1973 F100 4x4 FE 390 engine, C6 transmission.

Changed/replaced Radius arm pivot bushings and axle insulators, coil springs, and shock absorbers. Passenger side front radius arm has two bolt holes in the top to hold lower spring mount and retainer to the radius arm. I noticed one of these bolts was slightly bent after removing it, and replaced it with the same bolt (grade 8), which is a 5/8 head, I believe they’re 7/16-14 bolts. These holes were scrubbed out with a metal .50 caliber rifle brush and pb blaster, and the new bolts were coated with anti-seize compound. One of these bolts test screwed in easily, the other screwed in easily, then resisted, then strongly resisted. Did not force it further. I believe it MAY be too high to accommodate the lower spring mount plate and concentric lower spring retainer, and single lock washer and still give an accurate torque reading. Probably this is why the bolt was slightly bent; it had given a false reading and was too loose/high. Any recommendations on how to proceed? I could shim it with one flat washer, or could chase the thread, or maybe re-tap it? Or a combination of two? Really don’t want to risk destroying this hole thread, so was planning on shimming with one washer and then over torquing by 5 foot pounds…

ps. This radius arm design is the 4 bolt clamp around the axle type; then spring mount and retainer use the two bolts on top of this clamping design…

 

I agree with your plan with how to proceed. If the the thickness of the damaged thread stack is that of a flat washer then very little would be gained considering the risk of breaking something that is made of hardened steel off in the hole. I am confident that with the plate being secured in the manner in which you have proposed It will remain secure and perform as its' original design intended it to for as long as needed.

 

You mean “very little would be gained” with the use of a shim (washer), or very little would be gained by using a thread chaser or attempting to repair the thread with a tap? Clearly, with the thread damage, the bolt held and the truck remained operational, but the bolt was damaged. Using shims clearly will reduce engaged threads; whether those remaining threads are sufficient to accomplish the bolts intended engineered purpose at the recommended torque value (or higher torque) I couldn’t say. I have not used taps or dies. I believe one of its purposes is to repair damaged threads? Or is that risking losing the working threads?

 

Sorry, forgot to mention these bolts are only like an inch long, maybe less…

 

Just make sure you use a chaser tap rather than a cutting tap.

 

If you have an auto parts store that rents tools you can get something like this. I've used this one from O'reilly's before.


https://www.oreillyauto.com/detail/c...kit/ren1/67080

 

Yes you do what you have to to NOT break that bolt off in your radius arm for sure. Then you will get to learn how to use an (easy out), if you are lucky. I'd take it apart and use a thread chaser (chaser tap) and clean the threads. Then if that did not work maybe use a thread tap (cutting tap) and repair the threads until a new none bent bolt goes in the correct way, with the correct hdwr (one lock washer) and the correct torque. Also make sure the hole is cleaned out and the bolt is not to long, sometime the simple things get missed. Happens to me all the time.

Also you might want to drill a drain hole in that coil spring bottom cup somewhere. Why, because that cup catches and holds water, road grim, ect... and you can rust the heads off those bolts to the point that the required socket to remove them, will not fit it. Ask me how I know. Yes that is a hole rusted in the cup.

 

Why would you shorten the bolt engagement at the thread end then overtorque what is left? I'd clean the threads as best as I could, maybe even buy a bottoming tap if I felt the need. I once took a new grade 8 bolt and cut a pair of grooves across the threads to create my own tap, used a cutt off wheel. I was just used to chase threads, worked well, then discarded. I would use a wire to probe the depth of the hole and compare to my bolt and any taps I was contemplating using. Might be something in the hole? Those two bolts just hold a retainer down to keep the spring cup from sliding off of the top of the radius arm and the retainer is there to keep the spring seated in the cup when the front of the truck is in full rebound like "catching air", your shocks limit any "drop" travel.

I see that your "spring cup" has a cuttout on the wheel side to let it drain, not all do. Also the "inner retainer" has just a "wing" or tab that holds the lowest wire loop tight towards the inner most side away from the wheel.

 

Thanks for the responses. The theory of the spacer washer is to disengage the bolt just above the damaged hole thread, so as to have an accurate torque reading. I’m using a brand new grade 8 bolt, and have scrubbed out the bolt hole with metal brush and pb blaster. Bolt dimensions and length are exact and have worked well in 3 of the four positions in this application (two per spring bottom mount). Now, if I screw a thread chaser into an undamaged hole it will screw in like a bolt would until it reaches the damaged thread, right? And then you just power through the resisting bad thread, or is there some finesse and care involved? Thanks all…

 

I've used a few taps and bottoming taps (like a tap but not tapered so much at the end). Have you got the right tap? Reason I siggested checking hole depth was to compare to bolt length and see if a regular tap can clean the threads far enough for the bolt. I would not hesitate to use the bolt and a extra washer in this application.

 

If you are considering using the thread chaser now. Using a bit of cutting oil in the hole start your thread chaser. When you start to feel resistance back it out clean both the tool and hole using compressed air and wearing safety glasses. Then head back in the hole and take another wack and when you feel resistance repeat. Each time take a little more. The most dangerous part will be if when you feel resistance that you get to aggressive and try to power into it to far to fast. Just remember if you snap off the tool you have a real mess on your hands. Think finesse

If you've never done this before practice on a few holes to get a feel of what the tool is capable of, being aware that the cheaper varieties of these tools (harbor freight) the thread cleaning edge dulls rather quickly with use.

 

I'm going to say/ask something my wife would in this situation.

"Are you sure there's not just a rock or pebble in the hole?"

You would be surprised how many times my son and I have planned out an elaborate solution to a problem and then she comes up with the simplest that works so much easier/better.

Blow the hole out with air and poke around with a pick/tweezers to make sure it is the threads causing tour issue.

 

Well, here’s the thing; these bolts are 7/16-14, 1 inch long bolts, but the bolt holes themselves are drilled all the way through the radius arm and end cap, top to bottom. Holes taper down at the bottom (like a bolt needs a drain hole??) til exit. Scrubbed with brush all the way through multiple times without resistance, no obstacles. Did test bad hole today, with lower spring mount, retainer, and lock washer in place. Bolt screws in clean about to the level of the lock washer before some resistance starts, so probably single flat washer shim and upper torque range will be sufficient (55 ft-lbs)…

 

Gotcha. I forgot they go all the way through.

I agree with some of the others that the thickness of a flat washer would have minimal effect.

I'd get everything like you want it and go that route.

 

Like when Karl Childers fixed the man's tiller, He put some gas in it.