Air bag pressure

[RJ]

Thank you for all the feedback. I have been running at 65-70. I will bump a bit and see how it works. Thanks!!

Mikke60

As others have mentioned, you need to set the correct ride height before playing with your air pressures like you're talking about. So here's how:

Find a level parking area, and get out your measuring tape and a good quality bubble level. The correct ride height is when the top of the bottom step is between 14"-15" off the ground.  With the engine running, adjust your leveling system to center the bubble in the level, making sure that the step measurement falls within specs.

NOW you can note your air pressures for each corner of the bus.  Anything else, at least for running down the road, is opinion. Obviously, when parked in a campground, you can re-adjust accordingly with your bubble level, but return to the pressures noted above for highway use.

FWIW & HTH. . . 

RJ

[luvrbus]

The bubble should help,I see people all the time measuring 4 corners on the GM buses they have taken the 3 point factory levelers off

[tr206]

tr206

That page is for the GMC Motorhome, has no relation to GMC Buses!

FWIW & HTH. . . 

RJ

Yeah I went with 77 gmc 35' not sure what he has.

[Dave5Cs]

We still have the leveling valves just don't use them and are not hooked up. We have found the 85 in the front and 80 in the rear work really nice. We adjust at campgrounds when needed.  The ride height is about right also.
So Clifford why does it Suck?

[luvrbus]

I like automatic levelers like the manufacture installed,the 5 was manual I didn't care for needing to adjust all 4 corners,the 8 we kept the factory levelers on the 8 by adding a by pass and only used the 4 corner system when parked both my systems were made by Gary Nickeson when was building and selling those.The factory level will dump or add air to keep the same height when turning how do guys do that with a manual system,air bags never have the same pressure it is always changing with the factory levelers

[Coach_and_Crown_Guy]

The air bags are control by leveler valve or valves you need to set them to the correct height which I have no idea on your bus and your good to go. The levelers adjusts the air pressure in the bags to weight of the bus to keep the correct height at all times. You don't just set a pressure or your the pinion angles for the driveshaft will be wrong. Somebody here I am sure has the correct info for you.

What "Coach"? I suspect you're talking about a GMC Motorhome which is not a true GMC Bus. The bus would have leveling valves on all axles and there would never be any reason (or way) as originally built to even see, let alone adjust air suspension bag(s) pressures. If it's a bus, please be precise in it's model number which should start with a "PD" most usually followed by some other numbers. PD4104, PD4106, etc.. It could even be a TDHxxxx (Transit Diesel Hydro-matic) for Transit/Suburban buses.

If not then it's not a true bus as we are all expecting to be familiar with. The GMC Motorhomes were distinctly different and built as Motor Homes with medium duty everything and no relation to the bus standards in design or execution. They are Unicorns in all ways today and parts, support, manuals are all super difficult to find also because they didn't make all that many and they're rare as hell to find in running condition. Pics of the thing would help as well to identify it. The Motor Homes were Front mounted GAS engines with front wheel drive and the rear axles were simply trailing/tag axles. Not any kind of "bus". Only thing in common was the GMC brand put on it.

[Coach_and_Crown_Guy]

I’m sure this topic has been talked to death, but I would still like some feedback . I have. 1977 Gmc 35’ coach with air bags. The previous owner never got me up to speed on a lot of the systems, so here I am. I am currently running bags at 65 lbs,  if it seems a bit soft. Any advice would be appreciated. Mike

Oops. This is what I meant to reply to....

[luvrbus]

Oops. This is what I meant to reply to....

I don't know what 35 ft bus GM built in 1977 I never saw a 4905A 35 ft ,then I am not into GM buses either

[RJ]

I have a 1977 GMC 35’ coach with air bags. . .

All -

In his original post, Mike stated the above, basically a 35-foot GMC coach built in 1977.

Those that jumped on the GMC Motorhome thought process probably forgot that those were only built in 23' and 26' lengths originally, thus not even close to Mike's bus. In addition, they came with torsion bar front suspensions, and a single air bellows per side in the rear - a completely different design than GMC's coach production, which consisted of four air bellows per axle.

With that elimination, Mike's 35-foot 1977 GMC bus is either a Transit (TDH4523) or a Parlor (P8M4108), both of which came with air suspension.  If he posts the VIN, we'll know for sure which model he has.  Either way, the suggestion above about setting his ride height and level correctly first holds true for either model.

Cliff - The P8M4108 looks just like a P8M4905, just five feet shorter and with one less baggage bin. The 1977s are pretty rare, they only built 21 of them, and another 21 in 1978 before that model was cancelled in favor of the 40-foot coach, which continued in production until 1980.

FWIW & HTH. . . 

RJ

[Utahclaimjumper]

 
 Mikey O has an example of that bus,, and with the four corner system..>>>Dan

[chessie4905]

I believe GM stated max of 100psi in the 4104. Coures that is with the double lobe bags

[dtcerrato]

I believe GM stated max of 100psi in the 4104. Coures that is with the double lobe bags

The 4104 maintenance manual shows 75 psi maximum air bellows pressure.
There is no pressure shown on the bellows themselves.

[chessie4905]

Maybe I saw it on the Level It instructions.