Third broken front leaf spring since 3-2011

[Lumpy Grits]

Better yet, Ford 9" rear with 2 1/2" wide X 11" shoe brakes that "plums" right into a Jeep.
Been run'n one for over 20+ years with no issues and AWSOME braking. Still using OEM booster.

LG

[Roger]

Roger, I can take some time off this week-end if you can use a extra hand or two. I'm on-call so can't play anyway and I have a set of 3/8"x 5" spring bolts if ya need em. Do you have a angle grinder? I can bring mine if not and I have wheels too. Give me a call

Dennis, the spring didn't arrive. This weekend is out

Thanks...

[GP4Play]

Dennis, the spring didn't arrive. This weekend is out

Thanks...

Ok , I can come out Mon. thru Thur. after 1530, call me when they get to ya and I'll load the tools.

[Roger]

Perfect Dennis. I'll keep in touch.

[6spdYJ]

Pre-emptive apologies for the long post.
Roger, what seems to not have been explained here about the proportioning valve is how it does what it does. If you look back to any pre 1966 vehicle, the brake master cylinder only had one reservoir. This applied equal pressure to all brake wheel cylinders. Basically, 100% of pedal pressure multiplied by the internal square inches (volume) of the cylinder was divided by four wheel cylinders. For conversation's sake, let's say 100psi is developed in the single master cylinder. Now, divide that by four wheel cylinders and you see 25psi to each wheel. The downfalls were that there was no way to balance how much pressure stopped the weight of the vehicle in proportion to the vehicles balance. Essentially, a VW bug had the same braking characteristics as a '65 Impala SS. Not exactly, but I think you get the point. Also, if you happened to rupture a flexible brake line to either front wheel or the back axle, all braking power was lost. That's why manual emergency brakes exist.
Enter the dual reservoir master cylinder. They essentially have two cylinders - one for each reservoir. Both cylinders' pistons are moved by the same lever (the brake pedal) and are actually cut on the same shaft. In the case of a dual drum setup, the cylinders are the same bore size, so if you look at it, the bowl sizes are the same. If you look at a disc/drum brake master cylinder, the rear bowl (which actually serves the front brakes) has a bowl almost twice as big. With discs requiring a greater volume of fluid, the bore is a little larger - making the piston larger to move more fluid over the same distance of pedal travel. Since you can't put the bigger piston in first, the smaller bore has to go in front.
Now, you have the ability to tailor how much pressure and volume is moved to handle the vehicle weight distribution (typically 60% front and 40% rear). Obviously with such a short wheelbase, the weight transfer from front to rear can be pretty drastic. Add to that, larger tires and a higher center of gravity and weight really starts to stack up toward the front in a hurry. If the rears happen to lock up before the fronts, the rear wheels lose traction with the ground - effectively like being on ice and with the fronts now doing 100% of the stopping, the back end wants to slide around front and bad things happen.
What the proportioning valve does is allow you to fine tune how fast your rear brakes develop full pressure. You want your rears to help control the weight of the vehicle that's still supported by the rear tires in contact with the ground. By keeping this under control, you share the load carried by the fronts - requiring less pedal pressure to perform stopping.
By ading a rear proportioning valve and closing it at all, you are further reducing your rear brakes. If you fully open it, you've just wasted a bunch of money. I have never heard of a situation where a proportioning valve is recommended on the fronts.
I realize that I've been beating the rear brake drum (yeah, bad pun) but... If it was a problem with the springs, don't you think RE would have engineered for the loads that they're experiencing? The only possibility I can see with the springs is if they have a different part number for fronts and rears. The YJ is a cool animal in that you can swap front and rear spring packs with no adverse effects. The mount to center pin length is the same fornt to rear and the pins are centered. If by chance, the fronts and rears are swapped and for whatever reason RE designed the main springs different...
What you have to remember is that while the vehicle is rolling forward, the axle housing is only carrying the weight of the vehicle. As soon as you apply the brakes, the axle tube becomes part of the wheel - which is turning. Now, the housing itself is trying to turn and is only able to resist the force of the wheel by twisting the spring pack. Look at the wheel rotation. Now imagine the wheel and the axle housing locked together. As pavement is passing from front to rear under the tire, it tries to rotate the housing forward (diff cover down and pinion up in this case) Your springs are continually breaking right behind the axle - where the most stress is applied to the spring. Considering that you have 4.5" springs - and as far as I can tell minimal rear brake assist - I'd bet you are putting that section of the spring into reverse arch every time you hit the brakes. Ask anybody here, reverse arch is a leaf spring killer.
Have you thought of putting a camera down there to actually look at what's happening with the springs when you stop?
You may say you're not a mechanic, but this as all within your reach. If I can get it, you definitely can. If any of it seems over your head, just read it again each sentence until it makes sense, then on to the next - that's how I had to learn everything I know. If that don't work, I know there's a bunch of great folks here who can help interpret all of this.

[Lumpy Grits]

What you say works when all the brakes need the same PSI for braking.
Disc brakes require approx 40% more psi than "shoe" type for the same amount braking.
I wonder if that adjustable p/valve is D.O.T. legal.
I have been wrench'n on Jeep's for almost 40 years. Trust me when I say that the biggest deal with the "por" rear breaking has to do with the small brakes that where used on Jeep CJ's.
LG

[6spdYJ]

What you say works when all the brakes need the same PSI for braking.
Disc brakes require approx 40% more psi than "shoe" type for the same amount braking.
I wonder if that adjustable p/valve is D.O.T. legal.
I have been wrench'n on Jeep's for almost 40 years. Trust me when I say that the biggest deal with the "por" rear breaking has to do with the small brakes that where used on Jeep CJ's.
LG

Which is why caliper pistons are almost twice the diameter of drum wheel cylinders. Trying to keep it basic.

[Lumpy Grits]

Takes more psi to "pinch" a rotor than to push a "shoe" out against a brake drum.
Air brakes do the same "push" with a max of 125psi tank pressure.
LG

[GP4Play]

Rogers on the road and my belly's full. Thanks again for dinner Leanne.

[Roger]

Okay Gentlemen,
I want to thank everyone that participated in this thread. I learned a lot. Special tanks goes to Dennis - GP4Play - for coming out this afternoon and helping me with this.

I believe we found the reason the springs kept breaking. Look at he following photos:

If you take a close look at the spring pack bolt, you ca see a 3/16" sleeve between the the bolt head and the spring. I measured the depth of the receiving hole on the axle and determined that the hole was not deep enough for the bolt and sleeve to go all the way in. 3/16" too long, so we removed the sleeve and that gave us the proper depth.


In this photo, take a close look at the wear pattern on the spring. Because the spring wasn't sitting "flat" against the plate on the axle, with the u-bolts tightened up to 90 psi the spring had an arch between the u bolts that Dennis and I am sure put all kinds of strain on the spring that it wasn't designed to take. Apparently RE Express adds those shims to allow for tapered shims to be used to rotate the front axle:


We did take a grinder to the spring mounting plates. Note also that we removed the shim from the other front spring pack and also ground the plate edges.

Hopefully, this will end the breaking springs problem.

Again thanks to all and especially to you Dennis!

[6spdYJ]

Congrats on the fix Roger!

[Lumpy Grits]

Roger, what was the dia. of the center bolt shaft? Dia. of the head?
What was the dia, of the hole in the axle spring pad?
Yup, That long head was for a shim to go in between the spring pack and the axle pad.
LG

[GP4Play]

Your very welcome Roger, anytime