Rear Axle U-bolt Torque

[FL335i]

After seeing some posts about checking the U-bolt torque., some finding them loose... Found out my truck's u-bolts were pretty loose too. They probably had about 45 LB/Ft on them. I've never touched those bolts from the factory. Truck has 41k on it. I found the below torque spec from GM. Verified I have the 14mm u-bolts. Used a 1/2" Driver, Craftsman click type torque wrench. I know it's calibrated too. I tried a 2nd click type torque wrench and it was within 1 Lb. I take care of my Torque wrenches so I know they're not way off. Long story short, I set my wrench to 59 Lb/Ft and had to tighten them more than I would of imagined and more than makes me comfortable knowing I've been driving with them on the road like that. I believe on my rock crawler I had the U-bolts cranked down to 90 Lb/Ft. They were a bit larger diameter, 5/8" maybe, aftermarket build. Either way, I looked up online a bolt torque chart and for 14mm non grade 8.8's the range was 57-85 Lb/Ft. With 70 # being the recommended. I torqued all the bolts down to 59 #'s per GM spec. Did not turn them an additional 130 degrees as some specs indicated. Then I paint marked them with a yellow industrial paint marker. Weird how loose these things were from the factory... Maybe a dealer technician can chime in here and verify the 59# spec and if the 130* Turn is specified. And if this is common for them to be this loose.

 

14mm hardware = 59ftlbs
16mm hardware = 89ftlbs.

[SouthernSilveradoGuy85]

Mine were loose, I only checked them because I sometimes had a clunk and read where that fixed most people's clunking when you give enough throttle. I remember all of mine turning at least 1 full turn when I TQed them. This was the first time using my TQ wrench for something other than TQing lugnuts after rotating the tires.

[Ron.s]

I read 78#'s somewhere after a Google search. Didn't keep the source info, hope it's right because I torqued to 70. Guess I need to visit a dealer or maybe someone can confirm for us. Mine were about 40 and this made my truck well.

Edited April 3, 2016 by Ron.s

[FL335i]

^ you're saying yours were at 40 which is close to what I came up with. Not exactly the 59 # spec. I'm 99.99% sure the spec is 59 LB/Ft for the 14mm u-bolts and 89 Lb/FT for the 16mm u-bolts. FYI... 14mm = 9/16" bolt. 16mm = 5/8" bolt. Ron, 70 is on the upper end of what a 14mm bolt can handle from the torque tables I found online. I'm sticking to my 59 #'s unless we get info that says other wise.

Edited April 3, 2016 by FL335i

[FL335i]

I've driven for 2 days and about 200 miles. Truck drives different for sure. I could put $50 on two trucks before/after and pick the one that tightened the bolts. I have not had any rear-end clunking either since I tightened them.

[zmnypit]

I put 80ftlbs on mine. A buddy put 100 on his and both drive the same now. I was scared of going over 80ft lbs as it felt the bolt was stretching.

[FL335i]

^100? On 14mm bolts. Holy cow. Without knowing the grade of 14mm bolts GM used I would not go that high. I looked up torque tables for metric bolts and the non 8.8 classes max was in the 70-85 range. I'm good with my 59#. Truck does ride differently though with tight U-bolts.

[zmnypit]

^100? On 14mm bolts. Holy cow. Without knowing the grade of 14mm bolts GM used I would not go that high. I looked up torque tables for metric bolts and the non 8.8 classes max was in the 70-85 range. I'm good with my 59#. Truck does ride differently though with tight U-bolts.

Guys in this thread: http://www.gm-trucks.com/forums/topic/183075-spring-clamps-reduce-rear-vibration/page-1 are doing 110ft lbs. If I remember correctly the the u bolts used 18mm nut.

Edited April 5, 2016 by zmnypit

[Towerhog]

Again... 59ft lbs in a criss-cross pattern. Then 130 degrees in the same pattern.

[oneandzero]

I tightened mine up to around 85 and it made my truck ride worse. I loosed them back off and left at 50 for now.

So the 130° that just tightening the nut another 130° of rotation? Can't say I've heard of this before.

[Ron.s]

Double post

Edited April 6, 2016 by Ron.s

[Ron.s]

Wow, never had this happen.

Edited April 6, 2016 by Ron.s

[Ron.s]

Again... 59ft lbs in a criss-cross pattern. Then 130 degrees in the same pattern.

Don't want to act dumb but can you clarify the 130*. Is that an additional turn of approx 1/3 after torque to 59? (360*/3 is 120*) Seems that would make final torque quite a bit higher, maybe more than 70.

I'm used to going about 1/3 each pass so that I torque each bolt 3 times-In a crossing pattern. I went 25 then 50 then 70 on my final pass. My torque wrench is old and I doubt I'm getting a full 70. According to my look up these are grade 5 bolts and max recommended is 65. (1/2" or 14 mm)

[Ron.s]

.

Edited April 6, 2016 by Ron.s

[Ron.s]

Triple post, ha ha