How can I tell what gearing I have?

How can I tell what gearing I have?
cdlongjr

cdlongjr

Active Jeeper
Posts
433
Media
14
Thanks
0
Location
Newark, De
Vehicle(s)
1983 Jeep CJ-5, 1987 Wrangler YJ, 1974 J-10
I checked both rears this morning & I can find any tags or numbers on the housings. Is there a way to determine my ratios & weather I have any type posi units or not?
What would be the best gearing for highway/off road use? I'm thinking 4:11s. Most of my us would be highway, getting to trail runs & back. One outing is about 5 hrs away. I don't intend to do any rock crawling w/ the 5.
 
jack up one end at a time, put on jackstands.
turn 1 wheel, doesn't matter which way. Watch the other wheel. If it rotates the opposite way, its an open diff. If it rotates the same way, pretty good chance its got some kind of traction aiding device in it. You would have to pull the cover to find out what. then you can check the gears by a number of ways...

As for checking the gears without disassembly, WHILE ITS ON THE JACKSTANDS, turn the wheel and watch the driveshaft yolk. If it turns a bit over 3 1/4 turns, its 3:73 gears. IF it goes a bit over 4 turns, its 4:10. Pretty easy to figure it out once you do it and compare to available gear sets.
 
As for what gears to run, its pretty subjective on the personal use of the rig.
4:11 are pretty good all around gears with 33" tires. Good wheel speed for mud, but not too awful on the street. Good trail gears using low range in the Transfer Case .

I have 3:73 gears in mine, and it goes really good on the street and in mud, but sucks on the rock trails. I plan to install a granny gear 4 speed and possibly a Tera-Low gears set in the Transfer Case , giving me the control and low gears I need in the rocks, but still keep the great gearing I have for the street! Best of both worlds, and possibly cheaper than 2 new differential gear changes.
 
I assume that I turn the wheel 1 revolution & count how many times the driveshaft turns?
I have 31" tires.
 
Last edited:
cdlongjr said:
I assume that I turn the wheel 1 revolution & count how many times the driveshaft turns?
I have 31" tires.
Click to expand...
Correct, just turn the wheel and count the rotations of the drive shaft... :)
 
31" tires & the driveshaft yoke turned 1 & 3/4 turns.
 
?? was the other tire turning as well? It may need to be blocked up so it stays still.
 
My mistake! I have open rears. Only one side was jacked up. I put a white line on the driveshaft with that line down. My son rotated the 31" tire one complete rev & I watched the driveshaft. The yoke turned 1 & 1/2 revs. Now remember, they don't call me "The ole fart" for nothin'. I probably messed it up.
 
Make sure the tire is going through one complete rotation. The worst gearing you should have in that Jeep would be 2.73.
 
I went back out & marked the tire w/ a white paint stick. I turned the tire 10 revs while watching the white mark on the yoke. For 10 revs on the 31" tire, the yoke turned 13 & 5/8 times. Problem is I don't know what the POs may have done.
 
Last edited:
CD - There still has to be a problem. The highest gear put in your CJ was a 2.73, what you say you have comes out to be a 1.625 and they have never made those. That would be a Bonneville Salt Flat gear!

Can you tell us exactly how you are checking this? Don't leave out any step even as insignificant as you think it may be.

As a last resort, you don't have the cover off do you? On the ring gear there will be a set of numbers like 41 11 - that would equal a 3.73 ratio (41 teeth / 11 teeth = 3.73).
 
I don't have the cover off, but I will remove it if I have to.
I jacked up the left side of the rear axle. I turned the driveshaft yoke up & down, lining it up w/ a protrusion on the bottom of the housing. I then put white line in the center of the bottom yoke. Then I colored in one block on the front of the tire tread, in line with the front of rear spring. I rotated the tire 1 complete turn, 360 degrees while watching the driveshaft rotate. For 1 rotation of the tire, the yoke turned 1 & 3/8s times. Thn I had the neighbor down the same thing. 1 & 3/8s turns. The Transfer Case shifter was all the way back towards the seat & the tranny was in neutral.
Maybe the PO changed the gearing. If you remember when I got the 5, I had to really slip the clutch to get her moving. She clutches like nothing I've ever driven. Lots of gas & very little clutch movement. I was taught a manual Transmission should be idled off from a dead stop, but there's no way I can do that w/ the 5.
 
Before you pull that cover, put the Transfer Case in neutral also and try it one more time with only one wheel off of the ground and then try it with both wheels off of the ground.

The highest gear I can find for the AMC20 is 2.73, I hate for you to pull that cover for no reason...
 
:dung:!!! I forgot!!! With an open diff and one wheel on the ground you have to turn the wheel 2 times to get the ratio!!!

Sorry about that! Stupid me...

Looks like you have a 3.25 gear!

1.625 (rotation of drive shaft) /.5 (rotation of ring gear) = 3.25

1.625 * 2 = 3.25
 
YEP.... I did the same thing last week. 1 complete rev of the tire and just shy of 2 revs on the shaft. Beat my skull against the wall for an hour.... then called Dad for the answer. (At 83 years young, he still can outwork me :)). After finding out what I was doing wrong and then spinning the wheel twice, I came up with 3.73 's for my '79, with an open diff.
I believe there is a code stamped on the axle boss (A, AA, B, BB, ect) that you can cross-reference to a table to find the ratio (as long as they are still factory gears). I'll see if I can find it in my garage.
 
Let's hear it for Susie. Hip, hip, horrah!!!!!!!!!!!!!!!
Don't feel bad guys. Ya'll though I was nuts. BUT, I"M BACK!!!!!!!!!!!
 
Last edited:
You must log in or register to reply here.

Jeep-CJ Donation Drive

Help support Jeep-CJ.com by making a donation.

Help support Jeep-CJ.com by making a donation.
Goal
$200.00
Earned
$25.00
This donation drive ends in
Donate
Back
Top Bottom