Gearbox and Diff model

[Driv3r]

Is there a way to visually determining the model of gearbox and diff (ratio)? Just inspecting a potential parts car and need to know what gearbox and diff it has because the owner doesnt know.

 

Cheers

[worzella]

This has some great info about the whole gearbox mystery.:

 

and I think there is a whole diff summary article in the Article section of this FAQ that should help.

 

Randy

[worzella]

Right - found the tech article here:

 

 

[Driv3r]

Thanks Randy, I've read those. Just asking if there is a visual way of distinguishing lsd diff ratio by looking at it. Same as the gearbox (but need to know which 5 speed).

 

[Conserv]

2 hours ago, Driv3r said:

Thanks Randy, I've read those. Just asking if there is a visual way of distinguishing lsd diff ratio by looking at it. Same as the gearbox (but need to know which 5 speed).

 

 

If you can't remove the diff's rear cover, and see the gear markings or, at least, count ring-pinion teeth, or even jack up the rear of the car and count the number of axle rotations for each driveshaft rotation, you may be largely out of luck.  If the diff is, indeed, an LSD, chances are that it originated in an e21 and has ring/pinion number stampings, date stampings, and an "S" painted or stamped on the left front side front.  Mostly, however, unless the diff is freshly redone, it's really hard to see these markings from under the car.  There are substantial threads on diff identification that show these markings, but below are the relevant markings on the May 1978 3.64 LSD I'm currently running in my '76.

 

Top row of stampings = 11  S  40 = 3.64 (40 ring / 11 pinion) LSD ("S")

 

Lower column of stampings = 5 over 8 = May 1978

 

These are just barely visible on a freshly-overhauled unit that is in excellent condition and out of the car.  Reading them on a dirty old diff still in the car is....more challenging.  And, of course, how do you know for certain that a prior owner hasn't put a 3.91 ring-and-pinion set into a housing that originally held a 3.64 ring-and-pinion set.

 

Here in the U.S. -- I realize you are not "here in the U.S." -- odds are that an LSD in a 2002 is an e21 unit, as bona fide 2002 LSD units are rare as hen's teeth.  And...odds are that that e21 LSD is a 3.91, as the 3.64 units are somewhat rarer than the 3.91 units.

 

There are at least a couple of long threads that illustrate the differences among the post '02 5-speed transmissions.  You can obviously distinguish a close-ratio transmission by the dogleg shift pattern (and the 2002 close-ratio transmission, the 232/5, looks identical to the standard four speed, but with an approximately-4" extension sandwiched between the primary housing and the rear cover (photo below of 5-speed close ratio).

 

Good luck and regards,

 

Steve

 

Edited June 5, 2017 by Conserv

[Driv3r]

Thanks Steve, this is great. Cheers

[Conserv]

The final posting (by Mark) in this thread shows a couple post-'02 5-speeds:

 

But there are more comprehensive threads on the post'02 5-speeds -- with pictures!

 

Regards,

 

Steve

 

[Mark92131]

6 hours ago, Driv3r said:

Just asking if there is a visual way of distinguishing lsd diff ratio by looking at it

 

If it doesn't have the marking described by Conserv, jack the rear end up, take it out of gear and spin the driveshaft by hand.  If the rear tires rotate in the same direction it is an LSD, if the tires rotate in opposite directions, it is an open differential.  You can get a pretty good indication of the ratio, by marking the driveshaft and tire and estimating how many rotations of the driveshaft will produce one rotation of the tire.

 

Mark92131

Edited June 5, 2017 by Mark92131
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