Pedal to the floor. Brake Pedal that is.
 

I have a '72 with no power brakes. Always a chore for stopping power, but shes been braking much worse lately. The pedal goes nearly to the floor with little pressure, sometimes the BRAKE light even illuminates when this happens. If I pump the pedal 3-4 times firm braking is restored. Is this a leak?

I pulled the lid off the master cylinder and pumped the brakes. When the pedal was weak (on first one or two pumps each time) a shot of fluid would fire up out of the reservoir into the air. We're talking the forward reservoir which I assume is for the forward brakes.

I havn't driven the car very long. Suggestions on where to go/what to do with this servicing? :smash:

I also have a '72 with no power brakes and it has excellent stopping ability. It sounds like you need to bleed your system. If the fluid level hasn't dropped at all then you don't have a leak. As far as the fluid shooting up in the air when you pump the brake and the cover is off, that is normal. Just don't get any of that fluid on a painted surface. It instantly removes any paint it comes in contact with. Bleed those brakes. Good luck.

If you're not loosing any fluid it sounds like the centre seal in the master cylinder has failed.

Check for fluid leaks. Check the hose at each caliper on each wheel. Also look at the inside of each tire for fluid streaking on the inside of the rims or tires. Look for fuild pooling or wet spots. If you do not find any leaks, it is the seals in the master cylinder that are failing (as Golden indicated). You need to replace the master cylinder. Since you will need to bleed the system after replacing the master cylinder, now is a good time to do a brake fuild flush. I thought I saw a sticky post taking about how to bleed brakes...

Pump up the brakes and keep the pressure on the brake pedal.

If the pedal slowly goes to the floor and you don't have any leaks then I would suspect the master cylinder is letting fluid past the seal.

If the pedal remains firm then i would suspect air in the lines.

So I finally got around to bleeding the brakes, now I'm knee deep in this project but think I've found the problem.

First off, when I finally got a firm pedal from pumping up the brakes it would usually stay pretty firm for that application. But as soon as I let off the pedal and went to push them again the pressure was gone/much less and the pedal went right back to the floor. Driveable, but not very safely!

So I was going to start by bleeding the calipers but after reading online and then noticing the bleeder valves on the master cylinder today I started there. Never made it past the MC...

Starting on the front reservoir, I was able to pump fluid through a tube running from the bleeder back into the reservoir without much difficulty. Little bit of air pushed through the tube and then just a steady stream of fluid.

However, the rear reservoir was a different story. With all my pumping of the brake pedal I could never get the fluid to fill the tube completely. There was always between 1/4 legnth to 1/2 of the tube filled with air. Pumping slowly or pumping more vigorously made little difference. The best I could get it still seemed like air bubbles were being pushed from the bleeder up. Also, when the pedal is first pressed down from the top you can occasionally see bubbles that arn't coming from the bleeding tube.

So am I safe to assume the M/C seal is to blame? If so, how should I go about rebuilding it. Can I buy a local replacement part and gut it for the replacement parts so I don't have to wait on a repair kit?

Thanks for all the help so far.

Whether you buy a rebuild kit, or a replacement master cylinder to use the inards, whatever you do, don't give up your original master cylinder. Yours has the bleeders on it, and you won't find those on the replacements. Those bleeders make the bench bleeding, or on vehicle bleeding soooooo much easier! Keep that original master and good luck.:flag:

Good to know :thumbs: I think I'll put the extra time in to rebuild this one. Now to just figure out where to start...

i got the same damn problem. ive bled them 3 times and got a new m/c still only works for about 2 days of driving then looses pressure

Motive Bleeder.

Check your rotor runout. I chased a similar brake problem always needing to reblead the brake. I got my rotor runout down to under .002 and problem went away. I believe they say anything over .003-.004 can cause air to enter the system on these cars.

I'm hoping its the master cylinder since I've pulled it off the car and plan on rebuilding it! There wasn't any fluid leaking between the firewall and M/C flange though... And I'll worry about a gucci pressure bleeder after I can get the system to stop dumping air into the lines...

As for taking the M/C apart, I found the following thread:
http://forums.corvetteforum.com/c3-t...-cylinder.html

Looks like a legit how-to on the rebuild. I'm struggling to get this silly truarc snap ring off, though...

So I got the main piston removed from the master cylinder today. Pictures are below. I tried photographing the bore inside the m/c but that didn't turn out. The corrosion on this piston looks like surface rust to me, I feel like the bore should be ok for a simple rebuild. What do you guys think?

Also, is the seal in the second picture the one most likely to have failed? That should be the one closest the brake pedal connecting rod...

And then the last photo is of the master cylinder. I would like to verify that it is original, but I can't seem to find the julian date that is suppose to be on one of the brake line outlet faces. Worth saving this M/C?

http://farm5.static.flickr.com/4063/...8454888cf8.jpg

http://farm5.static.flickr.com/4062/...1a2f0f96f0.jpg

http://farm3.static.flickr.com/2775/...e14fb39e00.jpg

Had the same thing... Went straight to the floor and had no brakes. Bad booster.... replaced and amazing I have brakes again. Mast cylinder you will sometimes see a leak or see low fluid. If not theres prob no pressure in the booster.

Manual brakes. Surprised I havn't clarify this yet. Thank you.

I'm leaning towards just installing an aftermarket one to get the car driving and having this one replaced/reconditioned. Can anyone chime in on how to know if this M/C is original?

Look on the other side, where the front line screws into the m/c.
If it's original it will have a julian date on the flat surface right where it screws in.
Also, as mentioned above, it'll have bleeders.
There is also a casting number, 545xxx - not sure what '72 is.
Someone else should have that info.

Chris :thumbs:

Why bother?? if you going to actually enjoy the car for what it IS, and not some garage queen 'art' object, you don't need care about all that resto stuff.....

if you really want to, keep the core for posteriorarity....

:lol::smash:

I agree.

or, if it really is an original, you could sell it on ebay for $400 as an original 72 master cylinder to someone who is concerned about those things.

By the way, my rebuilt one from Autozone had the bleeders on it, but the bad one on the car did not. Interesting.

Nomar,
That is not an original m/c. An original would say delco somewhere on it with a GM part number cast into it along with a date code. The one you have is made by EIS, a manufacturer of brake parts. Buy yourself a replacement , bench bleed it and go for a ride...........