303M HydraMatic rebuild

[rustystud]

Using the special clamp tool again I compress the seal rings and install the rear drum assembly.


Now after installing the front and rear bands the drum assemblies are ready to go into the case. You need to "stab" the front shaft first angling the assembly into the case. The TM shows this. I don't have a helper to take pictures so I cannot show you how I do this .

Once the assembly is in place and the main support is bolted down, you can pressure test the whole assembly.
This hole applies the front clutch.
This hole applies the rear clutch.

After tearing down everything due to the high leakage, I checked the iron seals for clearance. Since I only have four seal rings at this time, I never checked this as it is a moot point. You need a .002" and .007" feeler gauge to check this gap. The gap must be over .002" and under .007" .
Everything checked out as I figured it would. Since most likely the military rebuilt it last.


Now everything is almost back to where I started this morning !


A quick note here about the clutch plates. There was two types of plates used. Waved and flat. This was used on both the steels and fiber plates.
Never use the wave plates !
They were originally used in the 302M transmission but replaced in the upgrade to the 303M transmission. These plates were originally used in the civilian HydraMatics and allowed a "cushioning" effect on clutch apply creating a "softer" shift. The problem is this allows clutch "slippage" which is not wanted in larger vehicles.

 

[rustystud]

This Monday I'll be taking all the pistons I have down to the machine shop to be modified to except rubber seals. Hopefully this will not take too long.
In the meantime I have seven HydraMatics to tear down. Lets see what parts I can salvage from them.

 

[rustystud]

I got the pistons back from the machine shop and reinstalled everything. Pressure tested it and all is fine.
But in the meantime, I tore down one of the five 303M transmissions I got in Canada two weeks ago and after cleaning it up found out it needs a new return wave spring in the reduction unit. This is becoming a problem. In the last four 303M transmissions I tore down; all needed a new return wave spring.
I am being forced to find a supplier of these wave springs if I want to complete this rebuild. There are several manufactures of wave springs, I just need to find one that makes one as big as the 303M needs.
Either that or a manufacture that is willing to make up some springs.
Since it has been fifty to sixty years since these transmissions have been built, these springs are shot. Putting one of these old springs back in service is just asking for trouble. Just like the one I tore down two months ago which had the wave spring shatter causing the apply piston to break.
So I'll continue rebuilding this transmission until I get to the reduction unit.
I need to cleanup a few more parts from the last 303M I tore down, then I'll get back to work.

 

[rustystud]

I'm still tearing down one of the transmissions I picked up in Canada. Today I found out the cause of death for this transmission. Water. Seems the last owner took his M135 for a swim.
There was extensive damage to many different parts of the transmission. The reduction units clutches where severely worn. The front and rear clutch packs were destroyed. Literally ! The front pumps vanes were totally worn out. The rear pump had damage. The reverse piston had so much heat the lip seal melted, and the cast iron piston cracked in three places. So many areas had damage.
So today I was inspecting the front clutches more closely and found the friction plates were shedding their paper material. The only thing that can cause this is water.
I'm sure your asking how could water cause high heat in the reverse piston and extreme wear in the front and rear pumps. Well water is a terrible lubricant for metal parts and will destroy a pump used to pressurize oil. Since it had no oil to pump to the system just water, all those parts needing lubrication had nothing and overheated.
Now whoever did this tried to drain the water and add back transmission fluid, but it was too late. Probably drove it back home after taking a swim. When I was still in the "Marine's Motor Pool" we were taught that you immediately drained all fluids after taking a swim with a Deuce or any equipment really. The only time you were allowed to drive any distance was in a "combat" situation. Then you just drove it until it died.
So for you crazy guys who love to take your vehicles out and play hard with them, take notice here. Automatic transmission vehicles will get destroyed from water.
Here you can see the melted seal.
There is melted rubber on the housing. It's the black spot at the top.
Here you can see the three cracks in the piston. I cleaned up the piston and then found the cracks. The piston was black from baked on oil.
You can see the wear on the pump vanes from the alignment rings.
I've never seen this before. A bronze selective thrustwasher broken like this.
There must have been some nasty hammering of the input shaft to cause this. That combined with the lack of oil totally destroyed this washer.

This poor transmission died a terrible death !

 

[rustystud]

OK, back to the rebuild.
Here's some pictures of my reassembly of the front and rear drum assemblies.
Here I'm installing the thrustwashers on the rear drum hub. This washer is the same size as the "Selective" thrustwasher used on the "Input Shaft" but it will not have a marking on it. The Selective thrustwashers have numbers stamped on them. Don't mix them up.
The hub is fully seated when it is parallel with the drum shown here.
This is one of three "must" have tools to assemble the HydraMatic transmission. The center support ring compressor tool.
Install one of the three snap rings here after the center support is first installed. You compress the top sealing rings to install the rear drum assembly. You put the drum on the shaft and gently apply pressure pushing the ring compressor down.
My post several days ago shows this.

There is one important note I need to make here. The thrustwasher and metal ring installed on the front drum assembly is the same inner size as the front oil pump drive gear thrustwasher. The diference is the "outer" size. The oil pump drive gear uses a smaller thrustwasher while the front drum assembly uses a wider thrustwasher. Don't mix them up ! I will take pictures of this difference tomorrow.

 

[rustystud]

Here's the picture of those thrustwasher's I mentioned yesterday.
You can clearly see that the left thrustwasher is larger. This one goes on the rear drum assembly.

 

[rustystud]

I did a little work on the 303M today. Though mostly I cleaned up parts.
I installed the front pump drive gear and the front pump.

 

[rustystud]

Here I'm installing the front pump.


This last picture is important. It's showing the raised edge of the pump you must have. The book calls for a protrudence of 0.003" to 0.015" . The reason for this is so the pump is held in place by the two bolts. If the pump did not protrude than the pump could spin in it's bore. Basically your
squishing the pump into the bore. The little washer is important to also help prevent the pump from spinning, but the clamping action is what really holds the pump in place.

A little side note; you can see I'm using stainless steel "Allen Head" bolts to hold the pump together instead of the #2 screws. This way I can actually torque the pump bolts and if needs be easily remove those pesky bolts later on.

 

[rustystud]

Here's what I spent most of the day on. Cleaning parts like this oil pan. What I found after spending over three hours cleaning it due to the mess it was in, and all the heavy coats of paint on it was this nasty little crack.

I was pretty pissed off when I saw this. I drilled a hole to prevent the crack from spreading in case some time down the road I needed this housing and have to weld it up.
What is really annoying is that crack should never have happened. It probably had a leak and instead of removing the fitting and putting on some thread tape or "Teflon" paste they just decided to torque it down until it stopped leaking. That kind of "shade tree mechanicing" really makes me angry. Because of his stupidity this person destroyed an irreplicable piece of equipment.
Just a note here; If a fitting leaks than remove it and put on some thread tape or paste and if that doesn't work, install another fitting. NEVER over tighten the fitting to stop the leak !

 

[rustystud]

Spent a lot of time cleaning up another oil pan today. One item I need to mention is the oil pan "welch" plug, commonly called a "freeze plug" . This plug is on the side of the oil pan and is not mentioned in any repair manuals as normally you would never need to replace it. In a normal running vehicle with a transmission full of oil there would be no rust here. But if for some reason you need to use another oil pan on your transmission, you need to check for rust in this pans oil pick-up tube. Especially if the owner of said oil pan kept it outside. If you have rust present here you should go ahead and replace this Welch plug.
I drill a 1/2" hole in the center of the plug and using a tapered pry bar "pop" the plug out.

Thankfully this plug is a standard 1" freeze plug.

 

[rustystud]

The other day I found something very interesting. I was cleaning up the "Output Shaft" when I noticed it was missing the "Input Shaft" to "Output Shaft" bushing. This is a small bushing (3/4" by 3/4" ) that acts like a "Pilot Bearing" on manual transmissions. It supports the end of the Input Shaft. It also acts as a restriction in the main lubrication oil passage. Without it, lubrication oil would just spray all over the place.
Think of it as a Main engine bearing (forget about the rod at this point) . Without it the engine would lose oil pressure and the components that needed this oil would be starved of oil. Yes the engine would operate for a while as the other bearings would help support the shaft, but it would fail much sooner than normal.
I installed a new bushing there, and it fit perfectly as it was completely machined out to except the bushing . So why was the bushing missing ? I checked the other shafts I had and all of them were missing this bushing. When I was an apprentice I don't remember this bushing being left out of a rebuild. That was over 40 years ago so maybe my memory is missing something. All my other HydraMatic rebuild manuals show this bushing and how to replace it. So why does the Military manual (TM 9-8025-2) "Not" show it ?
I do know the military manual is not complete, especially on the valve body. So was this bushing also missing from the manual ?
Would this help explain the short life span of the 303M HydraMatic Transmission ?
That is one thing that has been baffling me for some time now. A normal civilian HydraMatic will last well over 100,000 miles, but according to many individuals they claim the 303M transmission will only last 30,000 miles.
Now I have 4 more 303M transmissions outside waiting for tear down. If they also are missing this bushing that could be the "smoking gun" I've been looking for. Maybe they came this way from the factory by accident. Trust me it happens ! Since the military repair manual doesn't mention this bushing, the troops rebuilding this unit would also miss it. This could be the whole reason this transmission got such a bad rap. One missing bushing.
Of course I could be totally wrong.

 

[USMC 00-08]

I tore down one of the five 303M transmissions I got in Canada two weeks ago and after cleaning it up found out it needs a new return wave spring in the reduction unit. This is becoming a problem. In the last four 303M transmissions I tore down; all needed a new return wave spring.
I am being forced to find a supplier of these wave springs if I want to complete this rebuild.
Since it has been fifty to sixty years since these transmissions have been built, these springs are shot. Putting one of these old springs back in service is just asking for trouble. Just like the one I tore down two months ago which had the wave spring shatter causing the apply piston to break.

Is this what I have read about on here referred to as the "wavy release spring"? Seems like some people were saying to just remove it and things would function fine. I'll see if I can find that thread and if I remember correctly it might have been in the write up called Hydramatic Heaven by Major Tom.

Found it! Look at the fourth paragraph.

Hydramatic Heaven

I have owned hundreds of GMC deuces, have rebuilt many transmissions and am currently using several trucks. Transmission failure issues seem to be a regular topic. I have found that how you operate the transmission and diagnosis of symptoms are critical. Driving, the transmission prefers foot...

www.steelsoldiers.com

That is one thing that has been baffling me for some time now. A normal civilian HydraMatic will last well over 100,000 miles, but according to many individuals they claim the 303M transmission will only last 30,000 miles.
Now I have 4 more 303M transmissions outside waiting for tear down. If they also are missing this bushing that could be the "smoking gun" I've been looking for. Maybe they came this way from the factory by accident. Trust me it happens ! Since the military repair manual doesn't mention this bushing, the troops rebuilding this unit would also miss it. This could be the whole reason this transmission got such a bad rap. One missing bushing.
Of course I could be totally wrong.

View attachment 933346View attachment 933347

That is very interesting. Hopefully you have found the problem!

 

[rustystud]

Is this what I have read about on here referred to as the "wavy release spring"? Seems like some people were saying to just remove it and things would function fine. I'll see if I can find that thread and if I remember correctly it might have been in the write up called Hydramatic Heaven by Major Tom.

Found it! Look at the fourth paragraph.

Hydramatic Heaven

I have owned hundreds of GMC deuces, have rebuilt many transmissions and am currently using several trucks. Transmission failure issues seem to be a regular topic. I have found that how you operate the transmission and diagnosis of symptoms are critical. Driving, the transmission prefers foot...

www.steelsoldiers.com

That is very interesting. Hopefully you have found the problem!

Yes that is the "wavy spring" I'm referring too. You do need this spring contrary to what this gentleman said. Without it the piston will "drag" on the reaction carrier, causing wear and heat and ultimately wearing out the friction material on the piston.

 

[rustystud]

Took some pictures of the "output shaft" bushing. This will show you how important this bushing is.
Here's the busing in question. It fits into the output shaft.
I'm showing how the bushing will fit on the input shaft.
Here the bushing is installed and the "selective" thrustwasher is in place.
This is how the two shafts look together.
Without this bushing, the only thing supporting the input shaft is the planetary gears in the output shaft. This would allow the input shaft to "wobble" all over the place besides allowing the oil pressure to crash.

 

[rustystud]

I also installed the oil pressure regulator today.
Installing the valve and spring.

Installing the "reverse booster" valve.
Installing the copper crush washer.
Done.

 

[rustystud]

Today's project is setting the input shaft end-play.
Since I have no idea what the correct selective thrustwasher should be, I'll start with a number "3" .
After the input shaft is installed you install the output shaft with the selective washer installed .

If you look closely in the bore of this shaft you can see that small bushing I've been talking about. Now you install the output shaft.

Once the output shaft is installed you can install the two thrustwashers. One is steel and the other is bronze. The steel goes against the "reverse center gear" assembly. Then the bronze goes against the steel washer.


Now install the "reverse center gear" and bolt it in place using six 5/16" X 1-1/2" bolts .

We need to move the drum assemblies forward and hold them there. I used the special shim. You can use a screwdriver but be careful to not scratch the center support sleeve.

Using the special adapter, you can screw it in on the input shaft threads.
You don't need this adapter; it just makes life easier.
With my dial indicator installed I found I had "zero" endplay. So I removed the "reverse center gear" and installed a number 2 selective thrustwasher. After reinstalling the dial indicator, I found I now had .010" endplay. Perfect.

 

[rustystud]

I haven't been able to work on the transmission as much as I have wanted too. The wife has decided the yard needs to be cleaned up for winter. So I have been working towards that end.
I'll continue to post as I'm able too.

 

[rustystud]

That small bushing I found missing on those three output shafts can be purchased at "Fatsco" .
Here's the part number. H7-6 . There phone number is 1-800-524-0485 ext. 102 (Steve)

 

[rustystud]

Make that four output shafts missing that bushing. I truly believe this is the "smoking gun" on why these HydraMatics fail so soon. Without that support for the input shaft, it allows that gear to "flop" around and without that bushing oil flow is unimpeded and just blows out of the shaft. That means many bushings and bearings are not getting lubricated.

 

[rustystud]

Here's another shop note.
I've been tearing down another 303M transmission while I'm waiting for parts from the machine shop again. Here's a classic example of why I always take out those pipe plugs on any transmission. Those passages can get filled with gunk just like these pictures show.

If those passages had not been cleaned out, that crap could have gone into the main oil line and caused all kinds of problems. Clean out those passages !