Nut and Bolt Torque

Is anyone familiar with torque specs? I'm replacing the UCA front bushing bolts, and I'm confused about which bolts would be best. My '92 had star-drive heads, and the manual calls for 55 pound ft. The only way to meet or exceed this is to go to 7/16" bolts, (which will fit thru the bushing sleeve itself, but the control arm holes must be opened up a little) and use the fine thread (20 tpi vs 14 tpi). What I'm asking is, are the nuts for the 7/16" bolts (or any size for that matter) up to the task of the recommended torque for the bolt? Typically, torque specs deal with bolts. All are Grade 8, by the way. A while ago, I installed urethane bushings, and every so often, the bolts like to rattle loose. Is there a trick to keeping them tight without resorting to a thread locker type product? Thanks...

i get my 2 foot craftsman breaker bar and tighten them till i feel them stretch...then i check them again every time i offroad. Otherwise...nothin wrong with a little lock tight blue.

as far as nuts go... im sure there's a spec. somewhere. you could get a higher grade bolt/nut.

Torque has nothing to do with the strength of a bolt. Torque can be adjusted by lubrication (a bolt coated in SAE 20 is torqued 28% tighter than a non-coated bolt and SAE 40 is 31% yet the bolt is the same strength fine thread and course thread don't change the the strength either. A grade 8 bolt is still made of 150,000 psi steel. What is the strength of the original bolt? Also they make a grade 8 nut I'd use it it you are worried about the nut. The local ACE hardware sells them. They also have grade 8 flats if you need them. As for them rattling loose why do you not want to use lock tight? I have seen stuff set to the proper torque come loose from vibration. If vibration is an issue I'd use lock tight or you could smack the threads with a punch.

If vibration/loosening is an issue for you, you could use LocTite (I do anyhow - it also helps prevent corrosion and seizing, believe it or don't,) or go with a "deformed thread" locknut. I just can't bring myself to trust Nylon collars on suspension (even though I'm sure they work well.)

Installation torque for a bolt is actually measuring tension on the bolt - it's an estimate of applied preload. This helps to make the mechanical properties of the fastener/material more predictable. It also causes slight deformation of the threads, which helps prevent loosening in service.

The principal failure mode for a bolt is in tension - when the bolt is literally pulled apart endwise (it may also shear.) Either way, the critical dimension for calculating that critical load is the minor diameter of the thread - or the diameter through the thread root (bottom of the "V") Threads don't often pull out in steel, which is why a nut is not necessarily critical in calculating that - but you should use the same grade nut as you do bolt, just for consistency's sake.

There is no reason at all that a 3/8", 7/16", or 10m/m bolt will not be able to live nearly forever with an installation torque of 55 pound-feet - I've seen 1/4" bolts last years with that load.

As far as telling what the OEMR bolts were, what were the markings on the head? If they're numbers, it's a metric bolt (and the numbers are the ISO "property class" - 8.8, 9.8, and 10.9 being common,) and SAE H&T bolts have "hash marks" on the head - add two to the number of marks to get SAE grade (most common being three marks/Grade 5, and six marks/Grade 8.)

Anything else?

Actually, I just did all this.

You should use METRIC M10 bolts 70-80mm long depending on the type of UCA you're installing. Since they are metric, strength is an ISO grade and ISO Grade 10.9 is specified. That is slightly (only slightly) weaker than a GRADE 8 SAE bolt.

The "star" heads you spoke of are actually T55 Torx heads. DEALER OEM's are actually ISO 10.9 M10x70mm TORX. I installed 80mm lengths (hex head) as I have RE Adjustables and need the extra width.. I then torqued to spec.

This has been beat to death in so many threads lately. You can get any bolt you need as well as read up on all bolts and strengths and hardnesses at

http://www.boltdepot.com