How can you tell if you have a limited slip differential gear box? I've called 2 different Mazda dealers and have gotten 2 different answers. One told me to jack up the rear and if both tires spin in the same direction, you have a limited slip. That's the case for me. But then another dealer told me that you have to sit your car in some gravel or grass, and spin the tires to see. He also said that very few Rx-7's have limited slip. I don't really trust the 2nd guy, and I figured I'd better double check with you all to make sure.

 

If you have a turbo, its an LSD. If you have a S4 GXL, its an LSD. If you have a 88GTU, its an LSD, if you have a 89-91GTUs, you have an LSD.

Alternately you can jack up the car and look at the diff, there will be a tag on the fill or drain plug that says to use LSD only fluid if you have an LSD.

 

Not necessarily to either point. PO's could have swapped/parted the car out previously, thus it would no longer have it. For the second point, my LSD cover does not have said tag. I guess it maybe fell off?

Both Mazda guys were right about testing; although the easiest and most fun way to do it is to do a burnout somewhere (preferably somewhere with no people or houses or anything public nearby) and look at the tracks you leave. Two strips of rubber = LSD. One strip = Not so lucky. But if you already tried jacking it up and both wheels turn the same way, you've got LSD.

I'm not sure I'd agree with the second guy on the "not a lot" part. The GXL's, the GTU's, and the Turbo II's all had it...

 

thanks, I have an 91 convertible so I must not have an LSD. Would SAE 80W-90 oil be the correct oil to use for the rear differential then?

 

^ as Saavedro mentioned the PO may have switched the diff to an LSD.

You tested and it appears you have an LSD as both wheels spin forward.

 

Ok, thanks for the quick responses both of you!

 

you can make your own lsd just by welding something together haha

some of my friends do it.
but i recommend its a bad thing to do.. lol

guys ever heard of it?

 

Its called a welded diff.

 

oh here is called poss'ied

i just didnt know whats the real name
but now i know..

is it bad though>

 

I have always heard it as a 'welded diff'.

poss'ied reminds me of a posi diff as in GM's positraction. Which...was just an LSD.

 

The difference between a welded diff and a posi (limited slip) diff, is that, while a limited slip differential will transfer power to the needed wheel, a welded differential gives out ALL power to BOTH wheels at ALL times. This throws pretty much all handeling out the window. For you off-roaders, it would be like being in 4WD on pavement. For everyone else, try to picture as this may sound complicated...

When you take a sharp turn with an LSD, the inside wheel is allowed to turn slower than the outside wheel, causing you to be able to turn with more control. When you take a sharp turn with a welded diff, both of the wheels are still trying to turn at the same speed, so you're going to be skipping tires all over the place and not going to be able to control the car well at all.

So you could argue both points I suppose, the LSD is better for track handeling, and a welded is GOOD (But just as good as an LSD) in a straight line. So if you have an Open diff and only want to run 1/4 miles, go ahead and weld it. Just please don't go speeding all up and down on and off ramps of highways...

 

Yeah I know GM used it in the firebird/trans-am. They call it Posi Trac.

I have a 90 vert and I know my car leaves two skid marks when I burn out. I must have an LSD too?

 

do a burnout, if there are 2 tire marks, you have an LSD, if only 1, then you have a non lsd, 1 wheel wonder