Clutch assist cylinder

[RJ]

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. . .

[Stan]

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.

[Fredward]

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?

[Stan]

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.

[Fredward]

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

[Stan]

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.

[RJ]

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. . .

[Fredward]

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

[RJ]

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. . .

[Fredward]

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