OK,

Here is the story. I have 15 inches of vacuum, the master cylinder and brake booster are 100% gone through and new. This problem ONLY HAPPENS 50% of the time and ONLY IN REVERSE. The brake fluid has been changed and the whole system including the master cylinder has been completely bleed. All the vacuum lines and brake lines also have been checked for leaks.

So why does this happen? The pedal when backing up in reverse will go completely to the floor making me have to pump like crazy in an effort to stop the car!!! It is like I totally lose my brakes but ONLY IN REVERSE AND ONLY 50% OF THE TIME. I have drums in the rear and someone told me that the shoes flex differently under braking when in reverse. So what could be the problem?

Also, where should I take it to have it inspected. The local meineke shop in my area doesnt even have a POWER BLEEDER and when you talk to the guy on the phone, he almosted seemed to have a heart attack when I told him it was a 69 camaro. Almost like he was afraid to touch it!!!

are there any leaks? even if it is a problem with the rear drums, the fronts are still 70% of the braking power and if it feels like you almost can't stop the car, chances are it's something else. Maybe the mc or the proportioning valve? That seems like a really odd problem.

Everything checks out. It ONLY HAPPENS WHEN BACKING OUT OF A SPACE IN REVERSE!! And at that it only happens about 50% of the time. Problem is I dont want to be in a situation where I am backing out of somewhere and I cant stop and crash into someone, or something. It has gotta be a mechanical hangup somewhere. Maybe a shoe is overextended on the secondary side? Since when you go in reverse the majority of the pressure switches to the secondary shoe correct?

Just to make things clear, do you have disc or drum front brakes?

Mike

I have front Disc, and rear Drum

first thing you want to do is check the adjustment on the rear brakes. The shoes should just kiss the drums when the brakes are not applied. There should be an access hole that will lewt you access the star wheel between the bottoms of the shoes. When going forward, the drums are "self-energizing" the movement of the car helps apply the brakes. In reverse they are not.

What you describe could happen is the drums are adjusted too loose.

first thing you want to do is check the adjustment on the rear brakes. The shoes should just kiss the drums when the brakes are not applied. There should be an access hole that will lewt you access the star wheel between the bottoms of the shoes. When going forward, the drums are "self-energizing" the movement of the car helps apply the brakes. In reverse they are not.

What you describe could happen is the drums are adjusted too loose.

Just what I was going to say. Check the adjustment on the drums.

This situation is diffently different. Your back brakes adjust when going in reverse. The star wheels are side specific. One is right hand and the other is left hand. Another thing that I would check is if the rods from the brake cylinder, that expands your brake shoes are in place. If they are not, I could see why your brake pedal is going to the floor.

Quit driving your Camaro till you get to the bottem of this. There may be a time that you cant stop while going forward like 1% of the time. Phil

do you have the right parts installed as above and the long shoe on the leading side of the drum? I am pretty sure that is how they are. Might want to look at the brake hardware and see what's up. Broken spring? star wheels reversed ect.

Joe

OK,

I am convinced I have to have the most difficult unsolvable brake problem in the entire world. Brought it to MEINEKE. They completely dissassembled the back drum brakes, checked them grinded the surfaces of the pads and the contact areas and lubed them. Also checked the front. Checked all of the lines for leaks, Reassembled both back drums, adjusted them accordingly. The master cylinder cover leaks and they thought that it was coming from the back of the master cylinder so they disconnected it from the booster. It was bone dry in the back so they reassembled it. BLEED THE ENTIRE SYSTEM. Then the technician went to back it out of the bay and WHAM!! The pedal went right to the floor like a total loss of brake power. Just like I explained it before. Should have seen the look on his face. ALL FOUR GUYS IN THE PLACE STILL COULD NOT FIGURE OUT THE PROBLEM!! They rebleed the brakes and got air out of the back driver side . Drove the car again and it still has a NOT RIGHT feeling to them but they are better. But they STILL ARE NOT ANY BETTER THAN WHEN I WENT IN THERE!! I know it is only a matter of time when it will happen again.They even went as far as to tell me that they thought that air was getting sucked in through the cover. I cant believe that since the only way it would suck air is when the fluid runs too low other wise when you bleed the brakes with the cover off to keep the fluid level up it would suck air the whole time. I really am fed up with this sh&t. Getting to the point where I am about to pitch all the lines, master cylinder, booster, combination valves as well as the whole braking system drums, discs and all and start completely over with all new everything. I am convinced this is the ONLY FRIGING WAY I AM EVER GOING TO SOLVE THIS PROBLEM. I recently bought but have not installed the Hydroboost Unit. I called the guy from Hydroboost who has been VERY VERY PATIENT AND HELPFUL and even he said this is the oddest problem he has ever come across!! One more thing to add, the brakes will not lock up. I can stand on them with a Mack Truck and they will not lock up at all. ANY INFO would be greatly appreciated. Also if anyone is in the area that is an expert with brakes inside and out and is looking to make some cash let me know. I am in the Middleton Mass area.

Thanks
Mark

fluid is gone? Maybe the master is leaking and the booster is sucking the fluid into it? The booster is under vacume?

Joe

No fluid is not gone. It is leaking from the top cover. It is overflowing out of the top but the fluid is not empty.

(short shoe leads)

If they believe the problem to be air getting sucked in thru the cover they dont understand the system they are working on. You are correct about that.

What exact parts are you using, front, rear, and under hood, and who installed them?
do you have a digital camera?

I'm too far away to help in person.... about 14+hrs south of you in NC.

definitely an intriguing and disturbing problem...
sounds like you have maybe more than one thing going on.

You said the power booster and master cylinder have been 100% gone through. Was the problem there prior to this work being done? What do you mean by gone through? Rebuilt or replaced? Most may rule these parts out because they are new or rebuilt. Could be the wrong master or a faulty rebuild even if it is new. Piston in the master cylinder sticking in the bore or the piston spring is not returning the piston back to where it needs to be. Internal leaking between the primary and secondary piston. There would be no external fluid loss. All weird things that none of us have experienced.

Could the rod going from the brake pedal to the back of the master cylinder be too short or too long? There is an adjustment to the length.

If it were me, I would replace the master cylinder. You have already gone through your drum brakes and ruled out the wheel cylinders and no air in the lines.

Good luck and please post back when the problem is fixed. I want to hear the ending of this story. Phil

Will Do Phil,

I am going to replace the master cylinder and the vacuum booster. Like I said before I have the hydroboost unit so I will install that and install a new master cylinder. Once I have it out I will take the master cylinder apart and see if there is anything there I can see. Anyone know what to look for as far as any problems with the master cylinder when taking it apart? I will keep all of you posted. The thing that bothers me the most is that the system keeps drawing air in from somewhere over time.

I do have one more question to add. Just say for the sake of arguement that the pedal put a small amount of preload on the master cylinder. What effect would this have on the whole setup? Please only answer if you are 100% sure of what will happen in this situation. I am just trying to eliminate all of the possibilities. Also, in a question unrelated. With POWER brakes they say to use the bottom hole on the pedal. But with the Hydraboost they say to use the top hole. If both are power orientated why would you use the different holes?

I don't have the answers to your questions above, but did want to point out a couple thoughts I had. When bleeding the brakes, I'm assuming that you got fluid to flow properly from each side...

Keep in mind there is a flexible rubber line going from the body to the rear end, and that can deteriorate form the inside out just like the front hoses. That deterioration can block fluid flow, causing a loss of brakes. Since your problem is intermittent this is something I would consider replacing if you haven't already.

Have you looked over every inch of the hard lines? It is also possible that you have pinhole rust through leak somewhere in the system. I tend to think this less likely as it seems that would cause a consistantly low pedal.

Lastly, what about the distribution block/prop vaklve? There may be debris inside causing your problem??

Just a couple thngs that I didn't see discussed earlier. I do hope you find the problem soon!

Hello Bret,

Thanks for the comments. I have replaced that rear rubber hose, also replaced the combination valve. Didnt change the front hoses or any of the brake lines. But the way I m going looks like I may be changing EVERYTHING in this God forsaken car of mine!!

I also think the problem is in the master cyl. I once had a Grand Prix that did the same thing but it didn't matter which direction you were going. All the sudden with no warning the pedal would go to the floor. Let up and press again and it was fine. It would only happen once every couple of days but that was enough to scare the crap out of you. Replaced the MC, problem solved.

Well that is the scary part. It only happens when I go in reverse and only once in a while. The thing that I cant understand and that bothers me more than anything is the fact that air is getting into the system somehow. I dont know how but it is definately drawing in from somewhere along the way. All of the lines and connections are dry though. So where could it be drawing in the air? Wheel cylinders in the front and rear are dry as well.

I don't know the detail inner workings of the MC only in general but someone told me that a O-ring was failing in my case. Now how that can happen on a random basis was beyond me.

The smallest amont of air in the brakes can cause all kinds of odd probems . If the 50 % of the time it fails, the brakes have had time to cool down it could be a air bubble. If the brakes are getting real hot going forward and you stop they cool down and the air gets smaller and more compresable the pedel goes to the floor. Pay attention to heat they may be related.
One other thing to check is if the emegency brake bar is holding the rear shoes away from the stop at the top of the backing plate this would cause your shoes to not hit the drums corectly. If not that stuff its got to be the master!

The vacuum booster on these cars sits at an angle and needs the lower hole for the pushrod to be at the right angle to the pedal arm.

Hydroboost bolts straight to the firewall like manual brakes, so needs the top hole for the right pushrod angle.

If the master cyl had some pressure applied to it the brakes would drag, and the drag would increase the longer you drove as they got hot.

Lack of a residual valve for the drums could possibly allow air to be sucked in to the system. A seal or very slight hose leak can sometimes allow air in without fluid out.

When disassembling the master, you would look primarily for a blemish in the bore in front of the front seal on either piston, though it would most likely be in front of the rear piston (for rear brakes) considering your symptoms, IF this is the problem.
You could plug both ports coming out of the master if you suspect this, while it is still on the car.
apply the pedal.
open one plug, and allow the pedal to go down about one inch, then close the plug. Hold pressure. On the way back up, dont let it up all the way at once. Apply pressure in stages as you are leting the pedal back up, and see if it all of a sudden looses pressure.
or, open the plug in stages letting just a little pedal travel at a time, and see if there is a sudden and dramatic drop.
This is checking for a blemish in the bore past average travel of the piston.
repeat with other plug.
Drum brakes seem to normally allow slightly more travel from the master in reverse than they do in forward.

I am not offering a solution to the problem. I have no idea what it is, but there is some info, hope it helps.

oh, because hydroboost can use the manual pedal ratio, a little boost goes a long way. Vacuum boost uses a lower lever ratio. It relies almost soley on the power of the booster. Hydroboost in these cars uses the high lever of manual, so is like manual brake+boost. That might be why so many people like it so much. I dont care for the pedal feel personally.

Anyone have the part # for one of the part houses on that hydralic brake line that runs from the body to the rear axle? Couldn't find it on my search at classicindustries.com
I probably need this hose, even though I seem to be able to lock up the rear brakes, bleeding them doesn't yield a bubble free bleed no matter how many times I bleed them!

In the past whenever I've had a brake pedal go to the foor, in reverse, it has been a master cylinder problem. What I found (and this was on 3 different vehicles, 2 of mine and another of my brothers), was that the bores were oversize. In particular these were rebuilt units. They would last 4-6 months and then the pedal to the floor problem would start. And, just like you, not all of the time.

I (and my brother) finally purchased brand new master cylinders and the problem ceased. And it ceased over many years of using that same new master cylinder. It was upon checking the rebuilt master cylinders for piston to wall clearance that we found found it to be excessive. It has been a number of years, however, IIRC, we pulled the specs for this from the factory Helm manuals.

Another issue we discovered (as mentioned above in another post) was that not all of the master cylinders had the residual pressure check valves in place. This can be checked by using a tooth pick in the output port. Again, we learned the hard way when wheel cylinder after wheel cylinder would start leaking fluid. And the spongy pedal. . . Air would be drawn in along with fluid leakage.

Bob.

If you have no visible fluid leaks and the pedal goes to the floor, it's the master cylinder - replace it. :thumbsup:

OK,

For arguements sake, I have ordered a BRAND NEW, NOT REBUILT master cylinder for a 69 camaro with power disc,drum brakes. I am praying that this eliminates the problem all together. But I do have one problem that keeps nagging the crap out of me. Why after completely bleeding the system and while of driving the car( Meaning a couple of weeks ) do I keep getting air in the rear brake lines? Would a Bad master cylinder cause air to get into the brake lines? Where is the logic in it? Just trying to understand.

Funny but the more I think about it here is the whole scenerio from beginning to end on when I got the car. Maybe this will help.

1. Got the car and took it for a ride. The brake just about put me through the windsheild on the highway. Seemed like the front brakes were the only thing working.

2. Back passenger rear was not working at all, took drums off readjusted, Completely bleed the brakes in proper sequence and took it for a ride. The pedal felt a little hard and the front brakes didnt feel like they were working alone but the pedal didnt feel right and car didnt stop very well. Also is the time that the pedal would get hard as a brick when coasting into a parking spot and lose of pressure completely sometimes when going in reverse..

3. Bleed brakes again, noticed the flow was not that good.So I decided to change the wheel cylinders in both the rears. When I did that I decided to check the flow in the lines so I pumped the brakes and found still there was not good pressure. I traced it back until I had good flow and replaced both rear lines and the rubber hose in the rear on top of the axle. Now I had good flow through the lines at all ends.

4. Took it for a ride and still had brakes that were not that good and had the problem of when coming into a parking spot the pedal felt like it would get hard and not stop, and when in reverse it would lose pedal completely.

5. Wanted to go with a chrome booster and master cylinder so I got one, Used original booster that had been chromed, and a rebuilt chromed master cylinder. I sent it out to a brake expert who said the vaccuum booster needed to be rebuilt and the chroming process had screwed up the internals in the master and that it had to be completely rebuilt.(dont know how you rebuild a part that has been rebuilt already but ok).

6. Installed the new booster and master cylinder. Bench bleed the master cylinder and then bleed it on the car as well. Checked the clearance of the push rod and master cylinder and they matched. Inserted the pedal in the BOTTOM hole as required. Bleed the system and took it for a ride.

7. Still had the problem but not as bad in forward, but still as bad in reverse. Thought because of the cam that is in it that the vaccum was too low. I got the vaccuum to come up to 14 pounds at idle and the Forward hardness problem went away But the rear problem still remains intermittently.

8. Now I have a car that the brake still feels like it is not working properly. I have had many of these old cars with disc fronts and rear drums and they always felt good when braking. It would have a softer push to the braking action not this half movement feeling and the brakes in my other cars felt like they would always stop. This problem has been driving me crazy over the last year!!

I have the Hydratech hydroboost unit and a NEW MASTER on the way but am worried that I will install this unit and still have the same problems. Figured maybe this new info would help.

14" of vacuum is too low for most boosters. The new master and hydroboost will probably do the trick for both problems.

I am hoping that is the case, but still doesnt explain the air getting into the system with no visible leaks around the lines.

UPDATE!

I took the mastercylinder completely apart. EVERYTHING inside looks completely new!! No scoring or wear on any of the cylinder parts, seals everything is brand new. The walls are clean as a whistle as well. I even checked all of the ports and holes to see if there was any blockage at all. NOTHING. Starting to worry if there was anything wrong with it at all?

One other thing. If the system is getting air into it for some reason wouldnt it leak where it is drawing in air? The only connection that worried me is that I flared my own lines when doing the back brake lines. The flares looked OK to me and there is no leakage at the wheel cylinders but for some reason I didnt trust the flaring job that I did.

Check the piston to wall clearance using some feeler gauges.

Bob.

I was reading over some old posts and BAM!...ran into this wall right here. Please give an update so this saga will be complete.