This is interesting. I have an "89" GXL That was made 4/89 which I was told was still considered an 88 but it has all S5 parts. I was wondering if I had the 3.9 LSD Or the 4.1. Would this car have LSD? I am stumped on the whole it was made in 89 but is said to be an 88 when it has S5 stuff. Please learn me the information.
Charles

 

It's a series 5 89 and doesn't have LSD at all unless someone put it in.

 

You didn't help. What are the numbers on these differentials.

 

Easy check, look to see if there is a metal tag on the "fill" plug that indicates it as LSD.

However, sometimes the tag is taken off. So, alternatively, jack up the rear end with the hand brake off and gear in neutral. Hand turn one wheel forward and look under the car and see which direction the other is turning. If the other is turning forward also, you have LSD, if turning reverse, you have an open (regular) Diff.

If LSD, I have no idea how to know if it's S4 Clutch type or S5 Viscious. But, from your production date, if it's LSD, its most likely Viscious.

 

I need to know the gearing on it too. Thats the most important part of my question.

 

OK, then what size are your rear tires, and how worn are they?

 

Unless a previous owner for some bizarre reason swapped a LSD from a S4 GXL with Automatic transission, you have a 4.1.

To confirm, while you have the back jacked up, put a white mark on or near one of the bolts that connect the driveaxle to the mounting flange. Now, count the number of times the white mark fully circles around as you turn the wheel one full turn.

If it turns less than 4 times (read 3.9 times), you have 3.9 gearing. If it turns more than 4 times (read 4.1 times), you have 4.1 gearing.

If it turns 4.3 times, then it is totally defective and you should immediately pull it and send it to me for replacement.

Out of curiosity, did you try the Search button first?

 

Well Evil they are P205 60R 15's They are brand new.

 

4.1 is the stock gearing in all manual cars be it lsd or open.... little exception to the rule GTUs has 4.33 gears and for you auto pukes 3.9 is the way it goes....

 

HOZZMANRX7's post is probably the easiest method, but here is another one if you don't have the facilities or desire to jack up your car:

Find a freeway (70mph speed limit) that has a nice, long straightaway and good mileage markers. Drive at exactly 3500rpm in 4th gear from one mile marker to the next, with a friend sitting in the passenger seat timing the run with a stopwatch. Your tires should be approximately 77.55" in circumference, so your time for 1 mile should be:
3.909 Rear = 66mph = 54 seconds
4.100 Rear = 63mph = 57 seconds
4.300 Rear = 60mph = 60 seconds

 

Dude,
Thats goofy, But I like the sound of it. Thanks Evil.
Charles