Lower Control arm bolt comes loose

[55 Tony]

Lucky I caught this again, the rear bolt in the lower control arm was about to fall out. This happened before and I put locktite blue on it and torqued it to 55'# but it came loose again. While under there I checked the rest of them and the drivers side rear was loose 3/4 turn. It has been years and thousands of miles since last time I checked them, but WTF? I think it may be greasy inside the female threads so I sprayed it with carb cleaner and ran the bolt through a few times. Then I used the blue locktite and put it in and out 3 times with more locktite on each time. I have heard of this happening to others long ago on another group. The bolts had lockwashers, maybe I should try some double star lockwashers? Or should I clean it better/again and use red locktight?

[BamaNomad]

Are you referring to the bolts which hold the control arm shaft to the frame? (75 ft lbs), or the bolts which hold the control arm to the shaft? (55 ft-lbs, but don't torque until the car weight is on the wheels)...

If your bolts are properly torqued and working out, then something is wrong. I'd suggest removing the bolts, cleaning them thoroughly and lightly oiling and re-installing. These bolts should have a lock washer then the large 'washer', then the rubber. The friction of the rubber should prevent most of it from moving along with the lock washer. I've never thought of putting lock tite on those but I've never heard of them working out. Do you have non-rubber (poly?) bushings??

[55 Rescue Dog]

I would just put in new bolts, and use what a lot of OE's do, and use what I think used to be called Stover nuts. The ones that are dimpled so they turn hard, even when installing them. That is what are used on the C4 front suspension, and many other cars. Even good old safety wire, or a cotter pin would at least keep them from falling off. The a-arm bolts also need to compress on a sleeve too.

[55 Tony]

There are about ten or so accounts of this happening on the other group in just one thread, and one post says there was another thread about the same problem.

[chevynut]

I don't see what "problem" new bolts solve. Bolts don't just wear out and start loosening and the old bolts should be fine. There's no reason to replace bolts just to replace them. If it's the a-arm to shaft end bolts loosening, you aren't tightening them correctly or they're turning with suspension travel. Like bamanomad said, they need to be tightened to spec at ride height. If they're turning out, they're not compressing on the bushing sleeve tightly enough to keep the bushing sleeve from rotating or the serrations on the sleeve are worn out. Rubber bushings are bonded to the sleeves and they want to twist the bolt loose as the suspension moves. But if they're tightened properly it shouldn't happen. Millions of cars used the stock bolts and bushings with no problems.

Do you have the stock rubber bushings or urethane bushings? Urethane bushings aren't bonded to the sleeves and should rotate on them. IMO that makes them better than rubber.

[chasracer]

I think cleaning all the threads again with carb cleaner, let it dry out good and blue loctite would be fine. The way those work from the factory is the inner sleeve has the teeth or knife edging that the large washer rides against - there is friction there and it basically slows the a-arm down. In a drag racing setup, we would take large inside diameter washers that would fit over those teeth and allow the stock larger washer to glide freely. Other guys would grind the teeth down and achieve the same deal. Anyway, this would free up the a-arms and allow the front end to transfer weight back to the rear tires a bit quicker.

[NickP]

I don't see what "problem" new bolts solve. Bolts don't just wear out and start loosening and the old bolts should be fine. There's no reason to replace bolts just to replace them. If it's the a-arm to shaft end bolts loosening, you aren't tightening them correctly or they're turning with suspension travel. Like bamanomad said, they need to be tightened to spec at ride height. If they're turning out, they're not compressing on the bushing sleeve tightly enough to keep the bushing sleeve from rotating or the serrations on the sleeve are worn out. Rubber bushings are bonded to the sleeves and they want to twist the bolt loose as the suspension moves. But if they're tightened properly it shouldn't happen. Millions of cars used the stock bolts and bushings with no problems.

Do you have the stock rubber bushings or urethane bushings? Urethane bushings aren't bonded to the sleeves and should rotate on them. IMO that makes them better than rubber.

For the most part I would agree with this complete statement. Actually, I don’t disagree but just question it in theory. If the assembly was correctly assembled at rest, all components of proper size, serviceable or new, the action of the bushing/serrated sleeve against the cup washer really shouldn’t try to disengage the bolt/lock washer. True,the action of the CA in one direction may appear as though it would possibly rotate the cup washer/lock washer/fastener in one direction but the reverse motion back to, at rest should have the opposite rotational effect rather than a continual unlocking (for the lack of a better term) of the assembly. The function of the assembly is very dependent upon the condition of the parts and the proper assembly method as mentioned.

[55 Tony]

The bushings are poly and tightened to 55'# more than once, with blue locktight. Like I said above, there are quite a few other accounts of this happening if you know where to search for it.

[chevynut]

I think your poly bushings are made wrong (too long) and they're being compressed end-to-end too tightly by the washer. I took some length off of my poly bushings in my C4 front and rear so they would rotate around the sleeve as they're designed to do. My IRS would not articulate properly until I did that even with lube. I think the manufacturers make these things with crappy specs and tolerances and the mating parts have tolerances too. I would remove the washer and take some material off of the bushing by sanding or machining and leave the sleeve full length for the washer to bottom out on. A little compression of the poly isn't bad, but too much will turn the washer and therefore the bolt comes loose like you're experiencing.

Also lube the backside of the washer that faces the poly bushing with the proper lube.

[55 Rescue Dog]

Anyway you look at it, the bushing sleeve needs to be slightly longer than the bushing, and fit snuggly in between the mounting ears so the bolt can clamp the sleeve securely in place without binding up the bushing. If it was about to fall out like you said, it could wear the mounting holes in the frame oblong, and create new problems. I've never had an a-arm bolt loosen even with poly bushings, so you should easily find the reason for why it won't stay tight, because something's not right.

[Rick_L]

I think Chevynut's comments on the length of the bushing and sleeve are pretty much what's going on.

If the maker of the pu bushing just mimics the rubber bushing it's not going to do the job very well. If you want a bushing setup that's free to rotate, the Delrin/aluminum bushings may make more sense for a lot of applications.

I have seen the shaft end bolt work loose on a tubular control that had poly bushings. But those were not even close to the style of stock bushings. There didn't seem to be much that could be done other than Loctite and torque.

[NickP]

I think Chevynut's comments on the length of the bushing and sleeve are pretty much what's going on.

If the maker of the pu bushing just mimics the rubber bushing it's not going to do the job very well. If you want a bushing setup that's free to rotate, the Delrin/aluminum bushings may make more sense for a lot of applications.

I have seen the shaft end bolt work loose on a tubular control that had poly bushings. But those were not even close to the style of stock bushings. There didn't seem to be much that could be done other than Loctite and torque.

Maybe safety wire them.

https://images1.mcmaster.com/mvA/contents/gfx/large/90124a624p1-b01l.png?ver=1394028598

[55 Tony]

I've heard good and bad about PST, that's what brand bushings mine are, from about 25 years ago. For all I know, the bushing may have slid right in and I didn't know any better back then. Anyway I forgot that when I got new uppers with rubber, I was going to change the lowers to rubber but I forgot all about that. So new rubber bushings are in order.
I may or may not reply for a couple days, taking a short time off to see my sister 5 or so hours away. She needs help getting her house ready to sell and she is giving me some nice tools her ex left that are "in her way". Sounds like enough to pack my cargo van.

[chevynut]

If you want a free-moving front end to lift and shift weight better the poly bushings are better than rubber. Notice they have serrations on the end of the sleeves just like the stock rubber ones. The shaft, sleeve, and washer are all supposed to be held solid to the frame with no rotation. The bushing is supposed to rotate around the sleeve, but be locked into the shell in the a-arm so it doesn't rotate in the shell. Rubber ones are bonded to the shell and sleeve, and they restrict motion and "bind" when the suspension moves. That's why you have to tighten them with the car at ride height. The aluminim/Delrin ones are probably just as good or better as far as allowing motion, but they will give even a harsher ride since they don't absorb or isolate any NVH.

[55 Rescue Dog]

Mostly right on, but rubber does not bind. It can easily twist a few degrees under load, adding just a few pounds of progressive spring rate, which is why billions, and all production cars use them, and probably always will. They just plain work. In a race car, anything can be made to work, but it will never be smoother, or quieter than rubber. I don't know what the fastest current production cars currently use, but I would assume it is probably just a very well engineered rubber bushing.

[chevynut]

Rubber bushings acts like a spring, and as soon as it moves away from a neutral position the rubber is in shear and resists motion. Call that anything you want, but I call it a bind that gets worse the further you move it. It doesn't allow the suspension to act freely. The reason production cars use them is because rubber is cheap, and OEMs are concerned about isolating NVH which is better with rubber. But rubber has poorer performance characteristics due to its softness which allows things to move around and go out of alignment if enough force is applied. It's just a well-known fact of material choices and tradeoffs.

[55 Rescue Dog]

There have been so many people that have totally fucked up their rear 4-link GM suspensions by replacing the rubber bushings, and flexible control arms, with something hard. It has to be compliant to work as designed. I would love to know which state of the art performance production car uses poly bushings? The last time I looked, OE bonded rubber bushings are way more expensive than plastic ones, if you can even replace them. Usually you have to buy the whole assembly, which you might not even be able to buy. Then alternate bushings make good sense. If poly bushings are so perfect, why is that not the standard? There is so much to the story than NVH.

[Rick_L]

Here's something to think about. Rubber can be made in many degrees of hardness. The rubber in a suspension bushing would be measured in Shore A hardness.

Polyurethane can also be made in many degrees of hardness. The bushings on the market are probably only a little harder than the typical rubber ones. Thing is, if they are pour molded, it can be hard to control. Why are all the aftermarket bushings polyurethane? Because it's cheap to do. A harder rubber bushing would probably be better if made right. But it would cost more, and it's probably not a viable product to sell because of cost. If you want the bushing free, then use the Delrin/aluminum bushings. They will be free and predictable, and will have less deflection. PU bushings not so much.

The torque resistance offered by a rubber bushing is negligible and doesn't really contribute to spring rate of the suspension.

Then there's the typical polyurethane disintegration problem.

[chevynut]

You seem to have a mistaken impression of Polyurethane. Poly isn't "hard", it's typically harder than rubber and different Poly compounds are used to get different durometers for different applications. It's not rigid like hard "plastic" as you seem to think and it's relatively compliant so it can absorb some (quite a bit of) misalignment. You can't seem to understand that FACT.

I don't see how you can "fuck up" a GM suspension with poly bushings if installed correctly. And who the hell uses "flexible control arms"?

Rubber is used by OEMs due to its noise reduction and softer ride that some people want in a new car. Poly has been proven for decades and in millions and millions of applications as a performance improvement. If it didn't work, there wouldn't be so many companies offering it and motorists enthusiastically accepting it. Most people see it as an "upgrade" to their stock rubber bushings that tear and crack.


"The main advantage of a bushing, as compared to a solid connection, is less noise (https://en.wikipedia.org/wiki/Noise) and vibration (https://en.wikipedia.org/wiki/Vibration) are transmitted. Another advantage is that they require little to no lubrication (https://en.wikipedia.org/wiki/Lubrication). Disadvantages include:


Rubber bushings can deteriorate quickly in the presence of oils (e.g., motor oil (https://en.wikipedia.org/wiki/Motor_oil), mineral oil (https://en.wikipedia.org/wiki/Mineral_oil)) and extreme heat and cold.
The flexibility of rubber also introduces an element of play in the suspension system. This may result in camber, caster, or toe changes in the wheels of the vehicle during high-load conditions (cornering and braking), adversely affecting the vehicle's handling (https://en.wikipedia.org/wiki/Car_handling). For this reason, a popular aftermarket performance upgrade is the replacement of rubber suspension bushings with bushings made of more rigid materials, such as polyurethane. Polyurethane bushings are also available for many vehicles with approximately the same characteristics[citation needed (https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)] as the manufacturers original bushings, but with greatly increased durability.[citation needed (https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)] This is useful on vehicles that have a reputation for wearing out standard rubber bushings, but for which harder bushings with increased harshness of ride are not wanted."

[55 Rescue Dog]

Whatever. I would love to test drive a C7 and see how sloppy the suspension is. And, if you look at how the ancient GM 4-link rear articulates you would see everything needs to twist, and move in multiple directions. My 13 Tahoe PPV even still uses that basic design. If you tighten it up with stiff bushings, and rigid control arms, it will BIND! And that's a fact Jack. If you have oil and grease all over your suspension bushings, then poly would be a great choice.

[BamaNomad]

Man, I sure love this great information, pro and con, from you fellas..... :) giving us all the information so we can make our own informed decisions! :)

Thanks!

[55 Rescue Dog]

Here is a good article on rear suspensions, which I know the original subject was about the front, but about half way down it explains how the triangulated 4 link rear works and many others. It also mentions earlier in the article that trying to pivot a bushing in more than one arc can induce binding in any suspension. I have this book and it is a good read, and it gives some perspective into how one thing can affect another.
https://www.cartechbooks.com/techtips/muscle-car-handling-upgrades-rear-suspension-system/

[TrifiveRichard]

You might consider using red loctite, also. In my experience, it’s a lot stronger.

[55 Rescue Dog]

A jam nut is another option, but it still shouldn't loosen if it is clamped to the inner sleeve securely, and the lubed bushing free to pivot on it. If the poly bushings are not kept lubed, they can stick to the sleeve under load, which could cause it to loosen too. Unfortunately, unlike the rubber bushing which has no moving parts, you have to disassemble the suspension to lube them, unless they have zerk fittings, which most do not.

[NickP]

With, T=FR, how much force is required with an "R" of less than .500 to undo the fastener in question initially torqued to 55 Ft. LB?

[55 Tony]

I have a few miles on it since this happened and last night checked it with just a hand wrench and couldn't turn it clockwise. Yes the wrench is short and gives less leverage but it didn't budge. Felt like the locktight is working this time. Not that the locktight should be needed, but maybe the whole thing was too full of oil/grease to work the first time years ago? For the drivers side, I have to drop part of the steering linkage to get a torque wrench and socket on it. Not sure if that's with all tri fives or due to factory power steering?

[55 Rescue Dog]

I have a few miles on it since this happened and last night checked it with just a hand wrench and couldn't turn it clockwise. Yes the wrench is short and gives less leverage but it didn't budge. Felt like the locktight is working this time. Not that the locktight should be needed, but maybe the whole thing was too full of oil/grease to work the first time years ago? For the drivers side, I have to drop part of the steering linkage to get a torque wrench and socket on it. Not sure if that's with all tri fives or due to factory power steering?
You could put white paint index marks on the fasteners, and just visually check them from time to time too.