4x4 issues.

[2basco]

Just acquired a 1980 CJ7 - guy I purchased it from had it for 21 years. It has 67k original miles and everything is stock. 4x2 has no issues, however, when I try to run in 4x4, I can move about 10 to 15 feet then it feels like some one is putting on the breaks. I am not a gear head, but, my gut says I may have different gearing between the "front" and "rear" drive?

Any help to get me going in the right direction. Thanks.

Ray

 

[Old Dog]

I'd pull the diff. covers off. The ring gear should be marked with the ratio.
If not count the teeth on the ring and pinion and divide the numbers. For instance 41 and 10 would be 4:10's.
After all these years I'm sure they could use new oil anyway.

 

[2basco]

Thx. Plan on doing a lot of fluid changes over the winter.

 

[73CJ]

You can jack up A wheel, put it in neutral and rotate the driveshaft while counting the turns to make the wheel go one revolution. Thats your ratio.

With a locker, jack up both wheels. A helper makes it way easier.

Check both axles.

 

[Incommando]

If this is on a hard surface and the wheels are turned anything but straight ahead this is an expected behavior. Just in case...

 

[2basco]

Thanks for all the help. I am based in Wisconsin and plan doing a lot of updating this winter.

 

[JR74CJ5]

Just a thought... is that Dana 300 Transfer Case still stock single stick or Twin Sticked? (2 selecting sticks) If twin sticked, maybe in Low & High?

Otherwise as most have pointed out, this may be either a locker or just the characteristics of your rig.


~ JR

 

[2basco]

I Pulled the pumpkins and did a little math. Found 3.07 front and 3.54 rear. That problem figured out. Now need to fix. I have a Leek on right rear axle oil seal, tried to repair, could not pull plate. Thinking of replacing axle complete with disc brakes. Would prefer used, but, might buy new or remanufactured.

Is there an easy replacement? Basically unbolt the old rear axle and bolt on a new one. Dana 44 ? I Do not plan on any major off road activity, mostly ride on pavement or gravel roads. Also need to equalize gear ratio, should I go with 3.07 rear to match front or change front pinion and ring? I have 32 inch tires.

More winter fun.

 

[Incommando]

You have probably figured out that you can't trust any info provided by the P.O. as it seems impossible for him to not know about the axle ratio differences if he owned it for 21 years and he obviously failed to disclose that. Everything cannot be stock if the ratios have changed and it has 32's on it. To my mind that would make anything he said pretty suspect.

It would obviously be cheaper to get a complete 3.07 rear but personally I would switch both to 3.54. Even that ratio is not considered optimal for 32" tires.

There were two different axle widths used in modern CJ's and they are referred to as narrow trac (51-ish ") and wide trac (55-ish"). Your jeep's factory axles would have been narrow trac with the front being a low-pinion Dana 30 and the rear being an AMC Model 20. The rear would have a large round diff cover. I am only pointing this out as the most logical explanation for your gear ratio differences is if an axle assembly had been swapped. Although it could be the front I think it is more likely the rear as the front's 3.07 ratio was the standard ratio in '80 and the M20 is considered a problematic axle by many. I would not do anything major to a M20 rear without also upgrading to one-piece axle shafts at the same time. Just make sure of what you have before you start.

Swapping in a JY rear from another app is difficult if you want to maintain the same width and lug bolt pattern as the front. Often it is easier/cheaper to swap a matching set of axles from a donor to get matching widths, gear ratios, bolt patterns, disc upgrades, etc... There are a mind boggling number of possible combinations out there, though.

 

[2basco]

Thx. Found a note in one of the guys books that came with cj cross re a 78. he replaced the 80 rear with a 78 (confirmed with brake drum size).

Now that I know what I have, For the kind of driving I do, my gut says, better to "rebuild" AMC20 (with 1 piece) and match ratios. After some research, sounds like 4.11 would be the best for the tire size.

Thanks again for the response.

 

[Incommando]

While you are under that M20 and if you have access to a welder putting a few stitch welds where the axles tubes go into the pumpkin is a nearly free upgrade to cure the M20's habit of spinning axles tubes. That and the one-piece axles really pick up the M20. Adding a truss at some point it also good insurance. The actual M20 diff internals are as good as or better than the other half-ton axles.