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Old 02-05-2002, 10:12 AM
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Default Axel shortening tips

A few days ago I finished my first axel shortening project. Before I started I looked at a lot of axel posts and got a ton of info about models, length, ratios, the differential location, caster angles and so on, but found only a few generic tips about the nuts and bolts of the operation. It seems like a good topic for a comprehensive thread, so I am starting one. I'm sure you oldtimers will have plenty more tips and corrections for my bumbling.

The first problem was how much to shorten each side. I used the center of the spring on the differential housing as the reference point for all length measurements, since that was the one fixed point that was going to be in the same place after the swap.

On my D30 I measured from the reference point to the center of the lower eye of both yokes, and to the center of the other spring. Since I was doing a stock-width replacement, I tried to end up with the same dimensions on the D44. I also measured between the yoke eyes to use as a final reality check.

Then I got a Starrett angle/bubble protractor and measured the angles. I jacked up both ends of the Jeep, with the weight on the front wheels, and leveled it fore and aft. Then I measured the angle of the spring clamp plate, and the front of the differential housing (90 degrees from the pinion angle). Just for grins I also crudely measured the caster and found about 2 degrees.

Then I set the donor axel ('79 Cherokee) on a bench on jackstands. With a scissors jack under the pinion nose I rotated it until the spring perch on the differential housing was at the same angle as on my Jeep. Surprise, the pinion angle was within about a degree; no need to machine the perch.

Then I turned it upside down and took the same set of length measurements off of it, did the arithmetic and calculated how much to shorten each side.

Then I had a minor brain storm. I scribed a witness line on each yoke and on each side of the differential housing. I very carefully measured between these marks on each side, and recorded the numbers. Then when I was finished I repeated the measurements and knew EXACTLY how much I had shortened each side (both were about 1/8" longer than planned.) That way I knew how much to have Moser (http://www.moserengineering.com/, $85 the set) shorten the shafts.

I put a 1-2-3 block inside the yoke, resting on the end of the axel tube, and measured down the length of the tube the amount I wanted to shorten, and scribed a line. The block was necessary because the end of the tube is about 1/8" inside the yoke, and the yoke itself doesn't have any good, machined surface to measure from.

Then I put the housing in the bandsaw and cut it at the scribed line. I then put the yokes in the bandsaw and cut off as much excess tube as I could.

Next was one of the tough parts. I clamped the yokes on a table and ground down the weld with a 4 1/2" angle grinder. Used up three wheels and made a terrible mess of grit and steel dust. I ground down as much of the tube and as little of the yoke as possible, and ground until I could see the line between tube and yoke all the way around. Then I used the gas axe to slit down the tube, and knocked the tube out with a hammer and drift.

There were a few burrs inside the yoke which I cleaned up with a die grinder, and I used a flap disk on the 4 1/2" to clean up the end of the tubes. I took as little off as I could because I figured the tighter the better.

I put the axel back on the jackstands on the bench and with the scissors jack rotated it until the diff housing spring perch was at an angle that put the yokes vertical to result in the six degrees of caster I wanted. It was easier to do this than make the spring perch level and try to measure the caster angle on the yokes.

I found a couple of pieces of bar stock that were a few thousandths under .750, that were a snug fit in the yoke eyes. (Had I not found these I would have made something on the lathe to do the job. I could see no easy way to accurately measure the yoke angle.) I tapped the yokes onto the axel and worked them back and forth until the bars were vertical. Then I set up some lights so that I could see any difference between the yokes, by sighting across the bars above the yokes, and got the bars in the yokes parallel. They were probably off by less than a degree before that, but now were VERY close. I didn't want to live with a caster pull.

Then I beat the yokes on as far as I could with a big copper hammer, checking frequently to make sure they hadn't rotated. That got them about half way. I did not put any lubricant on first because I was going to use 7018 low hy rods and didn't want any contamination.

After checking that the yokes were still parallel I put the housing in the press and started pressing them on the rest of the way. They went on a little farther, and then pressure built up to about 35 tons when my rigging exploded. I redid the rigging, heated the yoke, just a little, and pressed them on with about 20 tons. I stopped when the tube was still inside the yoke, eyeball close to the way it had been on factory assembly. That might have been where part of the final error came from. I should have measured this accurately and pressed the yoke back on precisely. Brain fart.

I set the housing back on the jackstands, cleaned it again with 1,1,1, tri to get any vestiges of oil off, and tacked the yokes in four places. I cleaned the welds and went back to lay in the money maker.

I built up a new long-side perch out of 1/4 X 2 cold rolled, TIG welded it together, and set it in place on the tube. With the scissors jack I got the diff side perch level, put the long side perch on, measured, leveled, tacked and welded.

Then I went back to the original witness marked and checked my results. As I said, the new was about 1/8" long on each side. I still don't know where that came from, but figure it's good enough for who it's for (me).

I sent the axels and shortening instructions to Moser, put a coat of Rustoleum satin black on it, and went back to take the D30 apart.

Ok guys, now's the time to add your tips, and let me know what I might have done easier or better. All suggestions welcome. Notice that I did not address any issues involved in going SOA, outboarding the springs, or going wider.



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  #2  
Old 02-05-2002, 11:38 AM
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Default Re: Axel shortening tips

The "Yoke" you refer to is the knuckle that has the two ball joints. correct?
I going to be helping my friend cut down an axle for his YJ and this will be extremely helpful. Thanks for the excellent documentation.

Wally

78 CJ7 304V8,TH400,Dana 300 Twin stick,Custom HD-WT AMC20 detroit locker 4:10,D30 ez-locker 4:10,Built NOT Bought.
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Old 02-05-2002, 11:43 AM
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Default Re: Axel shortening tips

The end result is all that matters.
I did mine slightly different and I had a couple of other "Issues" in mind. I wanted to be able to use a stock D44 axle assembly so that spare parts would be just a trip to the junkyard away. In particular, I set my d44 up so that an uncut axle assembly could be used on the short side.
This also allowed me to keep one knuckle yoke in place, which made it easier to align the other yoke.
The only issue created was a pinion offset of 1.5". The offset has no effect so far at any speed.
I also used a wire welder to secure the yoke to the housing. If you look at the factory welds, they are single pass and penetration was not very good. I did 5 passes and penetration was very good (probably overkill).
I have a 35 spline Dana 60 rear being shortened as we speak. I had a machine shop do the shortening of the housing using a jig so the housing ends would be perfect. With a front end the accuracy doesn’t have to be as good.
Nice write-up.
My D44 Write-up

Trailhed.com
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Old 02-05-2002, 12:33 PM
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Default Re: Axel shortening tips

One thing that really aids getting the yokes back on the tube is heating them up. I put them in the oven at 400 degrees for about 30 minutes and you can practically tap them on with a two pound hammer.

'75 CJ5 with goodies
'63 CJ6 rolling chassis and body only
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Old 02-05-2002, 03:55 PM
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Default Re: Axel shortening tips

The yoke I refer to is the piece that goes on the end of the axel tubes. It has upper and lower eyes that the ball joint studs go into.

I had been told that it wouldn't be that tough to get the yokes pressed on, so I didn't bother preheating them. In retrospect I think that the way I did it was better, though. Because I was in no hurry at all, I could fiddle with the caster until I had it just right. Had it been preheated I would have been hurrying to get it on before it cooled. Then if it wasn't right I would have a mell of a hess.

I think the best bet for someone without access to a big press would be to do as I did until it was on as far as a brass hammer could take it cold, and then heating it with a torch. I only heated it for a couple of minutes, not even close to glowing yet, in one place, and it pressed on easily. If I hadn't had it in the press I think it would have gotten hot enough to beat on without much more heating.

One step I forgot to mention is measuring carefully the distance between the U-joint yokes while the D30 is still in place. When I get the new housing in there I can measure again and know exactly how much the driveshaft needs to be shortened.

I might have been born at night, but it wasn't LAST night.
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Old 02-05-2002, 04:36 PM
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Default Re: Axel shortening tips

why didn't you pound the knuckles off before cutting the tube. Cut the weld then pound the knuckles off the tube.. then you can get a more accurate measurement from the end of the tube.

JR

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There is life after asphalt.
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Old 02-05-2002, 04:53 PM
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Default Re: Axel shortening tips

Actually the measurement from the end of the tube was pretty accurate with the 1-2-3 block. I think that where I went wrong was not measuring carefully how far I had the yoke pressed back on. Also I could have been a little off on the axel cut. For maximum accuracy I should have cut the tube a whisker long and then ground it to exact length.

It probably would be pretty tough to get the yoke off the tube without cutting the tube. The bead is not just laid on top of the tube and the yoke, it penetrates an eighth or so into both. To cut the weld would require a lot of grinding off the yoke that I didn't have to do. Also, grinding off the end allowed me to see the line develop between the tube and yoke. And there's the matter of the press fit; 35 tons wasn't enough to move it cold, after all burrs and corrosion had been removed. The torch slice down the remains of the tube took all the pressure off and let the tube come out easily.

I might have been born at night, but it wasn't LAST night.
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Old 02-05-2002, 05:16 PM
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Default Re: Axel shortening tips

I did something similar where I cut the tube in half as close to the yoke (knuckle) as possible. I ground the weld and remaining tube until the infamous line apeared then pressed out the approximately 1" piece. This way a minimal amount of yoke is removed and no hammering is necessary.
For me it was just easier to handle the yoke with the rest of the housing removed.
Putting it back on was a matter of lining it up and tapping it on with a shot filled hammer.
I didnt have much trouble at all getting my yoke back on. It was a tight fit but nothing over a .002 interference.

Trailhed.com
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Old 02-05-2002, 07:53 PM
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Default Re: Axel shortening tips

One item that may be helpful to some is: Removing the one inch or so of tube can be easily accomplished by making two hacksaw cuts. Put the blade through the opening and reattach it to the saw frame. Do it right and the tube end will practically fall out.

80 CJ5, 52M38 Always carry a BFH and a screwdriver.
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Old 02-06-2002, 12:34 PM
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Default Re: Axel shortening tips

Before putting the D44 into the Jeep I weighed it - 130 pounds. The D30 weighs 85 pounds. Both are narrow track, no axels, no knuckles and no gear oil.

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