Allison MT653 Torque Converter Questions

[K-Unit]

Hello all! (First post so sorry if I am breaking and conventions!)

I have a 1977 Chevy C65 tandem. Not a bus, but I have some questions about the Allison MT653 (Same as the 643 but with the manually selected low gear). The truck is a gasser (427 tall deck) and I can't find much information on this combination online. I've seen that some people here have experience with these transmissions, so here it goes:

I have the transmission, but the torque converter is a TC370 and came out from behind a diesel. The TC370 stall torque ratio is 2.43:1, and from what I have read there was a TC350 that had a ratio of 3.09:1. So here are my questions:

1) I would assume that the gasser would prefer to have the higher ratio converter, or will the TC370 work fine?

2) If the TC350 is necessary, I have been unable to locate one. However, I found the part number for the pump assembly (PN: 2301859 for the TC350 and I can find those for a few hundred dollars on eBay. Since these converters are bolted together, can I just swap out the pump assembly to change the ratio? Was the pump assembly the only difference between the different ratios?

I do plan on hauling with it every so often to move some heavy equipment around, so that too leads me to think the higher ratio will be better. Information on these parts is severely limited online and is a couple decades before my time so any help is appreciated!

[cadillackid]

torque converter just slides into the transmission, its not bolted to the pump... the converter drives the pump via the ears on the neck of the converter..


if you have a transmission with an installed converter and are unable to remove the converter from the transmission if be wary that a bearing seized or somnething.. it should just slide off... its heavy at like 50 lbs on the 643/653 and will likely drop some fluid.. the torque converter gets bolted to the flex plate on the engine after the transmission is installed..


you'll install the torque converter in the transmission.. feeling that it seats all the way in, bolt the converter and transmission up to the bell then you install the flywheel to converter bolts (my 643 had studs so nuts get installed) after you bolt it up..


as for the ratio.. the difference is that a gasoline engine likes to rev higher to make better power esp starting out wit ha heavy load.. thus the lower stall ratio.. result is in a higher revving engine..


the other piece of this are your shfitpoints on the transmission. if you are using a 653 out of a diesel truck it likely had a max RPM of 2500-2700.. ths means you are always going to shift at that RPM range even when your throttle is buried to the floor..


your 427 tall deck likely is set to have a max RPM someplace around 4000 or a little over.. so you would want your buried to the floor shift RPM to be someplace in the high 3000s.. 3800 maybe? maybe even 4000.. im not sure what allison used for those..



while you can get some shift point adjustment with the trim wheels inside the pan, im not sure if you need different valve body springs or not to get that much difference in shifting.



in the world of ratio.. the lower the number the higher the ratio.., the bigger the number the lower the ratio.. lower ratios (higher numbers) give you more torque in the form of allowing the engine to reach further into its power band and also how the stator blades are set inside the converter to get more torque multiplication...



with you having the granny gear available you might be able to get away with the taller converter but the TC350 is the better choice if hauling big loads.. and the transmission being adjusted for the correct shift schedule.

[K-Unit]

Thanks for the response!

I believe that you are referencing the transmission oil pump, but what I was talking about was the pump that is inside the torque converter (I believe it's also called the impeller). I have attached a link to an exploded view that I found and it's referenced as 277A. Down in the description there are 3 different part numbers for the impeller, one for each the 350, 360, and 370. That was what I meant by unbolting the torque converter to change.

And yes, the shift points are going to have to be adjusted. I will probably have to wait until I get it installed to see if I can make what I have work.

And the granny gear, from my understanding, is not part of the normal automatic shifting. I believe that you have to come to a stop, shift into it, drive, stop again, and shift out of it. Although, you may be able to shift out of it while driving? I'm not sure...

https://www.google.com/url?sa=t&sour...bIdnaLzm0MCDop

[sportyrick]

I just threw away my 640 Allison with all the parts you would need (yes behind a 427 tall deck), I though who would want this old junk it's 50 years old............but I still have the 427 if you need it.

[K-Unit]

Thanks for the response!

I believe that you are referencing the transmission oil pump, but what I was talking about was the pump that is inside the torque converter (I believe it's also called the impeller). I found an exploded view of the converter assembly. Down in the description there are 3 different part numbers for the impeller, one for each the 350, 360, and 370. That was what I meant by unbolting the torque converter to change.

And yes, the shift points are going to have to be adjusted. I will probably have to wait until I get it installed to see if I can make what I have work.

And the granny gear, from my understanding, is not part of the normal automatic shifting. I believe that you have to come to a stop, shift into it, drive, stop again, and shift out of it. Although, you may be able to shift out of it while driving? I'm not sure...

[K-Unit]

Originally Posted by sportyrick

I just threw away my 640 Allison with all the parts you would need (yes behind a 427 tall deck), I though who would want this old junk it's 50 years old............but I still have the 427 if you need it.

Breaks my heart

The 427 I have runs good. Any chance you'd still have the flexplate? The ones I've go have a smaller hole pattern for the converter studs, so I'd assume they made a 168t with a larger hole pattern for that application. Otherwise I was going to put some new holes in one

[cadillackid]

Be careful with just drilling a flexplate. When I went from 500 series to 643 on my engine the flexplate offset was different. My original flexplate was convex and the new one flat.. I habe no knowledge of your build and what your previous setup was but offset is something to measure to see what flexplate you’ll need and also the pilot.

Sounds like you are referring to the stator inside the converter .. I’ve never swapped one. Every converter I’ve worked on is welded / brazed so I don’t disassemble them

[nikitis]

Originally Posted by cadillackid

Be careful with just drilling a flexplate. When I went from 500 series to 643 on my engine the flexplate offset was different. My original flexplate was convex and the new one flat.. I habe no knowledge of your build and what your previous setup was but offset is something to measure to see what flexplate you’ll need and also the pilot.

Sounds like you are referring to the stator inside the converter .. I’ve never swapped one. Every converter I’ve worked on is welded / brazed so I don’t disassemble them

I've heard with flex plates you can drill into them as long as you make four holes. A.k.a. mirroring the hole you drilled + 3. If you drill one hole, you have to drill 3 more in the same spot in a circle around it, and it's gotta line up perfectly. No hand drilling so it balances out. It's an expensive mistake if you mess up.

I've watched Derick from Vice Grip Garage do it once cause he didn't have the right plate and it worked out fine for him, but he also precision lined up the holes.

[K-Unit]

Originally Posted by nikitis

I've heard with flex plates you can drill into them as long as you make four holes. A.k.a. mirroring the hole you drilled + 3. If you drill one hole, you have to drill 3 more in the same spot in a circle around it, and it's gotta line up perfectly. No hand drilling so it balances out. It's an expensive mistake if you mess up.

I've watched Derick from Vice Grip Garage do it once cause he didn't have the right plate and it worked out fine for him, but he also precision lined up the holes.

Yea that was the plan, I was going to center it on the mill and put the holes in with the help of a rotary table

[plumbersnitemare]

K unit you need to call Dartco they are aftermarket and factory parts for all allison trans 812 378 9599 or 800 371 7957 they can get you correct flexplate and for what it is worth I would try the convertor you have and just take off in optional low gear and if needed for heavy loads shift manually

[s2mikon]

You will probably need a different governor to bring up your shift speeds. Also a vacuum modulator. You can try the converter and it may just work. Don't shift into or out of 1st / granny gear while moving. Its really hard on drive shafts.

[Mekanic]

B&M transmissions may still make the kit they did years ago.it is a governer weight and spring kit. It allowed one to adjust the full throttle shift point in GM transmissions. I can’t find the part number right now.

[K-Unit]

Originally Posted by plumbersnitemare

K unit you need to call Dartco they are aftermarket and factory parts for all allison trans 812 378 9599 or 800 371 7957 they can get you correct flexplate and for what it is worth I would try the convertor you have and just take off in optional low gear and if needed for heavy loads shift manually

Thanks for the info! I'll check into it

[K-Unit]

Originally Posted by s2mikon

You will probably need a different governor to bring up your shift speeds. Also a vacuum modulator. You can try the converter and it may just work. Don't shift into or out of 1st / granny gear while moving. Its really hard on drive shafts.

Yes, I will definitely need the modulator and governor/springs. Any ideas on where I could find them?

[K-Unit]

Originally Posted by Mekanic

B&M transmissions may still make the kit they did years ago.it is a governer weight and spring kit. It allowed one to adjust the full throttle shift point in GM transmissions. I can’t find the part number right now.

Was this a kit for the mt653 or just GM transmissions in general?

[K-Unit]

It also appears from my research that the 545/640/650s all used many of the same parts? (Governor, modulator, etc.) Is anyone able to confirm this?

[s2mikon]

When I rebuilt my mt 643r I used Dartco for all my parts. Top of the line quality. They may have the governor you need.

[cadillackid]

Originally Posted by K-Unit

It also appears from my research that the 545/640/650s all used many of the same parts? (Governor, modulator, etc.) Is anyone able to confirm this?

the governer, speedo driven gear (or sensor).. drive gear (or tone ring), modulator, neutral safety, reverse light switches are the same..

[K-Unit]

Ok, so after referencing the part diagram and manual, it seems like these are the parts I will need to get the transmission working with the 427:

-Governor 3600-3800 rpm: 6882736 (I.D. No. 739)

-Hold regulator springs 3800/4000 calibration: 6836976 (White/Yellow)
(I may have the regulator springs due to concurrent use with 2600, 3000, and 3200 MT653 calibrations and 2600, and 3000 MT643 calibrations)

-Torque converter high ratio pump: 23018596 (TC350) (I might try the lower ratio TC370 first)

-Modulator (Vacuum): 29501199 (Small Can)

The manual also states that if all of the shift points are off by about the same RPM, then the modulator spring force should be adjusted. I can't find much information on the different modulator springs, but the service manual does have part numbers for different modulator spring and valve combinations and their associated pressures. But like I said, I can't find any information on which ones to use in what application? I've attached a picture of the service manual if anyone can weigh in on this.

[K-Unit]

Also, if anyone is interested, here is the link to a PDF of the SM1317EN service manual for the MT 640 and 650, and the MT(B) 643 and 653 models.

https://wanderlounge.net/wp-content/...317-199907.pdf