perplexing brake bleeding problem
Thread Starter
Safety Car
Joined: Nov 2001
Posts: 4,424
Likes: 619
From: northern CA
perplexing brake bleeding problem
In the process of converting the single master cylinder over to a dual outlet master cylinder.
After 3 attempts (two tries with hand operated vacuum pump, one try pump brake pedal method) to bleed the lines of air bubbles, for whatever reason the brake pedal continues to remain spongey.
The master cylinder is a 7/8" bore dual outlet disc/drum unit. It was bench bled in place on the firewall after the two new brake lines were fabbed up to accommodate the installation. A 10# residual pressure installed on the line that feeds the rear brakes. .. All new wheel cylinders, flex hoses, and new brake shoes were installed. All brake line fitting connections leak free.
Not sure what to try next. Perhaps Motive pressure bleeder? .. All ideas welcome. Thanks.
John
After 3 attempts (two tries with hand operated vacuum pump, one try pump brake pedal method) to bleed the lines of air bubbles, for whatever reason the brake pedal continues to remain spongey.
The master cylinder is a 7/8" bore dual outlet disc/drum unit. It was bench bled in place on the firewall after the two new brake lines were fabbed up to accommodate the installation. A 10# residual pressure installed on the line that feeds the rear brakes. .. All new wheel cylinders, flex hoses, and new brake shoes were installed. All brake line fitting connections leak free.
Not sure what to try next. Perhaps Motive pressure bleeder? .. All ideas welcome. Thanks.
John
Race Director
Joined: Jan 2003
Posts: 17,750
Likes: 3,735
From: Central Arkansas
I have become a big fan of speed bleeder screws. They have a small check valve in them to facilitate bleeding. I loosen them about 1/4 turn, put a hose on them to the bleeder fluid jar and then pump the brake pedal slowly until I get a clear stream and then snug the bleeder tight. They have a sealer compound on them so no air gets back in the lines. It's a one-man operation. I have vacuum bleeders and pressure bleeders, and I've tried gravity bleeding - but these things have by far worked the best for me. It seems like no matter what method I try with standard bleed screws, air always gets back in the lines around the screw threads - except with the old 2-person, press the pedal, crack the screw, tighten the screw, release the pedal method.
I recently replaced all the brake lines on a Plymouth I own and installed speed bleeders while I had it apart. I had a firm pedal after the first round of all 4 wheels with minimal effort and mess. I have them on 2 cars now (but not the Vette yet) and I'm sold. If interested they are sold by Dorman and can be picked up or ordered in most local auto parts stores.
I recently replaced all the brake lines on a Plymouth I own and installed speed bleeders while I had it apart. I had a firm pedal after the first round of all 4 wheels with minimal effort and mess. I have them on 2 cars now (but not the Vette yet) and I'm sold. If interested they are sold by Dorman and can be picked up or ordered in most local auto parts stores.
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
If the rear drum brakes aren't adjusted up, that can give the sensation of a spongy pedal.
Last edited by MikeM; Apr 15, 2016 at 06:50 AM.
Drifting
Joined: Dec 2015
Posts: 1,369
Likes: 140
Often with new pads or shoes the pedal will feel spongy until a few miles are on the linings until they are seated properly. I just put a caliper on my diesel pickup last Friday and it was spongy until I drove it a mile or 2.
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,147
Army
I have become a big fan of speed bleeder screws. They have a small check valve in them to facilitate bleeding. I loosen them about 1/4 turn, put a hose on them to the bleeder fluid jar and then pump the brake pedal slowly until I get a clear stream and then snug the bleeder tight. They have a sealer compound on them so no air gets back in the lines. It's a one-man operation. I have vacuum bleeders and pressure bleeders, and I've tried gravity bleeding - but these things have by far worked the best for me. It seems like no matter what method I try with standard bleed screws, air always gets back in the lines around the screw threads - except with the old 2-person, press the pedal, crack the screw, tighten the screw, release the pedal method.
I recently replaced all the brake lines on a Plymouth I own and installed speed bleeders while I had it apart. I had a firm pedal after the first round of all 4 wheels with minimal effort and mess. I have them on 2 cars now (but not the Vette yet) and I'm sold. If interested they are sold by Dorman and can be picked up or ordered in most local auto parts stores.
I recently replaced all the brake lines on a Plymouth I own and installed speed bleeders while I had it apart. I had a firm pedal after the first round of all 4 wheels with minimal effort and mess. I have them on 2 cars now (but not the Vette yet) and I'm sold. If interested they are sold by Dorman and can be picked up or ordered in most local auto parts stores.
Pro
Joined: Feb 2015
Posts: 638
Likes: 133
From: Omaha NE
I can send my wife over...
She pumped the pedal for 15 minutes as I went from wheel to wheel trying to get air air out. What the hell? no luck! I calmly asked which pedal she was pushing?
Good news is there is no air in the clutch pedal.
She pumped the pedal for 15 minutes as I went from wheel to wheel trying to get air air out. What the hell? no luck! I calmly asked which pedal she was pushing?
Good news is there is no air in the clutch pedal.
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,147
Army
But, my wife and daughter were both taught to drive manual transmission by me eons ago - guess it pays to do it
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Pro
Joined: Feb 2015
Posts: 638
Likes: 133
From: Omaha NE
She grew up driving a stick, I guess to many years in auto has spoiled her. Lol
She doesn't even want to try my 61 with the big steering wheel and no power brakes. Plus she loves to enjoy cruising with the top off. I say a.d.d.
She doesn't even want to try my 61 with the big steering wheel and no power brakes. Plus she loves to enjoy cruising with the top off. I say a.d.d.
Last edited by 61corv; Apr 15, 2016 at 08:34 AM.
Melting Slicks
Joined: Sep 2013
Posts: 2,882
Likes: 2,178
From: Chicopee MA.
I tried everything to bleed my 57 Vett after I had installed new disks on the front, spongy every time. I took the wheel off for some reason and there , as plain as the nose on my face was a second bleeder hidden by the wheel for the other piston! 
Race Director
Joined: Jan 2003
Posts: 17,750
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From: Central Arkansas
Last edited by DansYellow66; Apr 15, 2016 at 01:50 PM.
Thread Starter
Safety Car
Joined: Nov 2001
Posts: 4,424
Likes: 619
From: northern CA
The brake shoes were adjusted tight enough for the drums to slip over. The car was also backed up a number of times and driven lightly to help seat the new linings.
Speed bleeders sounds good. Gonna give those a go. The car is level up on jack stands. Never had this kind of trouble before bleeding brakes. .. Thanks, guys.
John
Speed bleeders sounds good. Gonna give those a go. The car is level up on jack stands. Never had this kind of trouble before bleeding brakes. .. Thanks, guys.
John
Team Owner
Joined: Mar 2003
Posts: 26,118
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From: Greenville, Indiana
Just checking.
Melting Slicks
Joined: Apr 2005
Posts: 2,777
Likes: 105
Originally Posted by mrg
Speed bleeders sounds good. Gonna give those a go.Thanks, guys.
John
John
The only ones that I found to be of quality are the ones packaged by Russell Performance.
Vette brakes sells them.
Last edited by babbah; Apr 15, 2016 at 05:04 PM.
Race Director
Joined: Jan 2003
Posts: 17,750
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From: Central Arkansas
I did find that there were speed bleeders on the market with factory thread sealer applied and speed bleeders without sealer. I've only used the ones with thread sealer on them and haven't had problems so far. They only need to be cracked a small amount when bleeding so the sealer should last through quite a bit of use. I think I would avoid any that don't have sealer on the threads as they may leak past the threads as bad as many standard bleeding screws.
Drifting
Joined: Jul 2014
Posts: 1,556
Likes: 791
From: Massachusetts
I agree. The Corvette dual master cylinder is very difficult to bleed on the car. I ended up taking mine off and bench-bleeding it as recommended by several experienced members. That did the trick.
In theory you could accomplish the same thing by lifting the rear of the car to make the MC level. However, you must be sure that you are pushing the piston all the way to the end of its travel.
Thread Starter
Safety Car
Joined: Nov 2001
Posts: 4,424
Likes: 619
From: northern CA
The master cylinder was level when bench bled on the car. Dorman brand speed bleeders with the thread sealant replaced the standard type bleeders.
After another go round bleeding the lines with speed bleeders installed brake pedal feel is much improved. Still a bit of sponginess feel on the pedal, though. ..
Question on the Motive bleeder:
Is it better to fab up your own master cylinder block off plate and use C-clamps to hold the plate in place rather than go with the block off plate and chain hold downs that Motive offers?
John
After another go round bleeding the lines with speed bleeders installed brake pedal feel is much improved. Still a bit of sponginess feel on the pedal, though. ..
Question on the Motive bleeder:
Is it better to fab up your own master cylinder block off plate and use C-clamps to hold the plate in place rather than go with the block off plate and chain hold downs that Motive offers?
John
Drifting
Joined: Jul 2014
Posts: 1,556
Likes: 791
From: Massachusetts
The master cylinder was level when bench bled on the car. Dorman brand speed bleeders with the thread sealant replaced the standard type bleeders.
After another go round bleeding the lines with speed bleeders installed brake pedal feel is much improved. Still a bit of sponginess feel on the pedal, though. ..
Question on the Motive bleeder:
Is it better to fab up your own master cylinder block off plate and use C-clamps to hold the plate in place rather than go with the block off plate and chain hold downs that Motive offers?
John
After another go round bleeding the lines with speed bleeders installed brake pedal feel is much improved. Still a bit of sponginess feel on the pedal, though. ..
Question on the Motive bleeder:
Is it better to fab up your own master cylinder block off plate and use C-clamps to hold the plate in place rather than go with the block off plate and chain hold downs that Motive offers?
John
These days I just use an old MC cap with a hose fitting for adding about 5 psi air pressure (not brake fluid). I fill the MC and then bleed until I think it's time to refill. The trick is to never let the MC run dry or you get to start over. So far I've never missed.
The reason I went this way is that it eliminated the problem of sealing the Motive bleeder block to the MC, and it reduced the mess that I always managed to make when bleeding was done and I had to remove the Motive bleeder block.