1 Problem after another with trany swap

jmblake · February 17, 2011, 10:35:53 AM

Guys I'am having problems with my transmission swap, The old flywheel was 17.25" diameter and the new one on the automatic is 19.75" diameter and the starter is not going to work unless someone makes a ofset nose for one. As far as I can tell when the previouse owner had the engine exchange done I got the wrong bellhousing, The way this one is made the starter is above the motor mount and according to the book the starter is below the motor mount. The book says I should have a type 678 housing but I don't know what I got, My motor mounts match what a 2 axle coach would have. If anyone has any ideas on a different starter or do you think I will have to change the bell housing and if so any ideas where to find one. I already called nimco and they didn't have any. Thanks Jason

bevans6 · February 17, 2011, 10:59:35 AM

Here is a picture of my engine showing the motor mounts, kind of. the starter motor is tucked in behind the cradle, and the nose is just below the place where the motor mount bolts onto the bell housing. You should have an SAE 1 bell housing as stock, I am pretty sure, and the stock flywheel is 17.25" in diameter, or thereabouts, depends if you include the ring gear. If your automatic flywheel is 19.75" it's a lot bigger than stock. You will need to measure the bolt circle on your transmission where it bolts to the bell housing, if it is 20 7/8" bolt hole to bolt hole it is an SAE 1, if it is 23 3/8" it is SAE 1/2, if it is 26 3/4" it is SAE 0. Maybe your transmission is the wrong bell housing size to fit in your bus?

Now I had always been told that you could just bolt an auto tranny of the correct size directly to the stock bell housing, SAE 1, on the MCI, which is what makes me think you may have a tranny with a larger bellhousing. since the motor mounts bolt to the bell housing and fit pretty tight inside the cradle, if you go to a larger bell housing the motor mounts may not just bolt up and fit, they may be too wide.

Brian

kyle4501 · February 17, 2011, 11:05:47 AM

My experience is quite limited here, but I'll share what little I know (that shouldn't take too long.)

My 8V71 has the ~17" dia. ring gear.
My 8V92 has the ~20" dia.
Both bellhousings have the ~20 7/8" bolt circle.

Did your new transmission come off of a 92 series motor?
Are you trying to put it behind a 71 series motor? - maybe you need a different starter ring gear? ? ? Is it an automatic transmission? If so, you may also need to check the shift points as the torque curve of your motor may not work well with the current shift points. . . .

Seems like you may need to consult with an Allison service center - they should be able to identify what you need. . .

Good luck!
And, please keep us posted to your successful solution.

luvrbus · February 17, 2011, 11:10:42 AM

Jason, you have it right the starter for a 740 is towards the very bottom I can't give the number for a MCI bellhousing but for a Eagle you need 23510635 your bellhousing will work with the 5 and 600 series Allison but not the 740 depending on the air compressor you could have a 621 or in that area ? is the compressor on a 75 degree tilt like most MCI's tons of different bell housings for the DD

good luck

TedsBUSted · February 17, 2011, 11:22:24 AM

Quote from: jmblake on February 17, 2011, 10:35:53 AM
. . .The old flywheel was 17.25" diameter and the new one on the automatic is 19.75" diameter and the starter is not going to work unless someone makes a ofset nose for one. . . .

Hello Jmblake,
As to this possible solution, in my somewhat extensive heavy engine experience, I've never seen a heavy starter motor that does not center the drive in the housing's pilot hole, although many will "clock" or index, any change is still based on the same center-line. With the existing combination of parts, it sounds like your starter motor would need to move approx 1.25" outboard. Sorry to say, I don't know of any offset adapter or drive-end change that would accomplish this.

Good Day

Tom Y · February 17, 2011, 01:04:03 PM

Kyle, The difference with yours is the starter position. The smaller is a #2 starter position on a #1 housing. The other a #1 starter position on a # 1 housing.

Tom Y · February 17, 2011, 01:11:04 PM

Jason, You have the same as Kyle. The starter position smaller one a #2 larger a #1. ( assuming both have the same bolt up size, #1) You will need a # 1 position for the auto ( assuming it is a 700 series Allison, ) Ihave been looking into this the last couple weeks. What you need should be an easy find. Tom Y

kyle4501 · February 17, 2011, 01:27:17 PM

For what it is worth. . . .
Both of my transmissions are TH754CRs
The ~17" one was behind a 8V71.
The ~20" one was behind a 8V92 in a Prevost.

The good part is that my 8V92 matches up with the Prevost transmission, so that part should be straight forward.

The difficult part is getting the 'bus port' ready for the project.

luvrbus · February 17, 2011, 01:47:52 PM

Sell him the torque converter and starter ring from the old 754 with the 71 series engine Kyle not the way I would do but it will work just that is a weak converter for a bus

good luck

Tom Y · February 17, 2011, 03:09:27 PM

Kyle, Thats intresting. Someone from Allison told me within the last week that they did not use a smaller converter on the 700 series. Thats why it free advice. Tom Y

luvrbus · February 17, 2011, 04:28:35 PM

They haven't used those in years Tom but you still see a few from time to time wonder if Kyle has a wet style

good luck

kyle4501 · February 17, 2011, 04:46:56 PM

What is a wet style?

It looks like it is the front half of the converter. If I recall correctly, you have to unbolt it & remove to gain access to the nut/ bolt to remove the rest of the converter.

jmblake · February 17, 2011, 07:32:47 PM

Well today after on the phone for about a hour I don't know a hole lote more than I did this morning, First the starter ring on the transmission is 20.75" outside diameter and the # stamped on it matches what the MCI manual says it should be. And from the picture in the manual the starter should be below the mounts and mine is above. I have a call into Penndiesel witch is our local Detroit/Allison dealer but the tech guy hasn't called me back yet. MCI tech wasn't any help they said to call detroit/allison. I found a bellhousing at a semi local salvage yard but I am not sure it is the right one till I can get there and see it in person. So thats about it for today. Thanks everbody Jason

jmblake · February 18, 2011, 08:02:40 PM

Update
Well today after several phone calls and Penndiesel telling me I had a rare bellhousing hardly ever used, I found one at a truck salvage yard about a hour away. So i got my mechanic and we went up there and it was still atatched to the engine and buried at the far end inside a old school bus full of old detroit parts. after inspecting and the parts man calling another salvage yard about another hour away in ohio we decided to go there and see what they had and wala they had about a dozen all stacked up nice and neet in a old school bus. So we picked out the one that matched up the best with our bolt patterns and mounting points and loaded it up, then I thought I would ask if they had the flang for the drive shaft that goes on the allison. He took us over to the allison schoolbus and wala there was 2 of them, so today was a little better day, at least we got some parts, now to start changing all the stuff mounted to the bell housing. Just another little bump in the road. Jason

Chopper Scott · February 18, 2011, 08:10:52 PM

Congrats!!! One has to remember how many things the ole Detroits got hooked to and the combinations that were involved. Running them backwards, forwards, in busses, trucks, tanks, industrial , marine. They may be outdated but I doubt there will be another like the 2 strokers!!!