Only reason to add residual pressure valves would be if the master cylinder is below the level of the calipers to prevent drain back. If necessary master cylinders should have them built in on an OEM application. This has standard GM calipers on all 4 corners. The rears don't retract any more than the front. I'm familiar with master cylinder bleeding procedures ...been doing this for years.

But my question wasn't answered. What cars/master cylinders have a warning not to fully depress the piston when bench bleeding?

 

The new & rebuilt Delco Remy units sold by vendors. Which I will not name.
When my original MC starting failing, I checked around at prices for a replacement. Comparing not only prices but shpg charges, if a core return was involved and shpg time.
When I received my new MC, there was not a warning label on the box. I bench bled in a vise several minutes at different angles. No bubbles.
Installed on vehicle, bled entire vehicle, pedal goes to the floor. Bench bled again with ports plugged. MC would not hold pressure. H-m-m-m-m-m-
Called MC supplier who asked about my bench bleeding procedure. Over extended. I didn't know. I ruined a good MC.
It was thrown in a corner in frustration. Bought another MC. This time box has warning label. Go figure.
Lesson learned.
This is what happened to me and I have read it happens to others. I don't make this shet up. I doesn't take a rocket scientist to figure out there are some real finicky issues with repairs / parts on C3 brakes.
There is not a week gone by that a brake issue post has not shown up on this forum.

I like to warn people about possible damage due to improper parts or improper installation. You don't have to believe me and I really don't care if others do not heed the warning. I put the information out there. You can take it or leave it. Your car, your money, your time.

 

I think there is one distributor that sells many many different brake masters. They probably put a standard caution note in the box just to cover their butt. There might be some MC's that can get damaged.
I do feel your frustration bleeding the vet MC. I have probably pumped 2 gallons of fluid through my MC. They are kind of quirky.

 

Exactly right about the supplier.
I bet many rookie brake people tried to return MCs for a refund, claiming the manufacturer was faulty.
They are no dummies. Within ten minutes a technical advisor can have that faulty MC torn apart and verify whom is to blame.

 

Just curious, Exactly which MC did you destroy by pumping it?

 

Finicky parts i understand. Few manufactures can make descent parts now a days it seems. But in 23 years of doing this I've never damaged a master bench bleeding it. Maybe it's related to the C3 master only? Who knows. Thinking about it, I wanna say I think there is a set screw installed in some of the GM masters to keep the piston in the end of the bore from coming out/moving too far back, something like that. Installed into one of the bowls or underneath the bore. This could definitely damage a seal if the piston was pushed into it, but I dunno if they all have it or if it's even in a spot where it could contact a piston seal. But otherwise if the bore was machined properly there should never be a chance of this happening. I never had to work on many corvettes in my career, many caliper replacements yes, but not master cylinders.

Anyway, don't have to get so defensive. This is why I was asking. You obviously had this happen and seen it happen more than once, so I wanted to Info to file away ya know. When I get back to the truck I'll be bench bleeding the master again, different angles, and paying attention to how far I push the piston in.

 

Plain ole Delco for a Vette.

I should have kept it. Maybe buy a rebuild kit for it.
Hind sight 20-20.

And again for the record:
Maximum stroke in a vise is 1 & 3/8 according to the warning label.

 

This is the bore of a C3 master cylinder. This is the 1 inch bore for a manual brake car. There is a 1 1/8th inch bore for power brakes. You can see two white spots, one at 12 o'clock and one at about 10 o'clock. The one at 12 o'clock is the hole to the bottom of the rear reservoir. The one at 10 is the hole to the rear brake line. The seal slides past the 12 hole in the first 1/2 inch of travel of the pedal, when pressing on the brakes. One of the issues with the MC is trapped air. You can see the hole at 10 is on the side of the bore. This is what allows a bit of air to get trapped in the upper part of the bore. If the bore/MC is level when bleeding, air will never get pushed out of this hole. If you tilt the MC to the right or tilt the rear of the MC up, air will get pushed out one of these holes. There are two identical holes for the front reservoir farther in the bore, you just can't see them. The holes at 12 o'clock have constant fluid from the reservoir filling them. When you use a pressure bleeder, it puts pressure on the fluid to these holes, then pushes air/fluid out the hole at 10 o'clock. You can see that if there is air at the upper curve of the bore, it won't get pushed down and out the hole at 10 o'clock unless you tilt the MC. You can see the bore is perfectly smooth. It is possible when installing a new piston with seals into the bore to turn a seal over/inside out.

 

You should be a proctologist.

 

Is this because of my 1 inch bore,,,, or being ****. ha!

 

Silence is deafening. No comment on how a seal can get destroyed in this bore? Everyone who is scared to bleed a MC wants to know.

 

The physics says the front brakes do 75% of the work during a hard stop, due to weight transfer.

Corvettes do this with smaller pistons in the back, same psi, less square inches.

More traditional cars do this force adjustment with a pressure limiting valve for the rear (called a proportioning valve).

So if your equal sized piston system is working properly it should easily lock the rear long before the front. I vote for air.


C3 brake pistons set

 

You are 100% correct about the master bleeding.
Here is a link from about 10 years ago, same stuff.
Scroll down to see the pic of a master I opened up, shows the ports the seals ride over.
Also shows why one must tilt and rotate the master to get all the air out.
Only time you use short strokes is when it's an old master and even then it seldom ruins it.
As you can see this bleeding thing can be a tough process for some to really grasp the whole picture.

https://www.corvetteforum.com/forums...-bleeding.html

 

All right, I jacked up the back of the truck high as I could to get a level to indicate I had a good tilt on the master. Watched as a buddy pushed the pedal down slow, you could see the piston going by the holes no air came out into the bowl. But if I had him jab the pedal 3 or 4 times and stop, foot off the pedal I'd see bubbles after he stopped..small but still bubbles. We did this for 10 min, and I thought we got it all. It after driving it we didn't. It maybe feels a little better. But still air trapped in it. I'm gonna try again to see how much more I can get out. This is with tapping the body of the master with a hammer to dislodge or get the bubbles out. It's not like a vid I saw where it was one decent size bubble, then another...these were tiny bubbles. Rear resaviour only, which is where the air is definitely. And the bubbles are only coming out of the pinhole, not the large hole.

I may also just try and take it off and try to do this one the bench. But if I have to spend much more time on this crap I'm just gonna dump this rediculous master and out a wilwood on it and be done.

 

You are making progress. When you push the pedal you don't need to push to far, barely 1/2 way down, just tap it back and forth, making sure it comes all the way back to the top each time. Bubbles only come out during the first bit of movement. As you saw, after the holes are covered by the seal, air wont come out. Also make sure the rod from the pedal to the back of the MC has a bit of space before it contacts the MC piston. Just a few thousands. This insures you have full travel of the MC piston. Do you have a power brake MC, 1 1/8 inch bore,,, or non power brake MC, 1 inch?
I wouldn't take the MC off. It is easy to get air back into the MC from the time you disconnect the bleeder hoses to when you hook up the brake lines,

 

Thing is I never saw air come out when pushing it...only after it would get pumped a few times, when it would rest of see the bubbles come out of the small hole, not the bigger hole.

 

As you reliese the pedal the air followes the seals backwards/upwards in the bore untill it get to the holes to the reservoir. You are not pumping the air out, you are allowing the air to escape up and out uowards. By tapping on the pedal, this giggles the air and making it go up. You said before that you had to pump up the pedal to get solid brakes, does this still happen? It shouldn't. Does the pedal allow the piston to fully retract.
In the corvette the rear calipers are almost horizontal. Are yours vertical or horizontal? This makes the vet rear calipers very hard to bleed

 

Yeah I understand how the air is still stick in the master and how it's getting out. I thought I'd be seeing the bubbles as I push the pedal down as well as up as the air should be against the piston with the back of the truck up so the master is tilted.

The rear caliper bleeders are pointing up, I don't remember how vertical they are but I'm pretty sure they were near straight up. And yeah I still have air in the rear circuit somewhere. I haven't had a chance to go back and mess with it again.

 

I'm not worried after seeing noonie picture.
I don't see anything to snag on a seal.
Other M/C's might have something to snag on so why not take the advice and be careful?

 

Thanks.

I heed 90% of all warning labels I see.
Caution: Do Not Operate Your Toaster In The Bathtub.