Brake Bleeding Unnecessary on Deuce?

GammaGoatGuy

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I got a deuce from a friend. I drove it home but it has a leak in the brake system. After sitting for a few months, it now has no fluid in the master cylinder. He says it has a small leak that he has never been able to find, just add fluid and go, no need to bleed the brake system. Sounded a little funny to me as I always thought that you had to bleed the system for it to work right, although I guess if there is a leak, it’s just going to suck air in through the leak anyways. Also for added fun the e-brake doesn’t work either. Just have to drive it a couple miles at the moment but I thought I should run it by you guys before killing myself.
 
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gunboy1656

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DON'T put it on the road, without brakes. Find the leak, refill and bleed the lines.

You have almost 14,000 pounds rolling down the road. Even a couple miles is to far without them. what happens if soccer mom pulls out in front of you with?
 

73m819

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"thought I should run it by you guys before killing myself. "

OR SOMEBODY EALSE, all you need to do is ask yourself "would i went my family put put at this risk" if not ,dont put somebodys ealses

ps the black on dark od is hard to read
 

mbarber84

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WHOA trumps GO anyday!

The Deuce brake system is really sketchy, even when it is in perfect condition. I would advise going over the entire system, locate and repair problems, and THEN take`r for a ride. If there is a leak in the sytem, disaster could be right around the corner, and the parking brake will NOT stop the truck.

Be careful and good luck!
 

stumps

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Fixing the problem is essential, and should be done ASAP!

[Please accept the rest of this post as being for information only. It is not a recommendation in any way shape or form.... ]

If you catch an empty master cylinder reservoir just as the pedal goes away, refilling will very often restore proper operation... The master cylinder is capable of back bleeding the air out of itself, and a very short amount of the brake line below it. All it takes is refilling the reservoir, and a bit of pumping of the pedal to do the trick.

I have replaced master cylinders on other vehicles without bleeding the brakes. For this to work, though, it is essential that the lines that leave the master cylinder slope downward from the master cylinder.

Slow leaks in the wheel cylinders tend to remain slow leaks for a long long time. Slow leaks in brake lines or hoses tend to become gushers the first time you have to stop really hard, or whenever Murphy says it is time.

-Chuck
 

clinto

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Yes, you need to bleed it. Build a pressure bleeder and you can do the entire truck (airpack and wheel cylinders) in about 10 minutes. Do a search for pressure bleeder here on the site.

Then, find the leak. It's gotta be going somewhere. If you need some assistance, do a further search using words that would be common in this issue, "brake, leak, etc". There are some very good threads out there that describe where they leak and how to diagnose them.
 

Speddmon

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All of the above posts are very very important...DO NOT drive that truck with no brakes!!!!!!

Now, on to your question. Yes, you do need to bleed the brakes. While the brakes on a deuce are older, and only a single circuit system versus a modern dual circuit. They are essentially the same as on any other car out there. They are a closed hydraulic system. The only difference being that rather than using vacuum to boost the pressure, the deuce uses air and the air pack.

I find it hard to believe that the previous owner had a small leak and couldn't find it. In any brake system, but especially these older single circuit systems...any leaks and your pedal is going to the floor. With the deuce again, any leak means absolutely NO brakes as the fluid is going out through the leak and not to the wheel cylinders where it needs to go.

Get yourself a helper, fill the master cylinder with DOT 5 and crawl under your truck; and have the helper start pushing the brake pedal while you check each line leaving the air pack for leaks....if you don't see it, then you need to start checking wheels next. If you're loosing fluid it's not good. The brakes on the deuce aren't that hard to work on, so take some time and check them over really well. You and your family and possibly someone elses family will thank you for not killing them.
 

mckeeranger

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Slow leaks in the wheel cylinders tend to remain slow leaks for a long long time. Slow leaks in brake lines or hoses tend to become gushers the first time you have to stop really hard, or whenever Murphy says it is time.

-Chuck
And unlike newer vehicles, a gusher on a deuce means NO brakes. I mean none at all.
 

stumps

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The Deuce brake system is really sketchy, even when it is in perfect condition.
They are not! There is a wide variety of safety features incorporated into the Deuce system that you are not aware of: Tempered steel brake lines, with internal and external plating to reduce corrosion. Double flare joints. All steel hydraulic fittings. Brake hoses with two internal braids and two internal rubber linings. Self balancing wheel cylinders that adjust for brake wear and apply equal pressure to all brake shoes. Special DOT approved rubber compounds that are designed not to react with special DOT approved brake fluids. Tight fitting aluminum piston backers that eliminate blowouts of rubber piston cups....

The list goes on and on. What the deuce brake system doesn't have is a dual circuit fluid system. It is not resistant to ignoring inspection or maintenance of the system. It is not resistant to brake hoses or lines being severed either intentionally, or through abuse.

Even the most modern dual circuit brake system contains numerous potential single point failures. Some examples are: broken brake pedal pins and linkages, master cylinder failures of most any sort, Pedals, and vacuum/pressure assist units getting mechanically blocked from full travel. Broken master cylinder reservoirs, or reservoir hoses... And an important one: an operator that lacks the strength or physical ability to overcome a failure of the vacuum/pressure assist unit.

The only thing potentially "sketchy" about the deuce's single circuit brake system is the maintenance and inspection schedule it gets while it is under our control... a potential problem that dual circuit brake systems also share.

-Chuck
 

stumps

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And unlike newer vehicles, a gusher on a deuce means NO brakes. I mean none at all.
Keep believing that... if it helps you sleep at night. I had a line rust through on my PU truck with its Bendix dual circuit system, and I lost ALL braking action. The pedal went to the floor, and pumping did nothing. I had to stop the truck with a combination of steering, engine braking, and the parking/emergency brake.

Neither single circuit nor dual circuit braking systems are resistant to poor maintenance.

-Chuck
 

Keith_J

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Check ALL hoses, they want to spring leaks. Then look at each backing plate at the 6:00 position, there is a 3/16" slot on the outer diameter flange, if there is any liquid here, you have a leaking wheel cylinder.

DoD got cheap at the end of the service life and used wheel cylinders rebuilt with straight springs WITHOUT expanders. These are cone-devices on both ends of the wheel cylinder springs which force the cups out, making a positive seal. The straight springs WILL EVENTUALLY LEAK.

There is no need to get new wheel cylinders, get the OD Iron rebuild kits and a wheel cylinder hone. Take the WC off, remove the bleeder and pull the cups off. Push the pistons, cups and spring out. Save the pistons, throw the rest away. Use old brake fluid of the same type as a honing fluid, saving the brake fluid in the WC is a good idea at current price. Hone until uniform. Clean well several times, blowing out the connection holes. Wet the ID with clean brake fluid and install the cups, spring and pistons. Cover with new boots. Clean the pushrods, then wet the tip with fresh brake fluid and push through the boots. Reinstall with new copper gaskets (or switch them around so grooved side is next to the smooth side) and keep the bleeder screw loose. Top off the master cylinder and close the bleeder screw when brake fluid is steadily dripping.

If done on a 12k bearing service, it takes an additional 20 minutes. And it only takes 5 minutes to rebuild, well worth the $20 savings over a new wheel cylinder.
 

Keith_J

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They are not! There is a wide variety of safety features incorporated into the Deuce system that you are not aware of: Tempered steel brake lines, with internal and external plating to reduce corrosion. Double flare joints. All steel hydraulic fittings. Brake hoses with two internal braids and two internal rubber linings. Self balancing wheel cylinders that adjust for brake wear and apply equal pressure to all brake shoes. Special DOT approved rubber compounds that are designed not to react with special DOT approved brake fluids. Tight fitting aluminum piston backers that eliminate blowouts of rubber piston cups....

The list goes on and on. What the deuce brake system doesn't have is a dual circuit fluid system. It is not resistant to ignoring inspection or maintenance of the system. It is not resistant to brake hoses or lines being severed either intentionally, or through abuse.

..

The only thing potentially "sketchy" about the deuce's single circuit brake system is the maintenance and inspection schedule it gets while it is under our control... a potential problem that dual circuit brake systems also share.

-Chuck
All A2s have manual adjusters on the brakes. Some have nickel plated steel pistons. Some may not have the boot blow-off prevention modification (small notch at the bottom of the boot's outer seat on the WC).

And the A2C deuces have dual circuit. But with a common reservoir so if there is a single circuit failure, you will eventually run out of brake fluid. The A2Cs still have manual adjusters as these are non-servo systems.
 

Jake0147

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He says it has a small leak that he has never been able to find,
If the fluid is missing, it went somewhere. All six wheel ends need to be inspected. A master cylinder full makes a good wet "trail" on the tire that will lead right back to the issue, or a line/hose/fitting may be leaking. These can reach a low spot and drip without making an easily visible wet spot on the truck. The ground underneath may be a clue depending on the surface. There's also the air pack, which can leak brake fluid right out the vent, in which case it would probably be mixed in with all the crankcase slobber and may not show up very well at all.

just add fluid and go, no need to bleed the brake system. Sounded a little funny to me as I always thought that you had to bleed the system for it to work right...
Close...
For the brakes to work right you have to have the air out of the system. Often that means that if there is air in them, then it must be manually removed (by bleeding the brakes) but depending on the nature and location it may very well not be necessary in order to remove the air. Not an every day thing, but very far from unheard of or unbelievable.

I can't say that I've never taken a risk before, and I won't pretend that I never will again. However, given no parking brake, and a mystery failure in a single circuit brake system, you have a lot of eggs in one basket, and the handle is about to fall off. A couple of miles is better than a couple of hundred miles, but it only takes a couple of feet to run over your neighbors kid... Use good judgement.
Just for grins, (and anybody could benefit from this, not just the OP) get your deuce up to cruising speed, Do not touch the brake pedal or the parking brake, see what takes to get it to a stop on a slight incline, and better yet a slight decline. See if you can repeatedly nail first and/or reverse (which are unsynchronized) or getting the transfer case shifted to low and using second, so that you can stop the engine to hold the truck on said (very slight) hill once you do get it stopped. It is reassuring to know that you can do it, and a bit of a reality check to realize just how much difference a SMALL difference in incline can make, so that you can better plan your "other way out" in the event of trouble.





 

mbarber84

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Stumps,

to clarify, want I meant by "sketchy", was that they will not tolerate a hole, leak, or other malfunction, even if everything else is perfect. Just didn`t want to see anyone get hurt.

But I agree with everything you said :wink:

A+++ on the brake maintenance schedule!, I just wish I had the time to continuously check and re-check mine. Thankfully I don`t drive it that much.
 

stumps

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Hi Matt,

The Bendix brake system was developed to address the concerns over the older mechanical systems that used a variety of linkages, bell cranks and cams to actuate the brakes on cars. It was envisioned as a safety brake system... and it was. It also allowed front brakes that worked... a kind of important development.. The designers were mindful of the fact that there was only a single hydraulic circuit, that if breached would disable the brakes. But towards that end, they chose to keep the system simple, and to design the individual parts not to fail.

Single circuit hydraulic brakes, of the Bendix design, were used almost exclusively from the late 1920's through the early 1970's (in trucks). I think that would tend to indicate they were a safe and successful product.

I have owned 5 vehicles with single circuit Bendix brakes over my lifetime, and they have all performed wonderfully well. Most went hundreds of thousands of miles without any failures. Regular service and inspection were the key to that, though... and in the later years, DOT 5 brake fluid was a blessing.

I have owned 6 vehicles with double circuit Bendix brake systems. Two of the 6 suffered repeated failures that resulted in total brake loss. By my recall, I had two master cylinder failures, and two rusted through brake lines. In spite of the dual circuit, the rusted through brake lines did NOT leave me with any brakes! In addition, I had a friend who had a rusted through line on a '74 Dodge PU truck that left him without brakes... while I was in the truck, no less!

I know, I know, rusted through brake lines, how could I ever allow such a thing to happen?... especially when I am Safety Boy? Scolder of the lax... I guess I too got lax in inspecting the system because I believed that it would suffer any single point failure. I knew the lines were rusting, but I did nothing about it.

I know what will happen with single circuit brakes if I get lax, so I don't.

All brake systems are sketchy if you don't perform regular service.

-Chuck
 

TexAndy

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you might have a wheel cylinder that is leaking. This would account for the lack of fluid.
If he's just been topping off the master cylinder and going, he might have a really new looking shoe on that wheel, too. From what I've seen, the shield is not really good at keeping DOT 5 that's leaking out of the wheel cylinder from getting to the brake drum. A whole bunch of refills without addressing the leak could make this an issue.
 

m16ty

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And the A2C deuces have dual circuit.


That statement is a little misleading. Only very few of the M35A2Cs have dual circuit brakes. The latest model ones only.

I've got a 1972 M35A2C and it has single circuit brakes.
 

WingCO

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I would agree with 4 Star General. The only thing that makes this system 'sketchy' is a lack of PMCS (his last point), and, by the way, the M35A2 is almost 15,000 lbs. (empty) of very unforgiving steel. I once had a brake light pressure switch fail and start leaking about 3 miles from home base. I had to use down shifting and the hand (e) brake to nurse the vehicle slowly home (and I had relatively flat terrain). Now that was sketchy and really increases the pucker factor! I don't recommend trying this for kicks.

I would recommend, however, checking all of the connection points and fittings in the system, and if you have a 1988 or later you have dual hydrovacs (one at the master cylinder on the left and one on the right side of the vehicle (that's where the brake light pressure switch is located). After working on the system, do follow up inspections to make sure that the leak you fixed is not still leaking and to find out whether or not another weak point is beginning to leak. PMCS, PMCS, PMCS.
 
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