Rear axle U-Bolts Original vs. Repop

[Keith R.]

Got a chassis question. I was planning on replacing the rear axle U-bolts GM Part# 3723981 with new ones from Paragon (part # 125K). In comparing the two, I noticed that the ones I pulled off the car are about an inch longer than the reproductions and are about a 1/2" thick with a distinctly flat section on the end of the U. The repops are about .46" thick, the threaded area is 1.55" long opposed to the ones which came off the car which have a 2.59" threaded section. The repops also have a virtually indistinguishable flat area at the end of the U. Pics are posted. Are there any chassis judges out there who can tell me which are correct?

[Robert E.]

Re: Rear axle U-Bolts Original vs. Repop

I'll bump you question to the top.

[Bruce B.]

Re: Rear axle U-Bolts Original vs. Repop

I am not familiar with the judging aspect of the U bolts but make sure you get good quality parts.
I ran across some very poor quality ones which had bad material characteristics and the threads stripped when I torqued them to the specs.
They were Chinese imports.

[Terry D.]

Re: Rear axle U-Bolts Original vs. Repop

Keith & Gina
According to my judging sheets, two years old, the rear suspension is broken down into 5 catagories, frame&brake&fuel lines (13 points), frame stencil (2 points) rear suspension, all components (14 points) rear axle housing assy., driveshaft, & rebound straps (6 points) and mufflers, tail pipes & hangers (20 points). As you can see your particular part is not mentioned. If you want more info I would suggest you look in the front of the "Driveline" and contact your team leader, he will no doubt be able to tell you more than me. As for the difference in the u bolts, are you sure yours are original? I know back in the day when we raced a 62 we bought longer u bolts to bolt on a big set of traction bars Hopefully someone will jump in with the original dimensions.
Terry

[Keith R.]

Re: Rear axle U-Bolts Original vs. Repop

Thanks Terry - good idea. Perhaps they'll know or point me in the right direction.

[Bill M.]

Re: Rear axle U-Bolts Original vs. Repop

Keith:

My '59 has the OE 4-leaf springs, u-bolts, and nuts. I get the threaded length at about 1-3/4. The u-bolts extend about 1-1/4 below the 4-holed spring plate.

Bill

[Tom S.]

Re: Rear axle U-Bolts Original vs. Repop

I agree with the statement make sure it is good quality material. I had several problems with suspension parts on my 69. They are using alot of chinese material that is just not any good, not to mention unsafe. And most all the suppliers are selling it . Beware!

[Rick C.]

Re: Rear axle U-Bolts Original vs. Repop

FWIW, my u-bolts are 6-5/8" long, .465" diameter, and the threads are 1-11/16" long. There are no flat areas on the end of the U. More like the repro than what you took off your car.
Rick

[Keith R.]

Re: Rear axle U-Bolts Original vs. Repop

FWIW, my u-bolts are 6-5/8" long, .465" diameter, and the threads are 1-11/16" long. There are no flat areas on the end of the U. More like the repro than what you took off your car.
Rick

Thanks Rick. Do you know if yours are originals? BTW, a check of Joe Tipoli's Chassis Restoration Guide states that the Rear Spring U bolts are 1/2" -20 -13 1/4" Dev. Lgth. Not sure what "Dev. Lgth." stands for but if it means the total length of the bar before it is shaped into a "U" then that fits with what yours measure. Looks like the ones I took off the car are not original.

[Terry M.]

Re: Rear axle U-Bolts Original vs. Repop

Thanks Rick. Do you know if yours are originals? BTW, a check of Joe Tipoli's Chassis Restoration Guide states that the Rear Spring U bolts are 1/2" -20 -13 1/4" Dev. Lgth. Not sure what "Dev. Lgth." stands for but if it means the total length of the bar before it is shaped into a "U" then that fits with what yours measure. Looks like the ones I took off the car are not original.

Developed length is what the U bolt would measure if it were straightened, or put another way just what you said: what the bar was before it was bent.

[Dennis C.]

Re: Rear axle U-Bolts Original vs. Repop

I replaced the shock mounting plate on my 61 this past fall. I took this photo then. It is not a very good photo but maybe it will help. The one caveat is I can't say for sure it is original.

Dennis

[Rick C.]

Re: Rear axle U-Bolts Original vs. Repop

Keith,
I can't be sure they are original, but I think it's a pretty good bet they are not repros since I've had the car since '73 and I don't think there was a lot of reproduction activity at that time.
Rick