New to busses

Whaley · November 05, 2021, 04:54:32 PM

I just got a 75 mci mc8 with the 8v71
And after getting it home a 2 hr drive I moved it at the house after setting 3 days and when I parked it started hissing and the throttle is very stiff.
Is the throttle air controlled?

buswarrior · November 05, 2021, 06:26:56 PM

Thorttle originally was a series of rods, linkages and bell cranks.

The high idle, when engaged, blocks the throttle pedal movement.

Someone may have retrofitted an air throttle at some point in its life?

Where is the air leak coming from?

Happy coaching!
Buswarrior

Whaley · November 05, 2021, 06:32:20 PM

I haven't had time to trace it down yet but it sounds like the center between the front wheels
I'll look more into it tomorrow.
It got dark on me before I had much time to look at it

buswarrior · November 05, 2021, 08:23:59 PM

Quote from: Whaley on November 05, 2021, 06:32:20 PM
I haven't had time to trace it down yet ...
It got dark on me before I had much time to look at it

Add:
"the store closed before I got there"

"my significant other is mad at me"

"I have to wait for payday"

you've got the summary of the busnut life ahead of you!!!

You've only just begun...

happy coaching!
buswarrior

BusNit · November 05, 2021, 08:28:19 PM

I can attest to all of the above...

richard5933 · November 06, 2021, 03:34:33 AM

If the hiss after shutdown is coming from the front between the wheels it could quite possibly be the front ride height valve. Mine will hiss after parking for a few minutes, especially if I shut down just after parking. The valve is still trying to get the front of the bus at the proper height by exhausting air.

If it the leak continues for more than a few minutes, then it's time to start looking for something else. Lots of things with air in the front of a bus - everything from the air horn & wipers to brakes.

Next time you start up the bus, might be a good idea to do a DOT brake check to see how your braking system is doing re leaks/holding pressure. Pick up any CDL license manual for the steps to do this.

Whaley · November 06, 2021, 06:10:37 AM

The high idle switch was on not sure it was idled high did not sound like it
I turned it off and then started it it pumped up to 120 no hissing and the throttle seams ok. So it's fixed lol not sire if I should try to recreat the problem or not

luvrbus · November 06, 2021, 06:16:29 AM

Quote from: Whaley on November 06, 2021, 06:10:37 AM
The high idle switch was on not sure it was idled high did not sound like it
I turned it off and then started it it pumped up to 120 no hissing and the throttle seams ok. So it's fixed lol not sire if I should try to recreat the problem or not

Your air dryer purge valve was stuck open are you in freezing temp ? the air dryer between the front wheels can be a pain to service on the MCI so they don't serviced as they should

Whaley · November 06, 2021, 07:30:45 AM

I'm in Ohio and it has just started to get below freezing. How do I service the air dryer

chessie4905 · November 06, 2021, 09:49:22 AM

To do it right the first time for you, I would remove the complete unit and service it. Then you see how it goes together and service in future will be easier. Post a picture of it when off so we can see which one it is.

Whaley · November 06, 2021, 09:59:07 AM

Also I think my blow off valve may be leaking after it blows off for a short time so it may also need rebuilt

Ed Hackenbruch · November 06, 2021, 11:07:05 AM

Accidently hit my fast idle switch with my arm while driving down the freeway and suddenly had no throttle. Thought that my linkage had jammed or come apart, pulled over, left it running and went to the back to pull on the linkage by hand when i realized it was at fast idle. Turned off the switch and went on our way.

Dave5Cs · November 06, 2021, 03:40:06 PM

He should have an AD2 air dryer Long round thing hanging down in the front wheel well on the front wall bulkhead. The bottom has three keepers on it with the purge valve in the center. You take the bottom off and be careful with the wire attached it should be 24 volt and only activated at a certain temp when needed to have the heater come on. You replace the purge valve and there is a ball check valve also there and in the big nut at the side top air line going out of it that needs to be changed. There is a long screw that goes up the center that you will unscrew and the desiccant cartridge will come out which you will replace. the big O ring that helps hold and seal the bottom will come in the kit with the cartridge. NAPA will have all those things to rebuild it.

luvrbus · November 06, 2021, 04:20:52 PM

Quote from: Dave5Cs on November 06, 2021, 03:40:06 PM
He should have an AD2 air dryer Long round thing hanging down in the front wheel well on the front wall bulkhead. The bottom has three keepers on it with the purge valve in the center. You take the bottom off and be careful with the wire attached it should be 24 volt and only activated at a certain temp when needed to have the heater come on. You replace the purge valve and there is a ball check valve also there and in the big nut at the side top air line going out of it that needs to be changed. There is a long screw that goes up the center that you will unscrew and the desiccant cartridge will come out which you will replace. the big O ring that helps hold and seal the bottom will come in the kit with the cartridge. NAPA will have all those things to rebuild it.

LOL when you get the 3 keepers out then it has huge snap ring inside the housing to remove watch it because it can bite you and it hurts

chessie4905 · November 06, 2021, 05:04:45 PM

hopefully it is in decent condition and not all rusted up.