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Old 07-07-2018, 05:39 PM
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Replaced booster, now brakes work too good

Recently bought a 65 Chevelle, well built car, not like my last purchase but had a hissing from the brake booster.

Brakes still worked ok but had a massive air leak.

Picked up a replacement booster this morning, all the visual specs checked out so I brought it home, cleaned it and painted it.

After getting it installed and going for a test drive, I almost put myself through the windshield!

It is a disc/drum car with a single MC. ZZ4 crate with a 700r4.

Did I get the wrong MC? Of I am super careful I can modulate the brakes to a smooth stop but just a slight over application and it is the opposite of safe....

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Old 07-08-2018, 06:02 AM
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Couple of quick thoughts, MC should have 2 reservoirs, if it is nose diving could have the wrong combination valve also..

Gave up on the coupe ?


Pep
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Old 07-08-2018, 07:37 AM
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booster

You can tone it down a bit by adjusting the pin between the booster and M/C. Doesn't take much, just screw it in one turn.
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Old 07-08-2018, 09:07 AM
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Quote:
Originally Posted by 39 master View Post
You can tone it down a bit by adjusting the pin between the booster and M/C. Doesn't take much, just screw it in one turn.
That has no effect on the amount of assist from the booster. All it does is add slop in the system - free travel from the pedal before the brakes kick in.
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Old 07-08-2018, 09:18 AM
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Quote:
Originally Posted by rip-tide View Post

Gave up on the coupe ?


Pep
Nope, it should be out driving later today...

I need to look more at this current setup. the si ge reservoir has a single line output to a T, that's it. Originally drum/drum setup, that was factory.

A dual MC with a proportioning valve might be the ticket but another can of worms.

or maybe it is a bad booster with no progressive power. the pedal moves about 1/2 way with no response, then there is only a small amount of travel that does all the stopping.
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Old 07-08-2018, 10:43 AM
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Did you check or change the pedal ratio?
You need 6 to 1 for non boosted. 4.5 to 1 for boosted.
Usually a new linkage hole in the pedal about 1 1/4 inches lower helps.
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Old 07-08-2018, 10:46 AM
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I put the rod back in the lower hole. I checked last night quickly that there wasnt a lower hole. Without a flashlight in a dark garage I couldn't tell if there was a hole higher up the pedal.
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