Brakes sticking after brake pedal depressed

[RRdr]

Hello, new to the forum, I currently own an m 813 five ton truck, it hasn’t been moved in a while, when I went to move it I noticed it needed brake fluid and so I added dot 5 to the master cylinder and bled it out to the wheel cylinders starting with the furthest away and then finishing with the closest, after I got the pedal good and solid, I started the truck and began to drive it, After I pushed the brakes, I noticed that the brakes were sticking, the master cylinder piston had seated back to its normal resting spot, with full pedal travel, I did not hear air dumping after I let go of the brake pedal, once I cracked the lower bleeder screw on the air pack it relieved pressure and shot out brake fluid that was locking the wheels and freed up the brakes, when I did this again the same cycle would repeat( brakes locking then cracking the air pack lower bleed screw and freeing up the brakes. what kind of an issue could this be? Would it be in the air pack since we didn’t bleed it out after bleeding the master cylinder? Or what are some other things to troubleshoot or pay attention to?

 

[Bill Nutting]

Welcome to Steel Soldiers from Michigan. I can’t help you with your M813 but you have come to the right place. There is such a wealth of knowledge here you will soon have an answer to your break issue. When you get a chance, post a few pictures of your truck….

 

[G744]

Look for a blocked (internally collapsed) hose, or perhaps a set of shoes is adjusted too tightly.

They will get hot and expand, making things worse.

DG

 

[cbrTodd]

I don't know how similar the 5 ton master cylinder is to the one on a deuce, but this is the same symptom set that I had when crud was blocking the compensating port in the master cylinder in my deuce master cylinder. Check the reservoir and make sure there is no crud in it, especially any blocking the drilled holes that lead into the cylinder bore. If the reservoir was dry before you worked on it, and all you did was add fluid, this would be one of my prime suspects.

 

[RRdr]

I don't know how similar the 5 ton master cylinder is to the one on a deuce, but this is the same symptom set that I had when crud was blocking the compensating port in the master cylinder in my deuce master cylinder. Check the reservoir and make sure there is no crud in it, especially any blocking the drilled holes that lead into the cylinder bore. If the reservoir was dry before you worked on it, and all you did was add fluid, this would be one of my prime suspects.

thanks for the info, I was questioning wether to replace the master cylinder as well, I might just do it because the bore on the cylinder is rusted and we honed it and rebuilt it a few yrs back but it slowly leaks

 

[Ajax MD]

I also have an M813. Water (moisture) that has sat in the air pack can also cause problems like this. These trucks lack an air dryer. It's one reason why it's important to purge the air tank daily. Unfortunately, I am not well acquainted on the air pack part of the truck yet.

Paging @simp5782 to the white courtesy phone please...

 

[jatonka]

Just a chance that the glad hand at the right frontof the truck has gotten it's breather plugged with something, I had a similar problem some years ago that cost me a new airpack and a new master cylinder that didn't fix the problem. I told a Vietnam veteran about it and he told me to check that front right glad hand cover, sure enough it was set up and didn't release a shot of air when I released the brake pedal. It totally fixed the whole problem!!! Would have been a simple no cost maintenance job if I knew anything. JT

 

[RRdr]

Just a chance that the glad hand at the right frontof the truck has gotten it's breather plugged with something, I had a similar problem some years ago that cost me a new airpack and a new master cylinder that didn't fix the problem. I told a Vietnam veteran about it and he told me to check that front right glad hand cover, sure enough it was set up and didn't release a shot of air when I released the brake pedal. It totally fixed the whole problem!!! Would have been a simple no cost maintenance job if I knew anything. JT

Thanks for the info!, your talking about the glad hand in the front right hand fender from the drivers seat?

 

[jatonka]

Thanks for the info!, your talking about the glad hand in the front right hand fender from the drivers seat?

Yes that is the one that has the breather, or just a small hole in the center of it. It is the way air exhausts from the system when the brake is released. it's not a brilliant way, but it was the guv'mentway. I hope you find it was your problem. JT

 

[Bill Nutting]

Thanks for the info!, your talking about the glad hand in the front right hand fender from the drivers seat?

Be sure to let us know if this fixes your problem. How about a picture or two of your 813. You can’t get all this advice for free ya know!

 

[RRdr]

Be sure to let us know if this fixes your problem. How about a picture or two of your 813. You can’t get all this advice for free ya know!

I installed a freshly rebuilt air pack and new master cylinder, and bled all the system with new dot 5 and then ran it, I opened the right side glad hand, the brakes grab but delay when the the brake pedal is released. The air does relief sometimes rightaway releasing fluid pressure, other times it will take ten of fifteen seconds to release air pressure and during this delay if I let the clutch out it will kill the engine. So it has gotten better but not exactly road ready yet.

 

[RRdr]

I installed a freshly rebuilt air pack and new master cylinder, and bled all the system with new dot 5 and then ran it, I opened the right side glad hand, the brakes grab but delay when the the brake pedal is released. The air does relief sometimes rightaway releasing fluid pressure, other times it will take ten of fifteen seconds to release air pressure and during this delay if I let the clutch out it will kill the engine. So it has gotten better but not exactly road ready yet.View attachment 860917

Any other parts of the air system I should look at? That could be causing the delay in releasing the pressurized air from the brake system? When testing what you mentioned, I ended up removing that glad hand cover to rule out any issues with it