C4 Corvette / PBR brake system => poor performance => why? - Team Camaro Tech
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post #1 of 16 (permalink) Old Jul 5th, 08, 09:23 AM Thread Starter
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C4 Corvette / PBR brake system => poor performance => why?

Hello !

Now I installed the brake system, which I had questions about installation some weeks ago.

I installed:

92' C4 13" brake rotors used
92' C4 brake calibers used

New brake pads "no name"

new 1" Corvette master brake cylinder

original brake booster

The brake pedal is hard to press, not very sensitive.

It's hard to lock up the front wheels.

(Full brake power to the rear via proportioning valve)

Why this poor performance? Because of the MC diameter => original is 15/16"?

Bad brake pads?

I noticed that the brake performance is a little bit better with some warm up.

69`Camaro, 92`LT 1 / 94' BW-6 speed, shorty headers+Flowmaster, Vette wheels, Eibach/hotchkis springs, koni shocks, Nova rear, Corvette 13" front brake system
[all certified by German association for technical inspection with Oldtimer title]
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post #2 of 16 (permalink) Old Jul 5th, 08, 10:08 AM
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Re: C4 Corvette / PBR brake system => poor performance => why?

Quote:
Originally Posted by Markus View Post
Hello !

Now I installed the brake system, which I had questions about installation some weeks ago.

I installed:

92' C4 13" brake rotors used
92' C4 brake calibers used

New brake pads "no name"

new 1" Corvette master brake cylinder

original brake booster

The brake pedal is hard to press, not very sensitive.

It's hard to lock up the front wheels.

(Full brake power to the rear via proportioning valve)

Why this poor performance? Because of the MC diameter => original is 15/16"?

Bad brake pads?

I noticed that the brake performance is a little bit better with some warm up.
Did you use the top hole or the bottom hole to attach the clevis to the brake pedal? Manual brakes should use the top hole.


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post #3 of 16 (permalink) Old Jul 5th, 08, 10:38 AM
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Re: C4 Corvette / PBR brake system => poor performance => why?

Quote:
Originally Posted by Markus View Post
Hello !


new 1" Corvette master brake cylinder

original brake booster

The brake pedal is hard to press, not very sensitive.

It's hard to lock up the front wheels.
I would say you have a booster/mc issue. The booster is what would give you that soft pedal feel you want from power brakes. I'd start looking into if the booster is working and if the booster and master cyl are designed to work with each other.

...Dennis

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post #4 of 16 (permalink) Old Jul 5th, 08, 10:52 AM
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Re: C4 Corvette / PBR brake system => poor performance => why?

We have the same sytem on a 73 Camaro, but we used a 15/16" bore master cyl supplied by Baer Brakes. It works well. I think your master cylinder bore is too large at 1". A lot depends on how much vacuum you have. Low vacuum = low boost.
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post #5 of 16 (permalink) Old Jul 5th, 08, 10:53 AM
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Re: C4 Corvette / PBR brake system => poor performance => why?

ditch the booster and get a manual master cylinder for a mid 70's Chevelle- Cardone 1609 sounds right to me. it will cost about $20.
the master cylinder bolts right to the firewall and uses the top hole in the pedal.
if you have a disc/drum prop valve, either find a 4 wheel drum prop valve and install that, or gut yours to make it into a distribution block. put an adjustable prop valve in the rear line.
bleed it, and try to keep your face from slamming into the steering wheel when you slam on the brakes hard the first time.

you don't plan sincerity.
you have to make it up on the spot.

wanna hear about 20 years ago when i was too smart to know any better?
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post #6 of 16 (permalink) Old Jul 6th, 08, 08:09 AM Thread Starter
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Re: C4 Corvette / PBR brake system => poor performance => why?

Hello!

Ok, I should accept that I have to buy another new mc (the vette one's is pretty new too for 95). I don't know if I could buy a 77' Malibu here in Germany for not too much money, so after some research I noticed that there are mc's from a 87-89 Wrangler Jeep with a 15/16" bore size and with a "small butt" like Chevy which could fit my 69' booster (new for only 56)=> Does anybody know some more details? Fittins are the same => 1/2x20, 9/16x18?
The brake line fittings are on the engine side, but I have to change the lines in any case.

I'm just a little bit confused if the smaller diameter is the only reason and will rise the performance in this big manner I expect from these brake set-up.

But all the components are new or nearly new .

69`Camaro, 92`LT 1 / 94' BW-6 speed, shorty headers+Flowmaster, Vette wheels, Eibach/hotchkis springs, koni shocks, Nova rear, Corvette 13" front brake system
[all certified by German association for technical inspection with Oldtimer title]
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post #7 of 16 (permalink) Old Jul 6th, 08, 08:41 AM
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Re: C4 Corvette / PBR brake system => poor performance => why?

I thought it was more common to run a larger dia bore with the vacuum booster something like a 1 1/8". I know that's what is used in a more stock application.

I would start by removing the vacuum from your booster and comparing the pedal feel. If the booster is working at all there should be a difference. If low idle vacuum is the problem you can test it by reving the engine a bit. I've driven a couple if Z/28's that is you let idle in gear the brake pedal got rock hard but if you got the rpm up to 900-1100 the pedal was good again.

From there the power and manual MCs are different, the manual takes a long pin the power doesn't. I have a manual MC setting on the shelf (I think from cpp) that has a dowl like plug that converts it to power.

...Dennis

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post #8 of 16 (permalink) Old Jul 6th, 08, 09:10 AM Thread Starter
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Re: C4 Corvette / PBR brake system => poor performance => why?

Hello!

I think my booster works well. Without a running engine you could depress the pedal approx 1", after starting the pedal travels another inch. Then it's hard to press. Pressing the pedal several times I could notice the vacuum leak by the idle speed. My engine is an original 92' Corvette LT 1, so low vacuum could not be a reason.

During the first start I did something wrong with the booster, so it didn't work => It was nearly not possible to hold the car at idle and the tranny in "D".

My original MC with booster and 1 1/8" piston has a deep hole for the pin. Still the same as now the MC from the 68' Corvette manual brake.

69`Camaro, 92`LT 1 / 94' BW-6 speed, shorty headers+Flowmaster, Vette wheels, Eibach/hotchkis springs, koni shocks, Nova rear, Corvette 13" front brake system
[all certified by German association for technical inspection with Oldtimer title]
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post #9 of 16 (permalink) Old Jul 6th, 08, 09:37 AM
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Re: C4 Corvette / PBR brake system => poor performance => why?

Quote:
Originally Posted by Markus View Post
Hello!
My original MC with booster and 1 1/8" piston has a deep hole for the pin. Still the same as now the MC from the 68' Corvette manual brake.
This doesn't sound right since the power MC should have a shallow hole. The pin out of the booster should only be 1 1/2" or so.

...Dennis

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post #10 of 16 (permalink) Old Jul 6th, 08, 11:22 AM
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Re: C4 Corvette / PBR brake system => poor performance => why?

Yeah, not enough travel??????

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post #11 of 16 (permalink) Old Jul 6th, 08, 07:42 PM
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Re: C4 Corvette / PBR brake system => poor performance => why?

is it a 4 wheel disc brake setup, or are you still running the stock drums in the back?
if you still have drums in the back, then the 4 wheel disc Corvette master cylinder you are trying to use might be causing problems by fully extending the rear brake cylinders too fast and causing you to not be able to press the pedal farther.

you don't plan sincerity.
you have to make it up on the spot.

wanna hear about 20 years ago when i was too smart to know any better?
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post #12 of 16 (permalink) Old Jul 7th, 08, 04:06 PM
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Re: C4 Corvette / PBR brake system => poor performance => why?

Quote:
Originally Posted by DjD View Post
This doesn't sound right since the power MC should have a shallow hole. The pin out of the booster should only be 1 1/2" or so.
Older M/C's have the deep hole for manual as well as power brakes. Since Markus is using an original-style booster, the deep-hole master cyl "should" be correct. Please reference Mr. Pozzi's info HERE for more info.

As far as the 15/16 master goes, this SHOULD reduce pedal effort by {1 - (15/16)^2} or about 12% less effort compared to the 1" bore. I would be surprised if this would make a large difference in how the performance feels, but I am not certain.

One thing to check -- are you certain of the rotor and caliper piston sizes? I am seeing 12" as well as 13" rotors available. I also see calipers with 38mm or 40.5mm pistons (I believe the 40.5mm are for the rear). Is it possible that you have the smaller size rotors?

As far as the Jeep Wrangler master goes, it is not clear to me if this will bolt up directly. It is possible that the pushrod hole is not the correct size, the bolt spacing may not be correct, or the size of the "butt" may not be correct. I simply do not know.
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post #13 of 16 (permalink) Old Jul 10th, 08, 05:03 PM
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Re: C4 Corvette / PBR brake system => poor performance => why?

One other thought -- if you can find front calipers from a 1998-2002 Camaro (or firebird?) I think these will bolt right up to your existing brackets, but use larger 44mm pistons. This should give much more brake performance for a given amount of pedal pressure.

You may also want to try posting this question over at the sister site http://www.chevelles.com/forums/. There is more traffic over on the Chevelle site, so you may get more responses.
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post #14 of 16 (permalink) Old Sep 26th, 08, 03:19 PM Thread Starter
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end of story C4 Corvette / PBR brake system=>poor performance

Hello!

After >150 km of driving the performance of the brakes are (very) good. But don't ask me why. At the beginning it was not acceptable. Driving was nearly dangerous. But I noticed that the performance got better in very little steps in comparison to a normal brake pad / disc change. I still have the 1" Corvette M/C. The brake pedal force is ok. The brake force was 2x 310 daN.
In Germany you have to go to the association for technical inspection with the car and everything was ok. My whole car was ok and I got a certificate for a historic car. It is a little wonder because normally the car should be nearly original and my technical setup is more changed.

69`Camaro, 92`LT 1 / 94' BW-6 speed, shorty headers+Flowmaster, Vette wheels, Eibach/hotchkis springs, koni shocks, Nova rear, Corvette 13" front brake system
[all certified by German association for technical inspection with Oldtimer title]
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post #15 of 16 (permalink) Old Sep 26th, 08, 08:47 PM
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Re: C4 Corvette / PBR brake system => poor performance => why?

Thanks for the news!
Can you lock a front wheel now?
David

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