Is it a good idea to replace your front control arm bolts when upgrading to poly bushings? I was thinking that since they work a little differently than the stock rubber ones they might do better with just plain grade 10.9 bolts rather than the reduced shaft bolts that were used originally. Also, it's nice to have new bolts on such critical parts rather than old, rusty 35 year old ones. I'm thinking the reduced diameter bolt design is designed to provide a more even torque potential.

 

Not really.

The bolt clamps down on the sleeve, which is then held captive and immobile in the brackets. As long as the bushing sleeve fits tight on the bolt, there is no difference.

Now if your particular poly bushings have a larger ID sleeve, then...

None of that has anything to do with 10.9.Or old rusty. (beyond the obvious of course) If it fits, it works.

Never heard of "more even torque potential". Sounds like marketing mouth diarrhea to me.

 

Here's something I found that explains what I was trying to describe about why bolt shanks are reduced when they are in tension: https://www.nord-lock.com/insights/b...f-bolt-shanks/ . Manufacturers used these kind of bolts for a reason.

 

That's about bolts, not cap screws. Look alot the same but are not.

 

Zero issues replacing a-arm bolts.
stock bolts are all rusted and probably full of oxygen embrittlement.
I used fancy Zinc coated flange head bolts from BellMetric on my 92.
A-Arm bolts:2x:m12x1.75-110mm2x:m12x1.75-90mm

I got away with using 2x 100mm bolts with flange head lock nuts. But they were almost too short. I have maybe 1 thread past the nylon part of the nut

Unrelated pic of my old a-arm powder coated from leftover powder.
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Replacing 30-40 y/o hardware is usually a good idea.

 

One of our customers is a third party inspector for the Nuclear industry, their standard regarding Nylocs was the end of the bolt had to be at least flush with the nylon portion of the nut, it could not be below flush with the nylon portion. The way I see it if the Nuclear power industry is good with it, so am I.

 

Isn't the rule of thumb you're supposed to have at least two threads showing past the end of the nut when fully tightened? I'm not a big fan of nyloc nuts unless I'm using them on something that had them on to begin with. To me the all metal top lock nuts seem much more substantial and impossible to come loose over time.

 

I think in a lot of industries 2-3 threads past the nut is the rule of thumb though sometimes given space constraints of some mechanical designs that's not possible. Working in R&D for as long as I have this something that I bring up to our engineers quite often, some times it comes down to what's more important, this or that, "this" being a critical dimension that needs to be held to a certain tolerance or "that" being either using a jam nut with maybe 4 total threads and 2 threads past the nut or using a full size nyloc nut that may have 6-8 total threads with the end of the bolt flush with the nylon portion of the nut. Sometimes it's a case by case scenario.
Not saying that a nylon nut can't fail, because there's always the potential for and mass produced fastener to fail but in the 20+ years of using nylocs in the power distribution industry I've never witnessed first hand of a nyloc nut failing, maybe I'm just lucky that way