BillyTz06, thanks for the update. I don't have any suggestions but if you lived near by I would swap out your booster for mine to see if that might help. It's not that bad a job maybe 25 minutes to remove and replace.

 

Pete you might be right, this is a weird one. Billy did the booster come from the same company the master came from ?

 

Roger, I meant trying a manual MC on a PB car since the bore is smaller size than the Power MC.
Also, I just got back from the auto part store. I purchased a new check valve for the PB.
I got a tip to start the engine and build some vacuum then pull the hose off of the check valve on the PB within a few seconds of shutting the engine off. I did not hear anything. No air, sucking, etc. I pulled it out and I could not blow thru it and I could barely suck air thru it. The new check valve is more free flowing.
I have not test drove it yet, but will tomorrow. I am throwing this out for Billy, just in case. My problem might be just to low of vacuum, but figured I would try some quick cheap fixes first and share my findings here.

 

I changed some wrong ones like that. They don't work well. The pedal will be lower and softer yet. Vacuum pump or hydraboost is the cure.
If using vacuum pump, it only has to run when vacuum is low.

 

Locking brakes up on dry pavement is nice, but not really a necessity as long as it stops well.
I only lock them up for fun.

 

Noonie, I replaced the check valve on the PB today and took it for a trip around the block. I was able to lock up the front brakes at about 30 mph. I do feel a difference in the sensativity for the brakes, but it really depends on the rpm's I am currently at when I hit the brakes. Anything below 2000 rpms does not seem to be all that great. I probably need to go with a electric vacuum pump.

 

Hey Guys, Still under rain delay here. To answer a few questions: The booster did come from the same company as the master ..... probably not good !! I replaced the booster check valve yesterday and there was no difference when I started the engine .... pedal still almost to floor, had a new check valve in it any way that came with the booster. I ordered a new booster filter yesterday also, it will be in Monday. Talking about vacuum below 2000 rpm .... you should have more vacuum at or near idle than at higher rpm .... correct? We should have better weather this coming week so I'll be able to get the car back on the road to do more testing.

 

The roads finally dried off this afternoon so I just took the shark for a spin and I did a little testing while driving in an effort to find out why I had good pedal after driving for a short distance and I made a shocking discovery. But first I'll tell you what prompted me to do this senario. Yesterday I was at a pig roast and was talking to a hot rodder that I met about my brake problem. He seemed as baffeled as I am but later came over to me and said "I know what your problem is, you need to set your idleing up because you don't have enough vacuum at start up and idle". I thought to myself this guys nuts because at start up with auto choke engaged the fast idle is 1200 rpm and I still have low pedal and hardly any brakes. Then I read the above post by RebelRob talking about not much brakes below 2000 rpm. Well, the school I went to always said you have more vacuum at idle and low rpm than at higher rpm so your booster should have more vacuum at these rpms and you should have a higher and harder pedal. So, my driveway is on a slope and I was playing with letting the car roll down the hill and hitting the brake pedal while idleing and in netural to check the brake pedal height and stopping ability. The results were the same , low pedal and it would hardly stop. I then repeated the test and increased my rpm to 2000. PRESTO !!! Full pedal and perfect stopping. I did this over and over and found that I have fair brake pedal at 1500 rpm, perfect pedal at 2000 rpm and almost no pedal below 1500. This goes against my way of thinking but thats what's happening. Sounds like a vacuum pump or vacuum reservoir is in order and will solve my problem. I have no idea what has changed to cause this reaction since I first completed the build. Perhaps someone could elaborate on this hopefully "last problem" and offer a cause and solution.

 

Have you checked the booster check valve to see if it holds vacuum ?
How about the piping going from the intake to the booster check valve.
Make sure the fitting in the intake is clear.

 

I don't think you ever posted your idle vacuum.
Could be a small leak.
Additionally, a lower vacuum at idle than above idle normally indicates worn rings.
At least check your timing and/or valve timing unless you have a fairly radical cam.
With a healthy engine, if you rev it from idle, you should create an overrun condition and a healthy engine will shoot up to 25" of vacuum and because of the booster check valve the booster should capture and retain that giving you normal brakes. The overrun condition also happens at cruise or engine braking.

 

Rodger, yes the booster check valve holds vacuum and the pipes are new and clear. Noonie, the idle vacuum is at 15 inches, rings are not worn, its a brand new engine with a some what radical cam. Once I'm driving the car I can stop and start as in normal driving and the pedal is fine as long as I don't keep pressing and releasing the pedal to evacuate the vacuum out of the booster while I'm stopped. Do you think a vacuum canister might help or solve the problem. If you guys think that might be the ticket, I'll order one tomorrow.

 

Volume is important ,so make sure the manifold fitting is large enough.
Sounds like your almost there.

 

Started car this morning, had same low brake pedal, reved the engine to 2000 rpm, pushed on the pedal and still had the low pedal condition. I pumped the pedal and changed the rpm back and forth with same result so I stoped pressing the pedal and just let the engine run at 2000 rpms for a minute . Then I pressed the pedal and it was up and felt o.k.. I have not driven the car today. It seems that its not building vacuum quickly or something. Although this is going back to the premess that no vacuum, booster won't work, so I should have full hard pedal. This is beginning to mess my head up. Rodger, I have the original steel tube screwed into the back of the carb with the same original rubber hose connecting it to the booster filter and then to the check valve that I have always had on the car so being I have not changrd any of that from the original engine that came in the car, the volume should be o.k..

 

I just picked up the booster filter and ordered a vacuum canister with gauge. I'll install the filter later today and see if that makes a difference. The vacuum canister will be here Wed. so hopefully that will be the solution.

 

Why don't you drive with the vacuum gauge and record the readings you get at different rpms.

 

If you pull the hose from the booster will the engine stall ? It should be a huge vacuum leak. I've had cars that will idle with the hose off,they should not,its almost always a fitting full of crusty stuff restricting the vac flow.

Next time you do your morning start up wait longer before you push on the brake, I'm still trying to figure out if its a fluid thing or vacuum thing. Binding pistons or warped brake pads keep coming to mind if its a fluid thing.

 

WOW! This 'quick question' thread has rambled on for 6 pages.

 

The vacuum canister that I had on order finally arrived today and I installed it this evening. Started the car and revved the engine a few times until the vacuum gauge on the canister registered 20 inchs, pushed the brake pedal and it went almost to the floor again. Drove the car around the block and the pedal immediately came to the top with perfect braking performance. Cut the engine off and restarted it and the pedal was almost to the floor again. It seems the vacuum canister made absolutly no difference at all. Just wasted another "C" note. I did notice that the vacuum canister does not hold the vacuum after shutting the engine off. There is a check valve on the canister and a new check valve on the booster and I have new hoses. I wonder where the vacuum is going. I think that it should retain the vacuum in the canister for a good while, like at least over night. Do you guys think the new booster might be leaking?

 

Have you tried pinching off the 4 brake hoses and then stepping on the brake ?

 

Hi all, it's been a long time since I've visited corvette forum.
I had the exact same problem on my 68 vette big block with
power brakes. After changing a leaking left front caliper, I
too could not get any brake pedal and replaced the master
cylinder with a new one (still no pedal) So, I asked a mechanic
at work who is very brake and front end specialized. He said
that the corvette calipers are very easy to develop an "air-
pocket" in the calipers, and pressure bleeding will not help.
He recommended to find a comfortable stool, clear hose,
and a plastic mallet or screwdriver handle (I used a plastic
hammer that I bought from Sears ) and to keep on tapping
the caliper with the bleeder open until there are NO bubbles
at all (even the very tiny ones) . Also, you must keep tapping
until you've think you're done, and then some more. If
you have the orig c3 style calipers with two bleeders per caliper,
you must do it on both bleeders on all calipers. Do NOT pump the
master cylinder, as this will most likely cause more air to enter the
system. By the way, I read where you used a rubber mallet, this wont
work. Note: Start at the closest (left front) caliper, and work your way
back. It worked for me, and this was over a year ago! I just took
my Vette for a spin tonight, and the pedal is as good as ever!