How to line up a rearend with new perches?

[cuervo]

Hey

How are you guys lining up a rearend when you put on new perches?

I was trying to pull a measurement from the center of the pinion to the frame. Then I was checking from the leaf spring to the WMS but doesn't seem very accurate since the springs move around.


I'm a solo act today so I made this little helper.

 

[imiceman44]

Well if you had left a mark where the original pads were, it would be easier but you could measure from the backing plates or axle flange at the ends, you obviously don't want to measure from the pumpkin since it might not be centered.
That is a nice cradle you made.
I am making some similar but on a rack so I can store my axles vertical.
I usually don't need one for installation because all I do is put tires on it and roll it under the truck and then lower the truck on to it.
And I am always solo

 

[cuervo]

The original perches would not line up with my 1991 Suburban as the axle came out of a C&C.

I was thinking if I centered the pinion between the frame rails I should be good, no, yes? There are no backing plates, it's a disc conversion and the flanges on a Dually C&C don't come anywhere close to a SRW hub after concersion.

 

[Stomis]

I wouldnt trust centering the pinion seeing as how the 14b has an offset dif and it might not be truly dead center. If your anything like me I would really think this one out otherwise you'll be looking at your truck trying to find one tire sticking out more than the other.

One way you could do it that would be dead on would be to weld up a jig of say a piece of box or angle iron. Drill two holes in it and hang it on the spring with no shackle. Just shim it out centered with washers and jack the rear up til the pieces of metal meet the axle tube. Then measure and make sure both side are right to the back of your rotor.

It would sorta be like going off the springs but you know a piece of metal with no bushings substituting the spring isnt gonna flex to the side.

 

[imiceman44]

The original perches would not line up with my 1991 Suburban as the axle came out of a C&C.

I was thinking if I centered the pinion between the frame rails I should be good, no, yes? There are no backing plates, it's a disc conversion and the flanges on a Dually C&C don't come anywhere close to a SRW hub after concersion.

I guess I didn't make myself clear:
The flanges or the discs are what you need in the right place, so you measure from side to side then you get the center point.
From the center point you measure out your your spring pad centers, in your case I am guessing 1/2 or 3/4 ton so it would be 42.5" so 21.25" on each side.
Now to position you pads you measure them and take half that from the center and you got your position.
DO NOT measure from the pinion, it's not an accurate center.
The easiest would be to measure from flange to flange and then take 42.5 out of that and divide by 2, that will be the measurement from flange to center of the pad.

 

[pseudomike]

I measured mine from the original perches. I can't remember the difference 3" or so so I split it between the two. There is a little wiggle room as you noted due to the springs. Myself or someone else here could measure their perches from the backing plate mounting flange or something if you lost the original mark. Alternatively you could find the center from backing plate to backing plate and go from there. you'll need to now the perch spacing which slips my memory but is without a doubt on this forum somewhere.

 

[cuervo]

I do have the width of the 14SF perches. That would give me the distance between perches. I guess I could meeasure the back side of the disc and half that and mark it on the diff then measure out the old preches and check that.

 

[pseudomike]

You could probably measure it from the pumpkin flange if someone gave you that measurement. I'd check once I had it laid out to confirm spacing and center was ok. I could measure mine up later, I'm at the office right now.

Mike

 

[cuervo]

Thanks guys, I got it.

Got the 42.5 from the old rearend and got a width from the disc brake inner side. Divided the disce brake measurement to get a center line on the pumpkin then measured out 21.25 and made a mark. Put the rearend under the burban and jack it up off of the stands to get pinion angle.

I then measured the spacing from the back of the disc to the spring. I know the springs can move around but the measurements were equal.

 

[imiceman44]

Thanks guys, I got it.

Got the 42.5 from the old rearend and got a width from the disc brake inner side. Divided the disce brake measurement to get a center line on the pumpkin then measured out 21.25 and made a mark. Put the rearend under the burban and jack it up off of the stands to get pinion angle.

I then measured the spacing from the back of the disc to the spring. I know the springs can move around but the measurements were equal.

Good job.