samiam4

Well I'm using the 1 ton setup. 3 x12 inch shoes and 1 1/8 cylinders. Since you are running hb and a different mc. What mc are you using? Hb gives a higher line pressure, do I can see a possible problem w o the rwal valve.
I would think a larger piston diameter mc would help .. not sure if a drum brake rear hb mc would help too.

Bummer, I was thinking of doing that mod.

mknittle

I used a Chevy Astro van HB with a 1995 or so C/K 3500 master cylinder and 1 1/8" wheel 1 1/4"cylinders and no RWAL and no problems at all.

bigragu

If your talking about doing the hydroboost mod, by all means do it! The braking on this thing is unbelievable. Sure, I have a few tweaks to get it right, but tweaking is a part of modification, right? TCows, Mknittle, ouchieman, Fonder, all theirs seem to be running 99% all good. What they all did, different than me, is actually install a MC off of a hydroboost vehicle, wether diesel or not. Maybe some of them also took the proportioning valve that matches that setup.

Now that I know more about HB, that's what I should have done, and got that same MC, and I still can do it. I opted for a kit form, that was made for either disk/drum or Disc/Disc setups. It has a GMC style master. Mine came with a 50/50 reservoir, while our factory MC's are of a 40/60 set up. I just don't think it's liking those larger cylinders too much. As far as the RWAL bypass, I think I'm leaning on keeping it bypassed for now.

If you convert over, and find those 1 1/8" cylinders causing you to lock up too much, you can always revert back, like I'm doing.

1972RedNeck

3". I was locking up the back end so I figured I needed to keep the larger shoes that need more force to apply and go to smaller cylinders that apply less force.

bigragu

1972RN- forgot to ask if you belong to the RWAL delete elite team. Did you get sideways at all during those lock ups?

mknittle

I know one thing If I had kept my RWAL my truck would have likely been wrecked when that idiot pulled in front of going half the freeway speed.

1972RedNeck

Yup, the RWAL system is gone. I didn't log too many miles from the time I got the truck to getting the brake system working well as I was afraid of loosing control (or just not stopping) if I were to get in a situation were I needed to stop quick.

samiam4

Gave this some more thought today. So if you are running hydroboost- you've increased line pressure by ~50%. The hole idea on cylinders is to increase braking force on the drum. Bendix brakes are self-energizing. So there is a point where it will lockup quickly when you've overcome tire/pavement friction..

So you can add an RWAL back, but best braking might be with the 7/8 cylinders or perhaps 1 inch. Be aware that heavy fwd braking biasing you may warp front rotors. There was a factory service buliten against that on the D250's and the fix was to go to the bigger cylinders.

Michael

bigragu

Mike, most of my use of the truck, probably 98%, is unloaded. The other 2% is for the occasional run to the dump. If I was towing, yes, I could understand your theory somewhat.
If my front rotors warp, but I eliminated injuring myself or others due to a lock up and figure 8, reverse doughnut to follow, I'm ok with that. It's the emergency braking that I'm mainly concerned about, and possibly the wet weather.
Now hauling a trailer or fifth wheel, I realize that the bigger cylinders help that a lot, and adds to your theory.
I remember twice in that crazy Bay Area traffic, I locked up and skid partially to the right, before the hydroboost set up. Just 1 1/8" wheel cylinders, RWAL bypassed, and 3" wide shoes.

mknittle

You couldn't pay me enough money to put that RWAL back on mine.

samiam4

I hear you clearly and maybe I didn't respond wisely.

I've spun when I was having tc lockup issues.. no fun. As a whole, I really think the brakes are a weak point. I don't think regardless of RWAL any system level component failure should cause NO brakes.
I've had something trigger before and gone from fine to no front brakes. I'm not sure if it's RWAL related or proportioning valve-but Bendix didn't do us right.
I am similar to others, I commute with the truck and run rock, mulch or other home projects. Have towed heavy a few times.. but I can count them as less than once per year on average.
Currently, my rears are new and work well. The RWAL is functioning and the brake pedal is not horrible, but not like a rock either. Only 3k and some coin was spent. So I will wait.
Maybe it would be better to use a different proportioning valve? I have a hard time understanding why Shoes /cylinder make the difference. I thought the weight on the rear axle was the same between my D250 and a D350. Mine is an automatic running a D70U.

mknittle

There really is no proportioning valve in our trucks. there is a balance valve that has a pistin that floats back and forth between the front and rear lines from the Master cylinder. It's purpose is to equalize the pressures and to house the switch for the dash warning light. the proportioning is designed into the swept area of the pads/shoes and caliper and wheel cylinder size. There is a residual chech valve in the rear side of the master cylinder to keep a little pressure on the wheel cylinders.

samiam4

There's the issue- change from a balance valve to an adjustable proportioning valve!

Is this common with all bendix brake systems??

bigragu

I'm actually researching this now. My research has found me information that says, when installing an adjustable proportioning valve, it cannot be uphill of any type of ABS system( my RWAL is bypassed), and it cannot be used with in conjunction with any factory proportioning valve. But, for the life of me, I cannot find anyone(vendors like Summit, Speedway their tech support) to tell me if I need to remove my factorysystem(I have been calling it a distribution valve that houses the brake switch). One vendor, Aerospace, told me to remove it. But, like Mark said, if it is not a proportioning valve, why should I remove it?

My lock up and skid came before the hydroboost, from the larger wheel cylinder upgrades and larger shoes. My intense lock up and skid came after the hydroboost. Only then did I install an adjustable prop valve, but what's happening is I need to close the pressures a little over halfway to rid of the lock up and skid totally. But what's happening, is my braking must be done way in advance, cause I'm rolling more, instead of slowing down. Hard to describe. It's like pressing on the brakes and nothing is happening at the rears.
I truly feel that the smaller cylinders will fix this, and maybe I'll only have to close off pressures to the rears only a tad. That hydroboost turned my brakes into the Hulk, LOL!
According to the local gent who mirrored my brake mods to a tee, the smaller cylinders fixed the problem, and he does not have an adjustable prop valve. He kept the 3" shoes, and his RWAL module bypassed.

bigragu

I'm curious, Mark, or anyone with knowledge on this- I've been back and forth with a fellow dtr member who was helping me troubleshoot my brake light coming on. I've bled and bled and bled the brakes, till I started to bleed, LOL, and for the life of me, the brake light still keeps coming on when I mash on the brake pedal. No sponginess, but high and hard( pedal, that is). Even after the recent cylinder swap, and properly adjusted brake shoes, and new front pads, it still comes on.

Upon looking closely at that diagram Mark put up, I'm wondering if this is happening cause I used 1/4" brake lines from the MC to that distribution valve? The factory lines were 3/16", but no one had off the shelf lines in 3/16" that had the 1/2"-20 and 9/16"-18 fittings on them, only 1/4". I'm wondering if I'm over pressurizing by shoving too much fluid into that D-block to cause that metering piston to move ever so slightly to cause the light to come on.
Every time I test the brake switch by applying 12v to it with a lighted test probe, it shows that it's centered.