96 Mustang GT Posi Rear Question

dlascoskie · Post by **dlascoskie** » Sun Mar 12, 2006 6:31 pm

For all you ford guys.....

When I hold one wheel and my brother turns the other one, the differential slips on a very light amount of force. I was under the impression that it should be very hard to break it loose with just arm strength. So we re-shimmed it and tried it again, but we got the same results. Any thoughts on this?

Tim Royer · Post by **Tim Royer** » Mon Mar 13, 2006 12:06 am

Hey,

On stock possi that is very normal. My 8.8 rear has the same thing. I personally think they stink. My car has new clutches in it also and in a straight line it spins both but in a hard turn with heavy throttle I 1 wheel peel. That spin is slowing me down and I could use a Detroit locker or smoother like an Alburn. Detroit's have a violent engagement (ask Steve). I haven't had the chance to try anything else so I could say which is better.

Steve Tumolo · Post by **Steve Tumolo** » Mon Mar 13, 2006 11:38 am

The list of options reads like this:

Auburn: Work very well but even the "Pro" unit is known to be weak after extended abuse.

Torsen: A very smooth operating diff. But again they are not known for standing up to alot of abuse. And they are so smooth that if they do give up you might not realize it.

And then we come to the 8.8 Detroit Locker. For me and others it has proven to be VERY durable. I have had it for over 9 years and it is still as strong as ever. But on the flip side it is a brute. I like it but it did take some getting used to. When it locks in you know it.

What ever you do stay away from the Powertrax unit. It is complete junk.

dlascoskie · Post by **dlascoskie** » Mon Mar 13, 2006 1:41 pm

So are you guys saying that there's not any options for improving the stock piece?? The only solution is to buy something else? No upgrade kits or tricks to improving what I already own?

Tim Royer · Post by **Tim Royer** » Mon Mar 13, 2006 1:45 pm

HI,

BTW the only hill I have any trouble with wheel spin is turn 3 Weatherly. Otherwise it works great everywhere else at all other events.

This year maybe different. My motor has 150,000 miles on it and is a bit tired.

It will be different having a fresh motor in it I'm sure. I'll have to let you know.

Tim Royer · Post by **Tim Royer** » Mon Mar 13, 2006 1:55 pm

Hi,

Don't be mislead with your being able to spin that wheel a little with someone holding. It engages on input from the driveshaft which has little to do with how hard your wheel spins when someone holds it. The slip from wheel to wheel is much less when your in the throttle.

You must break it in also. Did you use a Slip additive? What fluids did you put in?

Tim Royer · Post by **Tim Royer** » Mon Mar 13, 2006 2:02 pm

Ford's works good.

4 ounce bottle of friction modifier - C8AZ-19B546-A

dlascoskie · Post by **dlascoskie** » Mon Mar 13, 2006 2:37 pm

I used the Motorcraft friction modifier. And I agree that it has to get worn in a little. I'm just wondering if I'm 7 seconds off your Duryea Record because my posi is slipping too much, or because I'm just SLOW.....lol....

Seriously though, I think I was experiencing quite a bit of free-wheeling in turns 2 through 4 of Duryea. I know that those are slick turns, and that's what I've always attributed it too, until I did this little test on my rear yesterday. I get what your saying about input from the driveshaft, but we can't break either of my brother's cars loose, no matter how hard we try. Also, I remember reading something about the amount of lbs. of torque required to break a rear loose, and that this was a good way to test if it was truly working properly.

Nice to hear that you'll be bringing the Mustang back to the hills with a fresh motor. It's a lot more fun winning a class when there's other people in it to compete against! lol.

Matt Green · Post by **Matt Green** » Mon Mar 13, 2006 10:26 pm

Steve, I'd have to disagree on the Torsen, unless the piece that's available for that rear just isn't too great...

Torsen is the absolute way to go for Road racing, but I'm not convinced it's the best on a hill. See, the Torsen works on a torque distrbution principle, based on a multiplier derived from the gear cut. Basically, the diff puts more torque to the wheel with more grip, but only as a multiple of the torque applied at the other wheel. If you can't apply torque at all (like a tight turn and a completely unloaded tire), then zero (lower torque wheel) times whatever multiplier is still zero torque to the good wheel. So long as both wheels have some kind of traction, the Torsen works, but if one wheel unloads completely, it just spins and nothing goes to the other.

I can explain it better if someone really wants to know, but it's a lot more typing.

RX-Midget · Post by **RX-Midget** » Wed Mar 15, 2006 12:34 pm

I looked into a Torsen rear for my car and the only comments that I found interesting go along with Matt's. From what I have heard, one problem with the Torsen is that if you completly unload a tire (inside tire as you nerf the curbing at an apex), it will spin up and then when it contacts the ground, the diff instantly sees a huge shock load and sometimes breaks.

Like I said, this is not my experience, but what I have heard about the Mazda Torsen rears that came in the Miata and the Mazdacomp part.

dlascoskie · Post by **dlascoskie** » Wed Mar 15, 2006 2:27 pm

who made the left turn at albequerque?

let's get back on the right road gentlemen.....does anybody know of any upgrade kits or tricks/tips to improving the bite of the stock unit on a 96 Mustang GT......a Ford 8.8 rear?

RX-Midget · Post by **RX-Midget** » Wed Mar 15, 2006 2:37 pm

dlascoskie wrote:who made the left turn at albequerque?
let's get back on the right road gentlemen.....does anybody know of any upgrade kits or tricks/tips to improving the bite of the stock unit on a 96 Mustang GT......a Ford 8.8 rear?

Sorry.
Hope this is more on topic.
If it is a clutch type diff, I found that the Red Line NS (no-slip) gear oil worked well in my clutch type diff to tighten it up.

B.

dlascoskie · Post by **dlascoskie** » Wed Mar 15, 2006 2:59 pm

ah, that's more like it! lol
did you experience any chatter or noise after making the switch? My car is also my daily driver, so it needs to be nice an quiet so i can hear my cds.....lol.

Matt Green · Post by **Matt Green** » Wed Mar 15, 2006 3:38 pm

Sorry, that's why I didn't go into the COMPLETE description of the Torsen...

You can load more clutches and plates into the unit to pack it tighter. You can also machine the spiders (if this unit is that style) to get a larger, flatter surface for contact, and to allow more clutches and plates...

Just remember, like Tim said, the dynamic breakaway torque is somewhat higher than what you'll measure static.

There is also a suspension issue here, with keeping that inside tire loaded better, but that's yet another thread hi-jack...

dlascoskie · Post by **dlascoskie** » Wed Mar 15, 2006 4:41 pm

RX-Midget · Post by **RX-Midget** » Wed Mar 15, 2006 4:44 pm

dlascoskie wrote:ah, that's more like it! lol
did you experience any chatter or noise after making the switch? My car is also my daily driver, so it needs to be nice an quiet so i can hear my cds.....lol.

I have no clue. My car is tagged for the street, but it is so loud I'd never notice

I've never heard anything when pushing the car around in the paddock, but then the diff is not loaded like Tim said earlier about how it locks up tighter when torque is applied from the driveshaft.

Matt hit on a good point about keeping the inside wheel planted better....

dlascoskie · Post by **dlascoskie** » Wed Mar 15, 2006 4:54 pm

it just seems like i lose all kinds of drive out of the turns at Duryea/Pagoda. I know they are tight, slick turns, but even when i squeeze the throttle on lightly it feels like its slipping and twiddling it's thumbs, and then it starts to hook up. and then when we tried this test and saw the results, we were concerned that it could be a contributing factor.

Steve Tumolo · Post by **Steve Tumolo** » Thu Mar 16, 2006 9:39 am

As was already stated the only real choice you have with a stock unit is to pack more clutches in the diff. and add some good fluid. Did you call Jerry Hartman and ask him? He might have a few other suggestions. Some guys also like the welded spider gear set up but I for one don't think it is a smart way to go.