Coincidence or a real problem?

A couple a months ago the drivers side spring perch broke at the top of the threads, yesterday the other side broke. The threads are 3/4" sae with self-locking nuts and were not loose when they broke. The perches were on the dropped axle when I bought it. Everything else on the Suicide front end is/was tight( split wishbones). This a coincidence or do I have more problems? Drives and steers great?

 

Top of thethreads? That's way down inside the axle bore.


I'd put up pics of the broken pieces, showing the break surface.


Without the pics, it sounds like a cast repro part, only because a forged perch would never break there, IMO. On a orig perch bolt, I would think the threads would strip if the nut was way overtightened, before the shank could ever break.

 

I tossed 'em. Breaks were new and clean and between two of the first threads below the "stem". Exactly the same. I don't know for sure, but probably "knock offs"? The holes in the axle widen at the bottom for the nut to attach.

 

Sounds like you may have had bad pieces. Something to remember is that the original nuts have a taper machined on them a lot like a lug not (only different) to centers itself in the "elongated" hole on the bottom of the axle and the original perch bolt had rolled threads instead of cut threads. A cut thread when stressed will always shear at the end of the threads. A lot of the after market stuff has cut threads instead of rolled threads.

 

same with me. Mine was stainless. I don't think it's an epidemic but it does happen.

 

Thanks, I think you hit the nail on the head! They definitely had turned threads and had tapered seats. I replaced 'em with Speedway's perches, so I'll be sure to keep my eye on them. Most likely they'll do the same, then I'll replace them with OE types. HAMBERS ROCK!!

 

Split wishbones can aggravate the problem. As the axle goes thru larger bumps, the axle is twisting thru the spring perchs.

 

Pretty much standard engineering stuff - stress risers at the top of the cut threads. It's amazing how much of the available hot rod things we buy now pays no attention to really basic mechanical principles - and subsequently breaks. Glad nobody was hurt.

 

could the threads been stretched by over torqueing since they were on the axle when you got it ??? I've seen damaged threads before, from a BFI ( the modern version of a BFH )

 

this was my first thought also. some guys are impact happy.

 

I had the same thing happen on my '39 Ford convertible,,I know when it happened on some really rough railroad tracks,,BTW,,I got the perches from Speedway Motors. HRP

 

Ha spend a week as a maintenance machinist. You don't need an engineering degree to know what happens to a machined bolt as opposed a bolt with rolled threads.

 

I never saw that happen with Gennie perches, even on roundy-pounders. (bent axles, snapped wishbones, broken spring main leaves, torn shackles...Never a broken perch)

But then came the '70s. I've seen broken axles, king pins, broken spindles (at the stub!)
Anything that could be reproduced I've seen fail, in at least a few instances.

 

With an original Ford perch these two ^ situations would not break it. Repro stuff is a piss poor gamble, especially on important parts. That's why I have no clue why so many cars on here are using that trendster ratrod perch setup going into the sides of the wishbones. It's just plain unsafe with repro junk.

 

I thought that was called a rolling bones front end. That's what I read in a magazine article anyway.

You can still find original Henry perch bolts of you just look around a bit. On repop you have no idea what aisian country the 14 year old that made them lives in.

 

Thanks everybody! The one's I installed are forged at least and from Speedway and probly BFE
. Pulling into my driveway puts a lot of twist on the front axle assy. I'm gonna come at it at a straighter shot and see if these work. If not, I'll get FORD OE type.

 

Willbe,
Did they both break in the driveway or at speed on the road? Did the front end collapse or come apart when it happened? Just wondering. Gary

 

And that's a suicide front end?

Pretty sure the ol snapped perch, combined with the subsequent possibility of the frame dropping into the road at high speed, is why that style of front end setup was coined "suicide" in the first place

Imagine that happening on a spring behind setup...with the perches through the wishbones....and having nothing to land on the axle as the frame drops...YIKES

 

PS...I'd make sure that nothing in the front end is causing a full time binding situation.

make sure everything is moving smoothly at the same arc...

the fact that both pins broke makes me suspicious that there could be an underlying geometry issue

 

Makes me think they must be cast iron, to break where they did; up inside the lower edge of the axle bore hole. That's a shear type force, like scizzors. A forged pin is impossibile to shear using a wishone and a Ford Axle. The axle could get hit so hard out at one end, that it would bend 90 degrees and still not break the pin.


You could look up the shear specs on that diameter of forged pin, and compare to a cast iron pin shear specs, and you'd never run a repro perch ever again.

That's why I mentioned the RR front ends with cast perches mounted through the sides of the bones. The OP survived just fine with two broken perch bolts, because the way his are mounted, and where they broke, the car is still drivable. If a cast perch "head" snapped off that new breed front end style, the outcome would be different. I don't know how R-B builds their perches on the bones, but I'd bet they sure don't use shit perches just slid through a sleeve in the bones. There are much better ways to do that front end style, compared to some I see on the net, and R-B is probably one of them.

 

Was there any indication that the perch pin bolt was loose? If so, the constant back-n-forth forces exerted on them (due to the split bones setup) could have weakened them and ultimately resulting in failure from fatigue.

 

Unless I would have hit a huge bump or drop off the likelyhood of the front end collapsing looks unlikely. Both became evident in town and produced a low speed wobble when I hit small bumps? One of them dropped the broken threads at the driveway, the other, after I noticed the wobble I checked and it was hanging by a thread and fell of when I tried to tighten it and was apparently broken before the driveway. The old perches where frozen in the axle and had to be worked out, new ones dropped right in? I've put 6 or 7 thousand miles since built and never hit anything. Lately, I had been experiencing "death wobble" at low speeds and switched front tires but this was before the perches broke and worse after they broke, of course? Switching tires helped a little. Coker bias plies.

 

Mine snapped going down a smooth road. I heard a clunk as something hit my fender. I saw something spinning in the road in my mirror and I walked back to find this in the road. I knew exactly what it was and went back to the truck to look and this is what I saw...

 

Bolts were self locking and not loose?

 

This shit is kinda scary, I'm gonna find a front-end guru(got one in mind) and get to the bottom of it! I'm old but I still got stuff to do yet and don't wanna die. ;o)

 

Personally I don't think that there is any bottom to get to. There is no epidemic. Shit breaks. I blame my situation on the PO and his installation. I'm sure your situation is different from mine. There does not seem to be a smoking gun here. IMHO

 

Too bad you tossed part of the evidence.

 

You can sleep better if you just find some original Ford perches which are high quality forged parts. If you have a 2" axle boss, they should fit.


These repro cast parts in any material, should not be used.


One thing I noticed in Tommys pics this time, that I had missed back when it broke; look at what looks like "not enough" threads where the nut was tightened.

Can't see for 100% sure, but if the nut ran past the end of the treads, the nut would feel tight, but there might not have been enough torque pulling the two tapers together.

This sure could explain why his broke just under the top taper. If that taper was not fully seated, rock solid, like a tie-rod taper is, then as the spring rocks the head of the perch eye, back/forth, it would stress that exact area of the pin.

Those "extra long shank" repro perches are designed to fit a repro 2-1/4 axle boss, and/or, a 2" 32-36 axle boss with the repro lower shock mounts. I am thinking the installer of that set, never looked to see if the perch bolts were threaded up far enough.


On the orig Ford perch bolts, they really are too short for a 32-36 axle if you try to use add-on shock brackets, or try to use them on a 2-1/4 axle with the thicker, later 2-1/4" bone yokes.

 

^ I agree with F&J; those pins look they they are made to accept lower shock mounts, so they are longer than stockers. If you don't use the lower shock mounts, the shank is too long to get the nut tight enough to lock in the pin. So it's possible that they were loose, and fatigued due to the constant back-n-forth stresses.

 

Nothing fell apart, I woulda had to hit a pretty deep drop off to get the perch to jump outa the axle. I simple noticed a low (10-15-mph) speed wobble over bumps.