MCI-5B transmission options

[Larry B]

I have tried searching in the archives with not much success.I am a new member and I am sure this question has been asked before but in case not here goes. I have an mci-5b with a four speed manual. Most of the time at least one more gear would be nice especially between 3rd and 4th. Are there any other transmission that will fit in the space left after an 8v71 has claimed it share? Has anyone on this site succeeded with a different trans. install in a 5b? Is the trans. to gear train housing bolt pattern the same on all 8v71's  ?  If a trans is bolted to a 6v92will it fit a 8v71? ( I know where a couple of seven speeds are on 6v92--reasonable)Beside asking the experience of the people here how does one find all this out??  bolt patterns--- clutch options--gear ratios--physical size measurements--etc..etc.    Larry

[bevans6]

The engine bay on the 5B is short.  If you have a 6V engine, an Allison 740 trans will fit and was a stock option with the 6V71.  A 6V92 is the same size as the 6V71, so it is a swap option.  An Allison 640 trans will fit behind (in front of, technically) an 8V71 but the trans is not rated for the torque of the engine - in practice they seem to last just fine.  A 654CR trans will fit with a 6V92, and that gives you a nice automatic 5 speed option.  I don't know of any manual trans options that will fit with the 8V71 that have more gears, but there probably is something out there... 

Brian

[luvrbus]

The seven speed is little over 31 inches long if that helps the 644 is 30.4 inches long and are a close fit on a 5 with a 8v71 seems like a 7 speed would fit you will find different gearing on the 7 speeds find one that suits you and they bolt up to a SAE 1 bellhousing which you have now

[TomC]

If you keep your 8V-71 a non turbo with 65 injectors, that will give you 300hp and 800lb/ft torque.  Eaton makes a 6spd overdrive transmission that is fully synchronized and only 25.6" long with 860lb/ft torque rating.  The gearing is 7.05, 4.13, 2.52, 1.59, 1.00, .78.  If you rev to 2100, the first to second, and second to third gear drop will be to 1250rpm.  The third to fourth, fourth to fifth will drop the engine to 1325rpm.  Fifth direct to sixth overdrive will drop to 1640rpm. 

If it were me, I'd not fool with any of this, but pull the 8V-71N and 4spd manual out and install a 6V-92TA with an Allison HT740 4spd automatic (the HT754CR 5spd is nice, but not as strong).  Then you'd have a 350hp and 950lb/ft torque engine that would truly make a hot rod out of your 5.  Good Luck, TomC

[bevans6]

What's the model number on that Eaton six speed, Tom?  The Spicer 8844 four speed is 28 3/8" from the SAE flange mount to the face of the driveshaft flange.

Edit - I think it's the FS-8306A.  It seems to have an SAE #2 flange, and I think the Spicer is SAE#1.

Brian

[artvonne]

 I have read the early MC5's used a 5 speed, but thats all I know. I have never been able to determine what gearbox it was, if it would fit later models or if something else would fit. If the clutch linkage is built into the gearbox, as I understood Brian to explain, its likely nothing we want to mess with. My 1975 8V71 4 speed MC5B with highway gears (rolls 55 plus in 3rd, 80 plus in high), made it up my very steep driveway without even slowing down, spitting rocks all the way. That was with a full entertainer interior made of 3/4 particle board covered in formica (very heavy). I doubt anyone will ever find a public road with a grade anywhere near that steep (22.5% grade). Probably best to just leave well enough alone.

 An auto will knock you down into the 4 to 7 MPG range. The standard 4 speed with highway gears is said to be able to do better than 10 MPG on level road if you can keep the speed down.  

 Just an FYI. at 5 mpg, you will consume 10,000 gallons of fuel in 50K miles. At 10 mpg you would only consume 5,000 gallons. At $4 gallon, that is a difference of $20K over 50K miles. Even 2.5 mpg improvement could save $10K over that distance. Seems not to matter to many people here, but I haven't found any money or fuel I like burning needlessly yet.

[wg4t50]

I do not know the MCI 5 Series, however the MCI 7 I had, used a SAE 1 Bell Housing and a SAE 2 flywheel, that makes for an interesting change over to the RTO910.
Just saying to make sure where you are with that setup, what triggered the thought was the mention of the Spicer 8844, which was in the MCI 7.
It is easy to ID the bell housing, if the housing has a slight protrusion for the starter nose, it is the SAE 1 with the SAE 2 flywheel.  Been there, Done that, etc etc...

[Aussiecoach]

Hi All great information

TomC do you know how that eaton 6sp compares in ratios to the 6sp spicer constant mesh 1463C? Would the eaton handle the 350hp from a 6V92ta?

Also I'd like to find if there is a seven speed overdrive box available with similar ratios and strength to the 1463C, anyone know


Cheerz
Glen

[Larry B]

Thank-you for all the great info. I need to let the info sink in before I do anything drastic.  If I had of been aware of this this site BEFORE I spent so much money on rebuilding the 8V71, you are right Tom I would not have messed with it. I can see now there are so many better combos. I have to get some miles out of 8v71 before changing engines. I am going to study the replies a bit, I might have some more guestions.  My trans. is not an 8844, it is an 8245 ( I will check that # at shop tomorrow) Any good or bad thoughts on that trans??     Thanks Larry

[TomC]

Glen-if I remember right, the Spicer 1463C is a twin countershaft non synchroed transmission that I believe is in the same transmission case as the 7spd version.  Both rated at 1400lb/ft torque.  The Eaton 6spd overdrive synchronized transmission is only rated to 860lb/ft-so your 350hp 6V-92TA would be a bit much for it.  Good Luck, TomC

[Aussiecoach]

Hi TomC-now you have my interest if the 6 and 7 speed are wrapped in the same wrapper. Is the 7speed you speeak of an Overdrive box and would you happen to know the model no and ratios?

I've tried researching this  a few times and never get too far as I don't think they were the most popular boxes around

thanx
Glen

[artvonne]

  Something else I read a year or so back. Not only is the MC5 short, with the motor offset the gearbox comes close to the left side engine cradle. Many of the other gearboxes are physically larger in breadth and may not clear the cradle. So if we arent screwed one way, were screwed the other.

  For me, not being into heavy HP and speed and seeing how much fuel I can burn, I would consider a 6V71n and try to get a big box of gears ahead of it. Yes, I realize the 6V71 is a dog, but when fuel hits $6 gal it might pay for itself.

[wg4t50]

Paul, I agree, the 6V-71 in good tune, with a manual gear box, while not fast nor quick, it will last as long as you will want it.  I have played the big HP games with the 8V, 12V-71 and the 8V-92. the 71 series is hard to beat in the long run, besides you will ot be fighting the cooling issues the gents with the bigger HP are facing, not the fuel burn nor the repair costs in general.
I now run a Cummins ISM500 HP, love it too, still have warm fuzzies for the  71 series.
Years ago, I was told by an old shop foreman the differences between the 71 and 92 series,
Rebuild the 8V-71 about $3,500.00 & run about 300 K miles
Rebuild the 8V-92 about $5,000.00 & run about 200 K miles, now he asks what is the best engine ?  Sort of makes it simple don't it.
Cheers

[Boise Belle]

My 1966 MCI 5A has a:
Allison Automatic Model #MTB 644  Ser #24200039737        Manf-5/3/85
   4 sp    55,000GVW      Heavy Duty Torque converter    2100 Valve Body

Been running it since 1988.  This trans was designed for a dump truck.  I think the only thing that had to be modified was the drive shaft.

This transmission has lock up in 3rd and 4th only.  I installed a bypass valve, which I got info off this site, and now it has lock up in all four gears.  Nice for Idaho mountains.

Only problem, with this configuration, when all the air is let out of the air bags, the drive shaft touches the axle.  So it needs a spacer added to the air rail bumpers.

good luck

[RJ]

Larry -

Thousands of buses ran with this powertrain in revenue service all over the North American continent, driven by hired hands who didn't care how they treated the equipment. In and out of terminals, in city traffic and on the highway, running across the flat midlands and crawling up and down Rocky Top, this simple powertrain managed to maintain schedules day in and day out for a million miles or more.

You mentioned that you've spent a few bucks rebuilding your 8V71N, which will now probably outlast you.  Unless you want an automatic for mindless stab 'n steer driving ease, if it ain't broke, don't fix it, IMHO.

FWIW & HTH. . .