Soft Brake Pedal
Thread Starter
2nd Gear
Joined: Dec 2012
Posts: 2
Likes: 0
From: Houston Texas
Soft Brake Pedal
I have a salvage title 77 vette, I am trying to restore. I have replace the brake booster, all 4 caliper and brake shoes. I bled the system numerous times, still the brake pedal is low (the car stops, but I am leery). Manual bleeding, pressure bleeding, nothing seems to bring the pedal up. What am I doing wrong here???
Safety Car
Joined: Jul 2005
Posts: 3,694
Likes: 833
From: WI
Did you ever get, or had a hard pedal after your previous bleedings? (I had to think of a good way of wording that!..ha ha). Or does the pedal go from a firm pedal to soft after driving it? Is it the same M/C that was on there when it was still working before all the work you did?
Are the caliper bleeder screws as you have the calipers mounted ....on the top?
Are the caliper bleeder screws as you have the calipers mounted ....on the top?
Le Mans Master
Joined: Jan 2001
Posts: 6,726
Likes: 1,379
Have you replaced the 4 corner brake hoses? You might try that if you have not and then do another pressure bleed.
I have a salvage title 77 vette, I am trying to restore. I have replace the brake booster, all 4 caliper and brake shoes. I bled the system numerous times, still the brake pedal is low (the car stops, but I am leery). Manual bleeding, pressure bleeding, nothing seems to bring the pedal up. What am I doing wrong here???
Race Director
Joined: Nov 2006
Posts: 13,199
Likes: 7,796
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
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Cruise-In VIII Veteran
I have found with many years of experience, that air likes to go up, not down.
Think Phoenix brake bleeder. Pushes fluid up from the bottom. Pushes air out the top. Also, get the rear of the car up. So as to get master cylinder level or front slightly down to get all trapped air out.
Best of luck.
Think Phoenix brake bleeder. Pushes fluid up from the bottom. Pushes air out the top. Also, get the rear of the car up. So as to get master cylinder level or front slightly down to get all trapped air out.
Best of luck.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Clue #1.
New booster. Why?
Is the new one a GM Delco or an aftermarket?
I assume the new booster was mated to the old master cyl?
What is the booster rod gap measurement?
It should be 0.060. Or around 1/16 of an inch.
Any less than that and the pads will drag the rotors constantly.
Any more than that creates way too much pedal travel, to the point where the master is not fully engaged until its too late.
Pedal is near the floor you ran out of room.
New booster. Why?
Is the new one a GM Delco or an aftermarket?
I assume the new booster was mated to the old master cyl?
What is the booster rod gap measurement?
It should be 0.060. Or around 1/16 of an inch.
Any less than that and the pads will drag the rotors constantly.
Any more than that creates way too much pedal travel, to the point where the master is not fully engaged until its too late.
Pedal is near the floor you ran out of room.
Intermediate
Joined: Aug 2022
Posts: 25
Likes: 5
From: Orange, VA
Sorry to jump on this thread with another question but!!
The booster changed in '77 from the black painted style to zinc plated. When you look at the information on adjusting the rod and the tool(s) available to properly set the gap, it specifically indicates ’68 -‘76 model years.
So, was there more than an exterior coating change for the ’77 – ’82 years and the rod is not adjustable?
Thanks,
Steve
The booster changed in '77 from the black painted style to zinc plated. When you look at the information on adjusting the rod and the tool(s) available to properly set the gap, it specifically indicates ’68 -‘76 model years.
So, was there more than an exterior coating change for the ’77 – ’82 years and the rod is not adjustable?
Thanks,
Steve
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Race Director
Joined: Nov 2006
Posts: 13,199
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
That's right Steve, you are high jacking this thread. And yes there is more of a difference than just color between 76, down and 77,up.
And if you swap both the master and booster at the same time as a matched set. You have no issues.
And if you swap both the master and booster at the same time as a matched set. You have no issues.
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
Clue #1.
New booster. Why?
Is the new one a GM Delco or an aftermarket?
I assume the new booster was mated to the old master cyl?
What is the booster rod gap measurement?
It should be 0.060. Or around 1/16 of an inch.
Any less than that and the pads will drag the rotors constantly.
Any more than that creates way too much pedal travel, to the point where the master is not fully engaged until its too late.
Pedal is near the floor you ran out of room.
New booster. Why?
Is the new one a GM Delco or an aftermarket?
I assume the new booster was mated to the old master cyl?
What is the booster rod gap measurement?
It should be 0.060. Or around 1/16 of an inch.
Any less than that and the pads will drag the rotors constantly.
Any more than that creates way too much pedal travel, to the point where the master is not fully engaged until its too late.
Pedal is near the floor you ran out of room.
Sorry to jump on this thread with another question but!!
The booster changed in '77 from the black painted style to zinc plated. When you look at the information on adjusting the rod and the tool(s) available to properly set the gap, it specifically indicates ’68 -‘76 model years.
So, was there more than an exterior coating change for the ’77 – ’82 years and the rod is not adjustable?
Thanks,
Steve
The booster changed in '77 from the black painted style to zinc plated. When you look at the information on adjusting the rod and the tool(s) available to properly set the gap, it specifically indicates ’68 -‘76 model years.
So, was there more than an exterior coating change for the ’77 – ’82 years and the rod is not adjustable?
Thanks,
Steve
the masters/cyl have different style hole depth in piston thus rod length issues
Thread Starter
2nd Gear
Joined: Dec 2012
Posts: 2
Likes: 0
From: Houston Texas
New user to the forum, navigation is not easy. That being I removed the master cylinder, (per suggestions) and discovered that there is zero clearance between the booster and master cylinder. The push rod came withe the master cylinder and is not adjustable. Can the push rod be bought separately? If it can, where should I look? This may correct my problem...thanks everyone
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
I have never seen a booster rod included with a new master cyl. Do you mean the rod came with the booster?
I am confused how you determined there was zero gap. There are only two ways to check that gap.
A special tool can be ordered on-line or a gob of clay and checking the impression in the clay.
Remember, 0.060 is a very small gap.
I doubt a booster rod can be purchased 1/16 of inch shorter.
Some members on this forum have actually ground down the rod end.
I do not recommend this.
Something else is going on with your combo. I suspect a mismatch of master & booster from two different sources.
Keep looking.
I am confused how you determined there was zero gap. There are only two ways to check that gap.
A special tool can be ordered on-line or a gob of clay and checking the impression in the clay.
Remember, 0.060 is a very small gap.
I doubt a booster rod can be purchased 1/16 of inch shorter.
Some members on this forum have actually ground down the rod end.
I do not recommend this.
Something else is going on with your combo. I suspect a mismatch of master & booster from two different sources.
Keep looking.