Securing axle U-bolts

[eggsalad]

Having decided my mono-leaf idea was a bust, I set out to reassemble my two-leaf springs, clean and paint everything, and reassemble.

The spring-to-axle U-bolts were originally installed with lock-washers. That was state-of-the-art in 1986, I suppose.

I'm more inclined to replace the lock-washers with flat washers and use blue Loctite on the nuts. I don't want to use nylock nuts because I will spend forever spinning them down the U-bolts.

What say the hive mind?

-eggsalad

[Treeview]

I've worked on leaf springs on small trailers up to heavy duty over the road trucks. All of the nuts that I've come across are about twice as long as their normal cousins. In the heavier load springs they've been fine threaded too. If I were concerned about a nut loosening I'd either use the appropriate Lock-tite, and NO other brand!, ointment

Double nutting works too. Tighten the first one to the required torque then run the next one up snug, hold the first in place and tighten #2 to the same torque.

Tom

[MtnDon]

Any place of moderate population should have a spring and axle specialist. Most of the customers will be trucks. The good ones can form u-bolts to almost any size radius bend and length. The best u-bolts have fine threads and the long nuts as mentioned.

Green loctite is handy for application after the things are tightened.

Nylock nuts are best spun with deep sockets and an air tool.

Final tightening is best performed with a torque wrench to specs and rechecked after some road miles. Do that with fine threads and you do not need the loctite. Torquing stretches the bolt just enough to maintain tension and keep the nuts tight.

[Shadow Catcher]

Because it is old technology does not mean it does not work well
http://www.portlandbolt.com/products/wa ... asher.html

[48Rob]

All the vintage trailers I've ever worked on, and most newer ones, employ lock washers.
I've never found a loose one.

Rob

[jgrote]

I would just use lock washers. They are your best option in this application. If I really don't want a nut to come off unless Itake it off, I'll use an awl and hammer to pound a small dent into the first exposed thread next to the nut. It takes a little experience to know just how much is enough to keep the nut secure, but not so much that you'll never get it apart later. If I REALLY, REALLY want to make sure a nut will stay in place, I tack weld the two together. Then all I have to do later is cut the weld to get it apart. But that is more time consuming and takes more tools....

[Dale M.]

Another option is a self locking nut.... they usually have special markings and crowned top, and are slightly distorted to look at them.... With locking nuts, you can forget lock washers, but have same tightening issues as nyloc's, deep sockets and impact (air or electric) tools are a blessing...

http://www.fastenersplus.com/products/n ... QgodmEMA2Q

All the spring shackles and u-bolts on my manufactured car carrier (tandem axle) use these....

Dale

[eggsalad]

Another option is a self locking nut.... they usually have special markings and crowned top, and are slightly distorted to look at them.... With locking nuts, you can forger lock washers, but have same tightening issues as nyloc's, deep sockets and impact (air or electric) tools are a blessing...

http://www.fastenersplus.com/products/n ... QgodmEMA2Q

All the spring shackles and u-bolts on my manufactured car carrier (tandem axle) use these....

Dale

This.

I went with the all-metal locknuts known as C-Lock nuts. My friendly, local, obscure hardware store had them on the shelf for $0.19 each in the 3/8"-16 size I needed. I added Loctite 242 for "suspenders and a belt" action.

[Kody]

One of the most vital points that no-one mentioned was the application of oil, grease or "Anti-seize" on the threads of the U bolt and the nut/s. It is absolutely essential NOT to apply grease or Anti-seize to the U bolts and the nuts. A very light application of oil can be used but only very little. If I need to use a lubricant on the threads, I use a quick spray of WD 40. If you use Anti-seize on these threads, you seriously risk stripping the thread if you tighten the nuts with a torque wrench and even more so if you tighten using the Strong Arm method. If the threads don't strip, you run a very high risk of the bolts snapping from the shock loads they endure. A nut/bolt, tightened to a specific torque as given by the manufacture of the trailer or bolts, will, when tightened after applying Anti-seize, will be over torqued by a factor of 5 or a lot more. The bolt torqued to this limit will suffer fatigue very quickly and or snap when it suffers an overload from a severe bump in the road. Anti-seize must never be applied to the studs of car wheels, trucks and especially boat trailers. It must never be used on highly stressed machinery as I have seen done in my travels. The correct lubrication is the amount of oil that the new bolt comes with. A bolt with fine threads is the most easily over tightened when using Anti-seize and also the most dangerous. The imposed tension load can be as high or higher than a factor of 8.
If you spin down the self locking nuts with a nylon insert using a high speed air tool, the friction of the nylon can actually melt the nylon and the self locking ability is destroyed. The use of Loctite is of great benefit in locking the nuts of U-bolts. If you are concerned about the exposed threads rusting, a light spray with a cold gal paint will solve this problem. Anti-seize has some wonderful areas for using it but never use this stuff on U bolts or car wheel studs.

Kody

[Dale M.]

Think you factoring numbers are a little high..... My reference materials, state to reduce torque anywhere from (dry torque values per bolt size) 25% to 55%, DEPENDENT of type of lubrication used on threads....

Them again I may be interpreting your "factoring" number wrong, but any bolt that is torqued to 5 times its rated value is sure to have real loss of structural integrity if not already broken...

Dale

[eggsalad]

One of the most vital points that no-one mentioned was the application of oil, grease or "Anti-seize" on the threads of the U bolt and the nut/s. It is absolutely essential NOT to apply grease or Anti-seize to the U bolts and the nuts. A very light application of oil can be used but only very little. If I need to use a lubricant on the threads, I use a quick spray of WD 40. If you use Anti-seize on these threads, you seriously risk stripping the thread if you tighten the nuts with a torque wrench and even more so if you tighten using the Strong Arm method. If the threads don't strip, you run a very high risk of the bolts snapping from the shock loads they endure. A nut/bolt, tightened to a specific torque as given by the manufacture of the trailer or bolts, will, when tightened after applying Anti-seize, will be over torqued by a factor of 5 or a lot more. The bolt torqued to this limit will suffer fatigue very quickly and or snap when it suffers an overload from a severe bump in the road. Anti-seize must never be applied to the studs of car wheels, trucks and especially boat trailers. It must never be used on highly stressed machinery as I have seen done in my travels. The correct lubrication is the amount of oil that the new bolt comes with. A bolt with fine threads is the most easily over tightened when using Anti-seize and also the most dangerous. The imposed tension load can be as high or higher than a factor of 8.
If you spin down the self locking nuts with a nylon insert using a high speed air tool, the friction of the nylon can actually melt the nylon and the self locking ability is destroyed. The use of Loctite is of great benefit in locking the nuts of U-bolts. If you are concerned about the exposed threads rusting, a light spray with a cold gal paint will solve this problem. Anti-seize has some wonderful areas for using it but never use this stuff on U bolts or car wheel studs.

Kody

When I lived in Michigan, I used anti-seize on dang near everything. Now that I live in the desert, the can sits lonely on the shelf. When I took the 28-years-assembled U-bolts off the trailer, the only impediment to loosening was paint.

I love the desert!

[Kody]

Hi guys,
I appreciate your replies re. Anti-seize, thanks for your input. When I worked for a major oil company in Ohio as an engineering instructor, I watched in some horror as I saw the fitters re-assembling the ammonia compressor. This compressor was similar to a VW engine, it was a flat four cylinder design and it was huge. The cylinders were held together with six long studs, at least 1-3/4 inches in diameter and about 18 feet long. The work crew were tightening the nuts down and using "Anti-sieze" on the stud threads, on the nuts and under the washers. I could see where this was so wrong so I contacted two of the major bolt manufacturing companies in the US for info. I showed the replies to the chief engineer/s and they were horrified to see the info I had collected. The results of the ammonia compressor shattering or exploding boggles the imagination. The compressor works 24/7 under huge stresses and was something not to be taken for granted. I still have the info from one of the bolt manufactures but have lost the other info somewhere in cyber space. If any one would like to read it, let me know and I will try and find it in my records and print it for you. The tensile load of 5 times being applied to the studs is correct.

Kody

[Dale M.]

Your experiences may be unique and not to take anything away from warnings, but for the average "Joe" building "something" the included graphic probably gives enough information that the average guy does not damage or weaken bolts when doing assemblies...

bolt torque.jpg (29.9 KiB) Viewed 1688 times

Dale

[KCStudly]

I'm with Dale; the lowest reductions that I have seen listed for common materials and fasteners with moly or high heat nickel lube is about 55/ct. That is a huge reduction in torque from a dry spec on unplated fasteners, no doubt, but not 8 or 10 times.

Your point is valid, tho. When using lubes, locking compounds (they act like lube) or non-standard fasteners (stainless, plated, etc.) consult a torque chart table. Torque spec.'s are based on an assumed level of friction and anything you do that affects that friction will change the amount of torque needed to stretch the fastener to the desired 80/ct of yield. This is why high perf engine builders measure actual connecting rod bolt stretch directly (the most critical fasteners in any engine), rather than using a torque wrench. What you are actually trying to achieve is the correct percentage of stretch to put the bolt just below its yield strength (if correctly designed, the fastener will never go plastic under load, so if you stretch it to very near plastic it will always be tighter than any operational load attempting to separate it). Torque readings are just an estimate to approximate that stretch. Add lube and it takes a whole lot less torque (due to less friction) to achieve the same amount of stretch.

It is often times very unclear what the OEM torque spec is based on. I have found situations where the OEM gave a torque spec in one place, then advocated the use of high temp lube in another, and the fasteners failed just from applying the specified torque. Had to call them up and tell them that their manual was wrong; and they ended up agreeing, sending me all new fasteners for free (big access cover on a catalytic exhaust converter for a stationary generator).

[H.A.]

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