Trailing Arm Alignment

[Howitzer]

Just bolted my axel on to my trailing arms on my '72 SWB. It looks to me that the left side of the diff. sits closer to the front of the truck than the right. I measured from the crossmember and it's seems to be about a quarter of an inch difference. I did have the trailing arm cross member out for sandblasing and painting.

Suggestions?

[BMERDOC]

I've measure thrust on several trucks and was kinda suprised about how far out they are. Are your trailing arm bushings good? Are your u-bolts completely tightend down?

[Howitzer]

Trailing arm bushings are brand new. Not the poly inserts but the whole case and rubber insert. U Bolts are Torqued down to 150 lbs. The measurement i took was from the trailing arm crossmember to the upper shock crossmember, so frame to frame so to speak. I replace the rivets with bolts, i'm wondering if i should unbolt the crossmember and wiggle it around to see if it'll straighten that part up.

I've also not installed the springs, shocks, or panhard bar yet, would this make a difference once everything is torqued down?

Thanks again.

[BMERDOC]

Yes, install the springs and panhard bar first. Measure from backing plate to frame on both side to compare distances.

It would be nice to make sure the frame is square before you took anymore measurements but I'm sure its probably not exactly square either. Loosening the trailing arm member, centering the axle side to side (measure from backing plates to frame is sufficient) and retightening the crossmember SHOULD get you where you wanna be.

[tincan1966]

Ok maybe it's me. but it seems you guys are talking two different directions. The forum poster I believe is saying the axle is farther forward on the left side(shorter wheelbase) and BMERDOC is referring to centering side to side. Am I correct?
Centering side to side is very important, too, as mentioned, and all components need to be installed and properly torqued.

As far as the wheelbase concern, I have run across this before on a 1970 C10 2WD. The trailing arm crossmember had never been removed and the frame checked square. Also my drivers' side was shorter by about 1/4". The only solution i was able to perform was removing the trailing arm bracket to crossmember rivets, fabbed a "shim" out of 1/4" steel plate and bolted the bracket back to the crossmember with grade 8 bolts. When algnment was checked, the thrust angle was good.

[Howitzer]

Yah, i'm talking about a shorter wheel base on the left side compared to the right. Centering side to side isn't a big issue, that what the axle saddles are for.

I'm going to bolt everything up and see how it measures out.

[BMERDOC]

Hhhmmm. The end result would be the same for Thrust or wheelbase. You shouldn't be worried about it until the panhard road and springs are installed. Have you put those parts on yet?

[Howitzer]

Not yet. Hopefully over the Christmas break. I'll measure it all up after i've got it all installed and see where i'm at.

[Howitzer]

So i installed the Panhard bar and am 1/8 of an inch out of center side to side (good enough i figure). Knocked out the trailing arm bracket rivets and installed some nuts as spacers just to mock up a spacing for a shim. Is that what you did tincan1966? What's the best place to measure length wise down the truck on the rear end to make sure it's lined up properly?

thanks.

[cableguy0]

I would remove those nuts and bolt it back down flat. After that loosen up the bolts in the crossmember itself. Push the drivers side back and pull the passenger side forward and lock the bolts down. After that remeasure and see where your at.

[tincan1966]

Howitzer -- I would measure from the center of that crossmember, diagonally to the trailing arm u-bolts on each side. Also, along the bottom of the frame between the trans crossmember and trailing arm crossmember, there should be some holes, approx 5/8" in diameter. These are control holes, used at factory during assmebly. Measure from these to rear axle- straight back on each side. Then measure from the passenger side hole to the drivers' side of the axle, then from the drivers' side frame hole to the passenger side and compare measurements, this will tell you if you are square to the frame.

You absolutely need to make a solid shim between the crossmember and trailing arm mount, which I assume you knew, since you mentioned the nuts were only for mock up.
Also, I assume your trailing arm crossmember is still riveted in place, so loosening bolts and moving it is not an option.

Being an 1/8" off, side to side, isn't bad, with the suspension hanging and no load. It should be off to the drivers' side, since when weight is put on truck, the panhard bar will raise up,where it attaches to axle, pushing rear axle, slightly to the passenger side.
Once you think you are close, install tires and set truck on the ground. Measure your wheelbase.

Hope this helps. These trucks were never truely square originally, I don't think! LOL!

[tincan1966]

Another note- I have seen these trucks have the rivets loosen over the years in the crossmembers, causing some shifting or "racking of the frame" ( one side moves slightly forward of the other). If I suspect this i normally square the frame, and either remove rivets and install bolts or tack weld each crossmember (not the front suspension
or trans crossmember)

I ran into this on my Suburban I am building-apparently it had been hit on the drivers side, directly on the bumper/front frame horn. Entire left frame rail was shifted 1/4". We squared it, and welded the very front and rear crossmembers. Been checked twice on frame alignment fixture since reassembled,and still square.