Hot Rod Roy - Excellent description of the compensation port and its function.
Booster rod length
Thread Starter
Advanced
Joined: Jan 2011
Posts: 77
Likes: 0
From: Winona Mo.
Booster rod length
I replaced the brake booster on my 93 a couple of years ago. I had been driving it with the rock hard pedal and pushing with both feet for too long. I bought the new one from O'reilly's and noticed the push rod was a little shorter than the original. I thought I could get by with just adjusting the stop light switch, I couldn't find any way to adjust the rod; it's not threaded on the end. I finally got the brake lights to go off by zip tying a piece of metal to the pedal where it hits the switch. The worst part is, now I don't have enough pedal travel to stop like it should. My daughter almost hit the garage door and told me to get it fixed. I also want to play autocross this summer and brakes are kind of helpful.
I read on a post here today that there is an adjustment on the front side of the booster to extend the rod. I wasn't looking for one on that end so I don't know. Do you guys know for sure if there's an adjustment on the master cylinder end?
I read on a post here today that there is an adjustment on the front side of the booster to extend the rod. I wasn't looking for one on that end so I don't know. Do you guys know for sure if there's an adjustment on the master cylinder end?
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
All booster rods are adjustable. They should always be adjusted when booster or master is replaced.
Copied from my past post.
The actuator rod from the booster might be out of adjustment. If too short will cause excess brake travel. If it is to long it will depress the masters piston and activate the brakes. Unbolt and pull back the master. Check the length of the rod. It should be approximately just below the imaginary surface line of the booster. It needs approximately 1/8 inch of clearance to the master due to heat expansion of the parts.
When adjusting the rod end bolt, the rod had to be held and the nut turned, in to shorten. I clamp the rod with thin vice grips VERY LIGHTLY and adjust nut. Depress the brake pedal half way down to get the rod out in the open so it can be worked on easily.
Jack the front up before you start. Then unbolt the master and make adjustments. After adjusting (if necessary) the rod, re-check brakes pedal and wheel rotation for dragging. Might take a few tries.
** Don’t mess with the plastic brake switch adjustment on the pedal. Two wrongs don’t make a right. It's a three function switch and you could affect the other functions.
Copied from my past post.
The actuator rod from the booster might be out of adjustment. If too short will cause excess brake travel. If it is to long it will depress the masters piston and activate the brakes. Unbolt and pull back the master. Check the length of the rod. It should be approximately just below the imaginary surface line of the booster. It needs approximately 1/8 inch of clearance to the master due to heat expansion of the parts.
When adjusting the rod end bolt, the rod had to be held and the nut turned, in to shorten. I clamp the rod with thin vice grips VERY LIGHTLY and adjust nut. Depress the brake pedal half way down to get the rod out in the open so it can be worked on easily.
Jack the front up before you start. Then unbolt the master and make adjustments. After adjusting (if necessary) the rod, re-check brakes pedal and wheel rotation for dragging. Might take a few tries.
** Don’t mess with the plastic brake switch adjustment on the pedal. Two wrongs don’t make a right. It's a three function switch and you could affect the other functions.
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Yes, the output shaft of your brake booster is adjustable. It's possible to adjust this with the booster in place, as the master cyl. can be pushed forward far enough without disconnecting the brake lines.
You'll need to grip the output shaft with skinny nosed pliers, then rotate the tip of the shaft with a small wrench, in the self-locking threads. The shaft can be pulled out of the booster a little bit to get ahold of the shaft.
When the shaft is adjusted properly, you should be able to see the piston in the master by looking into the first little hole inside the fluid reservoir. The piston should be clear of the hole when the brake pedal is at rest, and visible in the hole as soon as you move the brake pedal. (You do have clean fluid, don't you?) You should also see a "spurt" from this hole, which will cause a disturbance in the surface of the fluid as you first touch the brake pedal. Press the pedal too fast, and you'll get a tiny guyser!
If the output shaft is too long, your brakes will drag when they get hot. The piston must clear this hole to relieve the pressure in the brake lines as the fluid expands from warming up. You won't see the "spurt" if the rod is too long.
You'll need to grip the output shaft with skinny nosed pliers, then rotate the tip of the shaft with a small wrench, in the self-locking threads. The shaft can be pulled out of the booster a little bit to get ahold of the shaft.
When the shaft is adjusted properly, you should be able to see the piston in the master by looking into the first little hole inside the fluid reservoir. The piston should be clear of the hole when the brake pedal is at rest, and visible in the hole as soon as you move the brake pedal. (You do have clean fluid, don't you?) You should also see a "spurt" from this hole, which will cause a disturbance in the surface of the fluid as you first touch the brake pedal. Press the pedal too fast, and you'll get a tiny guyser!
If the output shaft is too long, your brakes will drag when they get hot. The piston must clear this hole to relieve the pressure in the brake lines as the fluid expands from warming up. You won't see the "spurt" if the rod is too long.
Last edited by Hot Rod Roy; Jan 12, 2015 at 01:16 AM.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The switches on the brake pedal are self adjusting. Push down the brake pedal and push the switches toward the brake pedal. They will make a ratcheting clicking noise. Pull back on the brake pedal as far as possible and they are set.
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
I have received/changed 2 boosters with short booster to pedal rods = pedal was to close to the floor.
The booster to pedal rod is not adjustable.
The booster to MC rod which is adjustable has zero bearing on the brake pedal static height.
IMHO you have 2 options to raise the brake pedal back to normal height. With either option the booster requires removal.
Option 1: Replace the booster. Check that the new booster has the correct longer pedal rod.
Option 2: Cut the booster to pedal rod. Machine a sleeve to slide over the rod. Make a 5/16 to 3/8 long slug to fit between the cut rod lengths & extend the rod. Slide the sleeve over the extended assembly & weld.
The booster to pedal rod is not adjustable.
The booster to MC rod which is adjustable has zero bearing on the brake pedal static height.
IMHO you have 2 options to raise the brake pedal back to normal height. With either option the booster requires removal.
Option 1: Replace the booster. Check that the new booster has the correct longer pedal rod.
Option 2: Cut the booster to pedal rod. Machine a sleeve to slide over the rod. Make a 5/16 to 3/8 long slug to fit between the cut rod lengths & extend the rod. Slide the sleeve over the extended assembly & weld.
Thread Starter
Advanced
Joined: Jan 2011
Posts: 77
Likes: 0
From: Winona Mo.
I didn't see anyway that the out put rod could affect the brake pedal height either. I don't have a problem with taking the booster back off and lengthening the rod, other than it's a pain to do. Like my favorite saying "never time to do it right, always time to do it over"
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Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
The length of the booster output pushrod does affect the travel of your pedal, because you won't have any application of the brakes until that first hole in the master is closed by the movement of the m/c piston!
And you've been suffering with lousy brakes for "a couple of years"? I'm very glad you are still a part of the Corvette Forum family!
Last edited by Hot Rod Roy; Jan 13, 2015 at 12:47 AM.