Brake frustrations!

[Bsmith720D]

So I’ve been having some issues with the brakes on my 1971 Deuce and I’m in need of some help or advice. over the course of a 2 years or so, I went through the whole truck and rebuilt or replaced the wheel cylinders as needed during my regular maintenance. i went through and took an air hose and blew out the lines to get all the junk out and replaced the rubber lines. I also bought a new master cylinder since the old one was pitted on the inside. I had the brakes lock up on me shortly after and figured it was the air pack. So I decided to buy a new air pack instead of rebuilding it. I went through and bled all the brakes last year and thought I was good to go. Shortly after I parked the truck in the barn for the winter. I just recently got it out and ran it for about 10 miles. I pulled it into the drive for about 15 mins (still running) and then headed back out on the road and only made it like 50 feet Down the road and knew right away that the brakes locked up. so I turned around and pulled into my drive. When I first got in the truck and started it, I felt the brake and there didn’t seem to be any pedal there. After driving it for a couple miles, the pedal firmed right up. Now the pedal is super stiff. Like stepping on a brick and the brakes are stuck out. I climbed under the truck and took the plug off the back of the air pack and didn’t feel or hear any air coming out the back of the air pack. I then loosened the fitting from the master cylinder to the air pack and it didnt. release the brakes. So I Then loosened the line on the top of the air pack running to wheel cylinder and the brakes released. I can’t figure out why the brakes keep locking up. It’s a brand new air pack and master cylinder. The little hole in the new master cylinder was way smaller than the old cylinder so I drilled it out to .030 thou. before I installed it, Cleaned it all up and installed it on the truck. I also went through and made sure the adjustment was right for the brake pedal. Can anyone send me the right direction on what to do because I’m lost.

 

[frank8003]

Where is the top of the MC vented to?
Did You lube the airpack as per the TM, as per the PS instructions.

 

[cattlerepairman]

It is unfortunate, but also bear in mind that the "new" air packs may have spent extended periods of time in storage by now and may have started to corrode internally or have lubricant harden inside them. I know that recently another member had an issue with a new old stock air pack, similar to what you describe.

If checking the MC vent (press and release the brakes and with the MC cap off and a flashlight watch for brake fluid welling up from the return hole!) does not lead to a clue, I'd think the air pack needs cleaning/lubing.

 

[Bsmith720D]

It is unfortunate, but also bear in mind that the "new" air packs may have spent extended periods of time in storage by now and may have started to corrode internally or have lubricant harden inside them. I know that recently another member had an issue with a new old stock air pack, similar to what you describe.

If checking the MC vent (press and release the brakes and with the MC cap off and a flashlight watch for brake fluid welling up from the return hole!) does not lead to a clue, I'd think the air pack needs cleaning/lubing.

So I’ve been having some issues with the brakes on my 1971 Deuce and I’m in need of some help or advice. over the course of a 2 years or so, I went through the whole truck and rebuilt or replaced the wheel cylinders as needed during my regular maintenance. i went through and took an air hose and blew out the lines to get all the junk out and replaced the rubber lines. I also bought a new master cylinder since the old one was pitted on the inside. I had the brakes lock up on me shortly after and figured it was the air pack. So I decided to buy a new air pack instead of rebuilding it. I went through and bled all the brakes last year and thought I was good to go. Shortly after I parked the truck in the barn for the winter. I just recently got it out and ran it for about 10 miles. I pulled it into the drive for about 15 mins (still running) and then headed back out on the road and only made it like 50 feet Down the road and knew right away that the brakes locked up. so I turned around and pulled into my drive. When I first got in the truck and started it, I felt the brake and there didn’t seem to be any pedal there. After driving it for a couple miles, the pedal firmed right up. Now the pedal is super stiff. Like stepping on a brick and the brakes are stuck out. I climbed under the truck and took the plug off the back of the air pack and didn’t feel or hear any air coming out the back of the air pack. I then loosened the fitting from the master cylinder to the air pack and it didnt. release the brakes. So I Then loosened the line on the top of the air pack running to wheel cylinder and the brakes released. I can’t figure out why the brakes keep locking up. It’s a brand new air pack and master cylinder. The little hole in the new master cylinder was way smaller than the old cylinder so I drilled it out to .030 thou. before I installed it, Cleaned it all up and installed it on the truck. I also went through and made sure the adjustment was right for the brake pedal. Can anyone send me the right direction on what to do because I’m lost.

It is unfortunate, but also bear in mind that the "new" air packs may have spent extended periods of time in storage by now and may have started to corrode internally or have lubricant harden inside them. I know that recently another member had an issue with a new old stock air pack, similar to what you describe.

If checking the MC vent (press and release the brakes and with the MC cap off and a flashlight watch for brake fluid welling up from the return hole!) does not lead to a clue, I'd think the air pack needs cleaning/lubing.

after I installed the air pack. I gave it a couple squirts of air oil. And I stuck an Allen wrench into the plug on the back of the air pack and could feel the piston right there. So I know the piston isn’t stuck down in the cylinder.

 

[Bsmith720D]

Where is the top of the MC vented to?
Did You lube the airpack as per the TM, as per the PS instructions.

I gave it a couple of squirts of air oil when I first installed the air pack. And my truck has the remote reservoir kit for the master cylinder. Now there is this line which looks like a vent by the master cylinder? It’s a small line that runs from a t block. And that line runs from the air pack to the engine bay.

 

[Godspeed131]

That line was the original vent line that attached to the 90 on the MC’s cap before the addition of the remote reservoir the remote should have a vented cap so no need for that one any more. Some one just capped it to seal it off from the elements.

 

[frank8003]

These trucks like having all the brake parts functioned, it all "keeps" better that way.
Put clean shop air into the right rear glad hand up to 100-110psig, it will show on the in-cab gauge. Then operate the brakes many times and often. No need to have engine running. Then one can examine, hear everything without engine running, wheels blocked and safely.
Did You remove the little splash plate in the MC?
see this PDF

 

[Bsmith720D]

Alright. So I went ahead and ordered a rebuild kit
for the air pack. And today I went through and tore the airpack off the truck and opened it. as I took it apart, I layed everything out in order on the bench. I didn’t notice anything out of the ordinary and everything looked to be ok. Although when i took the back plate off the back. The piston didn’t just spring out. It took a little finessing to come out. The cylinder was pretty well lubed and there is no rust on the walls.

 

[Bsmith720D]

These trucks like having all the brake parts functioned, it all "keeps" better that way.
Put clean shop air into the right rear glad hand up to 100-110psig, it will show on the in-cab gauge. Then operate the brakes many times and often. No need to have engine running. Then one can examine, hear everything without engine running, wheels blocked and safely.
Did You remove the little splash plate in the MC?
see this PDF

Took a little bit of looking around to figure out what you meant by the splash guard in the MC. But no the splash plate is not removed. I will be knocking it out and reinstalling

 

[cattlerepairman]

One issue I have seen described repeatedly by others is the vaseline like lubricant becoming hard, blocking movement of the main piston or the proportioning valve. Let us know if your cleaning and reassembling made a functional difference.

Sent from my SM-G950W using Tapatalk

 

[Bsmith720D]

One issue I have seen described repeatedly by others is the vaseline like lubricant becoming hard, blocking und movement of the main piston or the proportioning valve. Let us know if your cleaning and reassembling made a functional difference.

Sent from my SM-G950W using Tapatalk

Finally getting around and updating the forum here. I got the air pack rebuilt and all together. I also punched out that splash plate in the MC. bled the brakes and everything seemed to be ok again. I have about 250 miles or so on after doing that. Haven’t had any issues yet. I think its safe to say the brakes are fixed again. As I said earlier, the air pack looked good inside when I tore it apart. So I’m gonna assume the splash plate was causing the brakes to lock up. Strange though that when I bought the truck three years ago , the reservoir kit was already installed on the truck. the Brakes worked fine until I replaced the MC because it was leaking out the front boot due to bad pitting in the bore. Then it seemed shortly after, that’s when the brakes started locking up.
im just glad now that the brakes work properly again. the brake frustrations we’re getting old quick. Now onto the leaking pto on the trans