Another brake bleeding issue
Thread Starter
7th Gear
Joined: Nov 2018
Posts: 7
Likes: 1
Another brake bleeding issue
Hi Everyone
Quick question - I've been working on the brakes on my 77 and I've replaced every component. MC, Proportioning valve and rebuilt all the calipers. With the switch off I can bleed all four corners with zero air in the system and a firm pedal. The second the car starts the pedal can be pushed to the floor and the brake light comes on. My gut tells me the MC is letting fluid pass so I took it off to bench bleed it (again) and noticed when I cap the outlets and press the piston, instead of getting a firm feel fluid squirts up from the small hole in the bottom of the front reservoir and allows the piston to be fully depressed. The rear doesnt do this so I'm wondering if this is my problem? Should the master cylinder act like this? I dont think the pedal would ever get firm if the fluid can circulate back into the reservoir thru that tiny hole. I thought I knew my way around a set of wrenched but this restoration is making me re-think that!
Quick question - I've been working on the brakes on my 77 and I've replaced every component. MC, Proportioning valve and rebuilt all the calipers. With the switch off I can bleed all four corners with zero air in the system and a firm pedal. The second the car starts the pedal can be pushed to the floor and the brake light comes on. My gut tells me the MC is letting fluid pass so I took it off to bench bleed it (again) and noticed when I cap the outlets and press the piston, instead of getting a firm feel fluid squirts up from the small hole in the bottom of the front reservoir and allows the piston to be fully depressed. The rear doesnt do this so I'm wondering if this is my problem? Should the master cylinder act like this? I dont think the pedal would ever get firm if the fluid can circulate back into the reservoir thru that tiny hole. I thought I knew my way around a set of wrenched but this restoration is making me re-think that!
Melting Slicks
Joined: Jun 2011
Posts: 3,114
Likes: 592
Hi Everyone
Quick question - I've been working on the brakes on my 77 and I've replaced every component. MC, Proportioning valve and rebuilt all the calipers. With the switch off I can bleed all four corners with zero air in the system and a firm pedal. The second the car starts the pedal can be pushed to the floor and the brake light comes on. My gut tells me the MC is letting fluid pass so I took it off to bench bleed it (again) and noticed when I cap the outlets and press the piston, instead of getting a firm feel fluid squirts up from the small hole in the bottom of the front reservoir and allows the piston to be fully depressed. The rear doesnt do this so I'm wondering if this is my problem? Should the master cylinder act like this? I dont think the pedal would ever get firm if the fluid can circulate back into the reservoir thru that tiny hole. I thought I knew my way around a set of wrenched but this restoration is making me re-think that!
Quick question - I've been working on the brakes on my 77 and I've replaced every component. MC, Proportioning valve and rebuilt all the calipers. With the switch off I can bleed all four corners with zero air in the system and a firm pedal. The second the car starts the pedal can be pushed to the floor and the brake light comes on. My gut tells me the MC is letting fluid pass so I took it off to bench bleed it (again) and noticed when I cap the outlets and press the piston, instead of getting a firm feel fluid squirts up from the small hole in the bottom of the front reservoir and allows the piston to be fully depressed. The rear doesnt do this so I'm wondering if this is my problem? Should the master cylinder act like this? I dont think the pedal would ever get firm if the fluid can circulate back into the reservoir thru that tiny hole. I thought I knew my way around a set of wrenched but this restoration is making me re-think that!
https://www.corvetteforum.com/forums...-cylinder.html
The Amount of fluid that exits via the bleed holes should be very slow and only if there is air trapped in the MC piston. Using the above procedure will force the air against the MC piston seal and bleed it all out.
If you then get fluid still pushing out the bleed hole I would guess the mc is not working properly.
Instructor
Joined: Feb 2018
Posts: 150
Likes: 11
From: New Jersey
With the master cylinder in a vice and both output ports plugged, pushing on the piston should become increasingly harder to push in until it won't push anymore. Rap the master with a rubber mallet to make sure there's zero air trapped.
If you have the hoses recirculating from the outlet ports back into their respective reservoirs then the piston won't get harder to push, however you should stop bench bleeding when no more bubbles appear from the holes in the bottom of the reservoirs. Rap with a rubber mallet while pushing.
Also if somehow you compressed the pistons in the calipers to too quickly you may have flipped the seal/cup portion in the master if there was no place for the pressure to go or the seal is just shot.
Seals could in backwards too as said before.
If you have the hoses recirculating from the outlet ports back into their respective reservoirs then the piston won't get harder to push, however you should stop bench bleeding when no more bubbles appear from the holes in the bottom of the reservoirs. Rap with a rubber mallet while pushing.
Also if somehow you compressed the pistons in the calipers to too quickly you may have flipped the seal/cup portion in the master if there was no place for the pressure to go or the seal is just shot.
Seals could in backwards too as said before.
