Split Brakes

[rflegal]

Ok, I've read the threads and absolutely agree with the comments made about the need for a dual setup on brakes. I can't imagine what it must be like to drive a deuce and suddenlly be unable to stop! Given that the air-hydraulic booster from my truck is stamped '57, this is old stuff we're dealing with (even though I just rebuilt mine and it should be good as new). I'd feel better with a split system.

Looked at SMARPI9-2320-209-14P, makes sense to me. I picked up a second booster, now the question of the MC. I have to two solutions:

A) Use two deuce MCs, and tie them together at the pedal, modifying the linkage, like we do in racecars. This lets you adjust the linkage to the MC's independently to set bias, sort of like a proportioning valve. But now I'm moving the same amount of fluid to 1/2 the system (actually 1/3:2/3 based on WCs) What are the inpacts, do I need to shorten the stroke? OR

B) Find a suitable dual MC - the conversion ones from the military don't appear to be available. Is there an industrial equivalent? I have been looking at units for F700s with hydroboost, they look veeerrryyy familiar. I'm trying to find specs now. Equivalent bore and stroke, etc? A hydroboost unit should be very similar in terms of function. The hydro system I'm installing on my FJ 40 hits pressures of 1500#, similar to the airboost of the deuce at about 1500# @ 100psi. The MC doesn't make the pressure, the booster does. The balance of the system is set up to handle it.

I'm going to do this conversion as part of a full brakes sytem refurb (shoes, WCs, hoses). Any thoughts beyond whats in the previous posts? Anyone have non-military dual MC info. If we can find the equivalent MC, this isn't too hard a conversion/ With duals, its just more brake lines, NBD. Remote reservoir most likely as well.

One more thing, anyone think of why the might have mounted the air booster backwards on the RHS of the chasis, other than just ease of mounting?

 

[hndrsonj]

Memphis equipment has the master cylinders for $250. You will have to make the mount to install it though since they are different from the old trucks.

 

[emmado22]

dont forget a 2nd airpack.

 

[rflegal]

Already got one coming (airpack) Here's some pics of possible candidates for MC's, both of which sell for around $100 instead of the $250 for the military unit. Anyone got specs (bore & stroke) for the stock unit, either single or dual ciruit?

 

[onegmjack]

What are thie Master Cylinders in picture above from?

 

[m-35tom]

forget about brake bias, you have all drum brakes and it should all be the same pressure.

tom, with REAL power brakes.

 

[poppop]

I crawled under mdmorgan's duece at the Ga Rally. It left the military with dual brakes and the right hand side is mounted the same as the left, exactly on the oppisite side of the truck.

 

[G-Force]

I've also been doing research on this. What I have found is if you take the P/N for the master from the SMARPI manual and go to WBParts.com it will come back with a 2 3/4" bore in the specs. I don't think this is right as all the M/C's similar in shape to what it shows in the SMARPI are maximum 2" bore. Also, I have found that the bore of the wheel cylinders on single system and dual is 1 3/8". BUT the M35A3 has 1 1/2 " bore wheel cylinders. And also, all the parts listed in the SMARPI manual have AMGeneral P/N's. On the A3, the reservoir, master and wheel cylinders are Bendix parts. The master cylinder P/N comes up as good on Bendix website when you do a part # search. But no technical info is available.

 

[onegmjack]

m_35tom would it work if you used dual cylinder with out a porp.vaule?I heard people talk about adjustable porposion vaule,don't know if they still make them.Reading to SMARPI
9-2320-209-14&P it refers to a check value in the air line,when could you find one of them?

 

[cranetruck]

If it was me designing this "upgrade", I'd look at the reliability of the current system and compare it to the more complex one. By doubling the number of components, the probability of failure is also increased by a factor of two. You have to make sure that a failure that could occur in the simple system does not also occur in the more complex system in such a way that it makes the upgrade null and void..... just thinking out laud here....

In electronics, every component has a known failure rate and often have the markings to indicate this. This used to be important when systems were designed, don't know what the current standards are, but when substituting a commercial part for a mil spec part, the reliability may be effected too, degrading the whole system.
Look up terms like "mean time to first failure" and the like.

Again, just rambling, but make sure you know exactly what you are doing when modifying the brake system, every little detail has an effect on the total reliability. Consider every fitting, every bend in the tubing made to spec, pressure ratings and on and on.

Now, off-roading will increase the probability of failure due to physical damage, but then, the need for a panic stop may not be there either.

 

[emmado22]

GForce,
All the SMARPI parts have AM General part #'s cause they built the trucks (but not all the parts) This is a common thing in the military, as the prime contractor wants you to go back to them for the parts, as opposed to the real manufacturer or the parts.. And guess who's parts cost more $$$$? The M35A2 dual MC (and the same one used on the M35A3) is a Bendix, I bet if you called them (Bendix) with the PN, you can get some info. Calling AMG will get you nowhere. Good luck.

 

[stumps]

If it was me designing this "upgrade", I'd look at the reliability of the current system and compare it to the more complex one. By doubling the number of components, the probability of failure is also increased by a factor of two. You have to make sure that a failure that could occur in the simple system does not also occur in the more complex system in such a way that it makes the upgrade null and void..... just thinking out laud here....

I have had 3 brake failures in the double circuit systems in the cars and trucks I drive. In each case, I totally lost the brakes. Pumping did not help at all!

I would venture that if the master cylinders were working 100% correctly, the failures would have been contained to the circuit that had the problem, but that is not how it worked out. In each case, there was apparently some flaw in the master cylinder that was undetected before the burst line that caused the other circuit to fail. In one case, the master cylinder was the single point failure that took out the brakes.

I have never had a failure in single circuit brakes that resulted in catastrophic brake failure.... but then I pay a lot more attention to single circuit brake systems because I know they can fail catastrophically. Their simplicity makes it easier to keep a check on their condition.

Keep your hoses fresh, and replace any lines that have any corrosion with new high quality parts, pay attention to leaking wheel cylinders, and you will never have a problem. Drive gently, and even if you do have a problem, you will increase the odds that you will have time to stop through engine braking, steering, or the parking brake.

In life, it helps to be a little lucky too!

-Chuck

 

[hndrsonj]

If you have to have the origional parts call CSI they can order them from AMG. But, remember you will pay the govt rates for the parts!

 

[mudguppy]

If it was me designing this "upgrade", I'd look at the reliability of the current system and compare it to the more complex one. By doubling the number of components, the probability of failure is also increased by a factor of two. ...

i believe this statement needs clarification. while it is correct to say that you have twice the chance for a component failure by having twice the amount of similar components, the odds of having a system failure are quite lower. every layer of protection, whether it be individual zones or redundancy, will lead to an exponential increase in odds that the system will not see a simultaneous catastrophic failure.

i design machine safety systems for manufacturing equipment. redundancy is the most simple way to create reliability in a system. zoning a system (i.e. dual circuit brakes) will also increase reliability because it will contain a single failure and isolate it from the rest of the system.

... You have to make sure that a failure that could occur in the simple system does not also occur in the more complex system in such a way that it makes the upgrade null and void ... but make sure you know exactly what you are doing when modifying the brake system, every little detail has an effect on the total reliability. Consider every fitting, every bend in the tubing made to spec, pressure ratings and on and on. ....

that's good advice - right on the money, bjorn.

 

[rflegal]

I have considered this carefully. There is a reason todays vehicles have dual systems. I have personally experienced failure of one side of such a system (a hose that showed no visible signs prior to failure) and was happy to have the split system. My '59 Anglia has a single system, and I will keep it as such for authenticity in the restoration, but then, it has a 36hp flathead four and a three speed and only weighs 1664#s. How many deuces is that?

The deuce brake system is typical of the era and not hard to understand. The airpack is a bit more complex, but its just a booster, similar to a vauum or hyroboost in effect.

I value all the comments made regarding inspections, maintenance and proper technique and second them strongly, especially on something as old and as big as a deuce. This is why I have all new hoses, WCs with new shoes and hard lines were applicable. After rebuilding the airpack and ordering a new MC, I'm reasonably pleased that the health of the stock single system on my M36 will be up to snuff.

However, Mudguppy is spot on on the redundancy factor. I'm a mining engineer; we have systems on top of systems on top of systems underground.

The comments from Stumps about MC failure point back to my concept of using two stock deuce MCs. The only common point of failure at that point is the mechnical brake pedal/actuation. 'Course, the fact that there a brand new MC sittin on the work bench is driving that motivation a bit too. Guess I could sell the extra MC and buy the dual.

I still think the dual MC is more convenient with less fabrication. Would love to have the Bendix Number is anyone finds it. I was on the Raybestos site looking at the Ford F800 MCs and some chevys. Matching pressure calcs/capacity at the MC and WCs through the system should ensure original design integrity.

MC piston stroke is the one question I am considering. Ignoring differnces in line lengths, etc for a moment. if you use the same MC to activate 4 WCs instead of 6 (focusing on the rear axles), you only need 2/3 the fluid volume to fully brake. Worse only 1/3 for the front. Would the stock MC be too big for service in a split system X 2? I've got a brake/hydraulics ref in the shop I'll need to dig up and dust off the cobwebs, but off the top of my head, I think this is an issue. Would you lose pedal travel before full lock up with two deuce MCs supplying the same spec WCs or does the valving in the two airpacs accomodate that? I'll have to study some more. You could alter the pedal mechanical ratio however to accomdate. Some calcs are in order I think...

 

[wsucougarx]

Also don't forget the air tanks. My split system has a dual chambered air tank on one of the tanks. So I've got 3 air tank drains valves that I need to drain at the end of the day. The great thing about the A2 (not sure if same for the A3's) is the Master Cylinder incorporates the PTO engagement handle mounting bracket. I didn't know that until I asked DANMARTIN. Those PTO engagement handles are like $100 alone w/out handle at TNJ Murray. So if you plan on winching your newly split brake truck in the future this will help out

 

[rflegal]

Good point Mike! I forgot about the additional air. Does your split tank sevice the front and rear (1/2 tank -> FRONT, 1 1/2 tanks -> REAR)?

 

[DanMartin]

Check out this thread (post #10) for a quick diagram of what would be involved in 'retro-fitting' a split brake system from a later model A2 or A3:

http://www.steelsoldiers.com/deuce-modification-hot-rodding/28531-split-brake-system.html

It's a lot of work to make it work right...let's make sure we all understand the complexity before proceeding.

 

[rflegal]

Been studying the TM (SMARPI) and some of the posts... I don't think it will be all that hard once the MC issue is licked... I had missed the one from the thread you included though (thanks)...

Bear with me as this will be long winded. I started MVs with an M725. Alot of the guys on the 715 zone would use a corvette master cyl so they could "upgrade" to a dual circuit system. In a single circuit system, one part failure would result in no brakes. Same with a deuce. One of the guys put rockwell axles under his truck and was unhappy with his brakes. He did some looking and found a 2001 3500 master with hydro-boost worked out great. It has a 1 9/16ths bore. Anyone know what the bore is on a deuce master? Anyway, Could this dual circuit master be put on a deuce and have a second airpack added, so you could have a dual circuit system? I have looked around and not found much info on obtaining a dual circuit system that is made for the deuce.

This and the F800 hydroboost unit were the one I was looking at at Raybestos. The F800 unit is 1 3/4 bore and the primary outlet is smaller than the secondary. I think this or the 3500 would work and the mount looks darn close.

Studying the SMARPI, it can be done safely. The more I think about it, though the twin MC idea will require non-stock-deuce MCs. At that point, lots of fabrication on the mount, but then you could use a Wilwood unit with appropriate bore and stroke and a remote reserviors. Could be quite nice. The remote unit @ 1 1/8 bore runs $67. Times two still isn't bad.

Does anyone know for sure if the deuce MC has a residual valve buit in. The one that the PO had install on mine was from a CAT unit or some other industrial, and did not appear to have one. The rebuild kit I have for the MC I don't yet (shipped from OD Iron) seems to have one built in. Typically, a 10# residual is used with drum systems to account for the return spring pressures on the WCs without causing wheel drag.

 

[m-35tom]

keep in mind that when the system is working correctly, the MC does NOT apply the brakes. it only controls the air pressure regulator on the airpack. it is the MC on the airpack that applies the brakes. with no air pressure and ONLY then, does the primary MC push on the piston of the airpack MC to apply the brakes. you have several options for dual brakes and the one i favor is just as simple as any other. that is to do away with the primary MC and replace it with an air threadle valve which then controls air to basic air units with a MC on each. this is the most modern system out there and used by isuzu and nissan on their box trucks. it also reduces the pedal pressure to less than that of any car.

the next simplest would be to just add a dual MC and another air pack. adding 2 seperate MC's is just making it too complex for no good reason.

as far as rflegal's question about bore size, if you do go to 2 seperate MC's you still need the same bore size as stock to generate the correct pressure for the air pack control valve.

tom