Air hydraulic brake advice needed!!

[battlecat]

OK so I'm hoping someone here can help with my issue.


I picked up my new MV a 1975 M54A1C this past Thursday from GL and I ran into a couple of issues along the trip home. Note this is my first MV and first air hydraulic break vehicle but I'm very familiar with the hydraulic breaks on all other vehicles I have worked on for the past 20+ years. So here is the scenario issue.

The truck was having some fuel related problems so I stopped as a truck stop in Maine to research the filters and find some locally, We parked it and set the parking break. I found a local shop who was willing to help and look at it so off we go!! NOPE Breaks locked, truck won't move with the parking break disengaged and free. I checked the parking break no binds looked good as it was not holding the truck but it wouldn't barely move.

Feeling the impending doom of a tow from Northern Maine $$$$ my mates and I said the **** with it the shop is 2 miles up the same road let's give it a shot. The truck pulled out of the parking lot barely and began down the road, no more than a 1/4 mile down the road the break lights went off from solid and she was free at last. I had the mechanic look at the breaks while doing the fuel filter and he said by cracking the bleeder under the drivers side below the master cylinder the breaks freed up again/ let go and couldn't explain why.

The mechanic swapped the nastiest mud covered filters that I had ever seen in my life and cleaned the bowls and said good luck on your journey. $$ The truck ran fine for another 50 plus miles until we stopped for a drive bathroom break ( I know don't stop!) Guess what same issue break light solid and breaks holding the rig.

Having had success with the first rolling trip we did the same and guess what 1/4 mile and the break light came off and smooth sailing for another 30+ miles... Now the bad part.. opcorn:

About 3 miles from the NH toll I start to see the sighs of smoke coming from the truck while following behind, (maybe the diesel burning off)??? No the breaks had decided to lock again. Despite repeated attempts to contact the driver and passenger in the truck (possibly the noise inside the cab) they drove another mile or more (hopefully less before smelling the breaks.

The truck is now stuck on the side of the road all ten tires smoking. Truck is super locked up at this point. We gave it 20+ minutes to cool and I was able to open the master cylinder only to find crystal clear fluid approx 1/4 deep... Note I did see some leaking coming from the left front tire with a VERY small puddle by the tire. I'm thinking the best thing I can do is go grab some DOT 5 silicone break fluid and a bleeder wrench and other needed items to try and salvage it from a tow. I head to the nearest store pick up the stuff come back and go to put the fluid in now the master is full to the top with 1% milky looking fluid.

I asked my buds what happened while I was gone and they said the breaks/ truck popped air twice, the same noise when pushing the breaks normally. I started it let the air build up gave it some forward and back all tires free now and the peddle is kinda spongy when before it was rock solid at the top.. The truck drove safely home from there with very little breaks being used if any as we nursed it follow vehicle behind and a vehicle in front.

I'm planning on going through the whole system but being new to the air assisted hydraulic breaking system I though it best to check with some veterans to see if you could share your experiences and point me in the right direction. Any and all help you good guys can lend is super appreciated, I promise to pass it along in the future.



Battlecat

 

[gimpyrobb]

Rebuild the master cyl and the hydro-boost to start. Once thats done, pull the wheels off and check the wheel cyl and brake pads. Once thats done, re-pack the wheel bearings and you should be good to go(and STOP)!

 

[battlecat]

Rebuild the master cyl and the hydro-boost to start. Once thats done, pull the wheels off and check the wheel cyl and brake pads. Once thats done, re-pack the wheel bearings and you should be good to go(and STOP)!

Oh good a quick fix! I'm sure I should bleed the system a bunch also, would just junk in the lines cause this? I'm just thinking this might be something someone else has seen and dealt with in the past, before I go rebuilding all the major parts of the breaking system. Don't get me wrong, I do want a sound breaking system but I'm also looking to get straight to the heart of the issue if at all possible. Before posting I searched through a couple of threads using those specific words (hydraulic, breaks, locked up, etc) and couldn't really find this type of scenario...

I do like the grease idea! I guess if all of my rebuilding fails the truck will roll smooth...

 

[elkhtr]

My experience with the brakes on my m810 was a cascading failure of parts until all were new. Replace a leaking wheel cylinder, another would start leaking, etc. Just ended up replacing everything except the shoes and drums, which were fine. Proper shoe adjustment makes a huge difference in pedal travel. Good luck.

 

[battlecat]

My experience with the brakes on my m810 was a cascading failure of parts until all were new. Replace a leaking wheel cylinder, another would start leaking, etc. Just ended up replacing everything except the shoes and drums, which were fine. Proper shoe adjustment makes a huge difference in pedal travel. Good luck.

Thanks!


I just started looking up the parts list. I was reading another thread and it seems like that's the norm... I've got nothing to complain about, she made it home and whats a little elbow grease a few busted tools and some time getting to know the system..

Good thing I have some vacation coming.

 

[gringeltaube]

... Before posting I searched through a couple of threads using those specific words (hydraulic, breaks, locked up, etc) and couldn't really find this type of scenario...........

Next time try "brakes locked up", not breaks...
Here: many good threads to read that will lead you "straight to the hard of the issue"...






(BTW: I have edited your thread title.)




G.

 

[gimpyrobb]

Oh good a quick fix! I'm sure I should bleed the system a bunch also, would just junk in the lines cause this? I'm just thinking this might be something someone else has seen and dealt with in the past, before I go rebuilding all the major parts of the breaking system. Don't get me wrong, I do want a sound breaking system but I'm also looking to get straight to the heart of the issue if at all possible. Before posting I searched through a couple of threads using those specific words (hydraulic, breaks, locked up, etc) and couldn't really find this type of scenario...

I do like the grease idea! I guess if all of my rebuilding fails the truck will roll smooth...

What happens is, nobody drains the compressed air out of the air tanks when they are done driving the truck. This keeps all the moisture from the compressed air in the air system. That water makes its way into the airpack(hydroboost) and then it sits and rusts up. Once it rusts, you get sticking brakes, like what you described. Brake fluid is expensive, so it takes an extra hour to pull the master cyl and hone it, check the seals, and put it back together. Other wise you are going to waste time and brake fluid if you don't do it all at once.

MANY times you will get gunk in the wheel cyls and both pistons fail to move when the brake peddle is pressed. The truck you bought is old and has likely not seen any service on its brake system. Once you fix ONE thing, you will have to dig into the rest of the system as it fails and waste a lot of time.

I say go through it all as I have personally tried to short cut things and have learned its quicker to do it(ALL) at once.

 

[battlecat]

What happens is, nobody drains the compressed air out of the air tanks when they are done driving the truck. This keeps all the moisture from the compressed air in the air system. That water makes its way into the airpack(hydroboost) and then it sits and rusts up. Once it rusts, you get sticking brakes, like what you described. Brake fluid is expensive, so it takes an extra hour to pull the master cyl and hone it, check the seals, and put it back together. Other wise you are going to waste time and brake fluid if you don't do it all at once.

MANY times you will get gunk in the wheel cyls and both pistons fail to move when the brake peddle is pressed. The truck you bought is old and has likely not seen any service on its brake system. Once you fix ONE thing, you will have to dig into the rest of the system as it fails and waste a lot of time.

I say go through it all as I have personally tried to short cut things and have learned its quicker to do it(ALL) at once.

Thanks gimpyrobb.. That makes a sense. I was hoping to have her in the 4th of July parade but to be honest the truck is old and in need of the service it hasn't seen in who knows how many years, plus a paint job.. I'll update when done. I pulled the info from a a couple other threads for the air pack rebuild and master rebuild, I'm thinking just replace all the wheel cylinders while in there.

 

[Monkeyboyarmy]

Sounds to me like the front passenger side glad hand is plugged. That glad hand cover needs to be vented. It should have a small cap that is somewhat loose fitting on that cover to vent air.