1968. I got a new master cylinder. Correct for manual brakes. During the bench bleeding I made the rookie mistake, I pushed the rod all the way in. With a new MC what chance is there that I screwed up the seals during bleeding? I then bled the system after installation many times. Every thing else new or rebuild. Braking is just ok, wish they were better. The pedal doesn't sink to the floor when pushed and held. I am thinking about doing reverse pressure bleeding.

 

Doubt you damaged the seals on a new MC.
What sequence did you bleed and did you tap the calipers while bleeding?
I have always been successful by just using gravity bleed.

 

That's what I was hoping, a new MC should be smooth. I have bled them, back to front, front to back, upside down, inside out, gravity, almost tried sucking on the hose. Maybe I am just not familiar with the manual brake feel. I would think I could slide the tires on dry pavement but can't. I do have a bit oversized tire on the car.

 

Very likely at least one of the MC piston seals was damaged. There should have been a warning label on the shpg box or highlighted in the instructions:
Do Not Insert Screwdriver More Than 1 & 3/8" Or You Will Void the Warranty.

 

Stop struggling and go buy (or make) a pressure bleeder. I made mine from a garden sprayer years ago because I didn't want to wait to have one shipped and it works so well that I never bought one.

 

I ordered a rebuild kit and will use a reverse pressure bleeder this time. Will be interesting to see if the seals are scratched or cut, will let you know.

 

You can't go wrong with a pressure bleeder, for next time, either Motive with a large clamp, or a DIY system.

You should be able to lock up all four wheels when all the stars align.

 

before you remove the MC again try the following.
https://www.corvetteforum.com/forums...-cylinder.html

Then once you have all the air from the MC, use pressure applied at the MC to bleed the calipers.

1. Push each caliper piston in using the brake pads as support and block with vise grip or something to keep the caliper piston in position.
2. apply pressure at the MC
3. open the caliper bleeder to bleed.
4. once no air bleeds, remove the vise grip support at the pads to allow the caliper pistons to return.
5. remove air pressure at the MC.

Here is what I use to apply air pressure at the MC. ~ 20 PSI.

 

The only way to test the MC for possible damage is to isolate it from the rest of the braking system. To do that, you will need two MC test brakelines.
Your local NAPA should have "ready-made" steel brake lines about a foot long with fittings. Note that the front MC brakeline port and rear port are different diameters and thread pitch. Take that info with you to the store. Each test line will need to be blocked off on the other end. Smash, squeeze, pinch or install a brass cap.

Remove front & rear brakelines one at a time from MC. Quickly attach your test lines and bend upward to clear inner fender, etc. Now, you should be able to stand on the brake pedal. If that pedal moves, the piston seals are toast (post #1). If the pedal doesn't move, look elsewhere.

Never use a plug or a bolt in the MC line port. There is a flare inside, that is part of the castings that can be damaged.

You will need to to bleed the entire system again after testing the MC. You have introduced a bubble at the MC.

 

Yep,,, I raised the back of the car and bled the brakes also. I will compress the pads when I do the reverse pressure bleeding.

 

This tells me that the mc is good.
A lot of air in the system would give you a spongy pedal.
Pads good, not glazed?
Combination block/valve not offset?
Good fluid flow from all the calipers?
Did you have this condition before you changed the mc?

 

If one side of the MC has a bad seal the other side should hold the pedal from pushing all the way in,,, I am thinking.
Pedal has always been a bit spongy.
I have tried 3 different sets of pads.
Fluid flows well to the calipers when bleeding them.
My original MC was a 1.25 diameter, the correct diameter for a manual is 1.0 inch, is why I changed it... REALLY bad before I changed it.

 

SO,,,,,,, I got a reverse pressure bleeder and bled all 4 calipers. I had my wife watch the MC, no bubbles from the MC. I also bled them normally and did get a few bubbles in the clear tube.
The rear calipers are almost horizontal. I think this is an issue when bleeding them, especially the outside half of the caliper. These calipers have 3 bleeder ports, 2 on the outside, one on the inside. I think they are there for a reason. The outside half of the caliper being horizontal must be difficult to extract all of the air. I think bleeding that side by itself helps get all the air out of the system. I started by lowering the rear of the car to get a slight angle on the caliper. I used my pressure bleeder on the lower port, then opened the upper port on that side during bleeding. I kept the cover on the MC to keep the pressure isolated to the one side of the caliper. I did get a few bubbles.
I really don't think compressing the MC, all the way, during bench bleeding will hurt the seals. There really isn't anything in the cylinder that will scratch the seals on a new MC. Also during normal braking, I think the plunger is compressed most of the way, anyway.
Soooooo, after all this, my brakes are a bit better, but still just OK.

 

Get, or make, a pressure bleeder. You'll be glad you did. No need to involve anybody else during bleeding and it works like a dream.

 

Do you have Willwood rears? I don't, but I remember reading that bleeding them works better if you remove them from the trailing arms, or at least rotate them (you may need to block the shoes with a piece of wood or something). Stock rear calipers have two bleeders at the top. At the bottom is the fluid inlet, and on the other side a plug. You can remove it, but don't. Perhaps someone replaced the plug with a bleeder?

If you have a hard pedal, but poor braking, you need different pads, or something else is wrong. If you don't have a hard pedal, try pressure bleeding again, while tapping the calipers and junctions with a wrench. You still have air somewhere.

 

You don't believe compressing the piston too far will hurt the piston seals bench bleeding. Well, take that up with Lone Star and tell them they are wrong.

What happens is the seals get "rolled-over" from snagging on something in the bore. This renders the seals useless. And voids the warranty. Your local parts store will never know the difference if you return the defective MC. But Lonestar knows.

Keep in mind that the distance you're shoving in the piston on your work bench is greater than the distance the brake pedal would travel. The pedal has a stop.
Your arm & screwdriver does not have a stop.

 

Some/most pad need to be bedded to work their best.
Find a deserted road and heat cycle them with some hard/hot stops thrown in.
Search the net for specific procedures.

 

Yep,, did that.

 

I did talk to the Lone Star guy. He said if my seals were bad, there would be a leak out the back of the MC or the pedal would bottom out. I did get a set of FE semi metallic pads to see if they are better than organics. When I get my car back on the road, I will break them in and try them out.

 

That does & does not make sense. I think Lonestar misunderstood your issue or you misunderstood their answer. If either one or both of the piston seals are truly defective, I suppose there could be some seepage out the back. But that's not the point. Going all the way back to post 1 you questioned if the seals were damaged. You said the pedal doesn't feel right. If just one of the seals is bad you will have a half a pedal. You have pressure on one output line but not the other.

You state: fluid flows well to the calipers. That does not confirm the MC is building pressure.

It does not matter how many pads / rotors or whatever you put on the car, if the master is not building pressure you are not stopping on a dime. Your MC was bench bleed incorrectly. You can deny the MC is at fault here all you want. But it was never tested. I am not trying to be harsh here, but you have to go back to the begining and verify what's working, what is not.
You have to test the MC solo, all by itself, to see if its even doing its job. Outlined in post 9.

And because you went from a PB master to a manual master, was the pedal rod / MC gap ever checked?

Then proceed with your pads, etc.
I know brakes are frustrating but you will fix it right.