What's the blue valve for?
 

http://i156.photobucket.com/albums/t...s/blueknob.jpg
Seen these in some older trucks, mostly in movies :lol: Came across this pic and thought I'd ask here. My guess is it has something to do with old trailers that didn't have spring brakes?

i dunno what it is for but i can tell ya that an old MACK :wink:

The blue knob is for releasing the spring brakes on the truck so you can move it off the road or a little way to get it to a safer spot. This valve is fed from its own air tank. It is spring loaded and you have to hold it in to keep the brakes released. This is something not used any longer! (pre 1975) this is when the spring brakes were on the tractor only and not the trailer.

Gold star for mackman, nice! Not just any bulldog, but a cabover! Respect. It was an interior shot of this one, recently sold on ebay.
http://i156.photobucket.com/albums/t...COEbulldog.jpg

Thanks Fozzy, I knew someone here would know. Pretty weird feature, but I guess it makes sense. I had googled it a while back but didn't come up with anything, no wonder.

That truck would make my father homesick. That was what he drove for YEARS. He also drove R model Mack's hauling Harvestor silos on a dedicated contract to the Amish in Lancaster PA.

I drove one like that in Trucking school.. it sucked almost as bad as an "R" model Mack.. but not quite. :lol:

Man, I wanna try driving an R model! I almost had my chance recently, one of our guys borrowed one from another terminal and it had to go back. I told dispatch repeatedly I wanted to do it, and they said when the time came I'd be the man (they thought I was nuts, of course). I actually asked if I could use it on my run for a day, but they didn't want to risk me breaking down (I doubt it would have anyway). Well wouldn't you know, I come in one day and it was gone, they let someone else take it :roll: When I was a kid, and I thought of a Mack, an R (or U) model was what came to mind. Just wanted to experience one for myself, I'm nostalgic like that.

Those R Models were tough. Rough ridin, too. :P

Good transmissions. :|

One stick for 1-5, and the other for Low, Direct, and Reverse.

The outfit that do part-time farm work for have 2 R Models. When I driving, I just leave it in Direct, and just make her smoke. :P Heaven forbid if I ever have to back up, and try to get it in Reverse. :P

I drove an R model for like a year with the same tranny JR said it was a good truck the best is shifting in reverse. I love them older macks just somethin about them :D The U model is a ugly SOB.

I think I read that this "move it off the road" valve is still required (or at least common?) on buses...

Anyone who can drive an "R" model and like it are usually not able to get on the good rides at amusement parks...

I think so, the maxi's on a bus would make it a good idea..

Well am 5'8 fozzy and i had enough room in the cab Alot of people do say they have small cabs but it fit me fine.

I'm almost 6'3".. it was about as uncomfortable as it could get for me. Of course it could have been the seat and the way it was in there.. but it sure didn't work for me.

I saw an old Mack yesterday on the side of the beltway, pulling a flatbed. It was an old Overnite truck. I'll see if I can find something similar an post a pic, but I can tell ya it was old. Oh yeah, behind that Mack was an old International pick up truck, they had to be traveling together, or I entered a time warp. :shock:

I like those old trucks.

Something like this I think.

I like this one too, that's tough. It be fun to restore one for shows.

Plus if it was day cab there was no place to put your lunch box.

Apparently, I missed something. I dont get it. :|

"You have to be this tall to ride"
:lol: :lol: :lol:

I've seen them on Van Hool model motorcoaches.

New York State Commercial Driver`s Manual: "The tractor air supply control on older vehicles is a blue round shaped knob. You push it in to supply the tractor brakes with air and pull it out to shut yhe air off and put on the tractor emergency brakes".
Finally a wannabie had a chance to post something revelant :)

Anyway I have my roadtest this wednesday, hope everything will go well.

ok the blue valve...

while todays trucks come with 2 valves the yellow and red, while if u pull the yellow (tractor) you release both vales,

if you pull just the red you apply just the trailer breaks, if u hold the red and pull the yellow you only apply the tractor breaks and not both sets,

this is exactly what the blue button did, since the older break systems didnt allow you to be able to hold in just 1 button.

Yes, I would agree with that last post. I'm not sure of the reason for the button, maybe so you have an extra step to consciously keep the trailer brakes off..?

If you spinout climbing an icey hill, often times your tractor brakes alone won't hold your unit on the hill while you chain up so you need the trailer brakes as-well, you may even have to throw a tire chain behind a tire to hold on the hill.

I've seen a 2000 pete and a 95 frieghtshaker with these buttons, one was a black button.

I always thought that was the "Lot Lizard That Won't Get Out Ejection" button...

What you're speaking of is an "isolated reservoir valve".

Those were usually black and mounted separate from the parking brake and trailer valve.

As was said, the blue button feeds both the yellow and red button with air, if the blue one is pulled out, the red and yellow will not function.

I have seen mid 90's trucks that still had the 3 valve setup.

Had a 95 Mack with the blue, yellow and red buttons.

We have an 89 Mack Superliner with the three valve set up. They are marked as follows;

Red-Emergency,

Yellow-Tractor and trailer parking,

Blue- Tractor only parking.

When you pull the Yellow button out, it sets the brakes on both tractor and trailer, yet the red button stays in. When bobtailing, the blue button is the only one that is functional.

Yah, sure, whatever you say :roll:

I've seen newer Macks with all 3 buttons as well. The one thing they had in common was they were all Canadian market.

Here you go Ace, right out of the Mack manual. I was wrong though, the Red button says Trailer Air Supply, not Emergency, so you got me on that one. :roll:

http://i7.photobucket.com/albums/y28...r/scan0001.jpg

i drove an 81 r-model mack with all 3

When bobtailing, the blue button is the only one that is functional.




The yellow one still works "Ace"

Got me there Ace. :oops: