B

Posted by: TimT Jun 14 2004, 08:19 PM

Andy... 50/50= 80/80 LOL

the numbers represent the percentage to fully locked in each direction

going forward the dif would be 80% locked

and on decel it is 80% locked

Also I have a tendency to bias my answers based on lots of 911 experience...
(going on my 3rd year as a 914 owner)

its a good thing to be able to use compression to slow you car...

Posted by: SirAndy Jun 14 2004, 08:23 PM

Posted by: r_towle Jun 14 2004, 08:43 PM

Danger, Danger...I read more...what a real two sided coin this one...

I have been reading that a torque biased differential would be better for autox....this will be the sole purpose of the car for the near term, and when I feel the problem arise I think that then would be the time for a plate style limited slip differential......

Now which one, and who is Gt??

Rich

Posted by: seanery Jun 14 2004, 08:48 PM

gt is gaurd.

http://www.guardtransmission.com/

Posted by: TimT Jun 14 2004, 08:51 PM

GT is guard transmission

They make both plate style, and torsen style diffs....

Each of the diffs have pros and cons...

You may not which one is best for you until you try them both

Posted by: r_towle Jun 14 2004, 09:02 PM

TimT,

Who is the tranny guy in Conn.
I was told norwalk area. p car tranny specialist.

Rich

Posted by: Brad Roberts Jun 14 2004, 11:06 PM

Should be Translog. But be careful. He is one of the shops I called when I wanted to know what everyone was doing about the loose pinion races I keep running across in 901/914 boxes. He gave me the wrong answer ("we peen them")


B

Posted by: sixerdon Jun 15 2004, 07:09 AM

Rich and Brad,
Translog is no longer in business. Everything was sold at auction the day before the Hershey meet in April. That was Gary Wigglesworth's business. Rich, the guy you are thinking of is Gary Fairbanks in Norwalk, CT. I've been to his shop. He's got it together and services all stock and custom rebuilds for the historic crowd. You can find his ad in Pano under the classifieds.
Don

Posted by: TimT Jun 15 2004, 07:36 AM

Rich, try Gary Fairbanks

ooops someone else already mentioned him

Posted by: SteveSr Jun 15 2004, 08:41 AM

While on the subject of LSD's,is it possible to remove the diff carrier without tearing the whole transaxle apart? .................ie,....like out of an American rear drive car or truck?

SteveSr

Posted by: RON S. Jun 15 2004, 11:00 AM

It is removable on the 901 box.
But in the 915 the diff is flipped,therefore the whole trans must be torn down to get the diff out.
Ron

Posted by: r_towle Jun 15 2004, 03:38 PM

ok,
Gary Fairbanks is the name, thanx I just could not remember.

If I can take out the diff and add the TBD, given that the rest of it is already done.....what is involved???

Do I need to shim it somehow??? and where are the specs to do this???

Rich

Posted by: bondo Jun 15 2004, 05:04 PM

Posted by: r_towle Jun 15 2004, 06:34 PM

Bondo,
Brad was trying to find a good solution to loose pinion races and the shops he called all peen it over to hold it in...
Brads new solution is to get a new case (He know where to get them) and i recall a price of 6-7 hundred, not bad if you want to be damn sure.

Rich