Technical GM metric low drag calipers *FIXED*

Yes, I have an adjustable proportioning valve. I have more than 1100 psi on the outlet side of valve with it all the way open.

 

Where and how are you measurimg pressure at the calipers?

How old are the flexible hoses?

 

I recently replaced the hoses to the caliper with new braided stainless hoses. The 1100 psi is at the end of the hose at the banjo fitting where it attaches to the caliper. The 700 psi pressure reading of the caliper is at the bleed screw. I remove the bleed screw and attach my gauge line. The gauge has its own bleed screw. I bleed the system by various methods but I try to check the system by bleeding through a clear tubing to a jar so that I can visibly check the fluid for bubbles. I remove all bubbles until I have clear liquid.

As a side note I have bought gallons of brake fluid as I have worked my way through this project. A quart at a time. I have bought more than I have ever bought in all my years of working on cars. This has by far been the most difficult problem I have ever worked on. I have built entire hot rods in the time I have worked trying to improve these brakes.

I appreciate your time and any thoughts you may have.

 

Are you sure? The AFCO website description says they have "low drag" seals. Isn't that the source of your problem? From the website:
" 2-1/2" bore steel GM metric caliper is designed to be a used as a NEW stock replacement caliper. The caliper features a stock appearing virgin plated caliper body, new ground 2-1/2" stainless steel piston, and low drag seals. Each caliper is assembled and pressure tested. The calipers have a 5.5" bolt spacing."

 

In a sealed hydraulic system, free of air, pressure will be equal at any point where it is being measured.

 

I isolated these components to take the readings. I took the readings at the bleed screw and then I disconnected the gauge and connected it again at the point where the brake line attaches to the caliper at the end of the flex line, so that I removed the caliper from the test. There is a difference of pressure between the connections for the gauge. I further isolated and tested each individual caliper. Interesting that the two calipers have slightly different readings. One caliper has more of a drop than the other. There are no fluid leaks.

It seems that I have narrowed it to two possibilities. There could be air trapped somewhere in the caliper, that I can not get out. (the best answer) There is something pliable inside this system that is expanding like a balloon, that is allowing the pressure to change. My guess is the air but I do not know what else to do. I have removed the caliper, clamped the piston in place, and rotated the caliper in my hand while I bled the system. The bleed screws are pointed up but I wanted to be sure that I tried all possibilities. I have also tapped the caliper with a hammer while doing this.

I bet you are starting to see why I am so frustrated. I have been trying to improve the brakes on this car for the last two years. Currently the original 4 wheel shoe type brakes were far superior to the 4 wheel power disc brakes I have now.

 

Gimpyshotrods you need to lighten up .My car is an 1/8 th mile nostalgic drag car. It was a bit of humor . I see the need for the best brakes you can get for street cars .
With all of the stupid distracted drivers out there you need to be able to stop as quick as the big tires and little tire combo's that most street rods have.
I don't see the need for the latest 6 piston caliper's and carbon fiber rotors on the front of a car that has a 4 inch wide tire on the front . Most hot rods should be be rear biased to take advantage of the larger contact patch that is on the ground.
I am glad you live in a rich neighborhood that has those types of cars. Some of us are not that unfortunate.

 

I need good brakes and handling because of our terrain. We have the steepest streets in the country here. It is a lot of fun driving here.

 

If you are using a under floor mounted master cylinder you will need a 2 pound residual
valve on front & a 10 pound residual on rear if using drums. Sounds like fluid is running back
to master cylinder . Jerry

 

Someone put a 1000-foot mountain, right in the middle of our city!

A >30% grade is considered normal here.

 

Thats nice, but sometimes we get alot of snow .

 

Every so often, we get some too, and a whole mess of people die.

 

I'll bet, we have had snow here most winters, but we still have people that can't drive in it.

 

This is like printed ping pong.

 

Amateurs ^^^^
Check out Baldwin St , Dunedin NZ [where brakes rule over horsepower]

 

The only hot rod I ever built that had crappy brakes had GM metric calipers and a "Corvette" master cylinder. I'll bet I know why those brakes were so bad now! Gene

 

The photos of terrain are scenic, but getting back to calipers, has anyone used the AFCO calipers and found them to work better than the GM metric calipers with regard to reducing the pedal travel? The AFCO website states that they have "low drag seals" which is exactly the problem with the GM calipers.

Bob

 

They worked good on s dirt track car.

 

Ok I've got to ask this........

Do you have the calipers on the correct sides? Are the bleed screws on top and the hoses on the bottom ?

Can't tell you how many times I've seen this...

 

To answer your questions... yes, yes, and yes. I ordered the Afco calipers, should be trying one in a couple days

 

What push rod do these take? I've searched for OEM pieces and haven't found anything yet.....

1984-85 S10 4 cylinder with Disc / Drum manual brakes

https://www.amazon.com/Cardone-Sele...---14--------3&vehicleName=1984+Chevrolet+S10

 

The master cylinder in the link you posted seems to be the type with the shallow pushrod bore intended to be used with a vacuum booster, not a manual brake application.

B

 

Thanks Bob. Interesting. I copied the link provided by "Mimilan". I'll try the other link to see if they were swapped.

 

I had S-10 calipers and a FoMoCo dual bowl MC for a Maverick. Never had much pedal. That puppy would go almost to the floor no matter what I did. One pump gave me a little more pedal but......panic stops don't allow time for a "pump-up".
Once the guyz on here explained about the "step calipers" GM has I switched to a GM MC and things got a WHOLE lot better. Stops good.......good pedal......no more puckered butt hole with panic stops and 'mouth-breathing-millienial texters'! (sorry...just couldn't resist)
Short answer.....swap MC's to match calipers.
6sally6

 

From what I can see, they all have a shallow countersunk feature which seems to tie into the comments I've read where users worry about the push rod falling out. Some users have gotten creative to provide a retainer of sorts for their applications. If you're aware of a master with a deeper recess, please provide a picture or link.

Thanks,

- EM

 

I think Streetrodder is on to something. Disk brakes have a residual check valve in the master to allow fluid to keep some pressure on the pads. Drum brakes do not have said valve allowing the return spring to pull the shoes back and the fluid goes back towards MC. You stated:

"I bet you are starting to see why I am so frustrated. I have been trying to improve the brakes on this car for the last two years. Currently the original 4 wheel shoe type brakes were far superior to the 4 wheel power disc brakes I have now."

Did you use a disk brake MC or the one that was on there when it had drum brakes.

Pat

 

So what your saying if you have the GM disc metric brakes on front and the GM disc rear brakes with e-brakes, that the bore size of the master should be ? As I have a cast iron master cylinder on it ! and not a good pedal !
Cardone Select 13-1923 New Brake Master Cylinder is the one you recommending

 

To my surprise, my research shows the same thing. That's sure not typical. I'd find a way to positively retain the pushrod if I was using that mc.

 

This is just a thought for consideration, but could the low drag seal's retraction of the piston to a greater degree than a conventional seal be overcome by using a 10 psi drum brake residual pressure valve instead of the 2 psi often used for disk brakes? Perhaps it would retain the piston/pad much closer to the rotor and reduce the fluid volume required in the first pedal stroke?

Bob

 

Okay, here’s the update! The AFCO calipers mentioned earlier ARE the standard/regular style caliper. A little more expensive than the auto parts replacements, HOWEVER, they have solved the braking issue! These have the correct style seals and pistons to run with my style master cylinder (Ford). You can see the difference in the brake pad drag on the rotors in the pictures. “Low-drag” caliper has almost. .020 and AFCO has almost nothing! Thanks to all again, much better braking now. And thanks to gimpyshotrods for the help!