3.73???? 4.11????

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88chevota

88chevota

Joined
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How do I know if I am running 3.73 gears or 4.11? I bought some axles from a guy and he thought they had 3.73, but wasn't sure. they are definitely out of an fj60. the front axle is not trussed. I thought all fj60 came with 3.73 and the 62's came with 4.11

Driving down the interstate I am cruising at about 65mph and my rpms are at about 2500. I am running 35" tires. I thought I would be lower on RPMs.

I have a SM465 four speed tranny so the final drive on the trans is 1 to 1.

I am debating on going with 37's to help out with highway to bring down the rpms and of course it can't hurt on the rocks!:)

any help??? any experts?


here is a pic of the diff it it helps

pict3210op8ea4.jpg
 
D'Animal said:
That was way too easy if he has it apart.

Isn't there a way to jack the back of the rig in and turn the tire one revolution and see how many times the driveshaft turns?
Click to expand...

Yeah, but its kinda complicated with an open carrier because the driveshaft will only turn half as many times as its ratio would dicate if you just turn one wheel with the axle in the air.
 
gear ratio

The quickest way is what d'animal said. mark the drive shaft and rotate the tire 2 turns divide the driveshat turns by 2.
 
I've got a 4.11 from my 40 sitting on the garage floor. It has 37x9 on the ring gear. Yours may have some numbers too.
 
well the bummer thing is that it is all back together. any other options? I try the rotating deal. will it help if I only jack up one side and put it in neutral?
 
88chevota said:
well the bummer thing is that it is all back together. any other options? I try the rotating deal. will it help if I only jack up one side and put it in neutral?
Click to expand...

Yeah...just jack up one wheel, parking brake off, transmission in neutral. Mark the drive shaft. Turn the lifted tire one rotation. If the drive shaft rotates less than four times you have 3.73, more than four times, 4.11
 
Last edited:
Meh, way to tired. Thanks.
 
My 4.11's have a round flange where they bolt to the drive shaft.

don't the 3.73's have a " four cornered shaped flange"? at least the factory ones on my 83 did.
 
If you run the numbers (be honest with yourself about how tall your nominal 35s really are) you'll see that you are pretty much dead on in terms of the RPM you should be seeing at 65 with 3.70s (Cruisers never had 3.73s...)

If you had counted the pinion teeth while you had the dif open, you would have seen 10 of them. The ring gear has 37. 4.11 gears would still have 37 on the ring, but 9 on the pinion. the 4.10 gears introduced with the '80 series in '91 have 41 and 10.

These numbers are also marked on the side of the ring gear (37x9, 37x10 or simply "41" in a circle).

Pinion flange shape won't tell you much. 4.11s has "square" flanges, both fine and course spline and fine spline round. 3.70s had square fine spline, and IIRC round as well. 4.10s are all round.


Mark...
 
cool thanks guys! I have been doing the math some more in my head and my 35's are pretty worn down so I think you are right mark. 3.70's

are 37's to hard on 3.70 gearing or do you think I'll be fine? remember i have a 4 speed with no overdrive.
 
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