M35A3 Allison 653 - has anyone done it?

[Sgt Jiggins]

M35A3 Allison 643 - has anyone done it?

Hello,

I've arrived at a crossroads with my M35A3: after spending time the past few weeks, and with several quality folks throwing their shoulder behind the effort, it's turned out that the front pump I need for the Allison 1545 in my truck is apparently made of unobtanium.

A huge thank you to those you have pitched in thus far. Some valuable things have been learned (which I shared - search for 1545 retrans)

So now, I'm faced with using either a 545 or a 643. They both have their plusses an minuses:

545: pro: bolt up. Cons: no lockup and uncertain on gearing of 4th.
643: granny 1st, 5 speed, with (some?) lockups, and a beefier transmission. Cons: physically larger and potential bellhousing/tc housing issues ala length/overall fitment.

So.

Has anybody actually done the swapout of a 1545 to a 643? Not thought about it - but actually DONE it? If you have approached this and wound up not doing it, why not?

Regards,
SJ/JD

 

[snowtrac nome]

I don't think It could be done with out making the frame wider. the down side of a 540 is you are still going to be at about max torque of what that trans was designed to take .

 

[Sgt Jiggins]

I've heard tales of folks machining down the mount tabs on the transmission to get it to fit. So you're probably onto something there. I really don't know on the width yet - I need to get under there and take some measurements. I'm hoping somebody has some insight to share.

I do know I want to stick with the AT series to keep it mechanical as opposed to the newer electronic options. I really don't think I need that kinda complication in my life.

But who knows... maybe I do??

 

[snowtrac nome]

I manage a fleet of fuel trucks most of which have Allison 3000's in them I have a 3000 in my lmtv to the reality is I have had 0 problems with any of them except one tha fried a controller but that truck had been pleauged with other solid state problems ever since we had a battery arc.

 

[Sgt Jiggins]

I'm going to have to figure out something.

TIL 2 things though: there will be a freshly rebuild 1545 (minus the front pump) coming up for sale shortly. Mine. And secondly, there is a different, also professionally remanned 1545 for sale out there, now. Intact. For a price. Which to me is steep enough that it warrants other options. The tranny alone would be 3x what I paid for the M35A3 and M105A2 together. So, yea... not happening.

 

[rustystud]

The Allison MT640/650 series will fit in a Deuce just fine. The width of the Deuce frame is 34" and the MT640/650 is only 18" wide. The length is the problem. The MT640 is roughly 42" long and the MT650 is roughly 50" long. The weight is another problem. The MT640 weighs in at 510 Ibs dry, and with a retarder it's 638 Ibs.
The MT650 is another 50 Ibs more.

I have a MT643CR Allison, so here's some pictures showing the rough measurements.



Picture one shows the overall transmission. Picture two shows the width. Picture three shows the size of the "U"-joint . Picture four shows how it is mounted to the frame by these four bolt holes . Usually a simple piece of "L" angle iron. Picture five shows how the back of the transmission is mounted. The two large bolt holes usually attach to a large cross bar.

So after viewing all this you can see you can mount a MT640/650 series Allision to a Deuce but it will be difficult.
I would just buy a regular AT540 series front pump and be done with it.

 

[Sgt Jiggins]

How would an AT540 front pump work with the 1545 (or would it?) - a new stator too?

That's an awful lot of weight on those others. You've done this your whole life - AT540 series it is.

 

[rustystud]

How would an AT540 front pump work with the 1545 (or would it?) - a new stator too?

That's an awful lot of weight on those others. You've done this your whole life - AT540 series it is.

Yes a complete front pump assembly, which will include the stator support. Then you will need to replace the torque converter. A good low stall TH400 converter will work as long as it has the six mounting holes.

 

[Sgt Jiggins]

Is there any specific ratio I should be targeting with that torque converter?

(full disclosure: I'm talking out of my butt here as I know **** near nothing about automatic transmissions)

I've heard that there are different options/ratios that can go in with the TC?

 

[oboyjohn]

Up here North of the Border, our Canadian deuces were equipped with Allison MT 643's. They are 4 speed autos that had lockup in 3rd and 4th. But they are heavy, 767 lbs.

 

[Sgt Jiggins]

Up here North of the Border, our Canadian deuces were equipped with Allison MT 643's. They are 4 speed autos that had lockup in 3rd and 4th. But they are heavy, 767 lbs.

That's the thing about asking a question on here - ask 10 different people and get 13 different answers. lol
Part of me really wants that extra heft - because of the lockups and the fact that the truck isn't right near the high end of the torque curve out of the gate. But the other part of me isn't sure all that effort would be worthwhile.

Do you have pics? Measurements? I wonder if there are TMs specific to this build?

Thanks for mentioning this. Something to consider.

SJ/JD

 

[rustystud]

Up here North of the Border, our Canadian deuces were equipped with Allison MT 643's. They are 4 speed autos that had lockup in 3rd and 4th. But they are heavy, 767 lbs.

The MT643 weighs in at 510Ibs dry and 638Ibs with retarder. Add the 18 qts of oil, and you have your actual weight. Then there is the weight of the cooling system and hoses and extra oil.
This information is from my factory manual.

 

[rustystud]

Is there any specific ratio I should be targeting with that torque converter?

(full disclosure: I'm talking out of my butt here as I know **** near nothing about automatic transmissions)

I've heard that there are different options/ratios that can go in with the TC?

Yes there are a ton of torque converters you can use. So find the one with the highest "torque multiplication ratio" and lowest stall speed and go with that one. Usually it will be around 3:1 with a stall speed of 800 RPM .

 

[Sgt Jiggins]

Story time:

Years ago, I spent a fair bit of a day in a swamp, slithering around in the mud, trying to figure out how to get anything solid enough to jack up a dump truck so that I could get the tranny out from underneath. Wound up using a shovel instead. Long day. Payoff was a new-to-me NP435 to drop into my '51 M37. Loved the NP420 ratios, strongly disliked the non-synchro bit. Spent another few weeks learning, finding parts and rebuilding my first tranny. That NP435 is still in that truck today, doing just fine.

A bit of pain for what I consider a sizeable payoff.

That's kinda how I'm thinking about the MT643. I know it's gonna be some work, I'm gonna be back in the swamp again. And of course, I'm not as young as I once was. But man, I love me some granny gear and those lockups are icing on the cake.

Of course, once I find out what it all will wind up costing, I may just say to heck with it and do exactly as you initially suggested Rusty and go with a new stator and pump. Never hurts to consider options...

 

[Sgt Jiggins]

Then there is the weight of the cooling system and hoses and extra oil.

I'm thinking I'm ok with the weight. From what I learned from a new friend the other day, the front end mounts aren't used - it just leans on the bellhousing. The rear is held up somewhere forward of the tail. My thought there was to either fab something or see if the existing mount can be moved to accommodate.

The bit I'm still trying to figure out is the cooling system. Will the existing cooling system for the 1545 be adequate for the 643? If yes, am I going to need to adapt the heck out of it or is there a chance I might get 'lucky' and just be able to hook it all up?

Thank you

 

[rustystud]

I'm thinking I'm ok with the weight. From what I learned from a new friend the other day, the front end mounts aren't used - it just leans on the bellhousing. The rear is held up somewhere forward of the tail. My thought there was to either fab something or see if the existing mount can be moved to accommodate.

The bit I'm still trying to figure out is the cooling system. Will the existing cooling system for the 1545 be adequate for the 643? If yes, am I going to need to adapt the heck out of it or is there a chance I might get 'lucky' and just be able to hook it all up?

Thank you

The MT640 flows much more oil then the AT540. The coolant lines are twice the size as is the radiator. I believe the MT640 uses a AN18 or AN20 fitting .

 

[Sgt Jiggins]

The MT640 flows much more oil then the AT540. The coolant lines are twice the size as is the radiator. I believe the MT640 uses a AN18 or AN20 fitting .

That's a show stopper. I have no intention of getting into that kind of modification. 545 it is.

Thank you, Rusty, for helping me understand all of this!

 

[simp5782]

MT series use 3/4" hoses into # 12 and sometimes 14 on the heat exchanger.


Just buy a schoolbus with the 3116 in it and the AT545 already hooked to it. so you will have a spare motor for parts. Saw 3 sell the other day on different auction sites for under 3k.

https://www.steelsoldiers.com/archive/index.php/t-78336.html

 

[rustystud]

That's a show stopper. I have no intention of getting into that kind of modification. 545 it is.

Thank you, Rusty, for helping me understand all of this!

Glad to help.

 

[11Echo]

That's the thing about asking a question on here - ask 10 different people and get 13 different answers. lol
Part of me really wants that extra heft - because of the lockups and the fact that the truck isn't right near the high end of the torque curve out of the gate. But the other part of me isn't sure all that effort would be worthwhile.



Do you have pics? Measurements? I wonder if there are TMs specific to this build?

Thanks for mentioning this. Something to consider.

SJ/JD

A couple pics.