904 Transmission Stopped Going Into Gear

[Duster Captain]

Hello 904 experts,

I am having a frustrating problem with my trans.

The car is a 1972 Duster with a 225 slant 6 and 904 3 speed auto trans. This is my first MOPAR project. You can follow along my progress so far on this thread: 72 Duster Resurrection


This is what happened

I got everything together and drove around the block for the first time a few days ago. Everything was fine, shifting into gear ok-ish and then it slowed to a stop on the road with the rpm still high and in drive. I pulled over and consulted the internet which told me the kickdown linkage might have come off.

I check under the hood and sure enough, the kickdown rod had come loose from the carb linkage. The spring that holds it in place is missing. I reconnected it, then carefully shifted back into drive and the car moved. This happened once more on my 5 min drive back home. This was all at sub 30mph speeds.

This is what I have done

Once home, i put a spring on the kickdown linkage and it looks like it holds itself on the throttle for now.

But the car will only go into gear.....sometimes. I can get reverse if I shift to R and rev up a bit then let the car fall back to idle. That seems to get it to shift.

I can only get drive rarely by fiddling with the shifter and throttle. And even then it feels....slippy, not good enough to go on the road. The shifter travels freely across all gears and feels like it goes into a good detent for each gear.

I did a lot of reading and decided to check fluid level first. After warm up and idling in neutral, the fluid showed low on the dipstick. I added fluid until now it shows a bit over the full line while hot and idling in neutral.

But the car will only go into gear.....sometimes. I can get reverse if I shift to R and rev up a bit then let the car fall back to idle. That sometimes seems to get it to shift.

I can only get drive sometimes by fiddling with the shifter and throttle. And even then it feels....slippy. The shifter travels freely across all gears and feels like it goes into a good detent for each gear.

What do you guys think is next?

Kickdown linkage adjustment?
Shift linkage adjustment?
Drop trans pan and have a look?

Thanks

 

[Tooljunkie]

Well i dont want to be the party pooper, but if its been sitting, then likely the seals dried up.
A couple angles here,if you are dropping the pan to look for anything out of place,and see nothing, then adjust bands and replace filter.
If still no go,will need an overhaul.
As a last resort, there is a “snake oil” that sometimes works on stiff seals.
Atp AT-205.
I have used it and on occasion it works.
If its a ripped piston seal,only parts will fix it...

 

[AJ/FormS]

The tip-off is reverse
To get this gear to work, the low/reverse band needs to engage, and simultaneously the Hi-drum needs to come on.
To get any forward gear, the rear clutch needs to be operational.
To get any forward automatic upshift, the governor needs to be working.
So for the trans to operate as you describe, either: the fluid level is low, the pump is shot, you have a massive internal fluid leak, or all the seals simultaneously puked.There are a couple of other less likely possibilities, and tests for them.

I'm gonna guess the governor exploded,lol, or is stuck.. and the pressure died.

I recommend a pressure test at the L/R servo, in reverse. You should have 230 to 300 psi there, at about 1600rpm. If you're in the ballpark, this is a good sign.
If you're not in the ballpark, check the pressure at the governor port. Here the pressure should be a tested in drive, and should smoothly increase with speed showing around 15psi@15mph and increasing by about 1psi per 1mph,about. And should peak at about 75 psi at some point above 60 mph.

BTW, when the KD mechanism falls off, the trans should upshift very early, like by 12/15/maybe 18mph already into hi. The KD mechanism delays the upshifts, and increases the line-pressure to prevent slippage.
However, if the PO operated it like that for some time, the clutch packs could have been toasted.

 

[Duster Captain]

Thanks for the reply's everyone!

Im new to the strange world of automatic transmissions, so I'm doing a lot of reading on all this, bear with me.

From what you both said, does this sound like the correct sequence of steps to take here, in order of increasing effort?


1. Pressure tests starting with L/R servo as @AJ/FormS suggested because I can get reverse sometimes. Test all ports if that looks good. Should I just get an "oil and trans pressure tester kit" from the parts store like this?

Anyone know the fitting thread size on the trans? Does someone have a write up for this procedure? This is what "the book" has:

2. Drop trans oil pan, drain fluid, inspect, change filter and adjust bands as @Tooljunkie recommended. Also drain torque converter. Maybe throw some "magic" AT-205 in because why not. Test trans.

3. Contemplate dropping trans and rebuilding.


Does this plan sound good? For what it's worth, this is what "the book" says for this situation:

 

[TrailBeast]

Every single time a trans needs the throttle played with for the car to move it needs a rebuild.
(Sometimes) a full bottle of stop leak or "conditioner" can make the seals softer and they work for awhile, but it's a total temporary fix.

I have NEVER seen one come back from that by adjusting or changing any part except a really plugged up filter, and if the filter gets that plugged up it's coming apart inside anyway.

Sorry for the bad news, but that's just the way it is.

 

[Duster Captain]

Every single time a trans needs the throttle played with for the car to move it needs a rebuild.
(Sometimes) a full bottle of stop leak or "conditioner" can make the seals softer and they work for awhile, but it's a total temporary fix.

I have NEVER seen one come back from that by adjusting or changing any part except a really plugged up filter, and if the filter gets that plugged up it's coming apart inside anyway.

Sorry for the bad news, but that's just the way it is.

That's pretty much what I was afraid of.

I think I might pull the pan, look around, and replace the filter, add some "conditioner" and see what happens. If the trans is shot, what can it hurt?

If it needs the full rebuild, is this something a mechanically minded person can do at home? I know there are tons of resources and guides online, I would just like to hear from someone who has actually done it.

 

[TrailBeast]

That's pretty much what I was afraid of.

I think I might pull the pan, look around, and replace the filter, add some "conditioner" and see what happens. If the trans is shot, what can it hurt?

If it needs the full rebuild, is this something a mechanically minded person can do at home? I know there are tons of resources and guides online, I would just like to hear from someone who has actually done it.

Can't hurt to try it.

Quite a few have rebuilt their own that never did before, and there are a few of us that help when we can.
@j par
@cannucky
These two both did their own for the first time.

 

[Tooljunkie]

My kit is a foot behind me, hoping to start on the weekend. May take a few pictures while im playing.

 

[Bobzilla]

Don't bother trying to change fluid at this point. AJ/FormS and TrailBeast are correct. Do the pressure tests. If it has little or erratic pressure, it probably broke the torque converter hub. If it has steady pressure at full spec, the clutch packs are smoked. Usually leaking seals don't affect all gear ranges, and usually they smoke one clutch pack leaving eaither reverse gear working or first gear working. Your trans needs a rebuild, but the pressure tests will help determine why.

 

[cannucky]

They are easy to rebuild as long as you do 3 things . 1 download all the 727 tqflite rebuild videos from NSW Transmissions either get the sequence here or from Youtube and load them on your laptop. 2 lay a couple of sheets of plywood end to end on the shop floor to stretch the guts out on in order , you pop the pump end and drag the guts out so they spread out in order keeping everything organized .
This way you can replace the internals as units in order while watching the videos , this guy strips and rebuilds a 727 in like 20 minutes , the 904 is the same process .
3 Pester guys like Trailbeast , Moper ,OldKimmer etc...to help you guage clearances and get through any confusion you run into .
Like I said Easy !

 

[Duster Captain]

Thanks for all the input. Looks like I am in for a rebuild eventually. I might see what some shops around me charge for a rebuild, but I am down to take a stab at it. I have always been apprehensive about tearing into an auto trans, but there is only one way to learn....

Got a few things to sort out:

Rebuild Kit

I see lots of kits available from ebay, summit, etc. Anyone have a recommendation for brand/supplier? I imagine this has been asked many times, but I assume a 727 kit will not work on my 904?


Resources

I have the 1972 Plymouth Chassis Service manual.

I ordered this book:
https://www.amazon.com/gp/product/1613253354/?tag=fabo03-20

@cannucky Is this thread the video series you recommend? Video reference, TF727 600hp rebuild


I am just in the info gathering stage here, I may make another thread when I begin the actual rebuild.

Keep the good info coming, I appreciate it!

 

[cannucky]

Yep thats the series , pretty much everything is the same , you won't need to do the bolt in sprag because the 904 has it rivited in from the factory and the smaller drum diameter means less problems with that anyway . I went overkill , I called a supplier up here in Canada that machines some of the custom billet race parts you will find sold around the market ,I bought a billet steel front drum with a relocated groove to allow for an extra clutch and steel , it came with a billet piston and I added the 25 spring return unit plus some other goodies on top of a full race rebuild kit . Your needs may vary but I have a big hp stroker and I only wanted to build it once so I went over the top .

 

[cannucky]

I can tell you last time I asked rebuild prices were in the 1500+ range and the next time somebody tells me they want 1500 to throw a rebuild kit in my torquflyte they are getting punched in the face because it really is that easy to do , I took about 2 hrs because I'm not the guy in the video and mine has over 25k miles on it .

 

[VOETOM]

Duster captain, would you like to borrow some pressure gauges? I will send the ones I used in my photographs if you would like to try them. Let me know.
Tom Hand


QUOTE="Duster Captain, post: 1972058866, member: 51552"]Hello 904 experts,

I am having a frustrating problem with my trans.

The car is a 1972 Duster with a 225 slant 6 and 904 3 speed auto trans. This is my first MOPAR project. You can follow along my progress so far on this thread: 72 Duster Resurrection

 

[Bobzilla]

Rebuild Kit

I see lots of kits available from ebay, summit, etc. Anyone have a recommendation for brand/supplier? I imagine this has been asked many times, but I assume a 727 kit will not work on my 904?]

I would recommend using a good local supplier if you have one in your area, such as Transtar Industries. Many of the kits work just fine, but if there is a clearance issue during reassembly, a good supplier can work with you to get the parts you need. Another good way to go is using a specialty shop, such as A&A trans, Cope racing, or TSR racing. The parts are all the same no matter who you get them from, unless you buy a specialty part one of them makes on there own.

 

[TrailBeast]

Thanks for all the input. Looks like I am in for a rebuild eventually. I might see what some shops around me charge for a rebuild, but I am down to take a stab at it. I have always been apprehensive about tearing into an auto trans, but there is only one way to learn....

Got a few things to sort out:

Rebuild Kit

I see lots of kits available from ebay, summit, etc. Anyone have a recommendation for brand/supplier? I imagine this has been asked many times, but I assume a 727 kit will not work on my 904?


Resources

I have the 1972 Plymouth Chassis Service manual.

I ordered this book:
https://www.amazon.com/gp/product/1613253354/?tag=fabo03-20

@cannucky Is this thread the video series you recommend? Video reference, TF727 600hp rebuild


I am just in the info gathering stage here, I may make another thread when I begin the actual rebuild.

Keep the good info coming, I appreciate it!

Think about this.
There are more parts in a plastic model car kit.

 

[Duster Captain]

Duster captain, would you like to borrow some pressure gauges? I will send the ones I used in my photographs if you would like to try them. Let me know.
Tom Hand


QUOTE="Duster Captain, post: 1972058866, member: 51552"]Hello 904 experts,

I am having a frustrating problem with my trans.

The car is a 1972 Duster with a 225 slant 6 and 904 3 speed auto trans. This is my first MOPAR project. You can follow along my progress so far on this thread: 72 Duster Resurrection

Its the author himself! I'm going to get my own set of gauges but I appreciate the offer. I will probably bother you with a few questions when I get under way.

I would recommend using a good local supplier if you have one in your area, such as Transtar Industries. Many of the kits work just fine, but if there is a clearance issue during reassembly, a good supplier can work with you to get the parts you need. Another good way to go is using a specialty shop, such as A&A trans, Cope racing, or TSR racing. The parts are all the same no matter who you get them from, unless you buy a specialty part one of them makes on there own.

Good tip, I'll hunt around in my area and see what I can find. I see that most places have different "levels" of rebuild kit. Is there any way to know what I need before I open the trans up? Should I just get the "basic" kit for now?

Think about this.
There are more parts in a plastic model car kit.

That's good to know!

 

[Duster Captain]

Just FYI, I just got the following quote for rebuild from a local trans place (AAMCO):

$1120 to rebuild to stock including new TC if I bring the trans in
$1800 to rebuild plus R&R

I'm still down to rebuild it myself, but just for my info, are these prices reasonable for a shop to do this?

 

[Duster Captain]

Also, will I have to pull my torque converter out and look at spline teeth # and diameter to figure out which new one I need?

Anyone have any tips for new or reman stock torque converters? I'm seeing them online for much more than I expected ($300 range).

 

[Bobzilla]

The parts for these transmissions are not difficult to locate, and it does not sound like this is your primary ride, so I would suggest doing the tests and checking the numbers stamped into the case to determine what you have to work with, but waiting to order parts until you get it apart.
If it had to be back together in one weekend, I would say order a stock rebuild kit and converter to have ready to go.

 

[AJ/FormS]

Just FYI, I just got the following quote for rebuild from a local trans place (AAMCO):

$1120 to rebuild to stock including new TC if I bring the trans in
$1800 to rebuild plus R&R

I'm still down to rebuild it myself, but just for my info, are these prices reasonable for a shop to do this?

Wow! that's a lottacoin for a couple of hours work.

I have convertors from the 70's that I'm still using, although none were involved in serious meltdowns. Transmission shops used to flush them for a small fee.

 

[Duster Captain]

Update on this trans if anyone's interested.

I pulled the pan for fun just to look around. Pics below:

Well that does not look good. This is the pan as it was dropped. All kinds of bits in there.

Closeup of the pieces. I would guess this was formerly my low/reverse kickdown band?

There was a thick sludge of tiny particles in the bottom of the pan.

As a bonus, there was also this twig sitting in the dipstick tube.

I was looking for some confirmation that I need a full rebuild and this was more than enough. I am going to drop the trans, order parts and start the fun soon.

 

[Bobzilla]

Definitely wait to order parts until you get it out and opened up. Those look like pieces of the intermediate band (front postion in trans). Breaking only that band should have still allowed reverse gear and first gear to operate normally, if there was no major fluid leak. That means the damage may be worse than just a broken band. Hope it's not too bad though.

 

[cannucky]

Definitely wait to order parts until you get it out and opened up. Those look like pieces of the intermediate band (front postion in trans). Breaking only that band should have still allowed reverse gear and first gear to operate normally, if there was no major fluid leak. That means the damage may be worse than just a broken band. Hope it's not too bad though.

This ^^^ can't imagine that much crap and fluid that brown without expecting that all that grit and metal filings has been through the valve body and even through the splines , sorry bud but that could be nasty .

 

[cannucky]

Wow! that's a lottacoin for a couple of hours work.

I have convertors from the 70's that I'm still using, although none were involved in serious meltdowns. Transmission shops used to flush them for a small fee.

The scammer that did my resto here in Victoria had 4 trans shops and a seperate converter shop and charged $1500 min to rebuild a 727 to stock specs add on to that for any HD parts .