: installing posi rear end



carguy16
03-26-05, 11:22 PM
Ok, im confused on POSI rear ends.

Do you just have to opent he rear cover, pull one axle off and put the gear in? Or do you have to buy en entire new assembly.

I so badly want a limited slip or posi, for better traction, pulling out is a pain in the ass in the rain, even with traction control on. The right rear tire spins so easily, and the treads are good on them too.

Pricing? I've heard around the $500.00 dollar range.

N0DIH
03-27-05, 12:25 AM
You have to remove the "carrier", and replace it with one that has clutches.

OR....

Powertrax makes one that bolts in without removing the carrier, just pull the axles out (easy) and you replace the spider gears with a locker mechanism for around $400. And do it in about 2 hours in your driveway. Yes, I am thinking of it too, I hate not having posi!!

I am unsure how that will work with traction control (if this one applys the ABS brakes when it senses slippage, does anyone know?). Might be scary if it does and then locks up suddenly.

cadillacmike68
03-29-05, 06:11 PM
Before you try this, get a service manual, Cadillac had two different ring gear sizes and the axles were different (duh) for each. They also had two different drive shafts (regular and "cardan constant velocity") so you could end up with a lot of mismatched parts if you don't do your homework :confused: .

N0DIH
03-30-05, 10:07 AM
I was wondering if the double cardan joints were still around. They are by far one of the smoothest joints for long cars. In the "old" days, I had heard that Cadillac had a front and rear double cardan joints on the long cars. Olds/Buick got 1 double (I know, I had to replace one that got buzzy) and Chevy got plain U Joints. So much for common part bins....

Katshot
03-30-05, 10:27 AM
Since the car in question is a '94 Fleetwood, I'll tell you that there's only two ring gear sizes, 8.5" and 9.5". The smaller one is used on all standard Fleetwoods and the larger one is only used on commercial chassis cars such as limousines and hearses.
As for the T/C reaction to the change, I did a Detroit-Locker and installed 3.73 gears and after that, the T/C comes on at the least little bit of throttle and especially in any tight turns like in parking lots if you apply even a slight bit of throttle. I usually turn off the T/C as soon as I start the car unless it's snowing or icy out.

N0DIH
03-30-05, 06:56 PM
Can you use LT1 Edit to reverse the logic and make T/C default off and then turn on as needed?

9.5"? I haven't heard of it, but it would make sense, as the Suburban K1500/C1500 owners warn that towing near the 6000# towing limit of the Burb is a axle failure in progress for long tows. They all recommend the 3/4t to tow with. And that is with the 8.6" 10 bolt (aka, the same 8.5" case with a slightly larger ring gear).

I would assume that no 9.5" came with ABS, right? And likely no performance gearsets available? Any easy way to ID it? Is it like the one in the C/K2500 GM trucks?

Wonder why the T/C is so sensitive with the locker, I figured it would be less sensitive. Ideas?


Since the car in question is a '94 Fleetwood, I'll tell you that there's only two ring gear sizes, 8.5" and 9.5". The smaller one is used on all standard Fleetwoods and the larger one is only used on commercial chassis cars such as limousines and hearses.
As for the T/C reaction to the change, I did a Detroit-Locker and installed 3.73 gears and after that, the T/C comes on at the least little bit of throttle and especially in any tight turns like in parking lots if you apply even a slight bit of throttle. I usually turn off the T/C as soon as I start the car unless it's snowing or icy out.

N0DIH
03-30-05, 06:58 PM
When I get the books on it, I will look into a reverse T/C logic for it. That should be EASY to design. Make it reset T/C mode when car is first started and anytime power is removed. But it would need a bypass, as (at least on my 94) the T/C once off, needs a ignition cycle to turn back on. Unless I am missing on how.

Tom

ocjmakaveli
03-30-05, 08:11 PM
It might be cheaper to begin with to get a better set of tires than your stocks some really good high performance tires will not slip under most conditions excluding ICE. Of course it's always nice to have a second or too of a burnout at a stop if needed without a posi.

posi aren't cheap either and I would only recommend one after you surpass the 300 hp range I find it quite useless to have a posi with low-end low traction tires and still have stock hp. Just my opinion.

i was driving in horrible rain today in illinois actually hail fell a few minutes after i came home. Even in horrible rain that I could barely see in, my tires didn't lock-up 985 of the time when I was close to home and I was testing the limits of my tires there were about 2inches of rain on the floor yet i could stop very well with limited lockup of my wheels even when I slammed on my brakes.

Bottom line i think people underestimate a good set of tires and I think that dollar for dollar good tires will help you with acceleration, braking and steering.

This to me is more important than just good acceleration

Trust me I speak from experience with the stock caddy michelins i could slide 20 feet easily at any stop and I'd be going 10mph when it was snowy.

Nowadays I haven't had any slip with the pirelli's scorpion zero I have.

I'm not against a posi not at all i think it's needed but I don't think it should be a beginner mod.

Think about it and make sure that your willing to risk bad braking traction and steering control loss if you spend all your money on a posi.

3vs1

N0DIH
03-30-05, 08:34 PM
One thing I have found too is age of tires makes a huge difference. My 91 SDV has older Michelins that are good tread, but hard as a hockey puck, so they get you down the road, but are not the greatest for traction anymore. The front has a new set of Michelins and they are very good in the snow and rain.

My 94 FWB has Winterfire snow tires and Uniroyals on the Al rims. I think the Winterfires have better dry traction!! I just got the car so tire swapping isn't in the picture yet, but I do want better rubber. It does matter.

Oh, and my advice? Good tires on the rear, always, bad on front is safer. It is MUCH harder to keep the car from swapping ends with bad rear tires. Been there, done that....