I fixed my '72 by install a hydroboost......

went through it ALL, and I think that typical GM feeling on the brakes, ie squishy as hell soft pedal I never had much trouble flooring to the floors, on car after car, they all had that feeling they don't really have much brakes....over the years though I had proven I could lock them up though....

ALL vac assist boosters have that 1/2 soft squishy feel....even Ford and Mopar....and the imports too....part of the function of the system...

but on my shark, that feeling was grossly exaggerated and I went through hell wondering why, went to over sized truck master cylinders, played with everything 16x over....same crap.....

finally gave up and went to HB...fixed the problem, then got rid of the large truck master and went to a aftermarket unit from Pirate Jack racing, lightweight aluminum....

solid as a rock, tap the pedal and it stops NOW, not on the floorboard....

same deal on the motor home....and it's disc/drum like all the rest of my cars were....

I tore the booster apart, and it was fine internally, held vacuum even pretty good over hours....there is a tough little ~1" dia spring between the input and output shafts on the booster....I think that even though it's wound with 1/8" steel and tough as nails...under a foot with about 10x the force, it's going to collapse....the HB units are a hard shaft setup clean through....

 

Thanks for the pictures Noonie. That is the height of my pedal although my brake switch is of a different design. Your bleeder set up looks good. I tend to agree with you Rodger. The chrome master looks good but if it don't work it ain't worth crap. If this is the actual problem it has cost me a lot of money, time, agravation and a not so good change in my vocabulary when I'm working on these brakes. Thanks for everyones help so far.

 

WOW, a quick question but over a month's worth of answers and still not fixed. Bummer.

 

You got that right. A very perplexing situation !!!!!

 

I finally recieved the third new m/c from tuff stuff after a week. I've put the four new rotors on, four new calipers, all new pads, blew the lines out with air again and will put the new master cylinder on tomorrow after bench bleeding it and bleed the system again, hopefully for the last time, but if I can't get a good pedal the shop owner will bring his power brake bleeding machine over next week. However, the shop owner wants to use dot 4 fluid instead of the dot 3 I have been using. I know dot 4 doesn't get contaminated with moisture but I think you don't get as hard a pedal as with dot 3. What do you guys think I should use. The shop owner says dot 4 is all he uses on any car and has used it on all of the C3's that he has done with no problems.

 

I'm experiencing the EXACT same situation you are with my master cylinder replacement on my 73 over the last few days! It's VERY frustrating, but what I've been told is that I definitely still have air in the lines, even after using a vacuum bleeder. What I was told to do was to use a pressure bleeder and that will do the trick. So I'm trying that on Sunday and we'll see what happens. Good luck to you too!

 

Changing from dot 3 to dot 4 is not going to help!
You need a new power booster.

 

Yikes....I'm about halfway down this road. New master is on. Rebuilding calipers. Bled through a gallon or so of fluid so far, made the homemade bleeder.......I may just throw in the towel if you can't resolve yours !!!

 

dot 4 and 5 may not get contaminated with moisture, but the moisture will still get in teh calipers, and i've found, although the calipers are ss lined, they are still cast iron and teh bottoms of the cylinders are exposed to moisture, as are the springs,,,, i've disassembled teh calipers in my 68 a few times since i installed tehm, and found moisture and rusty springs,,, i cleaned them out, and rebuilt them...
just didn't want you to think dot 4 or 5 is "snake oil", that will eliminate moisture problems....

 

The shop owner has dot 4 in his brake power bleeding machine because that is all that he uses and is reluctant to clean his machine and use dot 3 just for me. I just want to make sure that I don't create any more problems by using dot 4. LORD knows I have enough problems already.

 

After pressure bleeding the system, my problems are gone! Finally got ALL the air out of the lines and she's good to go. My symptoms were the same as yours until I used the pressure bleeder. Good luck with your situation.

 

I'm happy you got yours fixed. Not so happy about my situation though. The shop owner came over Tuesday night and brought his BG power bleeder machine . We power bleed the system three times and got a good pedal but as soon as we started the engine and put my foot on the pedal it went to the floor again. Same old problem and believe me , it is getting old. We then pulled the booster and master cylinder off and checked the rod length from the brake pedal to the booster and adjusted it to the absolute end of the rod which wasn't but one thread on the rod. We put the rod that goes from the booster to the master out of the old booster into the new booster because it was .020 longer than the one that came with the new booster. Put everything back on the car and same as usual, pedal to the floor with engine running. Drove the car around the neighborhood pushing on the brakes at every opportunity and using the emergency brake to stop. That made no difference at all. The shop owner is coming over Sat. and is bringing a pressure tester to check the pressure at every connection with the engine off and on to isolate each component and try to put an end to this problem once and for all. I personally think that it is yet another bad master cylinder. If it is, the next one won't be from the same company as these three came from. I talked to tech support @ Master Power Brake today and told him my story and his responce was ... you guessed it .... BAD master.

 

Sorry to hear that.

Just to recap, some questions.
1-With the booster mounted did the pedal have to be moved from full up to insert the pin, and if so, how much?
2-With the engine off, pushing the pedal by hand, how much does the pedal move from normal up position? (in inches)
3-You are using a 1-1/8" dia master?
4-Which booster do you have? See pics below. One has recess for master, other doesn't.





If you really feel like it's the master, since they already agreed to it being bad, pull it apart and look at the bore. Frankly, If bad, I would hone it properly and reassemble, no harm done at this stage.
For 50 bucks, NAPA has premium new master. I have had the best luck with them lately.
Post some pics of the bore if possible.

 

That you still have the same problem is a real bummer to say the least! Hang in there! You are lucky to have a real expert to come over and help you.
There are some real full time mechanics on this forum that have offered some very good advise and it seems that they and you are stumped on this one, at least I am.
Lest see what the pressure tests indicate.

 

Sorry to hear you're still dealing with this...very frustrating indeed

 

Billy,
Sorry to hear that you are still having problems. I think that while the problem that you are having could be a whole bunch of defective M/Cs, it is unlikely. TJP440 and I have suggested that the booster push rod, between the clevis and reaction plate inside the booster may be too short. (Not the push rod from the booster to M/C.) After switching out all the parts and a boat load of money, it might be prudent to call Ecklers's technical support (as suggested in the linked post) for a push rod extension. A trip to the hardware store and you might cobble something together with a piece of all thread and a barrel bolt (the thingey you use to join two pieces of all thread). If nothing else it would eliminate the possibility, and shut me up.
Ed

 

Answers to Noonies questions:
1. I only had to wiggle the pedal a little from full up to get the pin in, no pedal travel at all.
2.With engine off I think the pedal travel by hand is about 1/2 inch. I'm not near the car now or I would measure it.
3. Yes it is a 1 1/8" bore master.
4.I have a recessed area in the booster for the master.
I have devised a method to increase the pedal to booster rod length and make it adjustable if I need to do it but at this point I think the rod length is correct. I heard today that the shop owner is bringing a brand new "reliable brand" master with him along with his pressure gauge tomorrow so hopefully we can finally get a positive result.

 

Today the shop owner came by but he left his pressure gauge at his shop. He did bring a new master and his BG power bleeder again. Every trouble shooting guide that I have read has pointed to a bad master. The shop owner thought that it was the master as well as all of the techs that work for him. He wanted to replace the master when he got here. I wanted to test this last new chrome one that we just put on before replacing it with his so we put the steel plugs in the brake line ports. When I pushed on the pedal it was rock hard as it should be, when I started the engine and pushed on the pedal, it went to the floor as the last master did. This should prove that the master is bad so we pulled it off and put his new one on. Bled the brakes several times and got a pretty good pedal, started the engine and pushed on the pedal and it went to the floor again. This could not be another bad master. We did not put the steel plugs in his master but I will. I have a couple of questions for the brake experts reading this.
1. Is installing steel plugs in the line ports of the master the most reliable way to test the master?
2. Should the pedal stay hard and at the top with the engine running as well as with the engine off and have you personally tested one with these results.
3. What would be the result of low vacuum to the booster. Don't just say the booster won't work. What would the result be , hard pedal, no pedal, no assist, what.
I have replaced every component multible times except the new booster and I only have the no pedal problem with the engine running so I"m wondering if the booster might be a factor.

 

I was hoping for a better outcome.
Bet your sick of buying fluid.

4-That sounds like the pedal cannot go higher no matter what. If the arm hits the pedal mount frame with the brake switch removed or adjusted all the way out you're good. I've run into some rebuilt boosters that have adjustable inner rods etc, but they are incorrect by oem standards. You can interchange the only two different oem boosters. There was no difference on the pedal side, just on the booster side to accommodate the short piston master. On the pic I posted earlier, check the pedal to frame clearance above the vac hoses for reference.

1-The only way to test it. As I said before, I've broken loose the seat back on one.

2-I test all of the masters I put in, just part of doing it, so you don't have to back up and second guess. With the engine off, you should get around 1/4" of pedal drop and running it should be about 3/4" drop.

3-Basic rule of thumb, the lower the vacuum, the less assist, the harder the pedal and higher.
With 18+" of vacuum, with these old boosters, your pedal will always be slightly mushy. By that I mean it won't be like a modern new car, the newer are designed for a lot more "pedal feel". It's really a very subjective question and answer. With 10" of vacuum, your pedal will be harder and require more effort. With no vacuum, there is a lot of effort required as you know.
Booster just works by inches of vacuum and diaphragm area.
If I had the time and inclination, I would try and retrofit a modern, small diameter, single diaphragm booster to a C3 and it would be perfect.


Post # 79
I still think it's the booster or your booster/master rod length at the very least. (By rod length I mean it is long enough to keep pressure on the reaction disk, but not long enough to cover the compensation port in the master and cause brake lockup).

Just for fun, an interesting test would be to take the chrome master, bled properly with and a pressure gauge and use a shop hydraulic press to test at what pressure it will fail. Anything over 1800 psi, the master is good.

 

I started my day fooling with the car again. I still had as good a pedal as yesterday maybe even a little better. Started the car and pushed on the pedal and it went to the floor but not quite. I had about a 1/2" of pedal. I turned each rotor by hand while my wife pushed the pedal down with the engine running and the brakes actually stopped each rotor. That put a smile on my face. I put the wheels on the car and took it for a spin through the neighborhood and the brakes were working although the pedal was virtually to the floor. I made a lot of laps around the neighborhood starting and stopping, as the laps increased the new brake pads started to seat and the car started to stop better so I ventured out on the road and increased the speed up to 50 mph and applied the brakes repeatedly trying to seat the pads more. The pedal height increased to about 1/2" again due to the heat build up I guess. I headed home very pleased that I had gotted to drive my car again after two months. So I now have brakes working but not much pedal. It would be unnerving to try to drive it in traffic. Talked to the shop owner and he seems to think I would be alright if we could raise the pedal height more by changing the booster to pedal rod length. He is not sure if we have any room to do that. We might have to relocate the brake light swich in order to let the pedal go to the stop. Now ...... why I suddenly got a little pedal with the engine running, I don't know but I guess its the master that he brought over yesterday because that is all we changed. Why I would have to adjust the pedal to booster rod to get a higher pedal height when my pedal height was fine when I first finished the car is a mystery to me. The shop owner is coming by Tuesday after work to help me some more.