Jump to content

U Bolt Tightening

THEREED

Recommended Posts

THEREED Enthusiast

THEREED

Posted
Posted

I have a 2014 CC AT and based on forum feedback decided to check my rear leaf spring u bolts. I tightened them to 59# and was amazed at how much I had to tighten a couple of them.

 

Drove it around today and I was amazed at how noticeable the difference is with the tighter bolts. A lot less clunk over big bumps and no more passenger seat vibration. The vibration before wasn't awful but seat headrest would vibrate at almost all speeds. This seems to fix it completely just by taking 10 mins with a torque wrench.

 

I'll consider this the second best thing I learned on this forum (turning off grade braking is number 1)!

 

 

Sent from my iPhone using Tapatalk

  • Replies 31
  • Created
  • Last Reply
SkiDooNick700 Enthusiast

SkiDooNick700

Posted
Posted

Agreed, I went under the truck one night with a torque wrench set to 50lbs and got like a half turn. My last trip to the dealer I asked my service writer about it he said they'll check it when its on the lift for the oil change. They torqued to 70 something and it really is amazing, and no more clicking sound on take off either.

Ron.s Enthusiast

Ron.s

Posted
Posted

You need to replace the U Bolts. Not only GM but all axel and spring guys will say the same thing. It's likely that they were torqued to spec at the factory and that results in the bolt and/or threads stretching. What caused them to loosen is anyone's guess but it may be the shims wore in or took a set. And the GM spec is torque and Angle (59/130*)-most of us haven't spent $975 for a digital torque wrench so can't torque to spec anyway. I went to a local shop and they up sized mine to 9/16" and torqued to 125#'s. Most shops make their own U Bolts-unplated 9/16" with rolled threads, grade 5 is what I have now. For $40 it's not worth the risk of using the old ones again, IMO.

Towerhog Enthusiast

Towerhog

Posted
Posted

Ok guys. The correct torque for the u bolts is as follows. Final torque is 59 ft-lbs plus an additional 130 degrees of rotation. Of course, this is on new u bolts. If you're stopping at 59 ft-lbs, then thats not nearly tight enough.

kp52 Enthusiast

kp52

Posted
Posted

I just did mine at 60 and left them a few minutes ago, they few I checked were at around 40-45 ft/lbs before they moved.

 

Most likely the spring pack compresses over time and some preload is lost. I didnt have any noise or any other issues, was just checking the air in the spare and figured I'd have a look since I was under there. If everything was fine at 40-45 ft/lbs it should be good at 60.

bgweed Enthusiast

bgweed

Posted
Posted

You need to replace the U Bolts. Not only GM but all axel and spring guys will say the same thing. It's likely that they were torqued to spec at the factory and that results in the bolt and/or threads stretching. What caused them to loosen is anyone's guess but it may be the shims wore in or took a set. And the GM spec is torque and Angle (59/130*)-most of us haven't spent $975 for a digital torque wrench so can't torque to spec anyway. I went to a local shop and they up sized mine to 9/16" and torqued to 125#'s. Most shops make their own U Bolts-unplated 9/16" with rolled threads, grade 5 is what I have now. For $40 it's not worth the risk of using the old ones again, IMO.

As long as you are replacing U-bolts, what about flipping them?

Zachlovesfood Enthusiast

Zachlovesfood

Posted
Posted

If you've never taken the u-bolts completely off, but simply tightened them more, there's no need to buy new ones IMO. Especially on a half-ton truck...

My u-bolts were under torqued from factory. I probably stretched those bolts for the first time by tightening them. I went over 100 ft. lbs.

I like it tight!

I've had no issues whatsoever. If I had to take my current u-bolts off now, I would definitely put a new set on for reassembly.

I just don't see the point if they weren't stretched in the first place, unless you're upgrading them... Heavy duty u-bolts are probably a must for people who tow heavy and regularly.

Just my .02

 

 

Sent from my iPhone using Tapatalk

SouthernSilveradoGuy85 Senior Enthusiast

SouthernSilveradoGuy85

Posted
Posted

If you've never taken the u-bolts completely off, but simply tightened them more, there's no need to buy new ones IMO. Especially on a half-ton truck...

My u-bolts were under torqued from factory. I probably stretched those bolts for the first time by tightening them. I went over 100 ft. lbs.

I like it tight!

I've had no issues whatsoever. If I had to take my current u-bolts off now, I would definitely put a new set on for reassembly.

I just don't see the point if they weren't stretched in the first place, unless you're upgrading them... Heavy duty u-bolts are probably a must for people who tow heavy and regularly.

Just my .02

 

 

Sent from my iPhone using Tapatalk

 

That's what I've always thought. It's not tightening them more, it's when loosening them when any bolt with high stress needs replacing. Usually head bolts and main bearing bolts for the crank. I TQed my u-bolts without loosening them when I first read about how people were finding the nuts not TQed causing the clunking. I think it was about 2 years ago and haven't had a problem with any clunking coming back and I don't drive it too easy.

Zachlovesfood Enthusiast

Zachlovesfood

Posted
Posted

 

That's what I've always thought. It's not tightening them more, it's when loosening them when any bolt with high stress needs replacing. Usually head bolts and main bearing bolts for the crank. I TQed my u-bolts without loosening them when I first read about how people were finding the nuts not TQed causing the clunking. I think it was about 2 years ago and haven't had a problem with any clunking coming back and I don't drive it too easy.

It definitely fixed my clunking and vibrating as well. I think these GM bolts are highly underestimated. Once properly torqued, they're good to go!

And quite honestly, I've never ever read of someone popping a rear u-bolt on these new trucks. I can imagine it wouldn't be an easy task, even if you were trying for it!

 

 

Sent from my iPhone using Tapatalk

SouthernSilveradoGuy85 Senior Enthusiast

SouthernSilveradoGuy85

Posted
Posted

It definitely fixed my clunking and vibrating as well. I think these GM bolts are highly underestimated. Once properly torqued, they're good to go!

And quite honestly, I've never ever read of someone popping a rear u-bolt on these new trucks. I can imagine it wouldn't be an easy task, even if you were trying for it!

 

 

Sent from my iPhone using Tapatalk

 

The way I drove and treated my '98 that would have been when a u-bolt would break. All the burnouts, going around corners too fast (while still being able to stay in my lane) and mudding/off road I'm surprised more didn't get messed up on it too be honest.

Zachlovesfood Enthusiast

Zachlovesfood

Posted
Posted

 

The way I drove and treated my '98 that would have been when a u-bolt would break. All the burnouts, going around corners too fast (while still being able to stay in my lane) and mudding/off road I'm surprised more didn't get messed up on it too be honest.

Haha, that poor truck! Can't deny the fun though, good times are good times.

 

 

Sent from my iPhone using Tapatalk

Ron.s Enthusiast

Ron.s

Posted
Posted

There is some bad advice posted in some of these responses. It's your truck and you can do what you want but take some time to research torque and U bolts. The GM spec is intended to maximize clamping force and if done correctly stretches the bolt so that it should not be used again. This is standard advice from any suspension guru. It's customary to add a lubricant to the threads like never seize so that you create less friction. Friction creates resistance and can distort actual final torque. That's why torque for a plated bolt is lower than an unplated, the plated has less friction. The GM UBolt is 1/2" but measures close to 5/8" at the threads since they have cold rolled threads. The bolt torque spec is based on a 1/2" bolt and 100 lbs is way over max. It's the act of torquing that stretches the bolt not taking it loose. And how accurate is your torque wrench? My dealer has a Snap On Digital wrench-they are very accurate, measure torque and angle and cost about $975.

What happens if you over torque the U Bolt? It will likely fail in some way and it may not be apparent and may not happen tomorrow. In my situation I retorqued mine to 70#'s and felt uncomfortable knowing that it was a guess on my part. And I was uneasy wondering why they came loose from the factory!

This resolved my issues for a few months but things began to change back so I attempted to remove the nuts to lube and retorque them since one was loose again. The threads on one had galled and I could not remove without using my impact wrench. I'm assuming that the loose one was actually the bolt stretching, doubt the nut came loose. In between I had made two dealer visits and they were no help, "no problem found".

I went to a suspension shop and had them replace with a larger diameter UBolt and have a few thousand miles with no issues. They told me that a bolt stretched beyond spec will eventually break. Metallurgy can vary so some bolts are better than others. Their advice is to always replace since there is no way to know about the bolts integrity once it's been torqued to max. (Outside of a lab) I had mine replaced for less than $40 so why gamble???

SouthernSilveradoGuy85 Senior Enthusiast

SouthernSilveradoGuy85

Posted
Posted

There is some bad advice posted in some of these responses. It's your truck and you can do what you want but take some time to research torque and U bolts. The GM spec is intended to maximize clamping force and if done correctly stretches the bolt so that it should not be used again. This is standard advice from any suspension guru. It's customary to add a lubricant to the threads like never seize so that you create less friction. Friction creates resistance and can distort actual final torque. That's why torque for a plated bolt is lower than an unplated, the plated has less friction. The GM UBolt is 1/2" but measures close to 5/8" at the threads since they have cold rolled threads. The bolt torque spec is based on a 1/2" bolt and 100 lbs is way over max. It's the act of torquing that stretches the bolt not taking it loose. And how accurate is your torque wrench? My dealer has a Snap On Digital wrench-they are very accurate, measure torque and angle and cost about $975.

What happens if you over torque the U Bolt? It will likely fail in some way and it may not be apparent and may not happen tomorrow. In my situation I retorqued mine to 70#'s and felt uncomfortable knowing that it was a guess on my part. And I was uneasy wondering why they came loose from the factory!

This resolved my issues for a few months but things began to change back so I attempted to remove the nuts to lube and retorque them since one was loose again. The threads on one had galled and I could not remove without using my impact wrench. I'm assuming that the loose one was actually the bolt stretching, doubt the nut came loose. In between I had made two dealer visits and they were no help, "no problem found".

I went to a suspension shop and had them replace with a larger diameter UBolt and have a few thousand miles with no issues. They told me that a bolt stretched beyond spec will eventually break. Metallurgy can vary so some bolts are better than others. Their advice is to always replace since there is no way to know about the bolts integrity once it's been torqued to max. (Outside of a lab) I had mine replaced for less than $40 so why gamble???

 

Yes of course tightening is what stretches the bolt, but we said it's when you loosen it after it's been TQed is when a bolt like that should be replaced. If all you do is re-TQ it then it shouldn't have to be replaced since it's just stretching a little bit more. Loosening it will make it contract so re-TQing the same bolt weakens the bolt. The bolt won't contract if you just TQ it tighter without loosening it. It might be a better piece of mind to replace the u-bolt anyways, but I honestly don't see how just re-TQing without loosening would make the bolt weaker. But I also guess we both will believe what we want to believe.

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.

  • Forum Statistics

    250.5k
    Total Topics
    2.7m
    Total Posts

  • Member Statistics

    342,947
    Total Members
    8,960
    Most Online
    Sothpaw27
    Newest Member
    Sothpaw27
    Joined

  • Who's Online   2 Members, 0 Anonymous, 423 Guests (See full list)

  • Latest Articles

  • Posts

    • Grumpy Bear
      Some Assembly is Required

      By Grumpy Bear · Posted

      www.enginelabs.com/news/what-i-learned-today-bearing-clearances-vs-oil-viscosities/     www.enginelabs.com/news/oil-viscosity-can-the-numbers-be-misleading/ The Big Lie… Coming full circle to the reason Lake discusses the Porsche engines in particular. Based on the 2000 samples in the SPEEDiagnostix database, increasing the oil viscosity in these engines, even those run on the track, showed no significant difference in results.   The smoking gun was in the oil chemistry. That is where the data shows higher instances of more wear. Molybdenum was the key; the higher the amount, the less the wear. Speed postulates that higher viscosity oils have more thickeners to artificially inflate their viscosity numbers. These thickeners lose viscosity under shear, and the result is that not all oils of the same viscosity have the same shear stability.   Having enough viscosity is the most important characteristic, but according to Speed, once that required viscosity level is reached, additive chemistry matters more than additional viscosity. Speed also states, oil pressure problems on the racetrack aren’t a viscosity problem; it’s an oiling system problem. Running a thicker oil is just a band-aid for an underlying oiling system problem.
    • Grumpy Bear
      Some Assembly is Required

      By Grumpy Bear · Posted

      Can it still be Assembled II?   Viscosity on the decline by various means. Heat on the rise making that worse. Engine RPM in the tank. Smaller motors with more boost trying to emulate an electric motor. Full torque, zero rpm. Then we will triple the OCI. Argh.    But wait....there is more. LSPI has pushed a shift from Ca to Mg and as that cost more PLUS the run to lower sulfur compounds the TBN is moving in the wrong direction for the increased OCI's demanded.    That not being enough to placate a demand for a parameter they can't measure the other sulfur bearing compounds are also under attack. That would be zinc and phosphorus sulfonate compounds. To some degree those are being replaced with boron esters and others, i.e. titanium ect. All of which have shorter service lives. And there there is the "Secrete Sauce" marketing for AW adds that 'Can't be detected by UOA's" but trust me because I (the blenders) never ever lie.    Spoiler alert; ALL additives are sacrificial! Smaller amounts of the old blended with less robust versions of the new do not equal longer service lives. So what are the blenders recommending? Wait for it.......   MOVING THE GOAL POSTS! OMG      Let's declare the long standing TAN/TBN crossover irrelevant and tell people that soot is a great 'graphite' based lubricant which can aid tribo films. Wait, what? Let's declare that the standards used for oxidation and nitration were to conservative and can be expanded. Let's tell them that because GDI fuel dilution, although being a VISCOSITY KILLER and an acid generator is actually okay because we have better base oils that limit viscosity failure limits. (Said knowing this is measured in fractions of a centipoise and in bases not commonly used in shelf oils)   Lying from the heart is not just the new normal but we have a public, a very young public, that is so ignorant of the facts and so sure of their "RESEARCH" into AI driven models base in regurgitated  instead of scientific research based unvarnished, peer reviewed FACTS that the incoming guard is loosing their grip on reality and the OEM's are tickled pink while the blends bend the knee.    You have an ever limited set of tools to work with. And sooner or later those will be taken from you as the API and the EPA strangle the last remaining fluids from the system. What you have left is your wits. If you care to use them.    At some point in the very near future it will not longer be possible to do "What is best for the machine", and be replaced with "The best you have access too". You WILL be rewarded with half the life and twice the cost. That isn't that hard to predict.         
    • Chuck FB
      Software Update

      By Chuck FB · Posted

      I trust you saw the other comment where he knew what he was talking about !. Yes, these darned newer vehicles with all their so smart they are stupid technology, goes and drains the battery down. As you might see my other comment, I installed a Noco 5 battery tender under the hood and at this point still have the cord routed so I have to lift the hood and then plug it in but am typically parked in a garage or a shed so its not risking the engine hood in the wind. That way I am assured or hopefully so of not finding I have a battery drawn down and can't even start the truck and that also damages the battery to draw it down too far. 
    • Chuck FB
      Software Update

      By Chuck FB · Posted

      I guess no surprise my guesses were wrong !, at least now I know if I ever happen to see it grayed out in my own truck as to what is going on.    I never happened to catch my truck with it grayed out, it seemed every time I would test to see if there was an update it never found anything and yet more than once I would check to see if there was an update and there was nothing, then a day later or even that same morning I would drive to town and after more than one engine shut down in town as I did my errands it would pop up that there is an update now ready to install and the only place I have a connection to the internet is at home by wifi so its not as if it grabbed the download while driving. I don't trust these new vehicles due to all the crap they can decide to do while sitting for some days not running and run the battery down so most of the time if I know the truck will sit for a few days I plug in the battery tender I have mounted under the hood and so the only time the truck must have downloaded software was when it was sitting in the garage where the signal is awful but I have that tender plugged in and somehow it managed to download it. I honestly detest all this crap, way to easy to leave a person stranded.    Since I don't trust any of it I don't do the install of the already downloaded software until I get home and sometimes have even sat in the truck to watch what its doing as its going through the process to its conclusion as its not like it is set up that it will tell you the next time you fire up the engine that the update that was initialed actually installed or installed properly. Yes I can go into the updates and see the list. After I go through the install where I feel its safe to do so in case it breaks down as a result, I will plug in the battery tender after the fact to recharge as I don't know how much power its taking just to do the install and that can take a while for it to install. 
    • nfisherman
      Software Update

      By nfisherman · Posted

      Thanks for the reply. All settings were correct and the engine was off, as it was supposed to be. It turned out to be something simple. I took a drive for about an hour. I must have had a low battery without knowing it. The voltage gauge on the display looked ok. At the end of my drive, I shut off the engine and the update prompt came up and it updated normally. It’s ironic because one of the features of the update is a reduction of battery drain. 

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...