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303M HydraMatic rebuild

rustystud

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Hello. Per my PM back to you, if you (or someone else) can provide a tracing of the gasket from the part, we can scan that and create a dxf file for our router. Maybe use a heavy paper and a accurate tracing and I think we'll be business.

Guy
I wrote back to you about the specs needed for this gasket. It is made of paper and some kind of fiber. It can handle temps above 300 degrees Fahrenheit and is resistant to oils and fuels.
 

rustystud

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By the lack of response to my last post about beefing up the transmission, I guess no one wants to know about this stuff so I'll stick to just a stock rebuild.
I will show everyone this one secret though.
The front pump has always been the weak point in the HydraMatic. Pontiac did something about it in 1948 to at least 1951. I haven't rebuilt any Pontiacs newer then 1951 so they could have used this pump in later years.
Here's a picture of what they did.
098.JPG099.JPG100.JPG
Your eyes are not deceiving you. That is an honest to goodness "gear drive" pump.
No vanes to break, or sliders to get stuck or worn out. Just a good solid gear drive pump.
I have two of these beauties and the best one is going into this rebuild.
So, if you come across an old Pontiac with the HydraMatic, buy the transmission.
 
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USMC 00-08

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By the lack of response to my last post about beefing up the transmission, I guess no one wants to know about this stuff so I'll stick to just a stock rebuild.
I want to know!! I just figured you were going to beef it up anyway, so was watching closely. I think the bad reputation of this transmission has been why very few people have an interest in the G749 series. We need guys like you to educate us!

I have at least one transmission that needs rebuilt. Only works in low range in reverse and first gear. Also two transmissions in parts trucks, so don't know if they work or not yet. I don't have any of the special tools or the knowledge to rebuild, but I do have the military manuals.

IMG_20240606_104048553~2.jpg

What are your thoughts on the longevity of this transmission? I have seen some people say it will only last about 30,000 miles.

I'll ask what others probably want to know as well....are you interested in rebuilding our transmissions too? What might that cost if you did?
 

rustystud

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I want to know!! I just figured you were going to beef it up anyway, so was watching closely. I think the bad reputation of this transmission has been why very few people have an interest in the G749 series. We need guys like you to educate us!

I have at least one transmission that needs rebuilt. Only works in low range in reverse and first gear. Also two transmissions in parts trucks, so don't know if they work or not yet. I don't have any of the special tools or the knowledge to rebuild, but I do have the military manuals.

View attachment 925216

What are your thoughts on the longevity of this transmission? I have seen some people say it will only last about 30,000 miles.

I'll ask what others probably want to know as well....are you interested in rebuilding our transmissions too? What might that cost if you did?
A properly built HydraMatic will last 80,00 to 100,000 miles easily. In my personal truck I rebuilt back in 1979, that transmission lasted over 40,000 miles and was going strong before I broke the engine. (The engine used a fiber cam gear and it shattered causing the valves to hit every piston. I was doing 60 MPH at the time so the damage was extensive !) The one thing most people don't do is the proper maintenance on it. After a rebuild the bands need to be checked every month until they seat in. Read: get worn into the drum. After about 5,000 miles the bands should be broke on. During that time you also need to change out the fluid. You don't want all that band material floating around in there. The fiber clutches also need to get broke in, so you end up with a lot of fiber material from them also.
After about 10,000 miles or so you will have a good running transmission that will give you years of faithful service. Just replace the fluid every other year. More if you drive it a lot. Remember the HydraMatic runs hot, and heat is bad "Ju-Ju" for any transmission. Replace the fluid.
Before I forget. Read the operators manual. People don't know how to shift this transmission. You never shift into reverse when the vehicle is moving. I know people will say you can "rock" your vehicle out of a stuck situation. Yes it will work. For a short while. Then after you fried the reverse clutch drum you will send debris all through the transmission. Wasting all those oil pumps (front and rear and reduction rear) and those nice thrust-washers and bushings and small bearings in all those nice planetary gear sets. It's really quite impressive to see all that damage due to someone not knowing how to operate their automatic transmission.
 
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rustystud

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As far as rebuilding anyone else's transmission. I cannot do that. The lifting of these parts alone causes me pain. Back when I was rebuilding these units, I could tear down a transmission in under 4 hours. Now it takes me 2 days. Rebuilding one took 2-3 days. I know people say you should be able to rebuild it in a day and a half, but if you check everything like your supposed to it will take an extra day. Now I will be lucky to rebuild it in a month. I knew one guy who was still rebuilding the car HydraMatic and he took a full week to rebuild one. The 303M is twice the work.
The only reason I'm rebuilding this unit, is because I always wanted to build and "modify" an old HydraMatic to withstand a modern V-8 engine like the Chevy 350. I have the bell housing for the Chevy and I will be buying a crate engine. One thing I did want to do, but I lack the funds, is to put in "Torrington bearings" in place of the bronze/brass thrust-washers. Also small roller bearings instead of bronze/brass bushings. If I had my way this would be an extreme transmission that would rival an "Allison" for durability! The machining work alone would cost me a couple of thousand dollars though.
So in the end, if you want the durability of an "Allison" then just buy an "Allison" .
Which I will be installing in my Deuce for my next project.
 

1944mb

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I don't know if that gasket exists anymore. I'm hoping it comes in the kit, but I'm not holding my breath.
As far as anyone reproducing parts for our 303M I don't holdout any hope. I talked with the Fatsco representative, and he said there needs to be a pretty good demand for any item to be "repoped" . Our 303M is such a rare creature no one would invest that kind of money for retooling to make our parts.
I do have numbers for the 3 roller bearings and they recently came in the mail. So bushings can be made in a machine shop, as can thrustwashers. The clutch plates are sold by Fatsco, except for the ones in the reduction unit. Thankfully those are "Bronze" and usually are in good shape. So the only parts we need are the gaskets and the lip seals (for the two large pistons) in the reduction unit.
I'm looking into a company that sells kits that would allow a person to make their own seals. Just need to find the right seals.
A person should be able to find a company that could cut the gaskets out. If we had a rating on the material need and a drawing. I have gaskets made on occasion from a local company. Naturally what I have made is not as intricate
 

1944mb

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Big Timber, MT
Just got off the phone with a gasket supplier we use in the hvac industry. Most of what we use are rubber/silicone based gaskets on commercial equipment. Ive had them custom make some weve needed through the years. They said to bring a nos gasket down and theyd be able to get the materials to replicate most any application. So if there are some we need for the reduction unit. Id say we start there at fabricating our own
 

rustystud

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Just a quick side note on the "fluid coupling" . This transmission does not have a "torque convertor" but a fluid coupling since it does not have a "stator" . That being said, there are several different styles or flavors of fluid couplings for the HydraMatic.

013.JPG This one came off a V-8 engine and is built for "high stall" to help launch the vehicle.

014.JPG This one came off an early 1950's "full size" car that needed "high torque" since it had a big but low revving engine. Torque baby !

015.JPG This one is from our 303M unit. It is also built for torque, but it does not have the fancy internal ring later fluid couplings did.
I'm debating whether to use the 1950's model fluid coupling on this rebuild or stay with the stock unit.
The fluid coupling unit almost never fails, but sometimes the "fins" can come loose. So they do need to be checked.
The "Torus housing" on the other hand can have severe wear on the input Hub.
001.JPG002.JPG004.JPG

The HydraMatic has a rubber seal for the "outside" of the hub and also a sealing ring on the "inside" of the hub. Both need to be checked. You can see the ring indentations in the second picture. You can also feel them easily. Usually, you use your fingernail to check for a groove. Here you can feel it with calloused hands ! This hub is shot.
If your hub has severe wear your only options are find another "housing" or have a machine shop make a new "hub" and weld it on. A ""speedy sleave" will not work on the inside of the "hub" .
I have debated with myself whether a machine shop could turn the "hub" down just .020" and fit a stainless steel sleave on the outside and on the inside of the "hub" . This hub is very thin though. I have one housing that has severe wear on the "hub" so maybe I'll take it to the shop and see what he can do.
 
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1944mb

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Fun
Just a quick side note on the "fluid coupling" . This transmission does not have a "torque convertor" but a fluid coupling since it does not have a "stator" . That being said, there are several different styles or flavors of fluid couplings for the HydraMatic.

View attachment 925331 This one came off a V-8 engine and is built for "high stall" to help launch the vehicle.

View attachment 925332 This one came off an early 1950's "full size" car that needed "high torque" since it had a big but low revving engine. Torque baby !

View attachment 925333 This one is from our 303M unit. It is also built for torque, but it does not have the fancy internal ring later fluid couplings did.
I'm debating whether to use the 1950's model fluid coupling on this rebuild or stay with the stock unit.
The fluid coupling unit almost never fails, but sometimes the "fins" can come loose. So they do need to be checked.
The "housing" on the other hand can have severe wear on the input Hub. (I see I forgot to take pictures of that. I'll correct that tomorrow.) The HydraMatic has a rubber seal for the "outside" of the hub and also a sealing ring on the "inside" of the hub. Both need to be checked.
If your hub has severe wear your only options are find another "housing" or have a machine shop make a new "hub" and weld it on. A ""speedy sleave" will not work on the inside of the "hub" .
I have debated with myself whether a machine could turn the "hub" down just .020" and fit a stainless steel sleave on the outside and on the inside of the "hub" . This hub is very thin though. I have one housing that has severe wear on the "hub" so maybe I'll take it to the shop and see what he can do.
Funny to me thay even back then they made a high stall unit for performance. Back when most performance people wouldve thought of a automatic as a sissy option. “Your grandma needs the automatic since she cant shift anymore”
 

1944mb

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I cleaned up the Chevy bellhousing that will go on this rebuild.

View attachment 925334View attachment 925335 Isn't she beautiful ! Now I just need to buy an early 350 cid crate engine and put them into my other M35 Deuce.
Of course, an original M135 would be the best platform to use but I don't see those much out here.
What wouldve been the original sbc that couldve been ordered with these? A 265 or a 283? Thats one thing ive always appreciated with gm -the interchangeability relative to other options.
 

rustystud

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What wouldve been the original sbc that couldve been ordered with these? A 265 or a 283? Thats one thing ive always appreciated with gm -the interchangeability relative to other options.
It was the 265 cid . Used from 1955 to 1956 . So this bell housing is pretty rare since 1956 was the last year of the "original" HydraMatic transmission in a Chevy truck. After that they went to the stupid "RotoHydro" or "Slim Jim" transmission. I have heard though; certain later models of Chevy trucks used the old HydraMatic but I cannot confirm this.
 

rustystud

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I thought I would share this little "tid bit" of information for those who are trying to justify using an old HydraMatic in their truck. This was not only the "first" automatic transmission, but it was also the first to have total lock-up in fourth gear. You ask how could that be with a "fluid coupling" and no lock-up piston.
The answer is in how the two "torus's" (drive Torus and driven Torus) are connected to the shafts.
1717942558210.png
If you study the diagram, you will see how the "Torus housing" is connected to the flywheel (which is connected to the engine crankshaft) and the "driven Torus" is connected to the front planetary which is driven by the torus housing. They are in total physical lock-up. This is a "true" one to one output, just like a "manual" transmission.

So when people start judging you and your truck just say, does your truck have an automatic transmission ? and does it have true total lock-up ? Well mine does !

Just want to say "Thank you" to whoever got my diagram straightened out. :)
 

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rustystud

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Spent the day cleaning parts. Thought this would be a good time to show another "trick" in rebuilding a HydraMatic.
The clutch pistons in the two main housings were made of cast iron until 1950 (give or take a year) . After that they were made out of "aluminum" . The only reason I can see is cost. Weight does not play a factor in an old cast iron HydraMatic. What does happen with the lighter pistons is you get a faster "apply" . This translates into a quicker and firmer shift. The military didn't use them as they wanted the solid metal sealing ring for those two pistons, but since those rings are now "unobtainable" it makes more sense to use the aluminum pistons which use a "rubber lip seal" . These seals are still being made.
I might have a couple of my cast pistons modified to accept the rubber lip seal. Once you do it there is no going back though.

006.JPG007.JPG
The "HydraMatic Division" also replaced the "reverse cone" piston with aluminum too. This piston is a direct fit for our heavy cast iron piston in the 303M . This is especially helpful if someone has a damaged reverse cone piston, which happens a lot. You cannot find this original cast piston just laying around either, but all HydraMatics after 1950 had the aluminum ones.
003.JPG004.JPG
 

m1010plowboy

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Any good news with your 40 year old present? Rubber is such a gamble I'm always curious how things look when opened. Let me know if yer rubbers are soft. Canada Post claims they delivered it somewhere so hope you got it. The Canada Post team appeared to use 12 days to deliver covering 64 miles a day. That makes sense because they'd need to stop and water the horses. The good thing is it was under $3.00 / day to feed the horses. Cheap and slow can not be understated.

Are you still missing a bunch of parts? Reduction reduction reduction?

001.JPG

If you get sample pics of what you're still hunting for I will get time in the rain to post on a private facebook site. If it's cool I would like to use your pics to stimulate some memories of the old...... I mean experienced fellas that have warehouses.

Great thread. Wish I was there because learning for me is hands on but I'm less intimidated ripping one apart so thank you.
 

rustystud

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Location
Woodinville, Washington
Any good news with your 40 year old present? Rubber is such a gamble I'm always curious how things look when opened. Let me know if yer rubbers are soft. Canada Post claims they delivered it somewhere so hope you got it. The Canada Post team appeared to use 12 days to deliver covering 64 miles a day. That makes sense because they'd need to stop and water the horses. The good thing is it was under $3.00 / day to feed the horses. Cheap and slow can not be understated.

Are you still missing a bunch of parts? Reduction reduction reduction?

View attachment 925761

If you get sample pics of what you're still hunting for I will get time in the rain to post on a private facebook site. If it's cool I would like to use your pics to stimulate some memories of the old...... I mean experienced fellas that have warehouses.

Great thread. Wish I was there because learning for me is hands on but I'm less intimidated ripping one apart so thank you.
Hey Dave.
Yes, the parts arrived today. Sadly, they are for a 301MG transmission so no reduction parts. The seals seem to be Ok, a little stiff but I'll soak them in some rubber conditioner and they should be fine.
The gasket for this unit would be really nice to have, also the seal ring that fits in the center.
009 (2).JPG
Also the gaskets for the reduction valve body (there are 3 ) would nice too.
008 (2).JPG If there are no gaskets available, I will attempt to make my own or send a copy to one of the guys here who has a CNC cutter attachment and see if he can make them.
The seal ring I will have to reuse. I'll try and buff it out to help seal better.
 
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