Gearing

I have an 1988 XJ 4.0 Rustys 4.5" lift newer AX-15(1993) and I running 33's.My question is how do I tell what gears I have, there is no marking on my front or rear ends(d30 front d35 rear) and going about 60 mph my speedo says 50 mph.

If you have a manual transmission with the 4.0 its probably 3.07. If 2.5 probably 4.10.

Yes I have the 4.0 but my ride does not seem to be the dog that comes with having 3.07's. Other than popping off the diff cover and counting teeth is there any sure fire way to tell .

Yes. Jack up the rear and put the trans in neutral. Turn both wheels together at the same time by hand and count how many times your drive shaft yoke turns with one full revolution of the tires. 3.5 turns on the shaft = 3.55 gears, a bit over 3 turns = 3.07, a bit over 4 turns = 4.10, 4.5 turns =4.56 etc.

(taken from another site)
Jack up 1 wheel, mark it and the driveshaft. Turn the driveshaft until the wheel has turned exactly 2 revs. The number of turns of the shaft equals the axle ratio

MojaveDXJ said:

Yes. Jack up the rear and put the trans in neutral. Turn both wheels together at the same time by hand and count how many times your drive shaft yoke turns with one full revolution of the tires. 3.5 turns on the shaft = 3.55 gears, a bit over 3 turns = 3.07, a bit over 4 turns = 4.10, 4.5 turns =4.56 etc.

(taken from another site)
Jack up 1 wheel, mark it and the driveshaft. Turn the driveshaft until the wheel has turned exactly 2 revs. The number of turns of the shaft equals the axle ratio

Click to expand...

This wont work properly unless you jack and turn BOTH WHEELS TOGETHER!! There is a doubling effect of the spyder gears that gives you false reading. I find it easiest to mark the DS and a tar then back or pull the vehicle forward one full revolution.

As a rule of thumb, 3:07 in 4.0 W manual tranny, 3:55 in 4.0 W auto tranny, 4:10 in 2.5 auto tranny. Then there is the towing PKG and other avalible Options the orig buyer could have selected. The firs formulas will cover the vast majority of senerios.
Good luck!!

CW

there should also be a tag on your diff identifying what gear ratio you have

cwlongshot said:

This wont work properly unless you jack and turn BOTH WHEELS TOGETHER!!

There is a doubling effect of the spyder gears that gives you false reading.

Click to expand...

MojaveDXJ said:

Yes. Jack up the rear and put the trans in neutral. Turn both wheels together at the same time.

Turn the driveshaft until the wheel has turned exactly 2 revs

Click to expand...

Fuel90 said:

there should also be a tag on your diff identifying what gear ratio you have

Click to expand...

RED RHINO said:

there is no marking on my front or rear ends(d30 front d35 rear)

Click to expand...