Rear axle ratio

[baltobernie]

Beware of trusting the manual when it comes to identifying 30-year-old cars. Many (most?) have had drivetrain items replaced by PO's. With standard tires, if your car has the 4.3 gear, it will show 4,000 RPMs @ 65 mph. Look for 3,500 revs with a 3.9

You should use/borrow a GPS to check the speedo; they're usually innacurate due to replacements, too.

[pope]

The easiest way to tell is if the pig bolts on, it is the 4.3. If it is self contained with only an inspection cover, then it is the 3.9

[baltobernie]

That's what I thought too, Pope, until I replaced an "older" axle & diff with a "newer" one, and didn't change ratios! It seems that some of the newer styles had a 4.3 ratio in their beginnings.

The ratio is also stenciled on the right side of the case, but this paint was never intended to be permanent. With undercoating and road grime, it is usually illegible. This one has a ten tooth pinion and a 39 tooth ring, for a 3.9 ratio. The 4.3 reads 10/43

[pope]

LOL That is so FIAT. Its impossible to peg year changes with them.

[ventura ace]

. . . or, jack up one side and count turns of the wheel vs turns of the drive shaft. Mark the tire and the floor, and mark the pinion and the diff case. Remember there is a multiplier of 2 if you're only turning 1 wheel. So turn the wheel 2 complete turns, and watch how many turns the drive makes. If slightly less than 4 turns, it's a 3.9. If slightly more than 4 turns, it's a 4.1 like mine (early years). If it turns almost 4 1/2 turns then it is a 4.3. If it is more like 3.5 turns, then it's the diff for an automatic transmission, about 3.56 I think it is.

A