any big truck mechanics out there

[fastlt1]

Im having some air brake. Problems on a 94 ford ltl 9000 dump truck. My jake brake switch went out today while going down a steep grade today loaded. Didn't have no where near enough brakes to stop. Can you say run away. Brakes are all adjusted. Two new maxis and a slack adjuster just put on. Good pads all the way around. Problem is half pedal is all the brakes I have then it just goes to the floor no less brakes just no more. When you have to get on them hard the pedal goes to the floor but it just like you have them half pushed. The harder you push should make the brakes stop more right. Any ideas the mechanic bless his heart can just about change a tire. Please any ideas I can put him in? Thanks,

[Jon4x4]

kinda sounds like the compressor isn't putting out enough air. second. the brake pedal valve could be bad also. but if i remember what i learn from school. there are also relief valves that tend to go out and could be letting out air earlier then they should

[1998454]

Air pressure releases the brakes, lack of locks them. When the pedal is pressed it is just operating a regulator, the further the pedal travels, the less air pressure there is to keep the springs from locking the brakes. I would put a gauge on a brake line and watch it as the pedal is pressed for air drop.
kinda sounds like the compressor isn't putting out enough air. second. the brake pedal valve could be bad also. but if i remember what i learn from school. there are also relief valves that tend to go out and could be letting out air earlier then they should

[Jon4x4]

True, damnit' its been a long time

[LeoP]

What is the thickness of the brake linings. When the slack adjuster has to go past the 90 degree angle, leverage is lost and the brakes don't stop as well as they have in the past. the drums being worn adds to this problem.

[6.0 Bowtie HD]

Did just the jake switch on the dash board go out? Or did the switch engage and the jake cut out. How much air does the system build. Slow to build? If the system is charging to 120+ and rapidly as normally I would look at treadle valve first before compressor.

[mudbuddy]

WOW lots of misinformation on this subject posted here. Air brakes work by pressing the pedal which allows air to flow to the application valves, the application valves already have tank pressure supplied to them, this decreases application time by not requiring the full flow of air having to be supplied by the pedal valve. I would start by going over the adjustment of all the brakes on all the axles. If you still have a issue I would perform a application pressure test at all the brakes looking for low pressure to one or more of the axles. I have found this on trucks and the cause is normally a damaged hose or tube. Are you sure there is really a problem and not driver error, sorry I have dealt with plenty of drivers who blame the equipment first. What you experienced with the pedal is normal for air brakes, it is just a valve and once it is open it can't open any farther and about 1/2 way to the floor it is open all the way.

If your mechanic can barely change a tire who is doing your DOT inspections? This is very scary to me, the guys who work in the commercial trucking industry will know what I mean.

[fastlt1]

It takes a good bit of time to build up pressure and not long for it to bleed off. Found out on the back axle the park brakes wasn't wanting to release everytime. Theh where sticking. So going to try a quick release valve. But it feels like not all the brakes are getting all the pressure. When brakes are applied some of the brakes sing to me. I think only one axle is getting full pressure. He jumpes in it on a freshly graveled road empties and takes off and locks it up. Looks like you have good brakes to me. Get hauling.

[fastlt1]

Another question there and three holes in a slack adjuster. Which hole gives more brakes they are in the middle now.

[mudbuddy]

Find a inspection station and accidently pull in. :)

[1998454]

Partially wrong...If there is no air pressure to the axle then the brakes are locked. That is the reason you cant hook to a trailer without hooking the air lines up, they are locked. Blow an air line...the brakes lock. Don't take my word for it, ask the mfgr. Air pressure overcomes the springs and releases the brakes.
WOW lots of misinformation on this subject posted here. Air brakes work by pressing the pedal which allows air to flow to the application valves, the application valves already have tank pressure supplied to them, this decreases application time by not requiring the full flow of air having to be supplied by the pedal valve. I would start by going over the adjustment of all the brakes on all the axles. If you still have a issue I would perform a application pressure test at all the brakes looking for low pressure to one or more of the axles. I have found this on trucks and the cause is normally a damaged hose or tube. Are you sure there is really a problem and not driver error, sorry I have dealt with plenty of drivers who blame the equipment first. What you experienced with the pedal is normal for air brakes, it is just a valve and once it is open it can't open any farther and about 1/2 way to the floor it is open all the way.

If your mechanic can barely change a tire who is doing your DOT inspections? This is very scary to me, the guys who work in the commercial trucking industry will know what I mean.

[mudbuddy]

You are correct, you need air to release the parking brakes also called (spring brakes) but the parking brake section of the 2 chamber rear brake chambers have no effect on stopping the truck with the service brakes.

http://www.flxibleowners.org/flxbk/sbrks.htm

[97Lifted]

Unless your primary tank loses air, then the SR1 valve will provide you to be able to stop with the spring brakes. correct me if i'm wrong?

[s3gulit]

Why are you still running manual slacks? :sigh:

get auto slacks, never have to worry at scales or on roadside inspections about maintaining proper slack again (generally speaking, yes certain situations arise but are very unlikely).

[mudbuddy]

The spring brake portion of the piggy backs are for parking and an uncontrolled emergency stop should the truck lose air pressure. They are either full on or full off if the dash valve is working properly. The service brake portion of the piggyback delivers the controlled stopping from the foot treadle.

And yes auto slacks are the way to go but this carrier doesn't sound like the type to upgrade for the sake of convenience or safety.

[LeoP]

Slacks do go bad, check the brake adjustment again, even autoslacks go bad and are required after a certain year, don't remember the year.

[97Lifted]

October 20, 1994!

[$outhernStuntin]

yes

[fastlt1]

Truck got sent to real shop to have a foot valve put on and a center pin. I hope this straighten it out. Need the job but need my life too.