Rear End U-Bolt Tightening
 

I'm re-doing the rear suspension on my 77 Trans Am. Got new everything. Trying to figure out the proper way to tighten down the U-bolts. I'm using rubber spring pads and 2 U-bolts per spring.

On my old rear end, the U-bolts were tightened down until the bottom plate was making contact with the spring perch on the axle tube, the rubber pads were squished significantly above and below the leaf spring.

The only official instructions I was able to find online were for the BMR leaf spring kit, which includes polyurethane spring pads. Those instructions state to tighten the U-bolt nuts evenly until the pads start to bulge.

So which is correct for rubber pads? Flatten the bottom plate to the spring perch? Or only tighten until the pads bulge? Or is there some other guideline I'm not aware of?

I looked it up in the chilton book and factory torq was 45 LBS
My 70 firebird rear started moving on the springs.
I don't have a problem any more. It will take a lot of
turns to get to the torq so your arms are going to get tired LOL

GT

That's what I went for originally, but that doesn't get the bottom plate anywhere close to the spring perch. There's still a wiiiide gap.

I don't understand why the original had the bottom plate completely flattened against the spring perch if that's not how it's supposed to be. Seems like as the rubber flattens and wears out, it would lead to all of that wiggling around on the U-bolts if it wasn't tightened right down.

IMO, I would shave/ sand those pads enough to get a little squish, but get the plates to butt up against each other. That's where it gets strength from. Would maybe better using 4 U-bolts.

Swapped out springs and insulators don't necessarily have the same thickness and compression of stock items 45 years ago.

I do have 4 U-bolts (2 per spring)

i tightened mine to the factory spec, ~45-50lb using new rubber pads or poly pads. the plate distance to the rear end on yours could have been retightened over the years or serviced by a guy with an impact that tightened too tight.

ive used poly on one car with stock springs, rubber on another with the PTFB springs that is drag raced quite a bit at low 11's, rear hasnt moved for 6+ years now. on my lower mile, 26k, original 81 the pads have at least a 1/8" gap if not 3/16 and the rubber pad is just slightly squished.

i would stick with the factory spec, tightened evenly, not squished out or anywhere near the plates bending or touching the rear.

These are also PTFB springs. What you're saying is reassuring. I currently have them tightened very evenly and to 50ft-lb, so I guess that's how I'll leave them. Thank you!