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Author Topic: Clutch assist cylinder  (Read 2782 times)
Fredward
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MC-5A #5401 8" roof raise 8V71 with MT647




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« on: October 30, 2007, 05:46:07 PM »

I'm working on the clutch on my MC-5. Pedal is way too hard to push. The linkage is free and works well when disconnected from the clutch shaft. I think maybe the cylinder isn't working? I have air at the cylinder and so I figure the next step is to take it off and see what makes it "tick". Do you know, can I just take it off the bus and pull it apart? I don't see any obvious way to take it apart.

I understand how it works, I think, from earlier posts, but now that I'm in there, I'm wondering what I will come across when I try taking it apart.

Fred
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Fred Thomson
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« Reply #1 on: October 30, 2007, 08:17:11 PM »

Well I answered my own question. I took it off and just popped it apart. Everything seems fine with it. Tested it with shop air and it works, so I just put it back together and tightened up the linkage where I could. That helped a little. I think maybe it needs an Allison 740 to really make it right.

Anyone know how to check how much clutch lining is remaining?
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Fred Thomson
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« Reply #2 on: October 31, 2007, 02:29:37 AM »

With the clutch pedal released, is the air cylinder perfectly horizontal.

Other things to check are lubrication of both ends of the clutch cross shaft plus any other grease points on the whole linkage because what may seem free under no load may be locking up under the loads imposed when the pedal is pushed down.
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JimW7
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« Reply #3 on: October 31, 2007, 05:26:05 AM »

Tonylee makes a good point. My 7 was getting hard to work, I adjusted clutch, to no avail. I removed linkage to check, and the bearings on the ends of the cross shaft were oblonged. It would seem to move freely with no load, but when you would step on the pedal with load, it would force the shaft into the slightly oblonged position in the bearings, and would force everything to work slightly crooked. I replaced bearings, now works fine. No harder to push down than my pickup.
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1970 MCI 7 serial # 8425
mikelutestanski
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« Reply #4 on: October 31, 2007, 06:49:11 AM »

Hello;        All good points.   ALSO:   Check the lube schedule (manual section 10 )  and the plate inside the doghouse door. That plate has a row of grease fittings...  In the manual section 10; figure 10-1 illustrates the master lube plate and fittings number 4 & 5 the bottom two are for the clutch cross shaft.. But if you grease then inspect where the fittings go to see if the grease went where it was needed.. If the fitting does not take grease then something is wrong..  (the fitting is blocked or the line is plugged etc etc)  visual inspection is necessary especially if the system is not working properly..
          Certainly a 740 is an option however it its the most expensive..   
     I replaced the manual with a 740 but for different reasons..   An additional 740 feature is the loss of approx. 1.5 mpg.
       Just some thoughts on maintenance.   hope it helps   
          happy busssin     Mike
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Mike Lutestanski   Dunnellon Florida
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Fredward
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« Reply #5 on: October 31, 2007, 08:01:42 PM »

I have more issues as it turns out. The clutch cross shaft bushings which are above the transmission appear to be very worn. So I need to remove the alternator and get in there to remove those bushings to see if they can be rebuilt or replaced. The shaft definitely moves laterally when it should only be twisting.

I also wonder if maybe the clutch lining is pretty worn.
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Fred Thomson
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« Reply #6 on: October 31, 2007, 11:02:52 PM »


 I think maybe it needs an Allison 740 to really make it right.




Sadly, Fred, an HT-740 won't fit in your MC-5A with the 8V71 - it's too long.

OTOH, a 6V92TA bolted to the 740 will work nicely. . . and if you bump the 92 up to 350 hp, wheeeeeeeee!!

All it takes is money. . .   Cheesy

FWIW & HTH. . .

 Wink
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RJ Long
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NCbob
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« Reply #7 on: November 01, 2007, 12:18:34 AM »

Fred, I had a similar discussion with Fred Hobe last winter and Fred told me that the only automatic which would fit in a '5' is the Allison 643. My understanding it that the 643 was used primarily in garbage trucks and many are still available but hunting one up might be a chore depending on where you live. Since I'm not far from ATL my guess is that I might find one there if I were interested.

Have you put a guage on the air pressure line to the clutch cylinder? It would be interesting to know if you're getting full system pressure to it or just 65#'s. I believe there's a  small regulator on the forward bulkhead in the drivers' side doghouse which might be adjusted for more pressure but that's a guess on my part. I won't fool with mine until we get to FL in another week or so.

We just missed a couple of those cylinders on the Eplace last week.

Bob
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Tony LEE
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« Reply #8 on: November 01, 2007, 03:26:01 AM »

"The clutch cross shaft bushings which are above the transmission appear to be very worn."

Yes, mine is on one end as well but just a little.  If you have the hatches in your floor still accessible, I would have thought you could do the job without removing the alternator.

The other cross shaft I was talking about is the one inside the clutch housing itself. That also has greasing points on each end.

Have you pulled the assist cylinder apart. It works much better with a clean bore and a bit of lubrication. Need to check whether the seals are leaking badly - get someone to push the clutch pedal with air up and see if there are significant leaks once the cyliner rod moves.
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Fredward
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« Reply #9 on: November 02, 2007, 07:04:08 PM »

Tony,
I found the grease zerks you mention and gave them a couple of shots. No my access hole is covered over and I could cut an opening but it might not be any harder than removing the alternator; its a belt drive one. But very valid points. The assist cylinder is horizontal when the clutch in engaged. I took in apart and cleaned it and lubed it. The connection to the operating rod from the front of the bus was loose so I replaced the bolt and tightened that up. The cylinder seems fine and does not leak.

Back together, the clutch seems easier to operate; I'll test drive it Saturday. Still planning to replace the shaft bushings.
Fred
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Fred Thomson
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« Reply #10 on: November 02, 2007, 07:05:20 PM »

Bob,
Thats an interesting point. I don't know how much pressure I have back there. Definitely worth checking because it takes a lot of force to move that clutch arm.
Fred
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Fred Thomson
Fredward
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« Reply #11 on: November 02, 2007, 07:08:32 PM »

Russ,
You should have never told me that. My neighbor has an Eagle 05 with a silver 6V92/740. The bus is just a shell and she is planning to just dump the bus maybe I should grab that engine tranny combo. Brian Diehl lives nearby; he knows all about engine upgrades! Are you sure it would fit? Isn't a 92 series taller than a 71? Its a tight fit back there in an MC5.
Fred
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Fred Thomson
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« Reply #12 on: November 02, 2007, 07:52:34 PM »

Fred, egads...I'd be the last one to try and bust your bubble...but if you'd compare the clearance differences between the 5's blowers and the later models you'd see that our fans are much lower...hence not enough clearance for the larger engines.

Let's face it m'friend, we wanted a 5, we're stuck with the shortcomings of a 5, they won't grow into a 6, 7, 8 or a 102...so ehhh? Let's enjoys them and live with 'em.  I love mine and wouldn't trade it for another bus.

And, for the record (Cliff) I wouldn't take a GM as a gift!  (inside joke guys...no offense meant.  Cliff and I
have this private war going..)

"I have found the perfect woman...who could ask for more?  She's deaf and dumb and oversexed and owns a liquor store"

Be happy with what you have...life could be worse!

Bob

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Brian Diehl
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« Reply #13 on: November 02, 2007, 08:10:47 PM »

Russ,
You should have never told me that. My neighbor has an Eagle 05 with a silver 6V92/740. The bus is just a shell and she is planning to just dump the bus maybe I should grab that engine tranny combo. Brian Diehl lives nearby; he knows all about engine upgrades! Are you sure it would fit? Isn't a 92 series taller than a 71? Its a tight fit back there in an MC5.
Fred

Sure, volunteering me for more engine work, eh!  Sure, just let me know when and I'll be there! :-)
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Tony LEE
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« Reply #14 on: November 03, 2007, 06:51:42 AM »

"might not be any harder than removing the alternator; its a belt drive one"

Possibly. I have removed the alternator on mine to replace a shorted stator - after removing the big air cleaner first - and the air cleaner brackets - and its a bit wearing on the arm and shoulder muscles that's for sure.

I left both hatches accessible and have been glad I did a couple of times, but not all layouts make it possible.

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RJ
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« Reply #15 on: November 03, 2007, 12:52:16 PM »

Fred -

Yeah, it fits. . .  Have seen it in both a 5A and three different 5Cs.  (5Cs were available new with two different OEM powertrains:  8V71/4-spd manual or 6V71/HT-740 automataics.)

BUT:

You have to fabricate a new mount for the turbo, the ones I've seen have been mounted on the driver's side of the engine.  As Bob mentioned, the squirrel cages are mounted lower in the 5s than in the later MCIs, so you have to work around that.  Not impossible, just takes some imagineering.

Plus, of course, you've got to upgrade the cooling system to handle the higher HP.  Not sure if the OEM 8V92 radiators for the MC-9s will fit a 5A, but that's what you should consider, as well as larger squirrel cages and a smaller diameter blower pulley.


NC Bob -

Fred Hobe's correct regarding the MT-643 being the only automatic transmission that will fit with the 8V71 engine.  It's a smaller unit than the 740, doesn't have quite the torque capability, but is still a good unit.  There's one model in the MT series tho that doesn't have a lock-up torque converter, so you'd want to avoid that one.  Sorry, I don't remember the actual model number, perhaps TomC might have the info in his references.  The MTs were also used a lot in skoolies, another source for used.

As I said before - all it takes is money!

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #16 on: November 03, 2007, 05:31:04 PM »

I think the most common Allison to use in MC-5 with 8V71 is the 644. A few years ago they were a common truck transmission.
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Fredward
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« Reply #17 on: November 07, 2007, 06:31:51 PM »

Replacing the tranny is something that I would not consider unless my clutch was shot. Which it may be nearing that point. Still trying to figure out how to measure the friction thickness. But I do know that the adjusting knob is about two turns from the end!

We've got a big locally owned garbage hauler here in the township that I will check with regarding MT 643 or 644. They do all their own mechanical work so they may have some rebuilds sitting on the shelf. Otherwise there is a place that advertises in MAK that sells rebuilds.

I suspect that the tranny swap is something we can handle here so the purchase price of the unit and related mounting parts would be the main expense. Is there a mounting kit to make that tranny fit an 871?
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Fred Thomson
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« Reply #18 on: November 08, 2007, 05:21:14 AM »

Fred: Beware of 600 series Allisons (653?) out of garbage trucks. They usually have the extra low gear which makes a bump on the side of the transmission that will rub on an airbag.
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Fredward
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« Reply #19 on: November 08, 2007, 10:05:11 AM »

Stan - thanks for that warning. Does that make it a five speed? Or just a four with granny gear? It looks to me like the MT644 is probably the thing to look for.

I assume I need to slide the engine/tranny out completely for this project. Just trying to figure out how big a space I need to clear in the shop before undertaking this adventure. I'm either going to replace the clutch or put an auto in. Either way the engine comes out, right? I guess the third option is to just sell it as is and buy a different bus.

Fred
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Fred Thomson
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« Reply #20 on: November 08, 2007, 05:45:45 PM »

Fred: They are a five speed with a very low gear that you would never use in a bus. I saw a MC-5 when it just arrived in a Las Vegas bus shop. The owner had the transmission installed in Los Angeles and he made it almost to Las Vegas before the air bag failed. When I talked to him, the mechanic had just given him the bad news and he was was pondering his next move.

I know a couple of MC-5s with 8V71 and 644 Allison. Once the transmission is mounted on the engine, I think the only other mods needed are the driveshaft length and the tranny cooler.  There are several choices on shifter mechanism, with the cheapest probably a Morse cable threaded through one of the old shifter rod or clutch rod holes to a mechanical shifter tower. If you go that route, consider putting the tower on the left side. It lets you turn the driver's seat around to be part of the living area.
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RJ
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« Reply #21 on: November 08, 2007, 06:52:27 PM »

Stan - thanks for that warning. Does that make it a five speed? Or just a four with granny gear? It looks to me like the MT644 is probably the thing to look for.

I assume I need to slide the engine/tranny out completely for this project. Just trying to figure out how big a space I need to clear in the shop before undertaking this adventure. I'm either going to replace the clutch or put an auto in. Either way the engine comes out, right? I guess the third option is to just sell it as is and buy a different bus.

Fred


Fred -

MT-644 is a four speed.  MT-653 is a five speed with the low granny first.  A tower shift unit out of an MC-8 or 9 will work fine, btw.

IIRC, you do not have to pull the engine to replace the clutch - only the transmission, dropping the driveshaft first.

BUT:

You should also pull the flywheel and have it and the pressure plate refinished for best results. 

Oh, and be sure to use NEW bolts, torqued in the proper sequence and to the correct specs, when reinstalling the flywheel.  Torque specs are in the DDA 8V71 shop manual.

FWIW & HTH. . .

 Wink
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RJ Long
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Fredward
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« Reply #22 on: November 09, 2007, 08:01:10 PM »

Russ,
That's good info. So if i put it up on the run up blocks; I could do the clutch pretty easily. Sounds kind of interesting. I'd really like an auto but driving the spicer hasn't been too bad but I grew up driving farm trucks so my perspective is a little warped.

It might be fun to pull the engine and put in an Allison. Lets see; how to spend my winter: skiing or pulling the Detroit. hmmmmmmm

Fred
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Fred Thomson
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« Reply #23 on: November 09, 2007, 08:35:28 PM »


Lets see; how to spend my winter: skiing or pulling the Detroit. hmmmmmmm



Fred -

That's a no-brainer.  Fix the clutch now before it REALLY gets cold, then ski the rest of the winter.

Wait till ski season's over to stuff in an Allison.  Who knows, maybe in the interim you'll find a good deal on a T-drive transit bus with a 6V92TA / HT-740 powertrain in it!

Have fun!!

FWIW & HTH. . .

 Wink
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RJ Long
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Fredward
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« Reply #24 on: November 10, 2007, 07:07:44 AM »

Probably a good plan. Of course if I lived in California It wouldn't matter when I tackled the project would it. ?
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Fred Thomson
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