Topic: Now I have solid brake pedal but not good stopping power?????
in Forum: C3 Handling Components
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Brakes were spongy, and did not stop quickly nor could I lock down the brakes in an emergency stop. (See my previous post on 68 brakes).
The shop that specializes in high HP vehicles and Hot Rods, have got the brakes solid and not spongy as before. But the car won't stop quickly. No locking down the brakes. It comes to a stop but not quickly.
The mechanic has gone through all the calipers, new rubber brake lines, the pads, master cylinder good. Everything concerning the brakes have been gone through.
I think he now is a little lost at what to do. He has worked on many corvettes and even went back and drove a 68 he had worked on in the past. He said it stopped like it should.
Now he has mentioned putting a gauge on the brake line to see how much pressure it is putting out to the calipers. I guess it has a certain pressure number to get the brakes to lock down. 
If this does not work then he wants to install a booster for the master cylinder. Which I think from 1972 on they all had the boosters.
My Cam is taking up most of the vacuum so he will need to put a electric motor of sorts to keep the vacuum up enough.
Any other ideas
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My first thought is a master cylinder, weak booster or vacuum loss....power brakes correct?
|UPDATED|5/2/2017 6:16:25 PM (AZT)|/UPDATED|
|UPDATED|5/2/2017 6:16:25 PM (AZT)|/UPDATED|
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It's possible it has the wrong master cylinder on it. Non-power brakes take a different master....it sounds like your car is non-power brakes, correct? I would verify it has the correct master on it before going thru the hassle of installing power brakes, but....power brakes are nice, so it might be the best solution all around, unless you want to keep it original.
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non power brakes, no booster.
Changed out master cylinders probably 7-8 times since 1989. All the shops tell you first that the problem is the Master Cylinder. Not the case here.
I don't know much about the booster, but if it works then I need the stopping power.
I only have about 5lb of vacuum pressure left with my cam, just didn't know how much a vacuum pump to increase the booster vacuum and what kind of noise this might make.
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Might try a vacuum reservoir with a check valve in it assuming that the 5" of vacuum is just at idle.
Power brakes were still optional in '73.
Power brakes were still optional in '73.
1973 L-82 4 spd
This has always been a non power, non booster car.
However all the master cylinders over the years have come from Auto zone, Napa or O'reillys. Wonder what vendors they got them from?
But now, no sponge, just brakes that won't stop fast, lock up or otherwise.
I guess we will try the booster, it will still look original in the car.
Then go with another master cylinder to go with the booster. An an extra vacuum source.
I don't use the rebuilt stuff. Unless it is a" have to case" being it is a 1968!
This just looks like one of those "BUBA" repairs. Where as you keep throwing new parts at it 
and trying to figure out what is wrong.
and trying to figure out what is wrong. 20111021145147r.jpg)
Are the brake pads and rotors in good shape? Glazed pads will have an effect as well as glazed rotors. Had this happen on my AMC quite some time ago.
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If by chance you have power steering, you might be able to set up a hydro-boost, rather than go the vacuum booster route.... just a thought, otherwise you might need to look into a larger bore master cylinder...
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A larger bore master cylinder will make the brakes worse! you need the multiplication of a small master and greater area of caliper pistons to make the pressure applied at the calipers higher, that's why the brake pedal moves a lot further than the caliper piston, simple hydraulics.
A power assisted master cylinder has a larger piston than a non assisted because it has the vacuum to add to the force of your foot, could it be that someone has fitted a power assisted master cylinder by mistake in the past and then subsequently just replaced like for like? The poster did say that the master cylinder has been replaced several times which in itself is unusual, I just replaced the one in my 70 as it was starting to leak but I think the one that came out was original.
My brakes are non assisted and my car stops very well, just needs a bit more of a push than a modern with servo.
Are all the flex hoses in good order as they can collapse internally and reduce pressure to the caliper, a good time to upgrade to braided PTFE hoses if your in any doubt.
Graham
A power assisted master cylinder has a larger piston than a non assisted because it has the vacuum to add to the force of your foot, could it be that someone has fitted a power assisted master cylinder by mistake in the past and then subsequently just replaced like for like? The poster did say that the master cylinder has been replaced several times which in itself is unusual, I just replaced the one in my 70 as it was starting to leak but I think the one that came out was original.
My brakes are non assisted and my car stops very well, just needs a bit more of a push than a modern with servo.
Are all the flex hoses in good order as they can collapse internally and reduce pressure to the caliper, a good time to upgrade to braided PTFE hoses if your in any doubt.
Graham
in Forum: C3 Handling Components
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