Booster to MC pushrod length???
Thread Starter
Instructor
Joined: Jul 2006
Posts: 208
Likes: 0
From: Hamden CT
St. Jude Donor '12
Booster to MC pushrod length???
Ok, sorry to bring up a sore subject but I finished converting my manual brake car to power. I added the new booster and power MC. All calipers were replaced previously, and all lines are hard or stainless braided. MC bench bled using backfeed tubes and all four calipers bled through completely using speed bleeders. I am using DOT5 fluid just because that is what I was using when it was manual brakes.
All of the following is with the car NOT running:
I have a fairly low pedal, if I press it really hard and lock it in place using a 2x4 against the seat the front wheels are really hard to move but can be rotated with enough strength. The backs can be rotated much easier. I don't think there's any air in the system. The only thing I'm not sure about is the pushrod length from the booster to MC. This aftermarket setup came with one 2.5" long and one 4" long. With the 2.5" one, no pedal, right to floor. With the 4" one I get the above conditions. Anyone know the right rod length to use with these aftermarket booster/MC setups. Thanks.
All of the following is with the car NOT running:
I have a fairly low pedal, if I press it really hard and lock it in place using a 2x4 against the seat the front wheels are really hard to move but can be rotated with enough strength. The backs can be rotated much easier. I don't think there's any air in the system. The only thing I'm not sure about is the pushrod length from the booster to MC. This aftermarket setup came with one 2.5" long and one 4" long. With the 2.5" one, no pedal, right to floor. With the 4" one I get the above conditions. Anyone know the right rod length to use with these aftermarket booster/MC setups. Thanks.
Last edited by ja1724; Nov 11, 2009 at 04:10 PM.
Burning Brakes
Joined: Oct 2006
Posts: 1,006
Likes: 28
From: Lutz Florida
Try this site: http://www.mbmbrakeboosters.com/Tech...ifcations.html. The Tech section discusses proper push rod length for the type MC you have. Scroll down to the bottom of the screen when you get there.
Last edited by stock76; Nov 11, 2009 at 07:21 PM.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
let me try and remember the specifics......theres a specification for when the brake pedal is suppose to start pushing in the MC guts......i'm sorry i dont recall this for sure so pls verify it ...having said that i think the pedal is suppose to engage at 2.75" off of the floor and at that point you should be seeing some bubbles start to come up from the rear most resevoir in the MC. i think i recall on my 69 the pushrod was adjustable at the end of the brake pedal. my point is if you dont see the bubbles with in the first little bit of pedal movement you will runout of pedal movement to stop the car
Last edited by bobs77vet; Nov 11, 2009 at 07:30 PM.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Ok, sorry to bring up a sore subject but I finished converting my manual brake car to power. I added the new booster and power MC. All calipers were replaced previously, and all lines are hard or stainless braided. MC bench bled using backfeed tubes and all four calipers bled through completely using speed bleeders. I am using DOT5 fluid just because that is what I was using when it was manual brakes.
All of the following is with the car NOT running:
I have a fairly low pedal, if I press it really hard and lock it in place using a 2x4 against the seat the front wheels are really hard to move but can be rotated with enough strength. The backs can be rotated much easier. I don't think there's any air in the system. The only thing I'm not sure about is the pushrod length from the booster to MC. This aftermarket setup came with one 2.5" long and one 4" long. With the 2.5" one, no pedal, right to floor. With the 4" one I get the above conditions. Anyone know the right rod length to use with these aftermarket booster/MC setups. Thanks.
All of the following is with the car NOT running:
I have a fairly low pedal, if I press it really hard and lock it in place using a 2x4 against the seat the front wheels are really hard to move but can be rotated with enough strength. The backs can be rotated much easier. I don't think there's any air in the system. The only thing I'm not sure about is the pushrod length from the booster to MC. This aftermarket setup came with one 2.5" long and one 4" long. With the 2.5" one, no pedal, right to floor. With the 4" one I get the above conditions. Anyone know the right rod length to use with these aftermarket booster/MC setups. Thanks.
Thread Starter
Instructor
Joined: Jul 2006
Posts: 208
Likes: 0
From: Hamden CT
St. Jude Donor '12
Not trying to be difficult but isn't it the other way around? The manual MC I had on the car had a shallow hole and the new booster/Power MC setup I just bought the power MC has a deep hole. Just trying to verify what's right.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
If one speaks of stock Corvette master cylinders, the manual has the deep hole/longer rod; the power has a shallower hole/short rod. The bore sizes are different too - the manual is 1", the power is 1 1/8 inch.
Thread Starter
Instructor
Joined: Jul 2006
Posts: 208
Likes: 0
From: Hamden CT
St. Jude Donor '12
Damn aftermarket crap gets worse every year. I'm not sure what this guy sent me. The MC does have a 1 1/8" bore BUT it also has the deep hole. I got it to work with the longer rod and now seem to have a pretty good pedal. I'm going to try to road test it this weekend to see how/if it stops good.
If she stops good can I leave this setup on the car or should I put a shallow hole power MC on with the shorter rod?
If she stops good can I leave this setup on the car or should I put a shallow hole power MC on with the shorter rod?
Instructor
Joined: Sep 2006
Posts: 175
Likes: 11
From: Omaha ne
WHen the pedal is in the full up position you need to measure the Pushrod length at the booster.
There should be about .030 of clearance between the pushrod when the master cylinder piston is fully back against it's stop and the pedal is at it's highest position. Hope this makes sense
It's kind of a PITA to do without a guage but can be done by taking careful measurements
There should be about .030 of clearance between the pushrod when the master cylinder piston is fully back against it's stop and the pedal is at it's highest position. Hope this makes sense
It's kind of a PITA to do without a guage but can be done by taking careful measurements
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Burning Brakes
Joined: Jan 2002
Posts: 935
Likes: 0
From: Trumbull CT.
I just did master, booster, calipers and brake lines. Not a conversion but a replacement of existing. I had the master off a few times to bench bleed, pump the brakes to bleed, Mity Vac the brakes, pump the brakes and on and on for way too long. Finally bought a power bleeder and put away the BFH I was about to use on the Vette. Brakes are good to go now. 
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
mity vac just dont work on the lip seal calipers....the lip seals really work best in one direction and when you apply vacuum to the bleeder it sucks in the air from around the seal....this is the same reason that the rotors that have run out issues have calipers that are filled with air
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
If one has o-ring seals, the Mity Vac can be used, but if one has Speed Bleeders, it won't work because the vacuum can't overcome the spring-ball check valve in the Speed Bleeder.
Also, gravity bleeding won't work either with Speed Bleeders for the same reason.
Also, gravity bleeding won't work either with Speed Bleeders for the same reason.
Thread Starter
Instructor
Joined: Jul 2006
Posts: 208
Likes: 0
From: Hamden CT
St. Jude Donor '12
Damn aftermarket crap gets worse every year. I'm not sure what this guy sent me. The MC does have a 1 1/8" bore BUT it also has the deep hole. I got it to work with the longer rod and now seem to have a pretty good pedal. I'm going to try to road test it this weekend to see how/if it stops good.
If she stops good can I leave this setup on the car or should I put a shallow hole power MC on with the shorter rod?
If she stops good can I leave this setup on the car or should I put a shallow hole power MC on with the shorter rod?
I wasn't happy with this road testing so...
I found a good spare power MC in my 'supply house' (garage). 1 1/8" bore shallow hole. Re-installed with the short rod, now I have great pedal and put your head through the windshield stopping. Thanks alot for the help guys! Only issue now is that it pulls pretty hard to the left on hard braking. I guess I 'll start a new thread. Thanks again.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Drove the car decent brakes but went a little to close to the floor. Locked 'em up from 50mph but pedal was only about 1/2" from the floor.
I wasn't happy with this road testing so...
I found a good spare power MC in my 'supply house' (garage). 1 1/8" bore shallow hole. Re-installed with the short rod, now I have great pedal and put your head through the windshield stopping. Thanks alot for the help guys! Only issue now is that it pulls pretty hard to the left on hard braking. I guess I 'll start a new thread. Thanks again.
I wasn't happy with this road testing so...
I found a good spare power MC in my 'supply house' (garage). 1 1/8" bore shallow hole. Re-installed with the short rod, now I have great pedal and put your head through the windshield stopping. Thanks alot for the help guys! Only issue now is that it pulls pretty hard to the left on hard braking. I guess I 'll start a new thread. Thanks again.
I'm still trying to figure this shallow hole deep hole thing out.
I thought all the pistons had a deep hole in them. All the black Corvette boosters I have removed have had long adjustable rods. The short rod boosters I have seen have been aftermarket.
Thread Starter
Instructor
Joined: Jul 2006
Posts: 208
Likes: 0
From: Hamden CT
St. Jude Donor '12
Does your 1 1/8" bore shallow hole master have numbers on it ?
I'm still trying to figure this shallow hole deep hole thing out.
I thought all the pistons had a deep hole in them. All the black Corvette boosters I have removed have had long adjustable rods. The short rod boosters I have seen have been aftermarket.
I'm still trying to figure this shallow hole deep hole thing out.
I thought all the pistons had a deep hole in them. All the black Corvette boosters I have removed have had long adjustable rods. The short rod boosters I have seen have been aftermarket.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
I'd sure like to know what the application is for the short or no hole master cylinder . I'm pretty sure none of the Corvette cylinders were short holes.
GM says in their parts book there was 1 master from 69-76 - 1 1/8" # 18009460
GM says in their parts book there was 1 master from 69-76 - 1 1/8" # 18009460
