I recently got my engine running again in my car ('79). It had sat still for about 3 months. As soon as I got the motor up and running again, I noticed the brake warning light was on. I figured I had connected some old wire up when I had reinstalled the dash that dealt with the parking brake which doesn't work. I ignored it and went for a quick drive around the block. As I approached my first stop sign I started braking but hardly anything happened and I nearly rolled through the sign. I turned right around and went back home.

I checked the vacuum at idle and it's reading around 10-12" which is actually higher than my old motor setup (I found some vacuum leaks while it was apart). First I noticed the brake fluid level was low in the front and *slightly* low so I added some and gave it another try - no luck.

Then I figured maybe it had been low enough to get a little air in the system by sloshing around during turns/braking etc., so I bled the front brake system. There was very little fluid coming from the bleed valve as my helper pressed in the brakes - it seemed to be just trickling out. This seemed odd but I gave it a try anyway - no luck.

Next I thought that the master cylinder must be bad since it was putting out so little pressure so I replaced it with a new one (a parts store adventure in itself). I then bled the brakes again and still saw hardly any pressure from the bleed valves. (**Also, is it always necessary to bleed both sides of the back brakes? The inside bleed valve on the back left side is frozen shut - I ended up rounding it off trying to get it open. Does this matter? I bled the outside one.**) Next, I undid the lines right at the master cylinder and pressed the brakes - the front side spurted a *little* fluid out and the back side just dribbled out. This didn't seem right but I reconnected it just to give a try - no luck.

I checked the linkage at the pedal just to make sure I didn't miss the obvious but it looks good to me.

I didn't think a bad vacuum booster could cause this sort of problem, but that's the only thing I can think of now. Am I missing anything else? Does nonuse for a couple months cause some sort of damage to the brake system?

Thanks a bunch for any help!

 

A bad booster would just make your pedal harder to use, it sounds like your pedal is probably soft. You probably have a leak somewhere. Sitting for three months won't do any damage to the brake system.

 

At least your warning light came on. Mine didn't. My 79, that had been sitting for over 10 years in my garage, required me to: replace all of my calipers, 4 brake lines, all of my hoses, and my master clynder. Now they work fine. Not sure what it could be on your car, I'd check all of the calipers and brake lines. Also make sure you bench bleed the master cylinder to get the air out of there.

 

ttt

 

I had nagging and re-occuring similar problems on my '70. I kept getting low pressure from leaky calipers (especially when the car sat), rusting lines, and leaky screws. I finally got tired of it all: I am rebuilding the entire braking system - stainless steel sleeved cailpers, stainless brake lines, rebuilt Master Cylinder, stainless parking brake cables.

However, you mention low pressure from the Master Cyl after replacing it?? I don't have an answer for that one.

:confused:

 

This could be a lot of things but but yes, you must bleed both bleeders on the rear calipers. Check the inside of your tires for signs of leaks (fluid sprayed out from the caliper.) If you don't see anything obvious, start pulling off the calipers and looking at the piston areas for leaks, the fronts don't even have to be disconnected from the flex line but the rears will. You are going to have to get those rear bleeders loose regardless. IMHO, if the system has not been gone through in a while, now is the time to take off all the calipers, replace lines, check everything and you will find the problem.
:cheers:

 

I am having the SAME problem...leaky calipers. If I put fluid in the MC I can drive for awhile with relatively decent braking but when I stop it leaks and then I have to add more fluid. Where are you getting your supplies for the brake rebuild job? Thanks!

 

Mystery Machine,
I bought my stainless steel (SS) lines from:
Vettbrakes (800-237-9991 http://www.VBandP.com).
I'll buy the rest of the stuff there or at:
Zip Products (800-962-9632 http://www.zip-corvette.com).
Both guys guarantee the calipers for life. I found cheaper prices but the vettbrakes catalogue goes into great propaganda about how their brakes are the only REAL 4 micron finish calipers and their O-ring engineering is so much better than the original design which they call a "lip seal" ring. Not sure if that's true or what...Anybody have an opinion on that? :nonod:


[Modified by vett70, 6:44 AM 10/24/2002]

 

Very nice description of the problems you're encountering...helps others provide usefull feedback and advice. If you're taking that vacuum reading at the manifold...it sounds low! Should be in the 18+ range.

Now the brakes...some of the suggestions here would be the route I'd take before proceeding with a booster replacement. Fluid does dribble out...it's not going to "squirt!" Sounds like your bleeding technique needs to be fined tuned by incorporating the proper sequence. Go from right rear, left rear, right front, left front. Also...I believe the sequence on the rears is to do outside first followed by inside. Then do it again. Also it is recommended that you run a hose from the bleeder into a container of fluid to not only catch fluid but to avoid air being sucked back into caliper.

As suggested, you will have to get those rounded bleeders out! Use vice grips or something. If you have to...take the caliber off the car

As suggested, if you just plopped the master cylinder in without a bench bleed...you've probably got air trapped in it. Remove it and bench bleed...fill with fluid then push on plunger slowly until fluid is coming out and their is not bubbling.

Also check your brake hoses for cracks or breaks. this may be a cause of loss of pressure and fluid leaks. If they are original in a high mileage car...they may be contributing to your nagging problems.

You're optons are to patch fix what you've started or start all over at the top by removing the master cylinder and bench bleeding. Then, removing those bad bleeders either on the vehicle or off. Once the mechanics are out of the way...proceed with bleeding sequentially. And yes...you must bleed both bleeders on the rear calipers. I don't have my manual in front of me but I believe its the outer first then inside bleeder.

Believe me...I've gone through the problems you've described. last year I completed a master cylinder rebuild than moved on to a caliber rebuild using the O rings...eliminating the springs. I use silicone. So I know it can be tedious, frustrating and cause one to lose all patience.

However having said that...the key is keeping your patience while proceeding methodically. Good luck and keep us posted




[Modified by hunt4cleanair, 7:17 AM 10/24/2002]

 

It bugged about the bleeding sequence so I ran down my manual...here's the correct sequence:

Left rear (inner)
Left rear (outer)
Right rear (inner)
Right rear (outer)
Left front
Right front

 

Had brake problems this summer, air pumping thru the new rebuilt front caliper due to my not adjusting the front wheel bearings correctly. After that was fixed, I noticed this week, a 4 year old rebuilt rear caliper is leaking. This led my to order 2 'O' ring calipers for the rear and 2 'O' ring rebuild kits for the front from Precision Engineering. They sell what they call Caliper 2000. I have heard that their piston design is better than VBP.

 

Bleeding sequenece doesn't matter that much, the master clyinder is fine it's not the booster and it not the brake pedal bearing.

It the Proportioning valve. It's stuck. I don't know how to reset it but look in a Haynes or Chiltons

 

Huntforcleanair is right....

Left rear (inner)
Left rear (outer)
Right rear (inner)
Right rear (outer)
Left front
Right front

Try to re-bench bleed your master cylinder then then folow bleeding sequence. To remove the frozen nipple use vise grips.
I just went through the same thing myself. Good luck!
:flag