Air Assist Clutch

[Fredward]

This MCI 5a has an air assist clutch according to the manual. I don't think the air assist is working. How should I trouble shoot it? The air line is connected to the cylinder. There is air at the cylinder as far as I can tell.  But the pedal is very hard to depress. How does it work? There is also a big adjusting knob on the clutch linkage that the manual does not mention.

[Melbo]

I have an 8 that I took in for service and asked the same question -- my clutch is hard to operate is this normal or is the air assist not working and when they got done servicing the coach they told me that yes the clutch was hard to operate but MUCH harder to operate without the air assist -- that is -- the air assist is working but the clutch is hard to operate.

Melbo

[Tony LEE]

Mine is an MC8 so "advice" applies to that model.
The big knob adjusts the clutch release clearance. To set it, pull the knob up until it engages the  the shaft. Holding it engaged, turn it clockwise until resistance is felt and then turn it ONE full turn anticlockwise and then drop the knob down to lock it.

The clutch assist WILL benefit from a strip down and clean of the piston and bore with a bit of oil to lubricate it on assembly. When I bought the bus there was no way that my old football knee would have stood up to the heavy clutch but after the clean up it is OK. Betty also drives it will no complaints - well, none about the clutch anyway. Steering wander is another thing despite it having been adjusted for slack as much as possible.
With the clutch pedal released, the cylinder and shaft should be exactly horizontal.
At pressures below 100psi the assist will be minimal but once the bus airs up fully, as you depress the clutch, nothing much happens until you get a third way down when you feel a sort of toggle effect and the foot pressure required is reduced for the rest of the pedal travel.

If the piston seals are leaking badly then the assist will be less.

There are lots of bearings and linkages between the pedal and the clutch release shaft and most of them need lubricating and checking for lost motion or seizing up. The clutch adjust knob will adjust for some of the lost motion.

There is a single sheet that gives the full layout and adjustment procedure. Not sure if it is in the files section of the MCI busnuts forum or not.

[Ncbob]

Fred, this is a subject I tried for a long time to get info about and it was solved when I pulled my engine for a clutch.

The cylinder is the same as the one for the OTR A/C compressor belt so if you still have that ...save the cylinder.

The air is to the cylinder all the time the bus is aired up.  When you depress the clutch pedal slightly that movement uncovers the port in the assist cylinder and the air helps depress the clutch.  Just that simple.  Releasing the clutch closes the port and you start over.  Look for a kinked or leaking air line to the cylinder.

Bob

[Fredward]

Thanks guys. I was wondering about how that knob was operated. It is not referenced in the manual from what I could find. I'm going to try changing that a little because the clutch has plenty of free play and barely releases when pressed to the floor. Regarding the cylinder, I've located it and there appears to be a splitter or check valve right ahead of it. (Then another line goes from there up to the skinner valves on the top of the engine.) But I don't feel the toggle effect so maybe I'll take it off and see if I can clean it up.

Bob, hows your clutch to operate?
Fred

[Tony LEE]

"I'm going to try changing that a little because the clutch has plenty of free play and barely releases when pressed to the floor"

Best not to fiddle with it a bit at a time. Follow the instructions exactly and if things still don't feel right, you may have to check the rest of the linkage.

That toggle effect may just be a characteristic of my bus and is perhaps not a good description of the feeling. The geometry is such that the assist is zero when the pedal is in the up position and maximum when the pedal is fully depressed.

When properly adjusted there is close to 2" free play at the pedal before the clutch release shaft starts to rotate and once the pedal is pressed to the floor, the clutch doesn't start to engage until the pedal is about half-way back up.

There are a few tees in that line because (I think) it also feeds all the engine bay auxiliary equipment including the belt tensioners and shutters and fast idle and engine stop valves.  No check valves close by that I know of.

Air up and then turn the engine off (or air up from the shop compressor) so you can hear any major oil leaks both when the pedal is up and fully down.

The cylinder is easy to remove (air down first) and the cylinder comes apart once one circlip is removed so cleaning it up inside is easy.

[Ncbob]

Sorry, Fred...didn't realize you'd asked me a question.  My clutch works just fine...my biggest problems is a bad leg. Luke was able to furnish new "o" ring seals and the sponge so I could rebuild mine.  One end has a snap ring that, once removed, allows you to slpit the cylinder in two pieces.  Rebuild is simple.

Hope this works out well for you, guy.

Bob