Need to know what gear ratio was on a 86 Trans Am, 4bbl, High Output, 305ci, 10 bolt rear.

I am 99% sure it is a 3.73 (the only ratio ever availbe on an H.O. L69)

Jack up one tire.... Mark the driveshaft and the jacked up tire.

In neutral, rotate the Driveshaft until both marks return to their original position. Count each revolution of the driveshaft and each of the Tire.

Take the numbers you get and put them in this formula...

Driveshaft rotations / (Tire Rotations/2)

IE 13 shaft rotations to 7 tire rotations yeilds 3.73 gears

13/ (7/2)

13/3.5

3.7142

~ 3.73 Gearing

I never trust RPO codes with things like that.

BTW this only works with Open rear ends.

If you have a 86 TA with the HO motor in it, you have a car with less than 100 units of its kind made. AFAIK that's one of the extremely few applications that would have gotten a 3.70 9-bolt.

If you have a car with a 10-bolt, it isn't a HO. It's a LG4 car.

Count the bolts. Take off the cover and look at the gears. All this crap about codes and counting drive shaft revolutions and speedo / tach readings is either subject to alteration after the factory built the car, or too inaccurate to believe.

Have you changed the fluid in the rear lately? If not, then it's long overdue. Explain to your wife that it's regular maintenance that needs to be done; and make a point of looking at the gears while you are taking the proper care of this somewhat rare and special car you claim to have that you should have long since been taking of it.

Not that I would know anything about L69 (HO) cars, or anything like that.

my car is an LG4. So what does that mean? Do I have posi or not. And what kind of gears am I running? There still stock.

THe LG4 is not the HO motor. It's the base model V8 in that year.

Take off the cover and look. It's the only way to know.

26 1986 T/A HO's were made.


To verify your axel you can look on your axel tube, passenger side, there is a stamped code there facing forward.

No need to remove bolts or anything unless you have alot of free time, just crawl under the car.

Also you can look on your carrier cover for an ID tag, most likely its gone.

Here is mine as an example:



Don

the point RB was tryin to make was GEARS CAN BE CHANGED..tubes are generally NOT....only way to know 100% is to

Relax quote man, I can read.

My answer to the original question still stands, regardless of anyone else’s input.

warrior_91, tell me your code and I will tell you what rear your car came with and if a posi or not.

The standard rear in 1985 for an LG4 was a 3:27 The 3:08 was optional. Source: 1985 Pontiac Merchandiser 8/84


Don