Is gear ratio info in the door codes?

**TokerM** · 10-22-2010, 09:22 AM

1999 Z28 - m6

Which one came with the gear ratio option, a4 or m6? If it was the m6, how do I confirm which ratio I have? I'm guessing the info is tied up in the door code somewhere.

**2000** · 10-22-2010, 09:38 AM

A4 came with the either 2.73 (door code GU2) or 3.23 (door code GU5). M6 all came with 3.42 (door code GU6).

**35th-ANV-SS** · 10-22-2010, 09:42 AM

That assumes your rear-end was never replaced or rebuilt...

You could jack the car up from the rear...mark the drive shaft with a marker...then turn the wheel 1 full revolution. Watch to see how many revolutions the drive shaft turns. That is your gear ratio.

Example: if you turn your rear wheel 1 full revolution and your drive shaft turns 3-1/2 turns...you have a 3.42 gear ratio. If it turns 4 turns, you have a 4.10/4.11 ratio....etc.

**Faught** · 10-22-2010, 09:49 AM

Originally Posted by 35th-ANV-SS

That assumes your rear-end was never replaced or rebuilt...

You could jack the car up from the rear...mark the drive shaft with a marker...then turn the wheel 1 full revolution. Watch to see how many revolutions the drive shaft turns. That is your gear ratio.

Example: if you turn your rear wheel 1 full revolution and your drive shaft turns 3-1/2 turns...you have a 3.42 gear ratio. If it turns 4 turns, you have a 4.10/4.11 ratio....etc.

^+1 thats how i did it.

**TokerM** · 10-22-2010, 09:52 AM

^^

Helpful info there, but I would have to guess that mine wasn't. Everything was bone stock except for the skip shift solenoid.

GU6 there... thanks!

**35th-ANV-SS** · 10-22-2010, 09:55 AM

Originally Posted by TokerM

^^

Helpful info there, but I would have to guess that mine wasn't. Everything was bone stock except for the skip shift solenoid.

GU6 there... thanks!

My way you don't have to

**TokerM** · 10-22-2010, 09:58 AM

Originally Posted by 35th-ANV-SS

My way you don't have to

My way lets me stay off the concrete... and... ummm... be lazy?

**35th-ANV-SS** · 10-22-2010, 10:01 AM

As much effort and time you've put into responding in this thread you could have already checked

I'm sure you have a 3.42...

You can also "guess" by seeing what RPM you are in 6th gear at 70. Should be around 1600 RPM if I remember right.

**TokerM** · 10-22-2010, 10:10 AM

Originally Posted by 35th-ANV-SS

You can also "guess" by seeing what RPM you are in 6th gear at 70. Should be around 1600 RPM if I remember right.

Now THAT is a far better way!!! I'd much rather push a gas pedal than push a tire!

It would also help if I had a working speedo... Its off by some pretty big margins. (following a car with a "working" speedo: actual speed-30, my speedo-21 highway actual-50 my speedo-38)

I was thinking it was just "wonky," since everything is stock, but now I'm wondering if maybe I did get a rebuild in there....

I changed the rear end oil this week (should have counted while I was in there,) and the gears looked really clean... Almost too clean :shiftyeyes: Like new clean...

Time to push a tire....

**TokerM** · 10-22-2010, 02:49 PM

Well... that didn't help....

Turned the tire, and the shaft wouldn't turn (just "twitched" 1/16 - 1/8 revolution then slipped)

Fine, we'll go about this the other way. Marked the tire, twisted the drive shaft til the tire made one full rev, and....

Drive shaft turned only 1.75 revs??

**Cutlass** · 10-22-2010, 05:48 PM

Its trickier than it sounds with a Torsen diff or an open diff. You have to have both tires spinning the exact same or you'll be getting the spider gear ratio mixed up in there.

**TokerM** · 10-22-2010, 06:35 PM

Could a general assumption that the spider halved the ratio be made? (1.715 x 2 = 3.43) I suppose it was slightly less than 1.75 revs on the drive shaft.