303M HydraMatic rebuild

[rustystud]

That's the problem. The TM only mentions the bushing in one short paragraph .
I knew about the bushing since I rebuilt the HydraMatic transmissions in civilian cars too.

 

[m1010plowboy]

By George I might have this figured out. Is your close-up pic the inside of shaft Q (7411533) ?

That would mean shaft N (7084954) gets shoved inside shaft Q....and the infamous 'slop' occurs between the boy shaft N and the receiver hole in shaft Q.

Is that right?




The description you posted from the TM 9-8025-2 the 301MG and 302M Hydra-matic transmissions manual helped a lot.

Were they sleeved from factory or is that something that happened when they went for maintenance the first time?

 

[rustystud]

Thats the shaft. The bores are already bored out on all the 303M shafts I've seen so far. Though only two where actually to the proper size. The rest I had machined out to the correct size.
So it appears this is a factory problem and not a rebuild problem. Though if the mechanics who rebuilt these transmissions knew of this bushing they would have had them installed I'm sure. Since there is just that small paragraph and little diagram mentioned in "TM 9-825-2" I can see how they would miss it.
That passage the bushing fits into is a "main" pressure galley. All that pressure just "spurting" out around the input shaft would eventually cause severe wear since no pump could keep up with that kind of pressure lose for long. Also the wear on the pump itself. That would also explain the high failure rate of the front pumps on the 303M transmission.

 

[rustystud]

I revised post #278 showing how to install the snap-ring holding the military shaft sealing unit on the shifter shaft.
Basically you use a deep socket to "push" the snap-ring into it's groove. Using a rubber hammer give the socket a good "wack" and it will seat. With new "O"-rings it can be a real challenge to accomplish this task.

 

[LItz]

Rusty,
With parts being so rare now have you any ideas about a more modern transmission and transfer case that could be used in the M135?

 

[rustystud]

Rusty,
With parts being so rare now have you any ideas about a more modern transmission and transfer case that could be used in the M135?

Yes, I've thought about it a lot. There are several options I believe can work very well.
One being the "AT500" Allison. Note I didn't say the "AT1545" Allison which was used in the M35A3 Deuce.
That one has several problems with the torque converter. The tried and tested AT500 Allison has been used for decades and parts are plentiful. Put a good NP240 transfer case behind it (one that has been upgraded to the "Titan" shafts) and it will last you decades.
I believe I posted my rebuild of the NP240 here somewhere.
The other one is the "1000/2000" series Allison used in the newer Chevys. My 2019 Chevy 3500 has one.
I bought three core 1000's for $300.00 each. I'm actually tearing one down right now.
I already built a NP240 transfer case for this build. I plan on putting this behind my "MultiFuel" in my M35 A2 Deuce.
Now cost is a factor here. The older AT500 will cost around $500.00 in parts, plus the actual transmission.
The 1000 series will cost me around $5,000.00. Thats because I'm using the extremely strong "Input-mid-and output shafts" and also the HyPo C-2 clutch assembly along with the "Raybestos" clutch plates.
I'm also using a three clutch plate torque converter. And of course I will need a "stand-alone" control module. All that costs "bucko bucks" !
A good "stock" 1000 will cost around $1000.00 to rebuild and would work very well in a M135.
The biggest problem will be finding an engine adapter for the GMC 302 . Of course, if you're already going away from stock with the transmission why not just put in a crate 350 Chevy engine.
Now that combination of a 350cid engine along with a AT500 or 1000 series Allison would make the old M135 get up and "dance" !!!!

 

[m1010plowboy]

Here's the transmission we dug out of the dirt north of Edmonton. It's not a 301MG hydra-matic. The side looks similar but that oil cooler is missing. Certainly one of the early hydra-matics closer to this 1940's article. https://macsmotorcitygarage.com/ins...atic-the-first-modern-automatic-transmission/

 

[rustystud]

Yeah, that looks like a "Pontiac" unit. Very disappointing !