Hi,

I have tried for several hours to bleed my brakes properly after redoing all my lines with stainless and a new master cylinder. I bench bled the master cylinder before installing and have manually bled each wheel but my pedal continues to go very low to floor. I also ordered a Autel MaxiCheck Pro to do an auto bleed, but i think there is a software glitch as it gets stuck half way ...i've sent to to support and they are checking out the issue, but i won't hear anything until next week...

What am i doing wrong? I dont see any leaks anywhere either. Can it be a bad master?

 

Also noticed the bleeder screw in my rear left caliper is on the bottom when all other three are in too. I am thinking the previous owner installer the wrong caliper. Would this cause a bleeding issue? I only had the h2 for couple Days before I started the fuel pump and brake line change so don’t recall if brake pedal was low, but I really don’t believe so.

 

1st well done so far, you have my respect

There are more experienced members on this subject, I'm sure they will cover other possibilites, but I'll do my best to help.

My LH rear caliper does indeed have the bleeder screw at the top, but logically if your brakes worked before they should again no? Perhaps a different make of part was fitted a some time in the past?

The attached is an extrct of the GM brake bleeding procedure if it's of any help.

Bleeding did seem to be a struggle at 1st. So, with a friend's help, I bled the master cylinder MC1 & MC2 ports (cloth placed underneath) and made sure all air was removed (otherwise you're just compressing air) it doesn't take long and removes this as a possibility.

For caliper bleeding, I used a clear pipe and a clean drinks bottle half-filled with brake fluid, placed higher than the brake caliper This prevents air getting sucked back into the caliper as any air bubles in the tube rise to the top! (see around the 7min mark in the video)

For auto-bleeding I used a TECH2 scanner, note it's sequence was front LHS, front RHS, rear RHS, rear LHS i,e, clockwise. It was a little frustrating at times because if there were any issues the sequence had to be restarted i.e. you can't jump a step.

Normally you'd start at the furthest wheel 1st and work back, it's odd the TECH2 does it as I metioned.

Be aware it's natural to "expect" the brakes to somehow be better than they were before, but they won't be, any deficiences in the braking system will still be there. The biggest improvment I made was by replacing the pads and rotors.

As for possible issues with your master cylinder, I've not been there (yet) so perhaps others can help.

 

Good luck!

 

What about reverse bleeding where you bleed from the calipers up to the master cylinder- That’s the method I used when I bled all my old fluid out and replaced with new - no need for tech 2 and it is perfect for abs equipped vehicles. Worked perfectly for me and you can do by yourself.
https://www.brakebleeder.com/product...brake-bleeder/

 

If the bleeder screw on that one caliper is on the bottom that is wrong. Likely that caliper is intended for the other side. That caliper cannot be properly bled if the bleeder is not on top (air rises). You might be able to take the caliper off, put something in between to keep the piston from blowing out, and hold it with the bleeder on top, bleed it, then put the caliper back on. I know on many calipers they are identical from side to side other than the bleeder location and often there are two bleeder screw holes with a plug in one and the bleeder nipple in the other and you potentially can just swap the plug and bleeder nipple between the two holes so that the bleeder is properly oriented on top for the side of the vehicle the caliper is installed on. I know the Tech2 has a special function in the ABS menu for bleeding the ABS module where you hold the pedal down while it presses back against the pedal several times.

 

You will need to get the auto bleed to finish if you have any hope in getting the air out. I bled mine with a mighty vac hand held unit to start with, then the auto bleed.

Also, the pedal will go to the floor unless the truck is running. Its designed to reserve basically one emergency stop of vacuum and thats it. Start it up and try the pedals again.

Tim

 

Mine does the opposite. The pedal gets tighter but when I start it it goes to floor. I took for test drive and it responds to brakes but once it brakes, the pedal gets soft and sinks to the floor.

I've tried the tube in a bootle with oil, I tried a compressed air vacuum bleeding system, but non work for me. Could it be a bad master cylinder??

Besides the tech2 unit, anyone had any success auto bleeding with autre or Foxwell??

 

you will not get a firm peddle with a caliper that has a bleed screw at the bottom, you may be able to flip the caliper over and stick it on the rotor temporarily to bleed it then put back in its correct position. You will also need to bleed the ABS system to clear the air out of those lines before finishing the bleeding process

Neal

 

Could also be a bad booster (Hydroboost). I just had to replace mine after I tried rebuilding it about 6 months ago (it was leaking). Worked fine for about 6 months after I rebuilt it but then my brakes and steering started locking together, if I turned the steering wheel at all my brake pedal would literally go down by itself.

Our H2's use a Hydroboost as the brake booster instead of a vacuum system. Hydroboost is actually far more powerful than a vacuum booster and is basically a hydraulic actuator system that works off of the power steering pump. It is between the master cylinder and firewall. It does not use, mix, or share brake fluid though (they are totally separate fluids and are not compatible).

My point is you have a lot of different systems involved that can all affect how the brake pedal feels and how effective the brakes are ranging from the master cylinder, individual calipers, the ABS module, proportioning valve unit, and the Hydroboost unit. Bleeding the brakes should be fairly straightforward though and generally do not need to worry about the ABS module unless air got into it. The Hydroboost usually will not present pedal problems but if that was having a problem and then mess with brakes it could be harder to determine what is wrong.