D 44 rear axle line up

[originalnvmj]

Having trouble centering a D 44 axle under my 92 MJ. The axle is out of a cherokee, it has been stripped, rebuilt and new M.O.R.E. SOA spring perches welded on. Axle is centered under the truck but sticks out 1/2 inch farther on the passenger side when measuring from the outside of the frame rail to the outside of the tire. Any help is appreciated.

[Eagle]

I don't understand the question. If it sticks out 1/2" more on one side than the other, it clearly is NOT centered under the truck.

 

First question: The Jeep axles should have the differential centered on the axle assembly. The distance from the diff housing to the spring perches should be the same on both sides, and the distance from the spring perches to the brake backing plates should be the same on both sides. If you have verified that these are correct, then the problem isn't with the axle but with the frame or the springs.

[Comanche County]

It sticks out 1/2" on one side because it is offset by 1/2", not truly a centered diff.

 

I take it you welded the perches at an equal distance from the differential housing. That's where the extra .5" comes from.

 

I left the stock perches on my D44. I just measured it to be sure. The distance from the diff (where the tube enters) to the inside of the leaf spring perch is 12" on the driver's side. Its 12.5" on the passenger side. If you measure yours from backing plate to backing plate then you'll also see that one tube is longer than the other.

 

I'd cut and move the perches.

[HOrnbrod]

Exacerly. The D44 left axle is 29.20" long; the right 29.70" long. Thus if you have the pumpkin centered under the truck, the right side will extend 1/2" farther.

[Pete M]

technically, if one tire sticks out 1/2" more than the other side, the axle is off by 1/4". :peek:

 

I'd be inclined to ignore a quarter-inch mistake if it meant re-welding the perches. :yes:

[HOrnbrod]

technically, if one tire sticks out 1/2" more than the other side, the axle is off by 1/4".

Picky-picky. But correct.

 

I'd be inclined to ignore a quarter-inch mistake if it meant re-welding the perches. :yes:

Agree. No one would know except you. :yes:

[Comanche County]

I would re-weld it because now that the housing is centered, but the pinion isn't because the pinion isn't centered in the housing.

 

It means, housing straight = pinion offset by .5", housing offset by .5" = pinion straight in line with the drive shaft the way it came from the factory.

 

I know its not a big deal, but it would be one of those things in the back of my mind always making me wonder about that U joint's longevity.

[Eagle]

The Jeep axles should have the differential centered on the axle assembly.

My bad. Didn't realize that, but I've not yet re-welded spring perches.

[HOrnbrod]

This thread brings up a point that I've always been curious about. The old MJ AMC-20 rear axles are the same length right and left. Yet the Dana 35 and 44 axles are of different lengths. Why? And don't say because they were designed that way. :D I'd rather just have to carry one spare axle to fit either side.

[Pete M]

I would re-weld it because now that the housing is centered, but the pinion isn't because the pinion isn't centered in the housing.

 

It means, housing straight = pinion offset by .5", housing offset by .5" = pinion straight in line with the drive shaft the way it came from the factory.

 

I know its not a big deal, but it would be one of those things in the back of my mind always making me wonder about that U joint's longevity.

 

 

In the end it won't matter. We're talking about a tiny, tiny fraction of an degree change. Plus you'd be amazed as to what sort of angles a U-joint will happily spin through as long as it is doing the same angle since new. :thumbsup:

[neohic]

This thread brings up a point that I've always been curious about. The old MJ AMC-20 rear axles are the same length right and left. Yet the Dana 35 and 44 axles are of different lengths. Why? And don't say because they were designed that way. :D I'd rather just have to carry one spare axle to fit either side.

 

I wonder if it has anything to do with the u-joints. Maybe so they're always in motion? I'd think that if the driveshaft was 90* to the drivetrain there would be a dead spot in the rotation of the joints. :dunno:

[Comanche County]

Its just that the center line of the pinion gear and spider/side gears are centered in the AMC 20 and thus the axle lengths are the same for both sides. The Dana axle pinions are offset in the casting of the diff just slightly and require different length axle shafts.

 

Dana/Spicer U Joints are supposed to be good for 21 degrees of rotation. But I think the most important impact to ujoints is torgue and rpm relative to angle. Somewhere there's a point of diminishing returns when it comes to drive shaft angle, sharper angles will create more heat and friction, thus cannot take prolonged periods of high torque and rpm like a jeep in 4-Low creates with a driver who's heavy on the skinny pedal.

 

Shallow ujoint angles will be fine on the highway even at freeway speeds. Even extreme angles may be fine at low rpm and torque, but you put an extreme angle on an offroad rig's ujoint and spin it at 1-3K rpm (at the axle, 4-6K rpm at the engine) with 300 or more lbs of torque like some of the modified jeeps out there,,,,and what do you think is going to happen? Kablooeey!

 

For longevity and dependability you want the drive shaft as straight as possible for street rigs or not.

[originalnvmj]

I measured from the backing plate on the axle against the brakes to the outside of the perches. Both perches are the same distance from the plates at the end of the axles.