Broken U-bolt Help

[67lngbed]

I was taking a little trip to the dump today and when I was backing up to the dumpster there was a pop in my front suspension. At first I just thought it was normal sweeks from a 40 year old truck but one of the guys there said theres something hanging down from under my truck. When I looked I saw the passenger side lca damn near touching the ground in the back. The only thing holding up was the shock I guess my question is what would make these break other than normal use. It wasnt rusted and it just snapped in half. At least I have friends who drive tow trucks.

[oldgold70c10]

Ouch!!! Its an easy fix, but still.... Glad you weren't doing 65 or 70 when that happened.

[Longhorn Man]

Look at the U-bolt real close, you may get to see what it was. Rust could have been a factor, over torqueing upon a rebuild, under torquing, but in all reality, there shouldn't be too many factors in this.

[john]

Some model trucks have a larger U bolt, You just have to ream the holes and that should cure the prob. Not sure of what year bit a vendor should know.

[Sweet72]

This has been addressed on the forum before. Not real uncommon. There is a heavy duty replacement u bolt.

[89 crew]

with repeated beating from normal use the bolts can crystallize. it most likely started from a very minor flaw in the bolt when it was made. Does the surface that broke look rough? a bit like fine sand? If so that is the answer to why! If it doesn't then look at the way it broke. is part of the broken area dull looking? like it is an old break? If so then it could be over tightening, or over stressed. (hitting a pothole he size of a small car.) Is part of the bolt worn away? if so then it was loose. If it is a crystallized bolt then you might consider changing the other 3. they have been through just as much abuse as the broken one.

[cdowns]

are those springs cut? and are the shocks the stock ones? if so and the shocks were bottoming out it will cause the ubolt to fail//if not i'd also suspect overtorqueing//proper torque should be right about 45ft/lbs

[PanelDeland]

Even though the pic isn't a close up it appears the U-bolt is crystalized.I don't see any rust to speak of but the U-bolt is 40 years old and has probably had it's share of bumps.Just something about the way it broke makes me think it's crystalized.

[67lngbed]

Thanks guys. I bought 4 new u bolts from the gm dealer but I have not worked on the truck yet. The front is lowered and I dont know about the shocks. I bought the truck the way it sits minus the front discs. I need to drop the back down about 5" which might take a little stress off of the front end. The thing that really bothers me is that I always heard noises from the front end.even after I replaced all the balljoint and sterring setup when I did the brake swap. Could the lca's be moving inside the U-bolts. I havent looked in to how they mount on these trucks but Im getting ready to find out.

thanks
karl

[cdowns]

easy enough to check those shocks with bottom mounting bolt removed push bottom all the way up into the top then take a marker and mark on the bottom shock body the position of the top shock sleeve then when you have the suspension back together and shock installed you can tell from the mark how much shock travel you have//i'm bettin not much and that there is the cause of your ubolt failure

[BLACK AND BLUE 67-72]

I've had the exact same problem with my 67 GMC, it's done it 3 times now twice when backing up and turning and the other while going across a small ditch going forward. And every time I had repalced the u-bolts with new ones and torqued them down like they were supposed to be. Now thay make a larger u-bolt 9/16" I think to fix this problem.

[67lngbed]

Thanks for the replys.

I will look into the shock problem for sure.

Does anyone know what year trucks came with the bigger u-bolts or are they strickly aftermarket.

Thanks
Karl

[chip46wis]

I replaced mine when I dis-assembled the A-frames for paint---they had wore and I didnt like the idea they were 39 years old----new ones were $22 from GM Now Im taking others advice and replacing all the studs for my lug nuts----

[67lngbed]

I replaced 3 of the four u-bolts yesterday the guy at the dealer gave me 7 correct size nuts and nowhere sells 9/16" nuts. but the po didnt line up the holes in the cross shaft with the dowel so the front of both shafts were not tight in the cradle. So im hoping that was the whole problem.

[chris71]

67lngbd, google Fastenal, they are a bolt distributor and have a bunch of baltimore locations, only thing is they sell stuff in packs, any kinda bolt/nut you can think of, even grade 14 for the military

[jlaird]

Ok so what is the torque supposed to be on the new 9/16" ubolts. My 69 chassis manual says 40 but that is for the stock 1/2" ubolt. The 9/16" must be more than 40. I found the attached word file that says 85, but seems like quite a difference. It sounds like this is important to torque correctly, so that is why i'm asking.

[67lngbed]

I probably should have asked that question myself. I just made them very tight and used red locktite just to make sure they didnt fall off. Let me know If you find out for sure.

[haysonj]

The nuts on those u bolts are crimp lock nuts and are not supposed to be reused. I had a shop put an a-arm on my one ton and the u bolts worked there way off in less than a month