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B-75 air controls


jimtruck
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I've finally got my truck running! My next order of business is to get the brakes working. I'll go ahead and admit that I don't have any experience with air brakes or their controls.

Inside the cab, I have a " Air 3rd axle loaded/no load" , "Truck tractor protection" , and a rotating valve that has "run-park" on it. There's also a lever on the steering column that says "not for parking".

To show my ignorance, I have no clue what these valves are supposed to do. If you guys could shed some light on this for me, I'd be grateful.

My truck has the camelback suspension. are both the axles supposed to drive all the time or is there supposed to be some kind of shifting mechanism to engage the rear axle, as I don't see anything back there except the brake air lines.

Thanks,

Jim

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I would assume run park would be your parking break for the truck. Tractor protection valve sends air to your trailer but in a major leak on your trailer or a break away situation it cuts off the air to your trailer so the trucks air system is protected meaning it won't drain all your air so you can still use the breaks. The 3rd axle loaded unloaded I believe is to pro porting the amount of braking power to your front breaks so in an empty situation you won't skid the front tires and lose control. The lever that say not for parking sends air (service side) to the trailer to apply the breaks. Older trailers didn't have park or spring breaks so you had to get close hook your glad hands up and pull on the Johnson bar to ally breaks on the trailer but not the truck so you could back under it. You can also use it for a tug test befor you take off making sure your king pin is latched. Hope this helps. Many more knowledgable people on here than I which I'm sure will make things even clearer for you. 

The problems we face today exist because the people who work for a living are outnumbered by the people who vote for a living.

The government can only "give" someone what they first take from another.

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Don't know. Mine from whaT he's described mine has different controls like inter axle and dry slippery valves so I was guessing maybe his were labels or worded differently. Like I said earlier, lots more knowledgeable people on here than I. 

The problems we face today exist because the people who work for a living are outnumbered by the people who vote for a living.

The government can only "give" someone what they first take from another.

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Here is same lay out as my B Mixer the 3rd switch sounds like a Lift Axle to me.  Post a photo and we can id them for sure.    Paul

B mixer dash.JPG

"OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK"  Thomas Edison

 “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’

P.T.CHESHIRE

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Hi Jimtruck

may I suggest a few helpers for you... air brakes are different from your car, you need to know how they work and more importantly when they are not working... these trucks are heavy and need them to work correctly... you've obviously grasped this and have done a good thing by asking here on BMT.

your local DMV will probably have publications that help a truck driver get their CDL, part of the training and examination will be knowledge of air braking system and components and how to pre-trip the truck of which the air brakes are a large portion. These publications will illustrate the components and plumbing as well as the theories of how compound brakes work.

where I live it is mandatory to have an air brake endorsement regardless of how you use the vehicle, in most states this is not needed for private trucks or RVs.

I hesitate to offer youtube as it is not always reliable info but some of the brake manufacturers such as Bendix offer very good info and diagnostics on the site.

I've uploaded a Bendix Handbook Adobe file I have, is this what you are looking for or too deep?

BC Mack

Bendix Air Brake Handbook[1].pdf

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Thanks for the replies!

BC Mack, that Bendix site will be helpful-thanks.

Does anyone have an air line/valve plumbing schematic for these trucks? This truck has been cobbled on and a schematic would be helpful to me. I'm going to try and put Maxi brake chambers on the back axle, so any advice there would be welcome. Ive already got the chambers, and I believe that I can make them fit.

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It's an air lock power divider. The air locked power divider does not slip until something breaks!  As it says should not be left engaged  unloaded on a solid surface such as asphalt, or concrete roadways where there would be hardly any tire slippage. 

This is the Air brake schematic for my B-61, B-75 should be the same.

My B and the few others I used in the distant past, the brakes disengage without air, be careful on initial start up. Mine and Horans have zero brakes until the air pressure it up.

 

B-61 air brake schematic.jpg

Edited by 41chevy

"OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK"  Thomas Edison

 “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’

P.T.CHESHIRE

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  • 2 weeks later...

B46 is a gasjob so the black know would be a hand throttle, middle knob is wiper switch, t handle to the left is a choke, bottom left flipper switch is a front brake air pressure limiting switch(for inclimate weather) and right bottom truck tractor protection is for trailer brakes(now a days used for releasing the trailer brakes)

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post-6-0-64947600-1408238925_thumb.jpg

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  • 1 month later...

I found out that the Third Axle Air valve is blocked off. I checked my factory build sheet and found that my truck never had a power divider. I don't know why the switch is there, but it definitely has been blocked off for a very long time.

The truck tractor protection valve works, and sends air to the trailer hoses when flipped.

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