Squishy brakes

Hello, I’m sure there are other threads of this but I feel like I’ve tried everything. Just installed new front brakes, did a disk brake conversion on the rear, new hard line going to rear, new master cylinder, and a new right H front brake rubber line and rear rubber line. Bleeding the brakes has been an ongoing issue I’ve been facing. I’ve gone through and bled the brakes 5+ times including vaccine pumps and good ole 2 person. I’ve bled the master cylinder. About 3 times. Each time has been thoroughly done 40plus pumps. I’ve tried pulling the rear calipers off and oriented them so the bleeder valve was facing upwards. There are absolutely no leaked in the system. It brakes decent but you have to pump the pedal twice before it reaches a good pressure but not strong enough to lock up or make the tires squeal. Any ideas?
Edit: I’m using dot 4, the fluid is completely clean, been flushed at least 4 times. Had just put on the front right hose today and the pedal needs pumping but is more consistent with being but at bottom. Feels like the car is running and the master cycle is working when off.

What master cylinder did you use and what combination valve? Are they new?

Ricko1966 said:

What master cylinder did you use and what combination valve? Are they new?

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Original valve. CPP master cylinder

justinbrugg said:

Original valve. CPP master cylinder

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What CPP master? Combination valves are different,disc/disc vs. disc/drum. I don't think that's your problem, but thought you should know. Does the pedal ever get hard with the truck standing in one place. Meaning if you bleed the brakes can you get a decent pedal while the truck is parked?

Ricko1966 said:

What CPP master? Combination valves are different,disc/disc vs. disc/drum. I don't think that's your problem, but thought you should know. Does the pedal ever get hard with the truck standing in one place. Meaning if you bleed the brakes can you get a decent pedal while the truck is parked?

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running a big cam so the pedal is pretty much equally as soft stationary and running. Motor just can’t pull vacuum for the master. I don’t know what the model master calendar is. I should probably change the valve then thank you for letting me know. I need to pump the brake to get decent ish pressure. Nothing that is enough to make the tires lock up though. I don’t think there are leaks if that’s what your trying to diagnose mostly because there is no fluid leaking and it holds the same crappy pressure.

justinbrugg said:

running a big cam so the pedal is pretty much equally as soft stationary and running. Motor just can’t pull vacuum for the master. I don’t know what the model master calendar is. I should probably change the valve then thank you for letting me know. I need to pump the brake to get decent ish pressure. Nothing that is enough to make the tires lock up though. I don’t think there are leaks if that’s what your trying to diagnose mostly because there is no fluid leaking and it holds the same crappy pressure.

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Can you get a get a decent pedal
PARKED!!!! I don't the combination valve matters at this point and try to find the master cylinder number.

when bleeding the brakes, are you using the combo valve centering tool, it keeps the valve centered when bleeding the brakes. it may shift one side causing a brake issue.
what rear caliper did you use, are the brake nipples not pointed up when they are installed?
maybe look into hydroboost setup, works well for big cams as it runs off of power steering system and not engine vacuum.
when i did my designed my custom brake setup, 2019 silverado front calipers and c6 rear calipers, the pedal felt normal, but took more effort than it should to stop. changed the master cylinder to a manual brake optioned truck. pedal is way lighter and easier to stop... feels very different but better
clint

Ricko1966 said:

Can you get a get a decent pedal
PARKED!!!! I don't the combination valve matters at this point and try to find the master cylinder number.

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No I can’t get a good pedal parked. Thinking good meaning a normal stiffness pedal. I forgot to mention I have a brake booster as well, but feel like that wouldn’t be the problem. Tried to match the master cylinder online and came up with:

7387BB-MC​

87chevy_com said:

when bleeding the brakes, are you using the combo valve centering tool, it keeps the valve centered when bleeding the brakes. it may shift one side causing a brake issue.
what rear caliper did you use, are the brake nipples not pointed up when they are installed?
maybe look into hydroboost setup, works well for big cams as it runs off of power steering system and not engine vacuum.
when i did my designed my custom brake setup, 2019 silverado front calipers and c6 rear calipers, the pedal felt normal, but took more effort than it should to stop. changed the master cylinder to a manual brake optioned truck. pedal is way lighter and easier to stop... feels very different but better
clint

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I’ve never heard of a centering tool. The valve is bolted to the chassis, so I’m not sure how that would work. I don’t think the loss of vacuum is causing the problem but I was looking into a vacuum reservoirs. I guess they store vacuum when running higher rpm for idle speeds if you need to brake.

This is a proportioning valve with the centering tool.

ali_c20 said:

This is a proportioning valve with the centering tool.

You must be registered for see images attach

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oh ok, never heard of that. I need a new valve anyways since converting to full disk but I’ll order one along with that. Thank you for the tip!

Where did you buy this master cylinder,that you can't get a part number. This whole is starting to sound goofy.

Ricko1966 said:

Where did you buy this master cylinder,that you can't get a part number. This whole is starting to sound goofy.

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Please read my replies . It’s 7387BB-MC. I bought it a while ago off summit.

justinbrugg said:

Please read my replies . It’s 7387BB-MC. I bought it a while ago off summit.

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I did read your replies, #8 you said you matched it up the best you could online to 7387bb-mc. There are too many things going on here you bought this here,that there, I don't know what parts you have,which ones match wh8ch 9nes are new,which ones were new at one point,and it's hard to get you to answer a question with a straight answer. How many times did I have to ask can you get a pedal parked. It was a yes or no question. I'm done. Good luck.

Based on that part number that is a disc/drum master.