Bench Bleeding Master Cylinder
Thread Starter
Melting Slicks
Joined: Oct 2010
Posts: 2,276
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
Bench Bleeding Master Cylinder
Have a question regarding the bench bleeding of my master cylinder.
Here's a quick video I just took.
EDIT: I cannot get the embedded video to play thru the forum for some reason, please click on the "watch on youtube" at bottom left of video.
I'm not getting any more bubbles out of either the hoses or the tiny holes on the bottom of the reservoir. All good there. 
But I do get a little vertical "spurt" from the bottom hole in the front bowl, but no "spurt" or any sign of surface disturbance except out of the bleed hose in the rear bowl.
Is this normal behavior or is the master cylinder showing a problem?
If so, for future reference, which is the correct behavior, spurt or no spurt?
Here's a quick video I just took.
EDIT: I cannot get the embedded video to play thru the forum for some reason, please click on the "watch on youtube" at bottom left of video.
But I do get a little vertical "spurt" from the bottom hole in the front bowl, but no "spurt" or any sign of surface disturbance except out of the bleed hose in the rear bowl.
Is this normal behavior or is the master cylinder showing a problem?
If so, for future reference, which is the correct behavior, spurt or no spurt?
Last edited by riverracer au; Jun 2, 2024 at 02:29 AM.
Race Director
Joined: Nov 2006
Posts: 13,151
Likes: 7,765
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
I've rebuilt more masters than I can honestly remember. Normal is a spurt.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Yep, looks good.
You can do another 10 strokes with the nose down in the vice.
Then another 10, nose up.
Remember. Do Not Shove the Piston In More Than 1 & 3/8 inches.
Or damage could occur to the seals, voiding the warranty.
Leave that bleeder kit in place until you are ready to attach brake lines on the car. That will keep the DOT3 from leaking out.
But regardless, you still have to do a complete 6 bleeder screws flush. You have introduced air bubbles into the system.
Click on my avatar to the left. Look for photo albums, bench bleeding for tips.
You can do another 10 strokes with the nose down in the vice.
Then another 10, nose up.
Remember. Do Not Shove the Piston In More Than 1 & 3/8 inches.
Or damage could occur to the seals, voiding the warranty.
Leave that bleeder kit in place until you are ready to attach brake lines on the car. That will keep the DOT3 from leaking out.
But regardless, you still have to do a complete 6 bleeder screws flush. You have introduced air bubbles into the system.
Click on my avatar to the left. Look for photo albums, bench bleeding for tips.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,007
Likes: 4,162
From: US-PNW
You may not be pushing quite far enough to see the rear spurt. Just to be sure it's open, stick a paper clip end or the like into the hole to clear it.
That spurting fountain action is what has ruined many fender paint finishes, be careful when the master is on the car and you pump the brakes with no cover on it.
That spurting fountain action is what has ruined many fender paint finishes, be careful when the master is on the car and you pump the brakes with no cover on it.
Thread Starter
Melting Slicks
Joined: Oct 2010
Posts: 2,276
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
So I gather what everyone is saying, is that I should see some fluids movement in the rear bowl.
I am slowly pushing the plunger in until it stops, haven't measured the actual distance.
This master would be about 10yrs old.
To be safe I'll throw money at it and purchase a new unit from RockAuto and hopefully it will be down here by the end of the week.
I am slowly pushing the plunger in until it stops, haven't measured the actual distance.
This master would be about 10yrs old.
To be safe I'll throw money at it and purchase a new unit from RockAuto and hopefully it will be down here by the end of the week.
Last edited by riverracer au; Jun 2, 2024 at 07:25 PM.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Do not turn in your core just yet.
Put the new & old masters side-by-side and compare. Especially at the piston portion.
The design of the rear of the master changed over the years.
It is imperative the new matches the old.
For your sake, let's hope RockAuto has the correct unit.
Some stores data base states: Fits All Vettes from 1800's to 2025, red ones, yellow ones . . . . . PB brakes, manual brakes, no brakes etc.
Put the new & old masters side-by-side and compare. Especially at the piston portion.
The design of the rear of the master changed over the years.
It is imperative the new matches the old.
For your sake, let's hope RockAuto has the correct unit.
Some stores data base states: Fits All Vettes from 1800's to 2025, red ones, yellow ones . . . . . PB brakes, manual brakes, no brakes etc.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,007
Likes: 4,162
From: US-PNW
So I gather what everyone is saying, is that I should see some fluids movement in the rear bowl.
I am slowly pushing the plunger in until it stops, haven't measured the actual distance.
This master would be about 10yrs old.
To be safe I'll throw money at it and purchase a new unit from RockAuto and hopefully it will be down here by the end of the week.
I am slowly pushing the plunger in until it stops, haven't measured the actual distance.
This master would be about 10yrs old.
To be safe I'll throw money at it and purchase a new unit from RockAuto and hopefully it will be down here by the end of the week.
The front and rear systems do not apply equally. The fronts apply more pressure so more fluid movement is expected. If the rear bench bleed hose is feeding back with a good stream of fluid then I'd not change out the master.
Melting Slicks
Joined: Dec 2014
Posts: 2,771
Likes: 2,296
From: Central UT
I just bench bled the master for our '68 Saturday, so it's fresh in my mind.
- To avoid pushing the piston too far, I put a small vice grip on the shaft of the phillips screwdriver just short of the 1 1/2" point and that works well.
- The front and rear 'squirt vs. spurt' was definitely a bit different. When no more bubbles, the rear was more of a 'disturbance' than the occasional squirt from the front.
- As stated above, I do the master level, then change it a bit so it's higher in the rear, etc. I always get just a few more bubbles when I do that.
- Also as stated above, don't chuck you old master until you know the rod will be the correct length. I helped a friend chase a brake issue recently after he replaced the MC. He got rid of the core and we found that the new MC had a difference and needed a shorter rod.
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Melting Slicks
Joined: Jun 2011
Posts: 3,114
Likes: 597
Have a question regarding the bench bleeding of my master cylinder.
Here's a quick video I just took.
EDIT: I cannot get the embedded video to play thru the forum for some reason, please click on the "watch on youtube" at bottom left of video.
https://www.youtube.com/watch?v=loKw8c5G-AQ
I'm not getting any more bubbles out of either the hoses or the tiny holes on the bottom of the reservoir. All good there.
But I do get a little vertical "spurt" from the bottom hole in the front bowl, but no "spurt" or any sign of surface disturbance except out of the bleed hose in the rear bowl.
Is this normal behavior or is the master cylinder showing a problem?
If so, for future reference, which is the correct behavior, spurt or no spurt?
Here's a quick video I just took.
EDIT: I cannot get the embedded video to play thru the forum for some reason, please click on the "watch on youtube" at bottom left of video.
https://www.youtube.com/watch?v=loKw8c5G-AQ
I'm not getting any more bubbles out of either the hoses or the tiny holes on the bottom of the reservoir. All good there.
But I do get a little vertical "spurt" from the bottom hole in the front bowl, but no "spurt" or any sign of surface disturbance except out of the bleed hose in the rear bowl.
Is this normal behavior or is the master cylinder showing a problem?
If so, for future reference, which is the correct behavior, spurt or no spurt?
Here is how I bleed the MC while on the Car. Works very well.
Get the last bit of air out from the brake master cylinder. - CorvetteForum - Chevrolet Corvette Forum Discussion
Thread Starter
Melting Slicks
Joined: Oct 2010
Posts: 2,276
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
Spent Sunday trying to get a firm pedal, that's why I thought it could have been the master cylinder.
there are no leaks from any calipers, rears had a couple of replaced pistons and 8 new seals installed about 2yrs ago.
I had a temporary bolt in place of the switch in the front brass distribution block to hold the shuttle from moving/tripping.
tried reverse bleeding with one of those Phoenix V5 units, pedal goes to the floor.
tried gravity bleeding to get the last out at the caliper nipples, pedal goes to the floor,
tried vacuum bleeding, pedal goes to the floor,
tried the rear up higher as mentioned above, still no difference.
at slow speed, car will stop, but I have long pedal travel, ie: it hits the carpet, defiantly no wheel lock up and skid to a stop.
so then i removed the master and retried bench bleeding it, that's when i noticed the spurt / no spurt.
there are no leaks from any calipers, rears had a couple of replaced pistons and 8 new seals installed about 2yrs ago.
I had a temporary bolt in place of the switch in the front brass distribution block to hold the shuttle from moving/tripping.
tried reverse bleeding with one of those Phoenix V5 units, pedal goes to the floor.
tried gravity bleeding to get the last out at the caliper nipples, pedal goes to the floor,
tried vacuum bleeding, pedal goes to the floor,
tried the rear up higher as mentioned above, still no difference.
at slow speed, car will stop, but I have long pedal travel, ie: it hits the carpet, defiantly no wheel lock up and skid to a stop.
so then i removed the master and retried bench bleeding it, that's when i noticed the spurt / no spurt.
Race Director
Joined: Nov 2006
Posts: 13,151
Likes: 7,765
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
Considering everything you have tried. And I believe those reverse bleeders to be very effective.
I am with you. Something must be up with that master.
I also agree with a few of the guys above in that the rear moves less than the front. But you still should see fluid movement. Perhaps the seal between the front and rear pistons is damaged.
At any rate this must be extremely frustrating for you.
Me, I'd be either rebuilding or replacing that master as well. Fingers crossed.
I am with you. Something must be up with that master.
I also agree with a few of the guys above in that the rear moves less than the front. But you still should see fluid movement. Perhaps the seal between the front and rear pistons is damaged.
At any rate this must be extremely frustrating for you.
Me, I'd be either rebuilding or replacing that master as well. Fingers crossed.
Team Owner
Joined: Aug 2004
Posts: 22,278
Likes: 203
From: Sussex,Wi
2023 Corvette of the Year Finalist - Unmodified
2022 C3 of the Year Winner - Unmodified
Do you know anybody with a "power bleeder" you can attach to the MC, and bleed down thru the calipers?
Even though you need to bench bleed the MC, I believe the forced pressure thru the MC will get any small
pockets of air out of the MC.
Motive makes a kit ~ $100.00 USD for the 68-82 vette MC. Motive Products 0252 Motive Products Power Bleeder Kits | Summit Racing
I had so many problems with my brakes, but it ended up being bad rotors (lip seal) that kept causing air to infiltrate
the system. I replaced everything, I got so pissed with the problems I was having.
Too bad you're located so far away, I got a brand new MC from Napa, lifetime warranty, just sitting on the shelf (already bench bled).
Even though you need to bench bleed the MC, I believe the forced pressure thru the MC will get any small
pockets of air out of the MC.
Motive makes a kit ~ $100.00 USD for the 68-82 vette MC. Motive Products 0252 Motive Products Power Bleeder Kits | Summit Racing
I had so many problems with my brakes, but it ended up being bad rotors (lip seal) that kept causing air to infiltrate
the system. I replaced everything, I got so pissed with the problems I was having.
Too bad you're located so far away, I got a brand new MC from Napa, lifetime warranty, just sitting on the shelf (already bench bled).