BusTalk

[serious whistler]

Hello,

I have 1976 GMC bus (Model T6H4523N).

I'm moving and planning to take bus with me, it starts perfectly, pressure is 120 (within 4-5 min), but it is not raising up (all of air bellows (Front and Rear) are not filling up) and gas pedal is inactive (When pressed nothing happens. No air?).

I checked for sound of air leaks and so far found 2.

See attached pictures 1 and 2 (look for red circle). This part is located in front center of the bus and was leaking pretty bad. I took it apart, it has spring in it that air pushes and disconnects wire that it attached to it. I was not able to repair leak, so I closed it all together and disconnected the wire. No leak anymore, but still no change.
http://freebookexchange.org/temp/part01.jpg
http://freebookexchange.org/temp/part01_closeup.jpg

Next leak is under the drivers side very front (kind of under break and gas pedals. Picture 3. Red circle). It is leaking (or sucking) air from that round mesh area. It looks like, maybe, it actually supposed to do that, but may be only at some point not all the time? (Also notice that it leaks off and on but mostly leaks)
http://freebookexchange.org/temp/part02.jpg

I live in Henderson, TN now, but have to move in next week or so (no pressure though, but I really would like to be on the road)

I called around and no one in this area is working on this type of bus (will keep looking) and was told I gotta do it my self and that it could be:
1. Stuck valves, that need to be banged with a wrench (3 in front? not even sure where they are located) (Not sure where to look)
2. Leaking dry rot cable, but so far the only leak I was able to locate are the two above. (Not sure where or how to look for more)
3. One of the tanks in nor functioning. (Not sure where they are located, and now to check them)
(I doubt that all air bellows went bad, but again what do I know)

It was driving just fine about 8-9 month ago without problems. Only one problem was a grinding noise when switching from forward to reverse without first switching drive to neutral mode. But there was no air issues. I started it about 2 days ago and it started right away, and sounds like it is running smooth, just not raising up and no way to give it gas.

Any advise would be very appreciated. Such as:
What do you think could be the problem/problems and what can I do to fix it?
Do you know any GMC guys around Jackson, TN area, zip code 38340?

Also do you know if repair/specs manual (like Haynes) exist for this bus and where can I get them? Or any good websites where I can ask questions and see problems of others?


Thank you so much in advance.

P.S. On picture 4 is a part located all the way in the back of the bus, driver side, and I remember you told us something about it when we were leaving, but forgot what. What is it for and what do I have to pay attention to.
Also is there a water tank in engine compartment drivers side where it said "caution hot water/steam", do I have check/fill water there?
http://freebookexchange.org/temp/part03.JPG

UPDATE:

I did press the brake pedal quite few times and it did fix the problem with leak.
http://freebookexchange.org/temp/part02.jpg

I also took apart this part cleaned it and looks like no more leak.
http://freebookexchange.org/temp/part01_closeup.jpg
http://freebookexchange.org/temp/FixedLeak.jpg

Air tanks:

It looks like this bus has 3 air tank. 2 in the back
http://freebookexchange.org/temp/BackTanks.jpg
and one located in the middle, driver side
http://freebookexchange.org/temp/DeadTank.jpg

I did bled two tanks in the back and some (little) goo came out.
http://freebookexchange.org/temp/BackTanks.jpg

The problem is that third tank is not getting any air at all.
I unplugged all of the hoses coming out of it (or in and out of it) and there is no air coming out.
http://freebookexchange.org/temp/DeadTank.jpg

So it could be that 3d tank is not getting any air from the 2 on the back?

I will try to trace and unplug hoses leading from back tank to the dead front one, blow though it, and see if the hoses are plugged with something.

I also unplugged the air hose from the throttle and there is no air coming into it. I left it unplugged, to see when air would start flowing.
http://freebookexchange.org/temp/Throttle.jpg

I also found 2 new leaks. Leaks are not very strong. The part is located between back tires.
http://freebookexchange.org/temp/NewLeak.jpg

I did bang on all the valves or what looked like valves.
I did shake the bus back and forward (I can move it, but somebody has to be in the back manually pressing on throttle as it is not getting any air.

[Rt4957]

I didn`t click on any of the pictures,,but just a guess was/is that your Leveling Valve/s were not getting enough air to raise the Bellows.

I own a 1975 40` Flxible,and once had a bolt come loose from the right side leveling valve,and sent the bus down on the right side.

Best thing to do is hunt down a Maintenance Manual from E-Bay of the bus you own.
Occasionally the "Right" one will show up for sale,or one close to it,it would be an added plus to get one from the company the bus worked for,,as there might be an option or something that another company did not order.

I was lucky enough to get a manual and also a copy of the electrical schematics from Flxible while they were still in business for my particular bus,,which had added options like full dash gauges all forward facing seats etc.

Owning a bus can be nerve wracking,,I myself start hearing "Noises" when far from home when the thoughts of breaking down or towing are the most scary.

It does teach you basic mechanics,,and I`ve heard many a story from friends of how they nursed a sick us home with a rope for a throttle cable or like myself using a small pair of vise grips to hole the leveling valve in the right place until I could get the right sized bolt.

Good luck with your Air Leak.

Rt4957

[Mr. Linsky]

S.W.,

First, let me welcome you to BusTalk and say that we look forward to helping you as much as possible.

I too did not look at the photos merely because they would be meaningless to me not being a mechanic.

My best advice to you in this case would be to try to make contact with the closest thing to an organized bus operation in your area - I don't know what city of any consequence you are near but that would be the best place to look.

With luck, you may find a mechanic who is very familiar with GM New Looks to help you or he might suggest someone retired from the company that might have the spare time to work on it.

Count your blessings in one respect - at least your bus has no air conditioner to give you more headaches!

Good luck and regards,

Mr. Linsky - Green Bus Lines, Inc., Jamaica, New York

[Bill D]

It sounds like your problem may be related to a pressure protection valve. This prevents air from flowing to the accessory air tank until the system air has built up to around 80 psi. Until this valve opens, the accessory tank will not fill, and the suspension will raise up. Also other devices such as the air throttle, doors and wipers will not work. The pressure protection valve should be located on the air line that feeds the accessory tank. It has been a while since I worked on a fishbowl, so I am not sure of the location. I will see if I can find a service manual at work tomorrow to get you more information.

The item you refer to as part #1 is an air switch. It is commonly used to activate electrical components such as the brake lights, or low air pressure telltale or warning buzzer.

Part #2 appears to be the brake application valve. Pushing down on the brake pedal opens this valve, allowing air to flow to the brake system.

Part #3 is the circulating pump, on the left, and the modulating valve, on the right. These control the flow of engine coolant to the heater and defroster of the bus. When the system is calling for heat, you should be able to hear the circulating pump running. If it is not working, one item to check is the gradustat (thermostat). This is located under one of the passenger seats about midway in the bus (directly over the underneath heater assembly). There is a dial with numbers indicating temperature setting. If this is set too low, The bus will not have heat.

I hope this information is helpful, and if I provide any more information I will pass it along.

Good luck!

Bill

[serious whistler]

Bill,

Thank you so much for your help.

I have few question.

What does pressure protection valve looks like?
Where would it be located?
Can you find a link to an image of it?
I goggled and found bunch of images, but not sure which one it is.
Something like this?
http://www.tonystruckparts.com.au/pr2.jpg
If I know I'll be able to located it.

I found this near AccessoryAirTank
http://freebookexchange.org/temp/AccessoryAirTank.JPG
Close up:
http://freebookexchange.org/temp/PressureProtectionValve.JPG

Is that it?

Once I located it would I have to replace it?
Or is there a way to test it first?
If it is faulty do I have to replace it?
Where can I get this part fast?
Can I bypass it if I do not find the part?

BTW thank you all for replies and your help.

What a nice board with good helpful folks.

[GBL Rebel]

You will not get air out of the throttle line unless the accel pedel in pressed down. Your new air leak in the rear is called the brake chamber. DO NOT EVEN THINK OF TAKING THAT APART UNLESS YOU KNOW WHAT YOU ARE DOING! There is a spring inside of it that will inflict serious harm if you make an error. The little part in the front with the wires is an air pressure switch.

I willing to suggest you find the main air tank on the bus, this is the one with the air line coming from the air dryer. With some air pressure in it TAP not beat, the check valve coming out of the tank. If a check valve is stuck closed, you will not get any air to the accessory tank. I have seen ice build up around the tank cause the valve to stick, so sitting 9 months could be your cause.

Most of these prats also can be found on trucks. A good truck parts store should have what you need and a good truck repair should be able to make repairs if they are a bit more then you can handle.

And please remember, you are dealing with air that is under pressure. Alot can happen if something blows up with 120psi behind it. Climbing under a bus when the bellows are up can be dangerous, all that has to happen is a leak and they come down faster then they go up. Wheel chocks and jack stands are a great idea.

I hope I have helped you with this info and it all works out for you.

[GBL Rebel]

Your photo titled Pressure Protection valve is a air pressure regulator.

[serious whistler]

GBL Rebel,

Thank you for advice.
I will not go near brake chamber.

So this is NOT Pressure Protection Valve?
http://freebookexchange.org/temp/PressureProtectionValve.JPG

Would it be located closer to main tanks?

Check Valve is different from Pressure Protection Valve?

Is Check Valve attached to the main tank?

Is it something like this:
http://maltedmedia.com/people/bathory/check-valve.jpg
or like this:
http://www.mh-valve.com/Pictures/Check%20Valve.jpg

[GBL Rebel]

Look at your photo labeled dead tank. The middle arrow almost points to it. Yoy have the nylon hose going into a 90 degree fitting, the big hex thing behind it that screws into the tank-- thats a check valve. There are many different looking check valve. This is where I would personally look. Usually its a check valve out of tank into the line to the next tank going through another check valve.

[Mr. Linsky]

S.W.,

I was going to suggest both Bill D. and GBL Rebel as your advisers but would not take that liberty without their permission.

You hit the jackpot with these guys because they're the best in the business!

Can't wait to hear that your baby is back in shape and running like a clock again!

Regards,

Mr. 'L'

[Bill D]

The picture you have labeled pressure protection valve is just that. It is also referred to as a pressure regulator. I will send by private message some information I found from another manual on this type valve, also called a PR-2 valve. They are made by Bendix and should be available at almost any truck parts dealer. You can remove the delivery line from the valve and check for air flow once the system pressure builds up. If you do not have any air coming out, check the input side for air. In my experience, this valve fails more often than a check valve, but since the bus has been sitting for a while, one of the check valves could also be suspect. As GBL Rebel emphasized, always put safety first when dealing with the air system. Make sure the wheels are chocked and that you have sufficent clearance to work under the vehicle when the air bags are deflated. Also make sure that there is no air in the system before removing any air lines. And even if the gauge indicates no pressure, use caution removing the lines, as check valves do keep air from exhausting from some portions of the air system.

Bill

[serious whistler]

Bill D and GBL Rebel,

Thank you for all your help.
The beast is raising up!!!
It was the Pressure Protection Valve
http://freebookexchange.org/temp/PressureProtectionValve.JPG

It has tons of white, hard crust that completely blocked the air flow.
I cleaned it and all is good.

I also checked the leaks around DD3 type maxi pot and they are not there anymore.

So again thank you very much for your help. Would not have done it without you.

Have a great day.

P.S. I do still have few questions.

What is this mystery tank on driver's side in engine compartment?
http://freebookexchange.org/temp/MysteryTank.JPG
It has following warning:
http://freebookexchange.org/temp/MysteryTankWarning.JPG

It mentions water. I never checked or added water there.
Is its something I should do?
What is this tank for?

What should be the tire pressure?
I have what appears to be rare 12R22.5 tires, can I replace them all on 11R?
Or have 2 12R in front and 4 11R on the back?

Also would 1971 GMC BUS COACH T6H S6M SHOP SERVICE MANUAL BOOK work for my T6H4523N?
There is one on ebay is it something that would be useful?
If not where can I get manual for my bus?

Also this part:
http://freebookexchange.org/temp/part03.JPG
that controls the flow of engine coolant to the heater and defroster of the bus. It is something I should make sure is working properly?
Is it an essential part? Would it damage the bus if does not work?

Thank you in advance.

[Mr. Linsky]

F.B.,

I would think that a great deal of the S6M manual would help you except of course for the transmission.

While there were about four upgrades in the production of the GM New Look over the years much of the basics remained unchanged and you should recognize quite a lot of the content of the specs.

Glad you got to the bottom of your problem.

Regards,

Mr. 'L'

[GBL Rebel]

Your mystery tank is called a surge tank. That is where you fill the anti-freeze. Keep in mind this tank is under pressure. It should have a pressure bleed valve to the right of the tank door/cap. As far as the circulator pump goes, if it is not working you will not get heat or a hot defroster. The engine waterpump will move the coolant around the engine and raditor but is not powerful enough to send it 40 feet to the defroster heater core or to the main heater core under the middle of the bus.

As far as tires, I have heard of 11R22.5 being used instead of the 12R22.5. They are a more common tire and a bit cheaper price wise. What I will say is make sure the load rating in enough. I have seen 305/85/22.5 used as well but they tend to rub a little when making a turn with the wheels fully turned in one direction. And if you were to get recapped tires, NEVER PUT THEM IN THE FRONT.

[HwyHaulier]

All -

In no case do I claim to be a tire man. I do know some of the practices best avoided. GBL Rebel counsels:
"...As far as tires, I have heard of 11R22.5 being used instead of the 12R22.5..." and adds it is wise to confirm
"load rating".

The business of the LR on steers makes me jumpy, even on the good days. Or, I'd say stick with exact GM
"OEM" practice. The engineers who "specced" were paid for the work, and they had their reasons.

In a related anecdote, I have had a long running chat with an affable goof who does not want to understand
why, from his easy chair managing, one cannot do low profile tires on modern "Low Floor" coaches. The tire
builder (manufacturer) engineering specs do not consider such a tire. (These modern city coaches are much
too heavy, overall and anyway!)

........................Vern.................