need serious advice on air assist clutch MC-5C

bevans6 · July 23, 2009, 12:41:57 PM

I have to figure out the air assist clutch. Since it's raining out, I though I would start with asking advice and otherwise doing research.

My coach does have air assist. It does assist something, but it ain't helping my knee... I think that the first thing to do is pull out the cylinder, clean it, look at it, try to rebuild it, test it. Where is it fed from? should it get full pressure or is it reduced by a pressure limiting valve? As anyone ever tried to modify the MCI system for greater assist? How much pressure should it take to hold the clutch in anyway? I estimate mine is well north of 100 lbs push pressure on the pedal. What is considered normal?

Brian

NJT 5573 · July 23, 2009, 01:38:16 PM

Brian,

I'm not familiar with your bus, but my old Eagle had an assist on it.

I would check to see that the air is not turned off to the slave cylinder first. They often develope leaks and will dump the bus air quickly if not repaired. So, make sure you have air then you can check the rest of it out.

Normally these units will drop the clutch with almost no effort when they are working properly. They are not overly expensive to rebuild and worth the price if that turns out to be the issue. To check for air to the unit, just take a wrench and crack the line in.

Tony LEE · July 23, 2009, 05:20:58 PM

"I think that the first thing to do is pull out the cylinder, clean it, look at it, try to rebuild it, test it. "

That's all it took to convert mine from clutch desist (likely to revisit a football knee long fixed but getting weaker at every gear change) to clutch assist (where Betty can drive it no problems). Lubricate when reassembling it. Air supply (I think) comes off the same supply as the radiator shutters and belt tensioners so no separate pressure regulation. (Mine is and MC8)

bevans6 · July 25, 2009, 04:50:36 AM

I pulled the air assist cylinder yesterday afternoon, cleaned it, put it back and actually not much difference. The rod ends were almost completely siezed in the clevis;, but a quick dive into the big bucket O'used rod ends found two that had lived their life in the suspension of a race car and were completely happy to start a new life in the bottom of a bus! That solved, cleaned it up, lubed it up, put it back. As noted, a minor improvement at best. It's fed from a manifold on the front of the drivers side engine bay, the same manifold that feeds the low air switch it seems, so I presume it's fed from the dry tank. I'm going to relub it and ponder next steps. My next idea is to replace the air cylinder with a larger diameter one to get more physical boost, but only after I check the adjustment of the linkage. It looked like the clyinder was in line with the linkage the way it's supposed to be but I didn't actually measure with a caliper or anything.

Brian

Sojourner · July 25, 2009, 06:55:21 AM

Quote from: bevans6 on July 25, 2009, 04:50:36 AM
I pulled the air assist cylinder yesterday afternoon, cleaned it, put it back and actually not much difference. The rod ends were almost completely siezed in the clevis;, but a quick dive into the big bucket O'used rod ends found two that had lived their life in the suspension of a race car and were completely happy to start a new life in the bottom of a bus! That solved, cleaned it up, lubed it up, put it back. As noted, a minor improvement at best. It's fed from a manifold on the front of the drivers side engine bay, the same manifold that feeds the low air switch it seems, so I presume it's fed from the dry tank. I'm going to relub it and ponder next steps. My next idea is to replace the air cylinder with a larger diameter one to get more physical boost, but only after I check the adjustment of the linkage. It looked like the clyinder was in line with the linkage the way it's supposed to be but I didn't actually measure with a caliper or anything.

Brian

Here a 2-parts photo of MCI-8 clutch adjusting instruction but #8 instruction plate is too blur to read. Someone may the OEM manual to read of what it said???

About changing air cylinder for a larger one....you should not need to because the OEM version is designed to give you the needed assistants. Example if this piston's surface displacement is 1 square inch with 120 psi will equal 120 pound of force.

Follow the instructions. Make sure the #4 point to the cylinder's mounting point is in a straight line....never below it or you will be counteracting with the cylinder's force.

Caution about the adjusting handle...you must lift it before turning to adjust.

Hopeful someone here have the #8 instruction plate information to post.

Sojourner · July 25, 2009, 06:56:35 AM

The other half of the photo copy

bevans6 · July 25, 2009, 10:52:42 AM

Thank you very much for the scans, they help a lot. Between them and what I have in my manual, I think I can do the adjustments.

Brian

JohnEd · July 25, 2009, 08:34:57 PM

Brian,

I have pondered this due to my having a very bad left knee: A switch that would control a electric air valve to the clutch-disengage cylinder. Second elect valve to dump air thru a restrictive,adj orofice, air valve to allow dead throttle start. "Clutch on a switch" for those really bad days. Not the lite days.

Does that sound doable or overly complicated to you? Must be braking a rule here someplace.

John

JimW7 · July 26, 2009, 09:36:51 AM

Brian,
I had a stiff clutch pedal on my 7. I went through the linkage, found the bearings on top of the the transmission case, where the linkage hinges were stiff, one almost seized. I replaced them, adjusted to the book, greased, and things were much easier. The original cylinder still works great, and takes little effort to push in. How worn is your clutch? Jim

bevans6 · July 27, 2009, 10:25:46 AM

The plate on my bus is worn down almost smooth, but it basically says how to adjust clutch freeplay. You lift up the adjusting handle (diagram of big round handle), tighten it until you feel resistance, and undo it one full turn, and push the handle down again to lock. That apparently sets up correct free play.

Brian

bevans6 · July 27, 2009, 01:45:17 PM

Well, I've reduced the clutch pedal pressure by about 40%, which along with realizing my chair is set too low (it's at max height, but it's a low chair base) will get me where I need to be. What I did that made a difference:

Took out and cleaned the air assist cylinder. I don't think there was a problem to speak of with the actual cylinder, but it was sticky and hard to move by hand. When I cleaned it and put some oil on it, it wasn't.

Replace the rod ends that the cylinder mounts between. 1/2" thread, 1/2" bore standard rod ends were completely siezed, the balls in their races, the balls on the clevis pins and the housings between the clevis sides. They retained just enough movement to allow the clutch to work and could not have been contributing to a happy experience.

Adjust the angle of the air cylinder. Not that you can actually see the angle very well (you could if you could put your head inside of the bell housing I suppose) but I adjusted the nut to raise the actuating end of the air cylinder about 1/4". It was too low before, so air assist didn't start when it should, and probably I was pushing against the air assist when at the very start of the travel.

Adjusted the free play. My clutch was engaging at the very top of the pedal travel. Not enough free play. Cranking that big handle all the way in, then backing it out exactly one turn made a big difference. it now engages roughly half way up, and is disengaged fully at the floor. Seems about the way it should be to me. This puts the clutch engagement point in a place where the air assist cylinder is actually helping a bit, so feathering is easier to do.

To do later - put the clutch assembly back into the regular maintenance routine (supposed to adjust the freeplay every 5000 miles) and actually lube all the joints next time I am under the back with a grease gun...

Thought this summary of what I did might help someone using the search tool months or years from now.

Cheers, Brian

Sojourner · July 27, 2009, 07:59:07 PM

Quote from: bevans6 on July 27, 2009, 10:25:46 AM
The plate on my bus is worn down almost smooth, but it basically says how to adjust clutch freeplay. You lift up the adjusting handle (diagram of big round handle), tighten it until you feel resistance, and undo it one full turn, and push the handle down again to lock. That apparently sets up correct free play.

Brian

Thank you for that plate's information..."You lift up the adjusting handle (diagram of big round handle), tighten it until you feel resistance, and undo it one full turn, and push the handle down again to lock."

Good that it helped.

Thank you for the follow up report.

Sojourn for Christ, Gerald