Brakes-no brakes

[Kaiser2boy]

I have gone over the breaks until I am sick of playing with them. I followed the adjustment procedures as outlined in the TM to the -T-.
The Mfg. of the master cylinder that I installed says I had to " power Bleed" the system. Not having any such power bleeder I took it to the local break shop here. The owner has worked on many older systems and was very familiar with the old dodge system.
I told the owner what was going on. He asked if I had bled the breaks and I replied "yes" several times and found no air.
He looked at the system and said, " you need to apply a tiny bit of pressure on the master cylinder plunger so it does not come back so far. It is allowing all your pressure to bleed off. He adjusted it a bit and the breaks have worked just fine now for several months of driving.
I was worried that they would drag but no such problem has happened. I took the truck out for several miles of in town driving where the breaks got used a lot. I drove home and jacked it up and spun each wheel to see if any were draging and al was well. I will keep it this way and see what happens in warmer weather. But so far so good.
I looked inside the cylinder and it looked like if I let the piston go fully forward it let the seal pass a tiny drill hole that bleed off any pressure. I am not talking about a half inch of reduction, I am talking about applying only maybe a 1/16 of an inch of pressure on the piston from fully out.
Like I said i am going to keep an eye on it and see how it goes.

[Kevin Tighe]

It always seemed to me that it is the brake return springs which push the fluid back to the master cylinder. The brake shoes should be adjusted such that they can only return to the point of free rotation of the drum and then stop. Once they stop, no more fluid should bleed back to the MC. If not the kinetic energy stored in the stretched springs, then what energy is pushing the fluid back to the master cylinder?
I don't think the push rod should be adjusted so that the little tiny return hole is covered. If the tiny hole really needs to be covered, than good engineering would dictate that the MC be manufactured so it was like that in a static position without the pedel/pushrod providing "pre-load".
Do you suppose that maybe the MC is not correctly assembled? Or that a washer might be missing between the piston and the clip that holds the piston in the bore?
These problems drive me nuts, I'm glad you've got it working.

[Charles Talbert]

This isn't right

This is what I can add. Once again the stock M/C has an internal residual check valve built in to keep this issue from happening. Malfunction of that check valve for what ever reason will cause the issue you have going on. If you realize that a problem exist, (obviously you do), yet don't take the necessary steps to get to the bottom of an obvious issue; then you take matters into your own hands not knowing if a serious outcome could result. First issue, brakes are not something to play around and experiment with; that could become life threatening really quick.

The issue could be the check valve in the M/C is the cause; not wanting to disassemble a new M/C to check it just because it is new is a rediculous reason for not checking that. Enough said there.

Back to shoe to drum adjustment; if you went explicitly by the instructions in the TM, you have wasted your time. It only works with new condition drums and mil spec new brake linings, neither of which have existed in years. The procedure for worn lining adjustments would apply somewhat, however is still not the best procedure. What Kevin said about correct adjustment on the top ends to keep the shoes from being pulled back too far holds much weight in this procedure. Sounds like what you have done is pulled the bottom ends too close, thus the top ends have to retract too much in order to keep the bottom ends of the shoes from dragging. Adjusting this type of brake is a different animal, the correct balance between heel and toe is crutial. I'd almost bet you have not reached that correct balance. A drum that is ever so slightly out of round makes it extremely difficult and requires pains taking adjusting to get a workable system. Sometimes it just isn't possible if the drums are very much out of round. The book doesn't even touch on any of that, thus the procedure described there can be and often is very misleading. The only way to successfully adjust them is to be very savy of exactly how this type of drum system works; the only way is to get it right once you completely understand it is to apply common sense to the adjustment procedure in order to balance it out.

The part most do not consider is the fact that with this system the cam adjusters and the force applied by wheel cylinders are both at the top end of the shoes. With most systems of today, the manual adjustment takes place at the bottom end only with the applied force at the top end. Since the m37 system has adjustments at the bottom and the top end of the shoes, that delicate balance of correct clearance so the shoes pivot into full length engagement with the drum comes into play. It must be done so that the entire shoe length comes into contact with the drum when brakes are applied. Most folks tend to adjust the bottom too close thinking the hydraulic pressure will force the top into the drum. Many times it does, but as a result of the bottom being to tight, the top has to retract more than it should in order for the bottom end to come out of drum contact completely. The balance I keep refering to is that the bottom and top ends of the lining contacts the drum simultaniously when brake is applied. This way the top adjustment can be tighter to the drum, resulting in the wheel cylinder piston not retracting as far back in by the force of the shoe return springs, which will result in less fluid returning to the M/C reservoir.

The check valve in the M/C works very well if all is right within the system. It can also be easily overpowered by the force of the return springs if the shoe adjustment does not have the right balance. This is exactly what Kevin's reply is suggesting that you check. I too am pretty sure this may be the majority of you problem.

One last thing; having pedal rod pressure continually on the M/C piston is NOT RIGHT; that you can take to the bank. So I guess the old timer has given bad advice. There should actually be a slight amount of free travel between the piston and the rod. You are not doing yourself a service by experimenting with such a band aid fix that could actually get you caught up in a serious problem. Waiting to see what happens before you address a known problem is not smart any way you look at it.

Several people have spent considerable time offering assitance in an effort to help you with this. Several have told you straight up that the approach you are taking is not a wise one. The ball is now in your hands; will you follow the advice of the one who simply told you what you wanted to hear or the advice from the ones who just tell you straight up that you do have a problem and have not gotten to the bottom of the issue. Your call.

[Kaiser2boy]

It always seemed to me that it is the brake return springs which push the fluid back to the master cylinder. The brake shoes should be adjusted such that they can only return to the point of free rotation of the drum and then stop. Once they stop, no more fluid should bleed back to the MC. If not the kinetic energy stored in the stretched springs, then what energy is pushing the fluid back to the master cylinder?
I don't think the push rod should be adjusted so that the little tiny return hole is covered. If the tiny hole really needs to be covered, than good engineering would dictate that the MC be manufactured so it was like that in a static position without the pedel/pushrod providing "pre-load".
Do you suppose that maybe the MC is not correctly assembled? Or that a washer might be missing between the piston and the clip that holds the piston in the bore?
These problems drive me nuts, I'm glad you've got it working.

I told a tiny lie. I did set the breaks the way the TM says to and it still had the problem. I went from useing that setting as a starting point. Then I went to jacking up one wheel and adjusting the bottom front adjuster until I felt drag and backed it up just enough to let it free wheel. I did this with all 4 adjustments on each wheel.
Still had the problem of when I let the M/C piston come fully to rest it would lose pressure and need to be pumped up again every time.
If the check valve was inop it wouldnt it allow fluid to come back all along the stroke ? why would it wait until the last split second? It holds fluid pressure for a few months now as long as I dont let it move one more 1/16 of an inch forward.
I fully understand that the breaks are not something to take chances with that is why I am spending weeks trying to figure out what the heck is going on.
I am going to go look at the MC again and see if the stop washer is there or not.

[Kaiser2boy]

Kevin, you mentioned the return springs. I did an experiment. I removed the brake drums, then measured the spacing between the shoes and then backed off the MC push rod to allow the piston to move forward the fraction of an inch to allow free play. Nothing moved on any of the shoes but inside the mc there is a sudden movment of fluid as if somthing bypassed and all pedal is lost .
It is a new MC from VPW. I was not too happy to see that it was made in China .
There is a stop washer against the retaining clip. How thick is it , I have no idea at this time. It just boggles my mind that allowing the piston to move just a fraction of an inch more can cause it to lose its prime and need to be pumped up.
There is no way to see what is going on inside the MC but there is something stupid happening in there.
I was starting to think that maybe the inside of the MC has a wide spot that allows the fluid to escape. There is no sign of any leakage anyplace.
The Mfg.say its because of air in the system. I keep thinking OK a little air in the system will give you a spongy pedal not cause it to go to the floor as if the system is empty.
I made an addapter to fit on the fill hole out of iron pipe.
It holds a full pint of Brake fluid. I filled it up and bled each wheel until almost all of the extra pint was gone and it did not change a thing. By the way at no time did I see any air come out nor did I see any bubbles in the MC tank. Very frustrating.
I can see the truck haveing a long pedal stroke if the brakes were worn down a lot or badly out of adjustment but having the pedal just go to the floor because of a small out of adjustment on the shoes does not make sense. If that were true then a truck as it is driving down the road could suddenly have no brakes at all because the brakes wore a bit too much. I just cant buy that. What a ultra bad design that would be.
I will get to the bottom of this problem but for right now it is totaly frustrating.
It is working right now and "seems" ok. My concern for right now is that with the tiny bit of "pre-load" on the piston it may cause the brakes to slowly drag if the wheel cylinders get hot. However I have driven it for quite a few miles in traffic with no problems ,,,yet.

[Charles Talbert]

Kaiser, you and I go just a little further than voices on this forum. I really hate to see an issue come out of this brake thing you have going on. If you are satisfied the shoe adjustment is ok, fine. I know something of your experience here and credit you with that. My next recommendation would be to change out the M/C to a non - Chinese unit and see if the same issue happens with the replacement unit. I personally have not seen any Chinese M/C's. Obviously if another unit fixes the issue, then you know the Chinese one is junk. Go back to the supplier for a refund and let them know they are selling inferior products. I've worked on a lot of these cylinders; in my opinion, your problem is either with a check valve malfunction or the shoe adjustment. These Chinese units may well have something about the residual check valve that is not set up to function correctly; heck they may not even have the check valve in them, who knows. I've seen similar issues with various Chinese components. It may be that the rubber parts used inside the M/C are not even compatible with brake fluid and crack or turn to jelly when fluid is added; I know this may sound insane, but it wouldn't be the first time I've seen something like that. I know a gentleman who has been an overseer of Chinese manufacturing. He tells me straight up, they can make a decent product; but if you tell them price is the principle driver of sales, they will show you just how cheap and sorry they can make it.

If I were you, I'd tear down that M/C to satisfy my own mind.

If push comes to shove; you can install an in-line residual check valve and cure the issue. However if the M/C internals are working correctly, that extreme shouldn't be necessary, but it is an option that will work in your present situation. My uneasy feeling is simply this right here; if something within is malfunctioning; how long will it be until you press on the pedal and it builds no pressure regardless of how much you pump it. If something is going on internally with your M/C, that is a very real possibility.

I'll go just 1 step further, if I had sold you the M/C and you notified me of this issue; I wouldn't insist that the system had air in it after hearing your procedural explanation. I would send you another M/C and ask that you return the problem one so I could disassemble it for my own inspection and diagnosis of what might be going on. If I thought there was even a remote possibility that I was selling bad brake components; I wouldn't rest until I verified all components in question with solid evidence. I don't understand why others would want to do any different. The liability could be huge, not worth that risk in my mind.

[Gsmith]

In his first post Kaiser mentioned originally having the described problem and then changing the master cylinder only to still have the problem, then noticing the push rod adjustment being in a preload condition. The options are obviously quite limited on the fix. I think as Charles suggested, another master cylinder should either cure the problem or dispel the theory. Have the brake shoes been changed? I know you said the wheel cylinders are good.
I do know when I restored my M43 I installed new shoes, m/c, wheel cylinders, return springs. I adjusted them initially feeling they should be close. When I got to the point of all new brake lines installed and ready to bleed them I did so and had no pedal! I told my son they still have air in them somehow, bled them again and still nothing. Jacked each wheel up and got really serious on the adjustment issue and that was it.

[Charles Talbert]

I agree it surely could be shoe clearance adjustment. I guess we may as well be quiet about it, I see nothing else for us to suggest on a long distance basis. We aren't there to actually check it out, so what else is to be said on our part?? If it were mine, I'd get to the bottom of it 1 way or another, but it isn't so that's that. I just don't take any risk factors with brakes; that is a 0 tolerance rule around here. I know an incomplete release of the M/C piston is masking some larger issue; something simply is not right if that has to be.

[maineSS]

Charles is absolutely right about tearing down the MC for a good look. One of the reasons the former owner of my truck sold it was that he couldn't get the brakes to work- even after installing a new MC from VPW. I couldn't get them to work for awhile, either- pedal went straight to the floor.

When I disassembled the MC, I found the Residual Pressure diaphram had been installed backwards- from the manufacturer. VPW did recommend making a pressure bleeder from a plant insecticide sprayer, after doing that, bleeding was simple, quick- and complete. When I fixed those two problems, I was able to get full brakes. Don't take anything for granted with brake systems if the slightest problem occurs.

[Kaiser2boy]

Well I'll be.
Today it was not so cold out in the garage so I took the bull by the horns and yanked the new MC out.
I took it apart and examined every stinking part looking to see if anything was amiss. I could not see any problems.
Then it struck me that there was a part missing. I looked high and low to see if I had lost the stop washer that fits between the piston and the lock ring. There was no stop washer. In another post I was asked if there was one in there and I popped off the boot and looked in and thought I saw a washer but it actually was the end of the piston, my bad.
I went and dug out the old MC figuring I could steal the washer from it,,,wrong it too was missing the washer. That MC was doing the same thing , going to the floor thats why I got the new one.
Anyway I fabed one on my old South Bend lathe and it eliminated the problem.
The washer ended up being .105 inch thich , just a smidge over the 1/16th of an inch I was pushing the piston with push rod.
With it all apart I could see that if the piston was allowed to move forward the 1/16th of an inch it allowed the piston seal at the output end to move a tiny bit over a hole that led to the resivour and bleed off any pedal I had.
I wish to thank all of you that pitched in on this frustrating problem.

[Charles Talbert]

All right! I feel better about your safety and well being tonight. I knew if you looked deep enough, you would find something.

One thing still puzzles me however; you said your new M/C came from VPW. We all know that they have a shop and offer service for these trucks as well as selling parts. Both you and MaineSS had new master cylinders from there that didn't work right. It would seem strange that since they also install parts in their shop, they would not have run into this issue with the M/C's they install?? Why did they simply try to tell you it's just air in your system? Are they aware of this missing spacer; and simply adjusting the push rod to hold pressure against the piston on the ones they install as you had to do to get yours to work? I wonder?? I can only say that liability risk are way too big for me to be knowingly selling stuff like that.

[Gsmith]

Excellent! We're all glad you didn't give up and were able to get it figured out. It's really a shame when one has to fix brand new parts!

[maineSS]

When I was originally looking at my MC, I thought something looked funny with the RP diaphram, but not having prior experience with these MC's, I buttoned it back up- and experienced continued problems. Then I got an exploded diagram of the MC and localized the failure.

There are a lot of subtle problems that can happen with these apparently "simple" MC's that are not documented in the shop manuals- maybe Gordon should add an MC troubleshooting section to his manual revision....