Air System Mack R Model

[nicste]

Good day. We are busy restoring a Mack RS797T, the air systems is a mess. I have the Bendix schematic to work off but that does not show a 4 circuit valve. Can someone advise if I am correct in saying there should be a 4 circuit valve after the supply reservoir and a third tank for the accessories, wipers, diff lock and gear selector of the third port on the 4 circuit?
If anyone has more schematic of the original air system it would be a great help

 

[1693TA]

I have three long hood R model Mack trucks. Two are RL797 series and one is an RL755 series. These are aluminum frame trucks where yours would be steel. All still have their original engines, transmissions, and rears as built. None have three air tanks under them but would be easy to incorporate if needed additional capacity. The newest is 1978 which is the RL755LST. My two other R models are straight number trucks having only two air receivers also.

 

[nicste]

Thanks, two air tank with a check valve on each in place of the 4 circuit protection valve?

The the have quick releases on the rear before the chamber of just relays, looks like someone has fitted quick releases on the rears after the relay on ours

 

[1693TA]

Each of the tanks has in inlet check valve and there is a double check valve under there so either tank will supply air to stop the truck if needed. I've not had any problems with braking in those trucks so not real familiar with what is applicable in that diagram as haven't needed to work on them.

 

[nicste]

That helps a lot, reassures me that the original system was very similar to the Bendix schematic, thanks for your input

 

[Truck Shop]

he the have quick releases on the rear before the chamber of just relays, looks like someone has fitted quick releases on the rears after the relay on ours

That was done in some cases years ago to prevent compounding on the service side to brake chamber.
works fine, but not necessary. When brakes are applied then released it will exhaust at the quick release
and not at the foot valve, it does speed up brakes releasing on application air. If that is what your asking.

 

[nicste]

That was done in some cases years ago to prevent compounding on the service side to brake chamber.
works fine, but not necessary. When brakes are applied then released it will exhaust at the quick release
and not at the foot valve, it does speed up brakes releasing on application air. If that is what your asking.

Yes, thanks. Not standard but it help getting the brakes released quicker