Ram Air Formula

Im having problems with the brakes on a 76 sting ray. the calipers are all new as are the rubber lines and the hard trailing arm lines. the lines going to the distribution block are new Stainless peices as are the front lines. the booster is new and good i think. it holds vacum ill put it that way. the master cylinder is brand new also. appearently the booster has been changed previously to a 77 version as the MC turned out to be one from a 77 and up as well. i went to replace the 76 one and it didnt work. i went to the parts store and matched it up to a 77 and up style.

the problem. no matter how much or how i bleed the lines the pedal will not get firm. im talking it goes to the floor everytime. the lines are free of air the master cylinder has been bench bled. the pedal pushes the fluid through the lines fine in order to bleed them. the pedal will not firm up and when the car cranks up it only gets worse with the vacum applied. the brakes appear to work even with the pedal to the floor. i say appear cause i havent driven yet since theres no pedal feel. however the rotors cant be turned by hand with the pedal down. but the pedal should not travel that far nor should it be that weak.

im completely stumped. ive never had this much problems with brakes before. ive tried every form of bleeding except pressure bleeding. the lines are free of debris and air but there is no pressure on the pedal. the only thing i can possibly think of is that the 77 and up booster and MC dont work with the 76 pedal. i dont see how it could be that but thats about all i can think of.

does any one have any idea whats wrong? please do not say continue bleeding the brakes. im am not kidding when i say it been done many many times. the pedal does not show any change in pressure not matter how many times or how the brakes where bled. any help or input is greatly appreciated. thanks you. :banghead:

Rockn-Roll

Welcome to the Forum!

It sounds like you have power brakes. You MUST start and run your engine at idle in order to bleed the brakes properly using the brake pedal to pump fluid through the system. There are also two bleeders on the rear calipers...unique to vettes.

Here is my brake help page:
http://67.116.80.82/Vette/BrakeHelp/BrakeHelp.html

Keep us posted.


[Modified by Rockn-Roll, 7:22 PM 8/24/2003]

Ram Air Formula

ok ill try that. yes it has power brakes sorry i forgot to mention that. is bleeding the system while the car running unique to vettes also. ive never done it that way nor knew it was necessary. thank you for the link.

Steve Grodin

Are you sure you installed the calipers on the correct side of the car? The bleed screws have to be on top. It is possible to install them on the wrong side of the car. You don't have to have the car running in order to bleed the brakes on a car with power brakes.

timbo79

I ran into the same problem.. Get a pressure bleeder and get them bled correctly.. check the lines (replace with s/s if needed, check the bleeder screws and lines for leaks as well as the pistons and seals... (and by the way, double check the rotors)

I actually ended up taking each caliper off, pressure bleeding and found a small leak in my front right caliper, which was brand nbew. Spray them with water from a spray bottle when bleeding. You will see if any tiny bubbles appear. (works on lines as well.)

Good Luck..... You can get a decent pressure bleeder for under $100 I ams ure someone can hook you into a link.

bmar

I would be more inclined to think that the problem is with your booster. If the booster is disconnected, you will still have brakes but it requires a lot of pressure on the pedal. this is what you have now for a pedal. when you apply the brakes and then release them, you should be able to hear the air rushing back out of the booster. may be a shot in the dark, but this is where i would be looking. Bill

Kevin_73

Does your booster have the correct pushrod in it?
You mentioned that the booster had probably been changed to the later (77 and later) style, and that the 76 master cylinder would not fit.
From what I understand the late model boosters have a fixed length pushrod between the booster and the master cylinder, the earlier model booster has an adjustable length pushrod.
It sound to me like you may not be getting full travel from your master cyclinder, which if this is the case, could be caused by the pushrod being too short.

Rockn-Roll

It is not unique. When using the factory installed brake application system (brake pedal, master cylinder, brake booster, and associated devices) to bleed the brakes then you must have the car running, or use an external vacuum source to supply the brake booster with vacuum. If you don't apply a vacuum to the brake booster then you will be putting stress on the brake booster diaphram and will probably tear it by mashing down hard in order to get sufficient fluid through the system. You can test the brake booster by disconnecting the hose at the carburator and see if it will hold a vacuum. If it will not hold a vacuum then the diaphram is torn and will need to be replaced.

As indicated by others you really need the master cylinder that is correct for the car especially if it's got power steering. The previous owner of my vette had problems with the brakes. I think that's why he sold it. He had replaced everything as well. All I did was have an open mind and use the bleeding and testing procedures that I outlined in my brake help web page. I discovered that one of the new calipers leaked. I replaced it and everything worked fine after that. Just because a part is new doesn't mean that there's nothing wrong with it. Keep an open mind and be methodical and you will be able to solve the problem and fix it.

Ram Air Formula

ok the MC is matched to the booster, but they are 77 and up styles.the car is a 76. the plunger on the 76 MC had a hole that went in an inch or so. the MC that was on the car didnt have such a deep hole. i matched it up to be a 77 and up style. the brakes worked before all this replacment went on. the booster holds vacum. i can run the engine then walk away come back a little later and pull the line off. you can hear the air rush in when i do this. the calipers are installed correctly. the only lines that were not replaced on the car is the intermediate line that goes from the dist block to the back two calipers. all the other lines are good. and there are no leaks anywhere. i can try tightening them again, but no fluid is coming out anywhere its not supposed to.

is there anything wrong with using a 77 and up mc and 77 and up booster on a 76 car?

ive tried reverse flow beedling, vacum bleeding, and pedal bleeding. did this numerous times each to each caliper. made sure no air was coming out on any of them and the pedal never changed. this is with the car on or off. the pedal goes to the floor. its a little stiffer with the car off, but no where near what it should be. thanks.


[Modified by Ram Air Formula, 12:05 PM 8/25/2003]

Steve Grodin

Per the Chevrolet Cassis Service Manual- Bleeding Instructions. "Do not use the power assis while bleeding. The engine should not be running and the vacuum reserve should be reduced t zero by applying the brake several times before starting the bleeding procedure." :chevy

Matt Gruber

see link in my profile for brake tips.
be sure to test drive a short distance.
it is NORMAL for the pedal to go to the floor if the car is not moving and your foot is on the pedal, engine on. :yesnod:

gliot1

I went through this over the last few months. The Chevy shop manual states to have the car turned off. What really mattered the most was the sequence of bleeding. Until you do this properly you will not get a hard pedal. Normally on most cars you go farthest to closest. Not on a good 'ole Vette. According to the Chevy manual, you go, LR, RR, LF, RF. On the rears do inner first, outer second. A rap with a rubbers mallet will help work bubbles out. I did not get a hard pedal until I followed this sequence. A couple of weeks ago a technical expalanation was given on the forum as to why the bleeding will not work if you do not follow the proper sequence. Bench bleeding the master also significantly helps. My orignal problem was my master cyclinder, but I went in circles on the bleeding, until I did this properly. I can lock 'em with the best of them now. My advice to all C3 owneres: buy the shop manual! they are not expensive and easy to find. I see a lot of inof on the forum in direct conflict with the manufacturures manual. I have found the manual to be right 99.9% of the time.

Rockn-Roll

That is amazing! Thanks for the info. I had no idea that the Chevy Chassis Service Manual said not to run the engine. I still believe it's wrong to put stress on your diaphram. It's also wrong to use your brake system in a way that is not according the the system design, i.e. using a power brake system without the engine running. If you want to follow the advice of the manual then be my guest. But, please consider that the book could be wrong because it goes against everything that is available outside of that book. All shop repair manuals that I have read, including those published by government agencies who are concerned about the safety of the public (as opposed to a company that is interested in selling parts that could break from using it incorrectly) indicate that using the brakes without the a vacuum supply for the booster will damage the booster. In fact, it's been awhile since I've replaced a booster, but I believe that the warranty card and installation instructions that come with a booster indicates that it should not be used without a vacuum source or the warranty will be invalidated, or at least says that the booster may be damaged.

So, please forgive me if I persist in offering advice that indicates the car needs to be running, or at least a vacuum source is available for to the booster.

No, there should be nothing wrong with that.

As for why it still gets air in it I must ask if you followed the brake help page that I offered. If you attach a hose to a bleeder nipple (with other end in a jar) and open the bleeder 1/4 turn then pump on the brakes about 15 times while watching the fluid come out then you will be able to see where the air is getting in at. You aren't driving the car so there no way that warped rotors or rotor runnout can be the problem even if the rotors were like a whole inch out of whack. My suspicion is that one of the new calipers have a hole just small enough to allow air in, but too small to allow fluid out. brake fluid molecules are bigger than air molecules so it's normal for a really small hole to allow air in, but not allow fluid out. You can detect a caliper that has such a hole by the procedure I've given. If bubbles keep coming out during 15 pumps of the brake then pull the caliper and return it for another one. It's also possible that the leak is in a line or connection, but since you have tightened them all several times I would suspect a caliper.