I recently saw a photo on Facebook where a tractor had 3 air valves on the dash, the traditional yellow and red but with a third blue one. I never drove a truck set up like this. When I asked what the third valve was for the answers weren't making sense to me. Can anyone explain what the blue valve is for? Thanks!
blue air valve is parking brake for tractor/truck only
Yellow button controls both tractor & trailer, red is trailer charge, blue is as said tractor parking. But that system was simplified with the MV3 two button yellow/red in mid eighties. The first MV3's were a bolt together white plastic valve that had several issues such as warpage between the two halves, incessive leaking was a common issue, doubt there are any left on the road that still have the white plastic valve. The MV3 can have either button pushed in while one is out, but pulling the yellow automatically trips the red also, but yellow can be pulled while holding red button in and vis/verse. The blue was liked for one reason for fact tractor brakes could be released while the red button was pulled setting trailer brakes only, allowing brakes on tractor to not freeze in winter parking. Below is a Bendix Test that describes what MV3 does and doesn't do, plus the often confused trip pressures that are or aren't regulated by Federal DOT Motor Carrier rules. * https://www.truckpartsandservice.co...endix-tech-tips-on-dash-valves-trip-pressures
I have never seen a truck with the Blue air valve. I read about them in a Heavy Duty Truck repair manual but it wasn't real clear to me. So it sounds like, pull the red knob sets the trailer brakes, pull the yellow knob, that sets the trailer and tractor brakes, pull the blue knob and that sets just the tractor brakes. Is that right? They must not use that setup anymore. What time frame did they use it or was it just an option?
Depending on your age probably not. The three button went out totally in 1984. Used from roughly 1968 to 84. Note-it was also used as a emergency release for tractor brakes on some brands by holding in. Not all were plumbed the same or not all had a tank designated as emergency air, some did some didn't. Air brake diagrams are generic when related to that.
So does the air for your trailer service line go from the treadle valve go through red button valve, or does pulling the red button trigger another valve like tractor protection
Kind of a combination on ones I've worked on. The tractor protection valve is the beginning. It has it's own air supply. When you press the red button in, that sends air to the TPV, that signal tells it to open and send air to the emergency line to release brakes on trailer. That signal also allows the service side to function. The treadle valve (and Johnson bar, if equipped) send air to the TPV, which in turn tells the TPV to send air to the service brakes.
My 2000 RD Mack tractor had the blue. I used it all the time with the lowboy trailer. You do need both yellow and blue charged to bobtail and obviously all three when hooked to a trailer. Pulling the blue only will not cause the yellow, red or both to automatically pop out.
I ran a 1990 mack. Got it brand new. It was just a straight truck but it came plumbed as a tractor. The air lines were plugged at the tpv. The blue button did nothing, I don't think it was hooked up. You could push the red button and it had air, but obviously did nothing. But it was the only straight trucks I have ever driven where the spike was hooked to the truck brakes. Obviously it had been hooked up that way, red button had no effect on it. It was great for dumping, or pulling out on a hill
Note the diagram below, which shows three button & two button valves. Red is supply through TP valve, Unless it also happens to have a TP valve with BTP for a BTP R14 service brake valve on tractor. *
And I forgot Mack continued the use of PP1 valves long after the rest quit using. A friend has a 93 Super Liner with three PP1's.
This diagram below shows a better image with type valves listed, in it shows a shunt line between the PP7 trailer charge valve and PP1 tractor park valve. When trailer PP7 valve is pushed it puts air through shunt to render tractor park valve useless, when trailer park valve is out trailer brakes set or no trailer at all then the tractor park valve is effective. The System Park operates no matter. The reason for a two button MV3 valve was three valve system was redundant because it is arranged so both can be operated independent of one another. This diagram below is the standard for use of a three button system although depending on how factory plumbed it could be different from brand to brand. *
Was it a regional thing too? I've been in NY all my life and was driving from the late 70s to 2000 and never ran into it here. I drove trucks from the early 60s up through new.
No it wasn't regional, most all brands switched to the MV3 simply because it became a integral one piece valve that took up less space and less plumbing. Early designs were the common flipper type TW-1, TW-4 or 11, with nothing more than a tractor/trailer charge valve using a PP1. TW-1 below. *
One of the reasons for brands to stop using the 3 dash valve yellow, red, blue design was the problem of drivers setting brakes with only the blue tractor park brake valve while both red & yellow were still pushed in keeping system charged. As described above the red valve trailer charge needs to be pulled in order for blue tractor park to work, because in the bottom of PP7 valve is a one way shuttle. Brakes were to always be set using the yellow system charge valve, which set parking brakes no matter what. There had been instances of new/rookie drivers only pulling the blue button, which depending on how plumbed never set any brakes with red valve still pushed in charging. Red had to be pulled in order for blue to work properly, if study diagram above it will be obvious.
Im not sure about other Mfg's but all the Mack's set up as tractors or straight trucks specd with trailer supply, R's F's DM's U's etc had the blue valve. 70's through 2000's or discontinued the model.
i'll throw in some more confusion- I ordered my either my '93 or '96 pete with a black push valve "push to charge trailer while parked" in addition to yellow & red
Totally not surprised, in those days special items could still be incorporated without dealer fuss. * Mack used the three button dash air brake control valves up until 1-15-2008. Federal DOT put a stop to as of 1-15-2008. Did not meet regulations they finally decided 24 years after MV3 was designed. * Below is probably the only current braking system incorporated in a 1960 B Model Mack. Two button MV3 dash valves, aluminum air manifold in bulkhead, E6 dual control treadle valve, with R12 relay valve using two QR1 release valves for quick exhaust and anti-compound- ing with park brake applied. Anything can be updated. *
I would like to see the finished overall pic of that B. Looks outstanding.
My Last One-Finished After two and a half years it's finally done. Many hours of work and aggravation went into this Mack. But it was something I had to do-My Last One. Would I do it over again? I can't answer that right now. Was it worth it? Yeah it was worth it to me. Did I learn anything along the way? Of coarse... HeavyEquipmentForums
What would she have had under the hood when she was a pup
Mack END 637.
Very neat truck. Long frame, long hood, mitered pipes. What engine does it have?
I saw the reply after I posted. Is that engine what they called the Maxidyne?
Outstanding. Can’t believe I missed the thread when you originally posted it.
Thermodyne * NTC 400 BCII CPL 449.
Thanks--Most of the whole story below--------------a derailed thread, sorry. * Mack-Phase Two New thread because the other became cluttered. The rails arrived Wednesday the 30th in at 4:00 pm. And so far the engine bay is cut in both rails and 98 holes drilled with a Hougen Mag drill. The rails were perfectly formed-right on the money each 30'... HeavyEquipmentForums
Can you explain what that is alittle more? It is a Cummins right?
Correct--this exact engine below. *
That was built before the 855?
Yes, 855 came on the scene in 1961, Mack Thermo goes back into 50's.