Yup! I'm back still fighting brake problems. Having creating a few threads in the past and got some good replies on my continuing brake problems, now I have a new one. I finally got good, clean, bubble free fluid from each bleeder by using a "homemade" pressure bleeder. I went around to each bleeder 4 or 5 times with great sucess. I jumped into the drivers seat, said a prayer, held my breath, crossed my fingers, and pushed on the brake pedal. WOW!!! Nice firm pedal about 1/3 of the way down. This was too good to be true. I pushed with both feet and still unable to get to the floor. YES!!!! But alas....I fired up the engine, let it build up some vacuum in the booster and....you guessed it! The pedal went right to the floor. Pumping with the engine running only helps ever so slightly. Kill the engine, bleed off the vacuum from the booster, and the pedal goes back to its nice, firm position. What gives? Am I on Candid Camera or something? New master, front calipers, 4 flex lines, m/c bench bled, .003 - .005 TIR on rotors, no leaks.......now what? Think I still have air somewhere? Help, help, help!!!! I have all my gearhead friends stumped too. BTW: I bought the car with the brake issues.....no extra charge. Figure this one out and I'll remember you in my will! LOL! Thanks in advance, guys!
Andy

 

Probably air.....Bench bleed the master then get your tiny hammer out and beat the snot out of the combo valve and all joints as you have fluid flowing.

 

Wow... Sorry to hear about your troubles. I just installed the VB&P brake kit (calipers, slotted rotors, ss lines) on my 82 last weekend. Being a novice at this i was afraid of bleeding them, while searching the forum I heard about speed bleeders. They made it really easy. They were about $20 per pair, might be worth a shot....

 

The speed bleeders do work pretty well at dislodging hidden air.You can get them at Advanced Auto Parts.

 

First, Does your brake warning light work? Test it by grounding the tan wire that connects to the combi valve,Brake light on Instrument panel should illuminate.That will test the circuit. To actually test the valve your going to have to open a bleeder, start at the rear, put a hose from the bleeder into a jar, now mash the pedal. Brake light should illuminate. Close the bleeder and reset light by masshing the pedal hard again. System should reset.
Repeat for the front. you should only have to do one bleeder on either end.
Once that checks out ok. you can pretty much deduce that the master or booster is giving you the problems

 

OK! I have a special snot hammer that I have been dying to try out. I'll post my resul;ts tomottow afternoon unless my wife uses the hammer on me!!!

 

Yes, the light works properly as experienced from previous bleedings. I purchased a new p-valve but could not get any of the lines loose. I thought I'd try the OEM valve on the car again anyway. Seems like I'm making progress, but still not quite there.
Appreciate your thoughts, though.

 

The m/c was bench properly bled prior to installation and I don't feel the problem lies there. I was pressure bleeding with 25# of pressure today to get me where I am at. It's hard to believe that tiny little air bubbles could be trapped against that much pressure, but it's worth a shot.

 

To the OP....I have had my vette for some 16 years now, and have worked on cars for 50 years...1/2 a century....
I going to make this short and definitive....

Make sure the calipers are SSteel lined I would thing all of them are by now...only been 30 years now....replace with O ring pistons, replace ALL hoses.....assemble with NO SPRINGS in the calipers...obviously replace any leaking lines...duh.....and I would replace that 'proportioning valve' which is nothing but a front to rear pressure switch, as they can leak at the electrical switch portion in the brass part there...just a splitter in the front lines to the front port on the m/cyl...and a direct connect to the rear port....

and the Pasty resistance....put on a Hydro Boost and toss that damn crappy vacuum booster in the trash it belongs....

untill then you will have problems....

BTW, any really truly excessive 'runout/pumping/air problems you have can be felt with securing the rotor on the hub and spinning the rotor, by hand in front, and engine in gear in rear....feel it by the shoes wobbling, you can feel a 1/32 or so wobble easy...close enough....that olde tyme crap of 4-5 mils is crazy....

I finally got to the above situation which has lasted some 3+ attention free years now.....AFTER fighting my brakes for some 12 years on and off.....

CASE CLOSED......

anything else is total as if have covered all the other bases and found the suggestions either false or false hope at best....

you want it right, you have to re engineer the system....

otherwise....GAFL....you will need it....

 

Thanks for the thoughts, comments, and suggestions. I have often wondered what it would be like to go back in time and "feel" what the brakes were like from the factory on a brand, spanking new C3 with zero miles. Surely the General didn't deliver soft or spongy brake cars to his dealers. They would still be sitting in the dealres' bays waiting to be "cured". LOL.

 

I have owned my 69 Vette for 38 years now, and except for a 13 year "big sleep" it has been on the road the entire time.

Here's a look if you;re interested: http://www.myruffhouse.com/1969_corvette.htm

The brakes are now just like they were when the car was new - a firm pedal and sure braking, directly proportional to the pressure on the pedal. The only non-stock parts are stainless steel hoses, speed bleeders, and of course stainless sleeves in the caliper cylinder bores. While a lot of folks swear by o-ring seals, in my opinion they aren't necessary as long as everything else in the brake system is within design specification. I don't have power brakes on my '69 so I cannot comment about them, but I would look into the booster being bad in your case.

Consider that Corvettes were competing and winning in big-bore sports car racing in the sixties and early seventies with these exact same brakes. The only difference with the heavy-duty brakes was that they had two retaining pins per pads, and the pad backing plates had a 90° fold on the outer side to prevent the backing plates from warping.

 

Something else that I've noticed is that nobody complained about vette brakes until the pressure bleeders came on the market. Using the tried and true method of using the brake pedal always worked before. A pressure bleeder will Not detect any air getting in the system...that will only occur if you have a vacuum in the lines such as when the brake pedal is released. If you use the brake pedal to bleed the system then the system will work when the pedal is used during braking...bleeding is not just getting the air out or whatever...it is intended as a test of the system...it has to be good enough to squirt a solid stream of fluid out the bleeder with no air bubbles...if you don't check for pressure from the pedal then you aren't doing a good job of testing the system.

Using a pressure bleeder is like checking a 9-Volt battery without a voltmeter...just place your tongue on it and see if you get a tingle, but that won't tell you if it's good or not cause even 2 volts will give you a tingle...and if the battery is leaking acid just a little bit then your tongue will be burned. Many auto shops use pressure bleeders to quickly fill up the system with fluid...saves them time; however, they must apply a vacuum to the system to see if it draws air into it...again...they can use something that does it artificially to save them time, but in the end they need to test the system with the brake pedal or else none of the other tests will be of any use. You'll be using the brake pedal to stop the car, not a pressure or vacuum bleeder.

 

It is my experience, coming from a GM family for some 50 years now, that GM and most other brands have this problem with 'soft brakes' and the sharks are just that much worse than normal for their designs.....this be wether it's a disc/drum combo, drum/drum oldie or a new one with 4 wheel discs.....all the pedals for decades are/have been soft right from the get go.....you CAN lock the wheels in a panic mode, and usually fairly easy in a planned stop/mode....but on a shark, it's more difficult to lock the wheels.....

nature of the beast.....

wife's '99 escort if soft pedal too, and my Dodge 3/4 ton work van is silly that way also....super soft, but it's a GM brake system as is the steering column....



obviously, I don't like that feeling, I find HB a much superior system....the feeling of confidence as opposed to maybe....

 

Thanks, everyone, for all your thoughts, comments, and suggestions. Most of which I totally agree with. Since I was pressure bleeding with 25# of pressure and now have a firm pedal (engine off), reason would tell me that going back to the old school of manual pump and release would generate somewhere between 1500 - 2000psi or more in the system and should blow any entrapped air right out the bleeders (after knocking with a snot hammer). All I need now is an assistant pumper with a good leg and knee (leaves my wife out!). I wonder if I could entice a wino (or winette) at the mission with a six pack for some help? LOL! Hmmmmmm.........I'll let you know if and when. TY again!!!!!