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Air Brakes '75 D700

85crewcabbie

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Recently brought home this '75 D700 cab/chassis. I was thrilled that it had air brakes after having a lot of difficulty finding hydraulic brake parts on a '75 D600 with the heavy duty six lug axles. My problem is I need either a shop manual or a Bendix specific air brake manual. Any advice for a newbie on what not to do in repairing them also appreciated.

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65 sporty

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Not very experienced in air brakes, I know enough to be dangerous. Without air pressure the brakes will set. Be extremely careful when working with the air chambers if replacing the pancakes, the spring has to be caged before taking it apart. Watch some video's before jumping in to it and a manual would be great
 

Basketcase

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Hit e bay for the manuals. Lotta factory books out there. And several Face book groups on the trucks. Agree on the brake chambers. Nice score BTW!
 

85crewcabbie

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Appreciate the responses. Checked ebay for a manual but Bendix specific ones were either from the 1940's (I had no idea air brakes were in use that far back) or 2000's and above. I had read about the brakes setting with no air but these are not thankfully so I can move the beast if necessary. I thought it was a good buy until I priced six new tires yesterday. May have to take out a 2nd mortgage on the homestead ! lol
 

7mopar

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Are you really certain it has air brakes and not hydrovac's.
If it has air brakes and moves without air some one may have locked them out or adjusted them to the point the chambers are released.
Chambers can be checked individually with 90 psi of air.
A picture of the air chamber and linkage may help.
 

85crewcabbie

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Definitely not a hydrovac system, at least of the GM variety that comes to mind. Not sure if that's the type system your referring to. Has an air pressure Guage in dash and air reservoir tanks on chassis. Also has open brakes on rear meaning I can see the shoes like on 18 wheeler tractors. I appreciate your skepticism though as it has a gas engine, a 361 big block, and not a diesel engine. It is an oddity as equipped. Someone else mentioned that about locking out the air chambers. They were a retired heavy tow opeator and talked about having to lock them out for towing. Part of the reason a year appropriate air brake manual would be most helpful. Will try to get more pics up. Appreciate the response.
 

7mopar

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Not at all unusual for a big gas truck. They all work pretty much the same. Unless it has the mandatory anti lock system of the day. But even with it the brakes should be set without air.
You know your going to have to get an air brake certification to drive this thing on the road. Unless there is some kind of farm exemption I am not aware of.
Back to the basics. Without air the brakes should be set. Upon starting the truck air pressure should develop in the tank. Most older truck had some kind of signal when enough pressure had developed and the brakes where released. If that is not the case you need to start looking for air leaks. From there it is basically adjusting the chambers back to where the brakes lock tight. Them backing them off enough to turn free.
Remember this all needs to be done with pressure in the tank.
Some where in the cab there should be an air release that will sit the brakes when parked and the engine running. So don't expect it to just start rolling with air in the tank.
But as you can tell. Get the air system up and running. Then worry about brakes.
 

85crewcabbie

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@7mopar - thank you for the info on the air system. Yes there is a parking brake set knob (yellow in color). There is a second red knob next to the yellow one but the function markings have been vaporized by the sun.

I think I lucked out on license issue. GVW of truck is 25,447 lbs. AZ law says an operator does not need an air brake license unless GVW is 26,001 lbs. or greater.
 

85crewcabbie

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Yes to PTO. Also has two speed rear. Attached is a pic of main air brake controls as well as a supplemental? control on the steering column. Three control panel in first pic has red knob on left with unintelligible markings but just realized its shaped like a stop sign and may hint at its function. Funny how the obvious isn't seen until a change in perspective. (lol) Yellow, middle control clearly marked "parking brake" . Gray knob on right is marked "reserve air". Second pic is odd hand control marked "not to be used for parking brake" Your help in educating me on air brakes is much appreciated.

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7mopar

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The old dodge looks like it had seen some abuse. Like many old trucks like that, it's only an old truck untill it no longer works.
 

85crewcabbie

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@7mopar - Don't know about abuse, but the Arizona sun has turned all the dash plastic to dust. Can you identify the function of the controls pictured ?
 
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