The Stovebolt Site Forums The Parking Lot Big Bolts Big Truck Air Brake question ...

... for Crenwelge (or anyone)...

The operation of my parking brake valve seems reversed (push it in to release the spring brakes, pull it out to apply). I removed the valve and the two airlines and even made sure (by running the truck) that the supply line was attached to the "in" port and the non-pressurized line was connected to the "out" port. I did reverse them to see if that made any difference and it just dumps the pressure out the relief port that way.

Do I have a bad valve (it's a SealCo, BTW) or what? It's actually been this way since I've owned the truck. Everything works okay, just backwards. I am trying to correct all the little issues on the truck before the big trip to Kansas City.

Thanks,
John

Good Morning John.
Sounds to me that it is working right.
Just like head lights, pull the knob out and the lights come on.
Push it in turns them off.
On our "67" 9500, the parking brake is on the steering colume, about a 6" lever. Easy to bump the lever when you climb in or out. I'd rather it be a knob on the dash.

Don

You should probably go back to the loser you bought it from and raise heck for selling you a defective, noisey, oil dripping, backwards a$$ brake valve truck!

Bill
I about choked on that one!
Good reply.

Don

Pushing in the brake release knob applies air, especially on dual chamber cans, to the bladder area opposite of the spring brake. It applies enough air to over come the spring. This is why, if you start losing air pressure, at about 60-65 psi or so the spring brake will start to apply.

The way you described it working is correct. Push in the yellow knob to release the parking brake. If you have a trailer attached, you push in the red knob to charge the trailer brake system. Once the air has gone to where it needs to go, you can start rolling.

John this is the way it should work. Try pushing it in with no air pressure it should pop right back out. Build pressure to 120 psi push it in shut the truck off push the brake pedal up and down when air pressure drops to around 60 psi the valve should pop out.
The valve is actually called a tractor production value. The operation of the valve is to apply the trucks spring brakes should the air pressure fall below safe operating range.
Please look up testing and operation of air brakes you should be familiar with there workings before operating any vehicles equipped with air brakes.
I was pretty sure you had a CDL if so revisit this portion of the testing if not you are most likely required to before operating the truck in question upon the highway. good luck have fun and stay safe.

Sorry I made a miss statement the trailer air supply valve red and shaped like a stop sign and on some trucks a third knob round and blue would be called the tractor protection valve. The yellow diamond shaped valve is is simply called the parking brake control valve.

However note on the old trucks like the 57 Kenworth I once had all the valves were chrome paddles like a light switch this was before the shape and color identification system that came about I think in the late 60's. But the operation was the same the parking brake would still set should air pressure drop too low. OK sorry now I am just rambling.
.

John, are you saying: "(push it in to release the spring brakes, pull it out to apply)" is how it's working, or how it should work? assuming you have the correct, labeled, knob? is it working the reverse of that labeling?

Bill

The labeling did not start until the 80's or so with the Bendix MV2 and later the MV3 valve. http://www.bendixvrc.com/itemDisplay.asp?documentID=5108
If an earlier one is labeled like the MV3, someone retrofitted it.

From the early 60's until the Bendix MV2 which was superseded by the MV3, there was no standard for marking. If there is a red or yellow button, it was retrofitted Sealco had a button about the size of a silver dollar. Bendix had a shiny button about the size of a quarter. But they both worked the same. The button is spring leaded. To release the brakes, you push in the button and it release the spring brakes. Whenever air pressure drops to around 60 psi, the button pops out and the spring brakes set., To manually set the spring brakes for parking, you merely pull the button. This button was completely separate from the tractor protection valve. The tractor protection valve was usually operated by a toggle lever which merely supplied air our shut it off. The same lever is still used for suspension dumps and 5th wheel sliders. The tractor protection valve itself was usually towards the back of the tractor and was a spring loaded spool valve. When it received air from the toggle switch, it charged the emergency line to the trailer and allowed the service line to the trailer to pass air to the trailer service brakes. In the closed position, it allowed one to bobtail the tractor. It also closed in the event of a sudden air loss, it shut off the air to the trailer and therefor was called a tractor protection valve.

The old style valves are still readily available. The MV3 valve was a big improvement, but the old style worked. Much of this brake stuff was retrofitted. MGM invented the spring brake in 1956. It was a cylinder with a piston with an O ring and was very unreliable, but it was better than what we had before. Spring brakes did not become mandatory on trailers until those that were built in 1975. By then Anchorlok had invented the twin diaphragm spring brake that we still use today.

2Ton, I don't think the parking brake was ever a lever as you describe. It is probably a trolly valve that was designed to supply additional air to the trailer brakes. It may even be inscribed "not for parking". If it is some way hooked up to your spring brakes, someone probably jerry rigged it.

Nope. Ford L9000 trucks and the C cab trucks came with the chrome lever for parking brakes. We had a lot of them in our fleet. The Ford C cab or cabover trucks were a short wheel base truck we used as a gas buggy.

Cabover truck

This is what our buggies looked like: http://cdn.soarr.com/dealerphotos/ericksontrucks/xl/20401209.jpg

Crenwelge
The lever is on the steering coluem on the "67" GMC 9500 Fire Ladder truck.
No brake knob on the dash.
When Fire Trucks were fitted with beds, the out fitters would make every thing work.
Your thoughts on a seperate trailer brake system makes sense.

Sunday afternoon, time to take the ladder down.
and see if there is any markings on the lever.

Thanks
2-Ton

I used a C model Ford with a Bartlett 5th wheel for a yard truck for a few years. It had a 534 engine in it that used several gallons of gas just to build up air pressure. It had a valve exactly like John describes for the spring brakes. However, it had a small chrome trolly valve which we didn't use because we only charged the emergency line to move trailers. The vehicle had originally been used as a truck tractor and the lever was used as a trolly valve for the trailer brakes. But I was not the original owner and I don't know what was original. I'm not sure if it even had spring brakes from the factory.

crenwelge
You are right.
I just put the ladder down and parked it in the barn.
The orange lever said "Not a Parking Brake"
I did not trust it any way and always scotched it.

Thanks for the advice.

Don

By the way, you would have a good time in KC in a couple weeks.

I'll have to go back out and try it again to see which way is which. The bottom line, though, is that it works opposite of how it's labeled on the Sealco placard. The handle is a yellow square. The truck has a tractor protection valve (round black handle) and it works as labeled/correctly. There is no third "emergency Brake" valve, though.

Billy -- I would go back to that dopey yahoo I bought it from, but I'm afraid he'll ask me for more money as I pretty much stole the truck from him as it was You'd probably like him if you met him. He actually reminds me a lot of you...

Dopey Yahoo!!?? I resemble that comment. Hey, thems the brakes!

I bet he's an alright guy though.

Sealco had a valve that was push to park,standard valve in Peterbilt trucks in the 60's, the knob was about the size of a silver dollar, thats all it did was park and release,below it was a push button with a knob about the size of a quarter it said push and hold for brake release, that was the emergency release knob.
What you may have John is the early Sealco plate that says push to park, and the valve has been changed to a newer style that is pull to park,a picture of nameplate and valve would be helpful.

ABento -- I think that's the case -- mismatched placard/knob and valve. I thought they were standard.

Billy -- The shoe only fits if you walk a mile in it ... or something like that ...

Exactly what I was thinking.
I have an old Sealco parking brake valve from a White 3000 and it works as it's tag describes, but it is opposite of modern parking brake valves.

John just has a replacement valve and an old tag.

Grigg

Or maybe the knob? They tend to break easily at the roll pin.

I believe you can still get that valve from Sealco, they are locate din Ax and most truck shops can get it for you, I can't remember if they will sell direct to the public or not, but will talk to us.
Also John there would have been a provision for a push to release button in th edash also, this operated from the emergency air tank to release your brakes at least once in the event you ran out of air in the main tanks, the newer valve in there most likely does this operation as well.