No brake pedal pressure after bleeding brakes.

I have a AMC M35 and I’m pretty new to these trucks. We’re bleeding the brake lines at each wheel cylinder, keeping the reservoir filled after each one. Spent at least 45 minutes bleeding the system, but there’s no pressure at the pedal. The master cylinder and air pack are pretty new. Any ideas?

Did you bleed the air pack first?

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cattlerepairman said:

Did you bleed the air pack first?

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We did, the bleeder screw on top of the cylinder has compressed air coming out every time we unscrew it.

Atlas78 said:

We did, the bleeder screw on top of the cylinder has compressed air coming out every time we unscrew it.

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Also, we have the technical manual and we unhooked the vent line on the air pack cylinder. Every time we press the brake pedal down there is zero resistance on the pedal itself and air will leak from the brass fitting. Is this common to have air release when the brake pedal is applied?

TM 9-2320-361-24 WP 0172 00
Did you follow that? That WP is four pages

Is the master cylinder vent disconnected from the vent/ fuel and axle vents?
Is the little hole in bottom of MC free and clear?
Use a pressure bleeder, can make one or buy one cheap.
Does it have a remote reservoir?
In anycase read the Ross common thing.

frank8003 said:

TM 9-2320-361-24 WP 0172 00
Did you follow that? That WP is four pages

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We have, but at each step there is still air in the lines. Not sure how we keep getting air into the system, there are no leaks.

frank8003 said:

TM 9-2320-361-24 WP 0172 00
Did you follow that? That WP is four pages

Click to expand...

Step #9 in this manual is concerning, the air pack looks to be a brand new unit and we may need to replace it?

I am confused. What brake fluid bleeder are you opening that gives you compressed air?

If you did everything perfect and had a perfect system. You could still have no pedal because of the master cylinder push rod adjustment or because your shoes need either a minor or major adjustment. M35 brakes are fun.

Where is compressed air coming from. Are the brakes being bleed with engine running?

frank8003 said:

Where is compressed air coming from. Are the brakes being bleed with engine running?

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This pic, (1) bleeder is unscrewed and there is a quick release of air then a sputter of fluid before a stream of fluid. (2) is the vent line I believe, when the brake pedal is pushed to the floor air is forced out from this brass fitting.
We tried bleeding the brakes while the engine was off and then while running, same results.

The M135 procedure was real easy so I'll share it in case it helps. The air side of the M135 brake system is drained before bleeding brakes so it's not bled under air pressure. The M135 brakes work even with all the air out of the system and air-paks are a week spot if not maintained.

Hope you get rolling again......

I'm not trying to be rude here, but Are you opening the bleeder than pushing the pedal all the way down than closing the bleeder BEFORE YOU RELEASE THE BRAKE PEDAL BACK UP OFF THE FLOOR? If you don't close the bleeder valve before releasing the brake pedal you suck air back into the system and you won't be about to get the brakes to work. IF you don't have a power bleeder it a two soldier job. If it a two soldier job they need to have a good communication skills. Soldier A who is opening and closing the bleeder valve is in charge. Soldier B who is working the pedal. DOESN'T MOVE UNTIL SOLDIER A SAYS SO.

I second the power bleeder suggestion. A garden sprayer can be made into one easily. Motive products makes a really good one as well.

if you already have a power bleeder or have the Soldier B thing correct. Then you have air getting in between the rear seal of the master cylinder and the bleeder valve of the airpack.

I found this thread to be a great resource >>

Is you underhood firewall side vent line still there, did it get the filter mod?
Filter could get plugged.
I bleed the brakes so many times I made it semi permanent with quick disconnects when I installed sightglass acting as remote reservoir.
I had zero problems pumping it to 8-10 psi and using a ittle NAPA bleeder one way fitting hose each position. I just had to bend up some wrenches to suit the job.

post #8 in here

That's a nice little set up. Do you remove the sight glass when you are done bleeding the lines?

18operator said:

That's a nice little set up. Do you remove the sight glass when you are done bleeding the lines?

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The sightglass remains as part of the system and is valved out when bleeding the brakes. As shown in .MOV the sightglass became the reservoir remote. I hawked eyed that and my aux air pressure gauge always. The sightglass was always fun to watch the fluid moving. One of my better inventions. I put valves and ways and means to make it all very easy to use. Worked on that for a couple of whiles but it turned out really good then made an idiot light so I could proove to me that the brake light switch was functioning always.

Atlas78 said:

This pic, (1) bleeder is unscrewed and there is a quick release of air then a sputter of fluid before a stream of fluid. (2) is the vent line I believe, when the brake pedal is pushed to the floor air is forced out from this brass fitting.
We tried bleeding the brakes while the engine was off and then while running, same results.

Click to expand...

That line you have marked as #2 goes to the driver side gladhand on the rear of the truck to supply air to apply trailer brakes. That line will dump air for as long as you have the pedal depressed. In normal operation without a trailer, the valve on the gladhand is closed to block that line.

The vent line is the shiny one closest to the camera, that the left 'leg' of your #2 arrow is over.

One man brake bleeder
This is what I used along with my pressure bleeder in post #15.
It made the job simple as it has a little check valve in it.
NAPA Part #: BK 7769089