Technical soft brake pedal after caliper change

I have been fighting this for awhile. Working on a off topic car, but brakes are the same. Everything was working, and had a hard pedal to start with. I swapped out calipers, pads, rotors, and rubber lines. Since then I have bleed them 3 different ways (pressure, vacuum, and leg pumping), and put over a gallon of fluid through them. While changing parts the front reservoir went dry, but should be no big deal. I started at the master, then went to the right rear and then left and so on. Pedal still soft and goes to the floor. I have driven it and it stops but soft pedal. Is it possible that the plunger is stuck in the master? When I push on the pedal I only get fluid to bubble in the front reservoir, is this normal? I did not remove master. I know that the cause is air, but how do I get it out? Is there any other possibilities? It does not have any leaks, I have checked many times. Bleeders are on top as they should be.

Thanks Tony

 

Caliper on the wrong side?

 

They are on the correct side. Bleeder is on top.

 

Raise the car front or rear as required in order that the master is pointing downhill some. Pushrod end up, opposite end down. Doesn't have to be a lot, so no need to dangle the car from the rafters! Then start bleeding.

Chris

 

Had something similar--my solution was gravity bleed. Master must be above all cylinders, start at RR and open bleeder for 15 min-just be sure to check master and never let fluid get low. If master is below floorboards, do you have residual valves? I wonder about the bubbles, not good.

 

Its not really bubbles as much as it is fluid coming back in the master. Master is above floor and it is a factory system.

 

There are two pretty stiff springs in there. Unlikely that either plunger would be stuck. Here is one I had apart recently to illustrate.



Most likely, you have air in the master from having run it dry. You’ll need to start at the master. Bench bleed it off the car.



Then reinstall and bleed the lines as usual. Try not to get any air in while installing, or at least as little as possible.

 

Might need to bench bleed the master cylinder.....I had something similar happen.... Had trapped air in the master cylinder that wouldn't bleed out thru the lines...

 

Break the fittings loose where they exit the master, and hold a rag under the fittings one at a time to catch fluid. Have someone push the pedal down and hold it while you tighten the fitting. Repeat for the other fitting, and then bleed the system again. I've occasionally found an air bubble trapped right at those exit fittings and this is the only way to get it out.

 

Just got done taking master off and bench bleeding, put back on bled system with pressure bleeder while master was level, and still have soft pedal.

 

Make sure that the calipers are "floating" i.e. that they can slide back and forth on the pins without touching anything on the spindle. Also, get someone to work the brakes while you watch each caliper for movement. There should not be any visual movement. Sometimes the new calipers don't fit exactly like the old one due to differences in castings and machining.

 

Sounds like air issues. Some thoughts...is the master retracting fully/proper pedal - master free play? Low drag calipers needing a stepped bore master? Distribution block plunger shift? If using a prop. valve, might open it fully for the bleeding. I've had only one problem child brake system that wouldn't bleed, until I did a pressure bleed. Good luck!

 

Is your master " bleeding by" ? Are your rotors running true ? Jack the wheels of the floor & try turning the wheels , if any free wheel , your caliper/ pads are " backing off" .

 

Had an issue like that on a ford tempo,had a flimsy pedal after just replacing pads,it turned out to be the pad was cockeyed in the caliper,pad was crooked?.piston was moving too far.it took awile to spot it,but i felt ike a fool when i did see it,check and see if the pads are straight in the space in the caliper. harvey

 

Just because the bleeder is on top does not mean they are on the correct side.

 

But did you break the line fittings loose to get rid of possible trapped air at the fittings that I previously mentioned?

 

GM Metric calipers?

 

Same thing I was thinking! The famous GM soft brake calipers. GM used to make two different calipers, but they have been miss swapped so many times, the part numbers no longer matter. I believe a search will tell you how to tell the difference.

The next thing is if you changed the master, its possible the booster rod adjustment isn't allowing the master's piston to full retract.

 

Quite possible that the master is damaged internally and leaking. Or bypassing. When bleeding, you have to be careful not to bottom out the master, more so with used ones. They get a ring of crust at the bottom of the bore over time. Then the rubber cup gets pushed past that and... it leaks.

 

If a master runs dry it needs remote bleeding, completely by itself. No way around that one. You can do it on the car or bench.
After that, bleed the lines right at the master with slow single pump. There will be a little air bubble stuck in the line . that air bubble goes between the master and line and plays a game like the runner in baseball between second and third base. Goes to line and sucked back to master.

If an older master cylinder gets stroked past its normal range it can grab debris from deeper in the bore and muck up the seals.

Another thing, physically pull the pedal up between every pump.

 

Pedal stop & return spring helps that

 

It may not be MC related at all. Check to make sure everything else is right. A 1" MC only displaces about 7/8 of a cubic inch. You get a stiff pedal when all the air is out AND everything is centered up and requiring no movement. If the new calipers are binding in any way, you won't get a hard pedal no matter how much you bleed the system.

If you want to prove that it's not the MC, put plugs in the outlet ports and step on the pedal. (I'm willing to bet it's hard as a rock.) Another way that can also help you is to use clamps and pinch the hoses down. This allows you to isolate front and rear brakes from the equation by simply unclamping one circuit at a time. Harbor Freight has neat little clamps for this. https://www.harborfreight.com/4-piece-fluid-line-clamp-set-65116.html

 

Yes I did.

I am working on a Ford 8.8 no metric calipers. Everything seems like it is moving correctly. I went back and checked for proper installation, and all looks good. I am taking the proportioning valve apart next to make sure it is not stuck. When I get it I will let ya know.

 

I would bet you still have air, I know when I came along ,sometimes when the pedal would go all the way down and trip the brake light where the proportioning valve moved all the way it would be a pain to get a pedal back. Get someone to help work the pedal to bleed them. Then whoever you get has to be able to follow directions LOL

 

You’d think it should but it really doesn’t.
leg fatigued pumpers usually think the important part is pushing it down, when the important part is returning it to full up.
Normal operation range for the plunger leaves debris and crud in the bore beyond that range. An open system will stroke the plunger beyond the normal range and into the crud zone. Pedal stop isn’t for that and in a different place.

 

I’m remembering needing to bleed those calipers loose from the mounting, the bleeders and port weren’t exactly up, or at the highest point possible.

 

Put a bit of grease around the bleed screws while you're at it. [to seal any air from sucking back in]

 

Is there a rear anti skid system to the rear breaks?

 

I'll stick with what I know , thank you , your opinion is your own , as is mine .