Air pack problem

[Rene M]

Well today a buddy " driving a Pinz" and i were out and i hit the brakes one to many times i guess because the truck just locked up at a light. The brakes got hard as a rock and needless to say would not move. No warning no sings that their might be a problem "ie, dragging brakes a hard pedal etc" . I was able to find that the brake fluid was under pressure and would not allow the fluid to bleed back. i was forced to open the bleed screw and let the pressure out. Luckely my office shop was two miles away " which i drove with out touching the brake pedal".
Anyone had this problem before? The truck has been pressure bleed and the fluid is very new... Maybe i should of left the old stuff in..lol

Is it better to rebuild the air pack of buy new?

 

[cornrichard]

I have to guess what truck you are driving. If it is a 800 series truck check the covers for the glad hands. I think they are meant to be vented. Sometimes the vents, small holes in the covers, plug. Then the brakes lock. Just pull them off and try the brakes, if they work then clean out the holes.

 

[Rene M]

Sorry, my bad. M813a1 5 ton.
The glad hands have dust covers on them yes and shut off valves. What i had a problem with is the hyd fluid under pressure going out to the brakes but not being allowed to return to the master cyl. the brake pedal just froze up solid.

 

[lsansone]

I believe the front passengers side glad hand is vented. the glad hand cover will have a little vent on it. it is different than all the other covers.

check that and see other threads that also talk about this exact thing

best wishes
lou

 

[jwaller]

sounds like a bad airpack to me. plan on a rebuild. I've seen 800's with and without vented gladhands. I doubt that is your problem. if you think it is then take the cover off and see. it's not your problem.

 

[Rene M]

I believe the front passengers side glad hand is vented. the glad hand cover will have a little vent on it. it is different than all the other covers.

check that and see other threads that also talk about this exact thing

best wishes
lou

Thanks Lou i will look but.. All glad hands have shut off valves on them and they have been shut off forever so even if it did have a vent the shut off would prevent a vent. the venting is handled with the quick drop air valve under the drives side. Or at least should be.

 

[Rene M]

sounds like a bad airpack to me. plan on a rebuild. I've seen 800's with and without vented gladhands. I doubt that is your problem. if you think it is then take the cover off and see. it's not your problem.

So whats better new air pack or rebuild this one? i was thing of both. Buy new and rebuild this one as a spare.. You can never have to many spares..

 

[rlwm211]

The factor that determines whether an air pack can be rebuilt is the amount of corrosion inside. The bores can only be honed so far before they are out of spec and you risk seepage past the piston.

Another factor on rebuilding an airpack is if you have the requisite skill to do so properly. I am not being sarcastic here, but if you are not sure, I would suggest either having someone who is experienced rebuild it, or buy a new one.\

This is a safety issue and there is no wiggle room.

Now as to your problem. did you bleed the air pack when the brakes hung, or the master? This is important. If the check valve in the master is sticking, or the relief port is plugged, you get the gradual creeping of the brakes to a lock up condition.

If the pressure is being held at the air pack then the actuator assembly, or the compensator assembly is sticking.

In re-reading your original post, you mentioned relieving the pressure with the bleeder, and that is on the master cylinder side of the airpack and not after the air pack hydraulic piston. This is significant.

I would do the following test to determine if the master is returning fluid to the resevoir.

Engine off, no air. Remove the fill on the master and position out of the way. While watching the fluid in the master, slowly press the pedal with your hand. There should be a "rush" of fluid momentarily back into the resevoir before you get a firm pedal. If you do not see this upwelling then there is either a problem with your master or else the linkage is misadjusted. If all is properly functioning in the master, head to the air pack.

Hope this helps

RL

 

[Rene M]

I am a heavy Diesel tech by trade so as for can i rebuild one , no problem.

On the test, i did preform this test there on the side of the road and i did get bleed back to the master which is why i went to the " fluid end" of the air pack and opened the bleeder there which relived the pressure in a huge stream with just a crack of the bleeder screw. as if the piston was still either under air pressure or the hyd piston was stuck in the engaged position.
Which leads me to believe that the air pack has locked up.

 

[DaveP]

the front service line should not have a valve on it. unless all the 5 tons i have been around are set up incorrectly. it should also be vented to avoid the situation you described should the pack bleed by.

 

[Rene M]

the front service line should not have a valve on it. unless all the 5 tons i have been around are set up incorrectly. it should also be vented to avoid the situation you described should the pack bleed by.

AS you post this i am frantic to find a picture i have taken of the front of the truck to see.. I will check it out.
My truck has been bastardized by the last owner and i have been working through a LOT of man made problems.

 

[Rene M]

the front service line should not have a valve on it. unless all the 5 tons i have been around are set up incorrectly. it should also be vented to avoid the situation you described should the pack bleed by.

Well, dont you just hate it when two large ears grow out of you head and you have this undesirable urge to say..." he haaa he haaaa

Yup some one installed a shut off valve " not stock" on the passengers side glad hand with a vent and that valve was shut off....
Truck works fine now and i feel real stupid!
Thank you to all those who tried to shine a light on the guy in the dark....

 

[rlwm211]

Hey, every time you learn something it is like putting money in the bank...

appreciate, accept and move on, this works for me....

RL

 

[DaveP]

no need to feel stupid. i had to figure out this very same problem on my first 5 ton. the vent was clogged and the brakes would apply themselves while driving. glad i could help you out and you are not the first one here to have this same problem.