Ive been working on these damn brakes all week. I cant get the master cylinder to stop bubbling, so I assume there is air in it which is the cause of my soft pedal. Ive bench bled it 3 times out of the truck and 3 times on and it still wont work. When I bench bleed it, I go until no more air bubbles come out and then longer, but once I hook up the lines it starts bubbling again. Is there some kinda trick I'm missing? This is happening on two different MC's. I dont want to have to take it to a shop to be power bled or whatever they would do

 

you probably have a leak somewhere, causing it to suck air once its bled up. Possibly where the lines screw into the mc, or maybe one of the seals

 

Yep, you have air entering somewhere.

Chris

 

rusted brake line, check for leaks aka pinhole.

 

I replaced most of the brake lines so no rust. Everything worked great before the cab swap so I know its not an issue with the calipers or anything like that. I'm gonna give it a good once over and check all the lines and bench bleed it one more time and if that doesnt work Im gonna have to take it to a shop.

 

How are you bleeding the lines. Remember start with the longest line. The passenger rear, then move to driver rear, onto passenger front, and finally the driver front. check your fluid lvl between each wheel.

If that isn't the case, is it possible you pinched the line when installing new cab.

Thats my two cents.

 

Maybe you bent/broke/loosened a line when you swapped cabs?.

 

I replaced all the lines after the cab swap, so they are fine. The brakes will work if I pump them 3-4 times and then they catch so it must be some air

 

sounds identical to how the brakes feel when i bleed mine.

 

did you properly bleed the RABS valve?
if not, you will never get the air out of the system, and the pedal will be spongy

 

I had to replace a good bit of brake line on a project, and wound up making 1 double flare that had split . It was hard to see with the nut on it, but still leaked/pulled air?

 

Did you buy the re-man master cylinder? If so take it back and buy a new master cylinder, re-mans are junk for our series trucks regardless who you buy from.

You will never complete the bench bleed successfully, it will never pump up solid.

Get a "New" one then be sure and bleed it as directed. Plug the front rear line ports and add fluid until about 3/4 full.

Then use something like a punch or screwdriver and while holding it level cycle the piston in and out slowly. Do not push the piston in all the way until it bottoms out in the bore, push the piston in each time up to 1" travel but no more then that. Continue doing so until the piston only pushes in about an 1/8" and its feel is rock solid, then and only then is it ready to put it on the truck and bleed the lines.

 

Problem was the new master cylinder that I bought. I took it off after bench bleeding it 6 times and got a different one and all is good now. Must of been a fluke that a new one was bad. Thanks for the help guys, especially on how to bench bleed the MC