: how to find out if it is limited slip?



gornati
08-11-10, 06:34 PM
i need to know if my 78 deville is limited slip..

how to find out?

jayoldschool
08-11-10, 06:57 PM
There will be a little tag attached to one of the bolts on the center section cover.

sven914
08-11-10, 07:22 PM
Go to an empty parking lot. Leave engine running. Place gear selector in "DRIVE." Place left foot firmly on brake pedal. Slam right foot onto the gas pedal. Hold brake until vehicle begins to move forward. Release brake pedal, while still holding gas pedal down. Bring vehicle to a complete stop. Observe tread marks, burned into pavement.

If there is only one, you have a standard differential. If there are two, you have a limited slip.

jayoldschool
08-11-10, 07:39 PM
Sven's technique works if you have a WORKING limited slip. After thirty years, it might be worn ;)

Also, with the high gears in his car, there may not be enough torque multiplication for the rear tire(s) to actually spin on a brake stand. And to further complicate things, it is possible to spin both tires without a limited slip.

The best way to check is for the tag, or to actually visually verify by pulling the cover.

I guess the real question is... why do you care? No snow in Brazil. Doubt you'll do much drag racing or road racing with the 78, too...

csbuckn
08-11-10, 08:00 PM
Isn't it if you have disc brakes, you have posi? Disc brakes only came with posi, posi only came with disc?

jayoldschool
08-11-10, 08:56 PM
That's one of the problems. He has disc brakes on a car that never came with them. A DeVille. The disc rear was standard on the 77-79 FWB. I don't believe that posi was standard, however. A quick check of the 77-79 options should confirm.

gornati
08-11-10, 10:55 PM
i removed the wheels, driver side have the calipers on the back, passenger side have the caliper on the front of the disc. still the height sensor is there, everything looks factory... i really dont know how it get there, but they are 4 wheels discs, looks like the brougham system... i will take some picutres.

sven914
08-11-10, 11:49 PM
Sven's technique works if you have a WORKING limited slip. After thirty years, it might be worn ;)


Well if that's the case, then he no longer has limited slip... Problem solved.

Aron9000
08-13-10, 12:17 AM
Go to an empty parking lot. Leave engine running. Place gear selector in "DRIVE." Place left foot firmly on brake pedal. Slam right foot onto the gas pedal. Hold brake until vehicle begins to move forward. Release brake pedal, while still holding gas pedal down. Bring vehicle to a complete stop. Observe tread marks, burned into pavement.

If there is only one, you have a standard differential. If there are two, you have a limited slip.


Or if you want to be a little less harsh on the car, go to the empty parking lot when its raining. Make a sharp right hand turn at about 5mph, then stab the gas about midway through the turn. If the inside tire just fries to nothing, open diff. If the whole rear of the car starts to rotate and does a donut on you, limited slip.

ewill3rd
08-13-10, 09:06 AM
Jack up both rear wheels off the ground and grab one side and try to rotate the tire.
If the wheel spins and the one on the opposite side rotates the opposite direction it is not limited slip.
If you can't turn it then it is posi.

sven914
08-13-10, 05:38 PM
^ Actually, some limited slips function like a normal differential when you do that.

jayoldschool
08-13-10, 06:47 PM
The correct test for a working limited slip is to measure the breakaway torque required to turn one wheel while in in the air. The procedure should be in the FSM. I know it is for the later B bodies...