Help please major brake problem

[tklm539]

Hello All its been some time since I posted. I am having a major brake problem with my deuce. Here is the description.

Start the truck, air alarm goes off. Trucks moves fine. Two, three hits on the brake and the pedal is hard as a rock and the brakes are hard as a rock. The only I can get them to release is to dump the air out of the tanks. Let the tanks fill up, two, three pumps and its instant lawn decoration!

I repainted the truck, so I thought this was to odd a coincidence but I cannot see any way that the paint could cause this.

Also checked MC..... full of DOT 5

I had a guy from the town look at it as he worked on them in the service and still no luck.

Any help or points to direct us would be greatly appreciated.

Thanks

Tom

 

[sandcobra164]

I'd guess defective airpack booster.

 

[hoop]

Clean the relief port on the MC.

Edit...and clean the Air Pack.

 

[doghead]

I'll guess Brake booster.

 

[gimpyrobb]

Sounds to me like the relief port on the master cyl.

 

[emr]

Sounds like paint to me, sand it all off... hey just sayin...

 

[Garandfan]

You have a bad air pack. You can release the air or crack the bleeder on the air pack all you want to release the brakes. You will still have the same problem. I'll bet your brake lights aren't working right either. It seems that it is a beginning sign of a bad air pack.... that is of course if you know the brake light switch is good.

 

[OPCOM]

yeah, PM the air pack servo.

 

[Billy Bobbed]

Mine did the same thing today after work.I always start my truck and let it run will I shut the shop down.I took off no
problem till I came to the stop sign,then it didnt want to move very well.So I pulled over,if I didnt touch the brakes it would
move,but when you hit the brakes it would lock up with a soild pedal.So going home I would barely touch the brakes,it was stop lights
all the way home so I would let up on the brakes to relieve the pressure will I wait on the light then it would be fine.So
when I got home I went in the yard and hit the brakes the front brakes were sticking.I keep hitting the brakes in the yard
for about 15 minutes and they started working again.I looked at my MC and booster and they look new,so I dont know
if this is going to happen again.When I aired down to 60psi the brakes worked fine till it got to 90psi.If its the air booster wouldnt it
lock both front and rear brakes.

 

[Heavysteven]

Sounds to me like the relief port on the master cyl.

What is the relief port? Is it the vent line coming out the top. Could you go into more detail?

Thanks

 

[rlwm211]

Look in your master cylinder, and press the pedal slowly and before the brakes take up hydraulically, you should see a upflow of brake fluid from the relief port. If you do, then you have an air pack problem. If not, then the master is holding the hydrauulics on.
The relief port is a very small port ahead of the main piston which allows the fluid to return to the master when the pedal is released. I would add that the pedal should be adjusted so there is a tiny (1/16th inch) amount of play before it starts pushing the piston.

Simple test to eliminate the master cylinder.

RL

 

[Barrman]

Another messy check is this. Make the brakes lock up, lossen the brake line between the master and air pack. Pressurized fluid means it is the master. Just a drip and the problem is in the air pack.

Realistically, you are better off pulling both the air pack and the master. Take them apart, clean them and put in new parts following the very easy to follow -20 step by step instructions. Brakes on a 14,000 pound truck are basically the most important system on the truck. Being careful, thurough and spending the money now is basically the only way to go.