Stock Ubolt Replacement

[Schurkey]

What is the diameter of the GM U-bolts? Do the dual-wheel trucks get thicker bolts?

My '97 C/K manual shows
C/K 1500 and 2500 at 81 ft lbs.
C/K 3500 WITHOUT dual wheel or 454, 81 ft lbs.
C/K 3500 Dual wheels OR 454, 109 ft lbs.
C3500HD, 187 ft lbs.

Which, translated, means 8.5" or 9.5" axle at 81 ft lbs. 10.5" axle at 109 ft lbs, and the bigass Dana 70 11" axle at 187 ft lbs. This manual often "forgets" about the 454 8-lug 2500s as having the same equipment and torques as the 3500s.

 

[evilunclegrimace]

What does it take to crush/distort the axle tube?

800 ft/lbs on a 9/16 U-bolt? Doesn't sound reasonable.

(Advertised torque ratings of impact wrenches seem to have only a fleeting relationship to reality.)

There's also the matter of fine-thread vs. coarse thread. The original U-bolts on my K1500 had coarse threads, the replacement U-bolts had fine threads. That's gonna screw with the torque recommendations.

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I agree, and another thing to keep in mind is the fact that when torque recommendations are exceeded you stretch the bolt and threads beyond their yield strength and that increases the likelihood of failure.
The U bolt toque on an International 9300 Semi truck is only 450 lb. ft. There are 24 nuts on a Semi's u bolt's, ask me how I know.

 

[evilunclegrimace]

What is the diameter of the GM U-bolts? Do the dual-wheel trucks get thicker bolts?

I do not remember off hand, but I think that they do.

 

[evilunclegrimace]

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[evilunclegrimace]

If you read this a MAXIMUM recommendation for U bolts. A 9/16-inch u bolt has a MAX torque of 131 lb. ft.
A 7/8-inch u bolt has a MAX torque of only 710 lb. ft. There are not any 7/8-inch u bolts on C/K suspension and tighter is not always better.

 

[Supercharged111]

The factory torque spec is 81 lb. ft. for single rear wheel trucks and 109 lb. ft. for dual rear wheel trucks.

With factory bolts, sure. Take a look at Schurkey's post for more variables. My 9/16 bolts were torqued I guess somewhere in the low 100s with a gun and they came loose. I honked them down with a breaker bar after that. Good to go.

 

[stutaeng]

What is the diameter of the GM U-bolts? Do the dual-wheel trucks get thicker bolts?

My '97 C/K manual shows
C/K 1500 and 2500 at 81 ft lbs.
C/K 3500 WITHOUT dual wheel or 454, 81 ft lbs.
C/K 3500 Dual wheels OR 454, 109 ft lbs.
C3500HD, 187 ft lbs.

Which, translated, means 8.5" or 9.5" axle at 81 ft lbs. 10.5" axle at 109 ft lbs, and the bigass Dana 70 11" axle at 187 ft lbs. This manual often "forgets" about the 454 8-lug 2500s as having the same equipment and torques as the 3500s.

This is what I recall from a thread here from last year or so.

The 454 2500/3500 and 3500 DRW got the thicker u-bolts, and therefore, the tightening torque is higher.

I thought these ubolts were TTY, but I don't believe that's a true statement. So torque applied is a clamping force to the axle tube?

That table is a good reference though. But isn't the 1/2" diameter too low? Not that any of these trucks had u bolts that thin...

 

[evilunclegrimace]

With factory bolts, sure. Take a look at Schurkey's post for more variables. My 9/16 bolts were torqued I guess somewhere in the low 100s with a gun and they came loose. I honked them down with a breaker bar after that. Good to go.

I under stand that different bolts have different torque specs . You stated that you "torqued your bolt to the 100's on a guess and they came loose" that is a perfect example of why you use an actual torque wrench and then retorque certain fasteners after a specified time/mileage.

 

[evilunclegrimace]

This is what I recall from a thread here from last year or so.

The 454 2500/3500 and 3500 DRW got the thicker u-bolts, and therefore, the tightening torque is higher.

I thought these ubolts were TTY, but I don't believe that's a true statement. So torque applied is a clamping force to the axle tube?

That table is a good reference though. But isn't the 1/2" diameter too low? Not that any of these trucks had u bolts that thin...

Yes the table looks like a misprint for the 1/2" bolt

 

[johnckhall]

Now I think it’s clear. Somewhere between 81-800 ft/lbs. As a follow up , I torqued them yesterday to 90 as recommended and will check again in 50 miles. I might check them in a couple of days just out of precaution.