My 06 H3 had been sitting for a while this year as I've been driving a company vehicle. Started up okay once in a while and kept the battery charged but never really took her out on the road much; just no time. A week ago, I finally started up the old girl and within 50km, I blew both transmission cooler lines; had them replaced. Then the mechanic said "How do you drive this thing with the brakes so soft?:" I knew they were soft, but my concern was to get the truck running and stop the bleeding of the trans fluid.

I figured the brakes needed bleeding as the pads and rotors looked okay. No sign of DOT3 leaking anywhere so I got my brake bleeder tool out and did all four corners and topped off the fluid once in a while. It felt better but I had little time. On the weekend I asked my daughter to help me with the "pump and hold" method to squeeze any remaining air out. At one point, the rear driver side stopped having any fluid come out; I had already done the passenger rear with this method. No fluid coming out of the bleeder concerned me so I got out from under the H3 and applied the brake pedal. I noticed the ABS light was now on, it wasn't on before. The pedal felt hard but did not seem to have a lot of travel. I took the H3 out and noticed immediately that I should not be driving as the brakes barely held.

I popped the hood and looked at the reservoir and it was full. I left it the truck parked and will investigate some more tomorrow. My question to the group is, could the MC have been damaged before (bad seals) and pumping the pedal made it worse and now the plunger is now seated deep in the MC? I left it hoping that it would work it's way back out in time and that I could just leave it with spongy brakes until I can get it to a repair shop. Could my daughter have been pressing down too hard on the pedal and set the plunger way in?

I noticed that there were rebuild kits available at one time but no longer available (GM Part 15240738). Complete MC are available from Rock Auto but at about 500 Cdn. What are my other choices? Would a Colorado MC fit in the same era? A used MC?

 

Your description of bleeding the brakes is suspect. There is a much different procedure for the H3's. You may have gotten air in the system when you tried to bleed them.
Page 115 in the attached pdf has the procedure.

Also, I believe the entire brake system is hummer specific.

 

I wasn't aware of this and thank you. I followed the procedure and the pedal goes all the way down and now I have absolutely nothing. I put the tools away and will leave it to the experts; brakes are not a thing for the shadetree mechanic to mess around with when it's this serious or complex. i have a suspicion it will be a master cylinder though.

Stay tuned,.

 

If the pedal went to the floor during bleeding/or MC went dry, there's a good chance air is now inside the MC. Same process to bleed the master cylinder with an assistant: pressure on the pedal, open the line, close the line before the pedal hits the floor! Repeat on both lines, then proceed with the process on all 4 wheels. Communication is the key!

 

Copy that. It's hard to gauge what an 11 year old is doing at the pedal LOL. But she's the only person I have to help me so it is what it is. I appreciate all of the tips but I'm going to have it towed to the shop and hopefully, it is just air and not a mechanical failure.

 

DIY:

 

I've done this as well!!

 

Then you need to start the air bleeding process at the MC, any air trapped in the MC will NEVER get out via the calipers.

 

Did that according to the manual posted in an early reply.

 

AIR OR LEAK?


1. Place a clean shop cloth beneath the brake master cylinder to prevent brake fluid spills.
2. If you disconnected the brake pipes from the master cylinder, you must perform the
following steps:
1. Ensure that the brake master cylinder reservoir is full to the maximum-fill level. If
necessary add Delco Supreme 11®, GM P/N 12377967 (Canadian P/N 992667) or
equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.
If removal of the reservoir cap and diaphragm is necessary, clean the outside of the
reservoir on and around the cap prior to removal.
2. With all brake pipes installed securely to the master cylinder, loosen and separate the
left front brake pipe (4) from the left front port of the brake master cylinder.
3. Allow a small amount of brake fluid to gravity bleed from the open port of the master
cylinder.
4. Reconnect the brake pipe to the master cylinder port and tighten securely.
5. Have an assistant slowly depress the brake pedal fully and maintain steady pressure on
the pedal.
6. Loosen the same brake pipe to purge air from the open port of the master cylinder.
7. Tighten the brake pipe, then have the assistant slowly release the brake pedal.
8. Wait 15 seconds, then repeat steps 2.5-2.7 until all air is purged from the same port of
the master cylinder.
9. With the left front brake pipe (4) installed securely to the master cylinder, after all air
has been purged from the left front port of the master cylinder, loosen and separate the
right front brake pipe (3) from the master cylinder, then repeat steps 2.5-2.8.
10. Turn the ignition key to the ON position.
11. With the right front brake pipe (3) installed securely to the master cylinder, after all
air has been purged from the right front port of the master cylinder, loosen and
separate the left rear brake pipe (1) from the master cylinder, then repeat steps 2.5-2.8.
12. With the left rear brake pipe (1) installed securely to the master cylinder, after all air
has been purged from the left rear port of the master cylinder, loosen and separate the
right rear brake pipe (2) from the master cylinder, then repeat steps 2.5-2.8.
13. After completing the final master cylinder port bleeding procedure, ensure that all of
the brake pipe-to-master cylinder fittings are properly tightened.
14. Turn the ignition key to the OFF position. Depress the brake pedal 20 times.
~
3. Fill the brake master cylinder reservoir with Delco Supreme 11®, GM P/N 12377967
(Canadian P/N 992667) or equivalent DOT-3 brake fluid from a clean, sealed brake fluid
container. Ensure that the brake master cylinder reservoir remains at least half-full during
this bleeding procedure. Add fluid as needed to maintain the proper level.
Clean the outside of the reservoir on and around the reservoir cap prior to removing the cap
and diaphragm.
4. Install a proper box-end wrench onto the RIGHT REAR wheel hydraulic circuit bleeder
valve.
5. Install a transparent hose over the end of the bleeder valve.
6. Submerge the open end of the transparent hose into a transparent container partially filled
with Delco Supreme 11®, GM P/N 12377967 (Canadian P/N 992667) or equivalent DOT-
3 brake fluid from a clean, sealed brake fluid container.
7. Have an assistant turn the ignition ON, then partially apply and hold the brake pedal. DO
NOT pump the brake pedal. Fluid will flow when the bleed valves are opened.
8. Loosen the bleeder valve to purge air from the wheel hydraulic circuit.
9. Tighten the bleeder valve, then have the assistant slowly release the brake pedal.
10. Wait 15 seconds, then repeat steps 7-9 until all air is purged from the same wheel hydraulic
circuit.
11. With the right rear wheel hydraulic circuit bleeder valve tightened securely, after all air has
been purged from the right rear hydraulic circuit, install a proper box-end wrench onto the
LEFT REAR wheel hydraulic circuit bleeder valve.
12. Install a transparent hose over the end of the bleeder valve, then repeat steps 6-10.
13. Turn the ignition OFF. The assistant will now have to pump the brake pedal for fluid to
flow from open bleed valves.
14. With the left rear wheel hydraulic circuit bleeder valve tightened securely, after all air has
been purged from the left rear hydraulic circuit, install a proper box-end wrench onto the
RIGHT FRONT wheel hydraulic circuit bleeder valve.
15. Install a transparent hose over the end of the bleeder valve, then repeat steps 7-11.
16. With the right front wheel hydraulic circuit bleeder valve tightened securely, after all air has
been purged from the right front hydraulic circuit, install a proper box-end wrench onto the
LEFT FRONT wheel hydraulic circuit bleeder valve.
17. Install a transparent hose over the end of the bleeder valve, then repeat steps 7-11.
18. After completing the final wheel hydraulic circuit bleeding procedure, ensure that each of
the 4 wheel hydraulic circuit bleeder valves are properly tightened.
19. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11®,
GM P/N 12377967 (Canadian P/N 992667) or equivalent DOT-3 brake fluid from a clean,
sealed brake fluid container.
20. Slowly depress and release the brake pedal. Observe the feel of the brake pedal.
21. If the brake pedal feels spongy, repeat the bleeding procedure again. If the brake pedal still
feels spongy after repeating the bleeding procedure, perform the following steps:
1. Inspect the brake system for external leaks.