904 Transmission Stopped Going Into Gear

[CudaFactHackJob]

Eventually you're going to sell this transmission when you go to a V8. I like to think ahead. You'll get more for it with V8 parts in it. Otherwise slant six trannies are a dime a dozen. Or, you could use these guts in your V8 trans. Something to think about.

 

[Duster Captain]

Fair point I will keep that in mind.

 

[Duster Captain]

I have more sub-assemblies apart.

Here are the pictures and my thoughts on re-use vs. replace for each. Any advice is appreciated.

Oil pump looks good. Will clean and reassemble.

Direct clutch disks and steels. Look gently worn. I'll replace the frictions and re-use the steels.

Forward clutch frictions and steels show heavy wear, heat discoloration, and scarring. Looks like this is where everything went bad for the trans. I will replace everything here except maybe the forward apply pressure plate and direct forward pressure plate if they are still flat.

Bushing in forward drum shows some wear and scratches, should I replace it? I should probably just replace all bushings, right?

Forward clutch piston looks good but seal was so stiff it was very difficult to remove the piston and the rubber started to come apart when I flexed it by hand.

Do I need to remove the shaft from the drum? How is that done? That big brown washer is flopping around. Is that the "front clutch fiber washer"?

Forward drum with clutch assembly removed. Do I remove that snap ring to completely disassemble? Do I even need to do that?

Finally, what about my torque converter? It is a blue one and looks to be in good shape. Should I just re-use? Pay someone to flush? Get a new one?

Thanks everyone.

 

[TrailBeast]

I have more sub-assemblies apart.

Here are the pictures and my thoughts on re-use vs. replace for each. Any advice is appreciated.


View attachment 1715214281
Oil pump looks good. Will clean and reassemble.


View attachment 1715214286

View attachment 1715214287
Direct clutch disks and steels. Look gently worn. I'll replace the frictions and re-use the steels.


View attachment 1715214288 View attachment 1715214289
Forward clutch frictions and steels show heavy wear, heat discoloration, and scarring. Looks like this is where everything went bad for the trans. I will replace everything here except maybe the forward apply pressure plate and direct forward pressure plate if they are still flat.


View attachment 1715214290
Bushing in forward drum shows some wear and scratches, should I replace it? I should probably just replace all bushings, right?

View attachment 1715214291
Forward clutch piston looks good but seal was so stiff it was very difficult to remove the piston and the rubber started to come apart when I flexed it by hand.


View attachment 1715214292
Do I need to remove the shaft from the drum? How is that done? That big brown washer is flopping around. Is that the "front clutch fiber washer"?

View attachment 1715214293
Forward drum with clutch assembly removed. Do I remove that snap ring to completely disassemble? Do I even need to do that?

Thanks everyone.

Do not use burned steels even though they are flat, as heat creates hard spots that won't friction evenly when they apply.

Absolutely replace that bushing on the drum, as that centers the drum on the stator for the sealing rings to center on the hub.

You definitely found hard rubber that causes "Morning Sickness" and no move symptoms.

The input shaft can stay on the drum, just clean all the nooks and cranny's.

That brown washer is exactly what you think it is and can be reused of it looks solid.
They are a little brittle, so don't tweak on it too much checking it.

From what I see you are doing fine.

OH, and if the rest of the pump looks that good there shouldn't be a problem reusing it.
Just put a new seal and bushing in it and don't forget to RED lockite BOTH the seal and bushing in place, and stake the bushing into the pump body.

Note that when you put the bushing in that you position the bushing seam 90 degrees away from the staking indents so as not to cause the bushing seam to open or disfigure.
I use a 1/8 or so drill bit and a ball peen hammer to stake the seal in.

This is the idea on the staking of the bushing, and after doing this I always fit it on the converter and turn it a bit to smooth of any high spots in the bushing.

 

[Duster Captain]

Do not use burned steels even though they are flat, as heat creates hard spots that won't friction evenly when they apply.

Absolutely replace that bushing on the drum, as that centers the drum on the stator for the sealing rings to center on the hub.

You definitely found hard rubber that causes "Morning Sickness" and no move symptoms.

The input shaft can stay on the drum, just clean all the nooks and cranny's.

That brown washer is exactly what you think it is and can be reused of it looks solid.
They are a little brittle, so don't tweak on it too much checking it.

From what I see you are doing fine.

OH, and if the rest of the pump looks that good there shouldn't be a problem reusing it.
Just put a new seal and bushing in it and don't forget to RED lockite BOTH the seal and bushing in place, and stake the bushing into the pump body.

Note that when you put the bushing in that you position the bushing seam 90 degrees away from the staking indents so as not to cause the bushing seam to open or disfigure.
I use a 1/8 or so drill bit and a ball peen hammer to stake the seal in.

This is the idea on the staking of the bushing, and after doing this I always fit it on the converter and turn it a bit to smooth of any high spots in the bushing.

View attachment 1715214316

Thanks for the input.

I will be sure to replace all seals and bushings, that a good tip with the red locktite and staking method, I will post a pic when I get to that point. I hope to order all my rebuild parts today.

One thing I forgot to ask, what is the method to see if a torque converter is good to re-use?
mine is the blue one for what thats worth. Apparently a trans shop can flush it for me, thoughts?

 

[TrailBeast]

Thanks for the input.

I will be sure to replace all seals and bushings, that a good tip with the red locktite and staking method, I will post a pic when I get to that point. I hope to order all my rebuild parts today.

One thing I forgot to ask, what is the method to see if a torque converter is good to re-use?
mine is the blue one for what thats worth. Apparently a trans shop can flush it for me, thoughts?

Yea, it sucks to get one all back in and have the pump seal pop out.
They actually make a retainer for that and I have used those before, but never had a bushing pop out after the red Locktite.

Reusing a converter is never recommended, but a man has to do what he has to do.
If it worked before, it will probably be ok unless it dumps garbage back into a new trans.
Flushing a converter is better than nothing, but it doesn't do much really.
If you didn't have a bunch of garbage in the pan when you took it apart, then the flush is better than nothing.
If there was garbage in the pan like metal flakes the converter should be replaced.
Color of it means nothing really.
Don't forget to flush the cooler lines both directions with solvent a few times.
(gas works too, but just be careful about the mist that comes out, as it is highly flammable)
Both directions tends to get more junk out of the nooks and cranny's.

 

[Duster Captain]

Yea, it sucks to get one all back in and have the pump seal pop out.
They actually make a retainer for that and I have used those before, but never had a bushing pop out after the red Locktite.

Reusing a converter is never recommended, but a man has to do what he has to do.
If it worked before, it will probably be ok unless it dumps garbage back into a new trans.
Flushing a converter is better than nothing, but it doesn't do much really.
If you didn't have a bunch of garbage in the pan when you took it apart, then the flush is better than nothing.
If there was garbage in the pan like metal flakes the converter should be replaced.
Color of it means nothing really.
Don't forget to flush the cooler lines both directions with solvent a few times.
(gas works too, but just be careful about the mist that comes out, as it is highly flammable)
Both directions tends to get more junk out of the nooks and cranny's.

Here is is by the way.

I agree with you but I'm kind of stuck on the TC problem.

I've heard people say:
"flush it, look into it at the splines and re-use if good" and also "always replace the TC, no exceptions"

There was gunk in the pan (see post #34 and 22), not sure how bad that is....

I would like to replace but the problem is that I cant find anyone around town that has them.

Where should I be looking for these? Buying a used one that I know nothing about is the same as me re-using mine, so I would need to find a "new" one.....thoughts?

 

[CudaFactHackJob]

I only replace bushings that are bad. That pump bushing looked pretty good to me; a lot of them show copper when new. The drum bushing looked worn, but also check the pump cover surface where that bushing rides and replace the pump cover is there's wear. Check the inside of the pump cover for wear from the forward rings. Also check the inside of the direct drum for wear from the direct rings. Any wear; replace the drum. Replace that converter. It looks worn in the bushing area and it might be grooved in the seal area. Check it for cracks emanating from the square cuts toward the front. If you stick your finger inside you'll find the weak spot of the 904; the converters are thinner forward from the pump tangs and that's what makes them crack. You can tap it and oil will come out of the crack; then you can see it. Bottom line, although the filter will protect the valve body and converter from contamination by large particles, the problem arises when new hot fluid hits the built up layers of contamination that have been compacted into the outer perimeter of the converter. While all of this has been a build up of very fine particles that can't damage much, it gets washed out in large compacted chunks that will clog your new filter again and again. Rebuilt converters aren't hard to find. If the composite thrust washers are brittle then replace them. Put a new on on the front of the output shaft. You can put two on the pump to reduce endplay.

 

[TrailBeast]

View attachment 1715214352
Here is is by the way.

I agree with you but I'm kind of stuck on the TC problem.

I've heard people say:
"flush it, look into it at the splines and re-use if good" and also "always replace the TC, no exceptions"

There was gunk in the pan (see post #34 and 22), not sure how bad that is....

I would like to replace but the problem is that I cant find anyone around town that has them.

Where should I be looking for these? Buying a used one that I know nothing about is the same as me re-using mine, so I would need to find a "new" one.....thoughts?

Yea, no way would I trust that converter after all that was in the pan.
Think of that thing spinning at 2-5k and what the stuff in the fluid does.
It packs a fine powdered combination of burned clutch material and aluminum dust around the entire inner surface, and it's almost impossible to get out without having the converter cut open and rebuilt.
I seriously doubt flushing would even come close to getting that junk packed in the converter out.
I would do almost anything to not use that one again, as it's just to risky on a fresh rebuild.

I only replace bushings that are bad. That pump bushing looked pretty good to me; a lot of them show copper when new. The drum bushing looked worn, but also check the pump cover surface where that bushing rides and replace the pump cover is there's wear. Check the inside of the pump cover for wear from the forward rings. Also check the inside of the direct drum for wear from the direct rings. Any wear; replace the drum. Replace that converter. It looks worn in the bushing area and it might be grooved in the seal area. Check it for cracks emanating from the square cuts toward the front. If you stick your finger inside you'll find the weak spot of the 904; the converters are thinner forward from the pump tangs and that's what makes them crack. You can tap it and oil will come out of the crack; then you can see it. Bottom line, although the filter will protect the valve body and converter from contamination by large particles, the problem arises when new hot fluid hits the built up layers of contamination that have been compacted into the outer perimeter of the converter. While all of this has been a build up of very fine particles that can't damage much, it gets washed out in large compacted chunks that will clog your new filter again and again. Rebuilt converters aren't hard to find. If the composite thrust washers are brittle then replace them. Put a new on on the front of the output shaft. You can put two on the pump to reduce endplay.

The problem with not replacing the pump bushing is that it locates the pump gears in the pump housing by locating the pump drive cogs on the converter, so not changing it can lead to pump damage purely from the pump gears running off center causing low pump pressure and quicker drain back of the fluid when not running.
The pump tries to run off center anyway, just purely due to the function of the pump pressure pushing it to one side, so it's pretty darn important to replace it always.
If you look at one of those bushings it will be heavily worn on one area more than the rest, which lets the center gear of the pump get off center.
When that happens it starts dumping cast iron dust into the fluid and quickly distributed it through the rest of the trans killing it, and likely doing so much wear damage as to make the internal parts completely trashed and not even reusable.
The filter will not save the trans from that iron dust, and it takes the converter with it.
It's just not worth a 50 cent bushing to risk it.


Also have to be careful about stacking washers as to not get the sealing rings so far out of place that they don't direct fluid where it needs to go.
If you look in the drum on the other side of that bushing there are slots where the fluid goes through so the clutches apply.
To much washer can misalign the rings to the point the fluid can't get into the drum.

You or I might get away with different spacing, and I have done it before, but for someone new to it probably best to stick to normal endplay practices.

 

[TrailBeast]

I only replace bushings that are bad. That pump bushing looked pretty good to me; a lot of them show copper when new. The drum bushing looked worn, but also check the pump cover surface where that bushing rides and replace the pump cover is there's wear. Check the inside of the pump cover for wear from the forward rings. Also check the inside of the direct drum for wear from the direct rings. Any wear; replace the drum. Replace that converter. It looks worn in the bushing area and it might be grooved in the seal area. Check it for cracks emanating from the square cuts toward the front. If you stick your finger inside you'll find the weak spot of the 904; the converters are thinner forward from the pump tangs and that's what makes them crack. You can tap it and oil will come out of the crack; then you can see it. Bottom line, although the filter will protect the valve body and converter from contamination by large particles, the problem arises when new hot fluid hits the built up layers of contamination that have been compacted into the outer perimeter of the converter. While all of this has been a build up of very fine particles that can't damage much, it gets washed out in large compacted chunks that will clog your new filter again and again. Rebuilt converters aren't hard to find. If the composite thrust washers are brittle then replace them. Put a new on on the front of the output shaft. You can put two on the pump to reduce endplay.

Although I disagreed in a couple of places, you do make very good points.
You must have done some of this kind of work in the past.

 

[TrailBeast]

View attachment 1715214352

I would like to replace but the problem is that I cant find anyone around town that has them.

Where should I be looking for these? Buying a used one that I know nothing about is the same as me re-using mine, so I would need to find a "new" one.....thoughts?

Every single local trans shop has access to new converters, as that business just can't be done without it.
What they want for one is what would concern me.
Maybe ask about rebuilding yours, and if that doesn't work do the best you can on a replacement.

 

[CudaFactHackJob]

Yup, a lil while now. I rebuilt my first trans in a 73 Dart back in 1980. I'll be 70 next year. My very best advice to you at this point is "Don't order anything until you've made a list of all the parts you need." If your direct drum is bad and the pump cover is bad, plus the converter is bad...that's beginning to add up to more than another trans would cost. Even most bad 904s have a better converter than yours. Post pics of the inside of the direct drum and the back of the pump where it rides. Also, if you have any destroyed thrust washers, check those surfaces involved for scoring. ..I don't see how you could be very adept at replacing bushings yet at the same time not be able to identify a bad one.. From the pics you've posted, I can see that too little attention is being paid to critical areas. I'm advising on this build because I like to see folks rebuild their own transmission; especially a 904 and a lot of viewers might be interested for their own build. But in all honesty, I don't have high hopes for this build if you're going to cherry pick my advice; because everything I suggest is tried and true over a span of almost forty years. Like my 8th grade nun teacher used to say, "A word to the wise is sufficient".

 

[Duster Captain]

After reading everything, these are the steps I plan on taking:

-Replace everything that comes in a standard rebuild kit, including all bushings.

-Replace torque converter. I finally started to find some places that can get them around town for around $100.

-Replace direct drum, it is heavily scored from band. Also replace band.

-Inspect composite thrust washers closely for brittleness.

-Inspect pump cover for wear from bushing and wear from sealing rings. Post pictures.

If your direct drum is bad and the pump cover is bad, plus the converter is bad...that's beginning to add up to more than another trans would cost.

Direct Drum(need): $40
Front Pump Cover(may not need): $100
Torque Converter(need): $100
Master rebuild kit w/steels, bushings, bands, etc: $130

Total: $270-370

If you know of a reputable source for a freshly rebuilt 904 for close to $370 delivered, please share it.

I don't see how you could be very adept at replacing bushings yet at the same time not be able to identify a bad one.. From the pics you've posted, I can see that too little attention is being paid to critical areas. I'm advising on this build because I like to see folks rebuild their own transmission; especially a 904 and a lot of viewers might be interested for their own build. But in all honesty, I don't have high hopes for this build if you're going to cherry pick my advice; because everything I suggest is tried and true over a span of almost forty years.

The reason I am on this forum is that I have never re-built a transmission before. I am here to learn from the experience of others as I learn a new skill. If I was an expert at identifying and inspecting the critical areas of a Torqueflite 904 transmission, this thread would not exist.

Also, advice from experienced people is sometimes contradictory, as in the case of the bushing replacement:

That pump bushing looked pretty good to me; a lot of them show copper when new.

The problem with not replacing the pump bushing is that it locates the pump gears in the pump housing by locating the pump drive cogs on the converter, so not changing it can lead to pump damage purely from the pump gears running off center causing low pump pressure and quicker drain back of the fluid when not running.

I am a mechanical engineer with years of experience designing, building, and servicing parts. I just need some constructive guidance to point me in the right direction here.

 

[CudaFactHackJob]

Well, that's good to hear because you're going in a lot of wrong directions. Unless your "master" kit has selective thrust washers, it's filled with a lot of useless parts. I buy core transmissions for $50. I wouldn't pay that much for yours unless it had a partial throttle kickdown valve body. You don't really have a good core to start with. With fluid you're already looking at $400 for your build. That's just nuts for a slant six 904. The pump cover should be the same price as the direct drum. But more to the point, with that twisted line killing lube pressure, you basically have a pile of junk there. You must look closely at every single wear point, and I'll bet you find a lot more damage. A good used slant six trans is usually around 150-200 and that includes a good converter...and you don't even have to buy fluid. I read threads like this one all the time and they serve to discourage most beginners from rebuilding their own transmission. A 904 is the easiest transmission to rebuild, but starting with that one is a recipe for disaster. Oh, I'm sure it will work, but who knows for how long. If you miss one little thing, it's all for nothing; and that trans was extremely fried so I'm having doubts that you'll be able to find every single flaw. There are 904 rebuild kits on ebay for under $60; with steels and free shipping. You want to spend an extra $70 for a band and some bushings. Buy another trans. Or two.

 

[Duster Captain]

Buying another transmission is not feasible for me, I am going to go ahead with this rebuild if for nothing else than to learn.

So on to the next issue I have.

I bought a replacement front drum because mine was scarred on the OD. The drum I bought was a "4 friction" drum from a v8. I got this due to recommendations to upgrade from the 3 disk drum in my 904.

Therefore I also bought a rebuild kit with 8 friction disks total (4 for front 4 for rear).


My issue is that the kit had 4 thick frictions with slots on them and 4 thinner frictions that are smooth:

My rebuild kit came with 4 of each of these.

The new smooth frictions are significantly thinner than the new slotted ones.

My old front drum used 3 "waffled" frictions, so I figured I should use the new "slotted" ones in my new 4 disk front drum:

This is what was in my old front drum. 3 "waffled" frictions.

So i put all 4 of my new slotted thick frictions in my new 4 friction drum and the clutch stack is too thick to install the wave lock ring:

This is my new 4 disk front drum with all 4 of my new thick slotted frictions and new steels. There is no room to install the retaining ring.

Out of curiosity, I installed just 3 new thick slotted frictions (and 3 steels) in my 4 disk drum:

This is my new 4 disk drum with 3 new thick slotted frictions and 3 new steels. The groove for the retaining ring is exposed and installs easily. The largest gap between the wavy ring and the front steel plate is right about what the book says it should be for a 3 disk setup.


What am I missing?

Did someone sell me a 3 disk drum instead of a 4 disk like I asked for? 3 new slotted frictions looks like it works fine...

Do you use the 4 thin smooth rings in the front drum? Pretty sure the old rear drum had the smooth frictions. The old front drum had the waffles...

Thoughts?

BONUS:

This was the most frustrating 45 mins of the entire project so far. I know there is a special tool but I am very stubborn. Finally got it but it was no kiss on the cheek.

 

[CudaFactHackJob]

Yikes!! That looks DANGEROUS!! Hey if nothing else, just notch a 2x4 about three feet long and attach it to a pivot on your bench. Your C-clamp business is outrageously toying with a visit to the ER. Ya, that's a three plate drum. You can still put four into it if you use a lower pressure plate from a forward drum on top; if you can't return it. Those ring surfaces look a little sketchy.

 

[Duster Captain]

Yes the C-clamps were a poor choice, I should have just gotten a proper spring compressor. But its done.

I'll probably just put 3 disks in my drum, this is just a slant six that I'm going to change later anyways.

I've also realized that my thrust washers look worn out and too thin:

Both look pretty worn

The min thickness per the book is .059". Looks like I need new ones, another delay in the rebuild...

 

[CudaFactHackJob]

They still have gray on them; they're good. All new thrust washers will wear down quick after you install them and open up the end play. I'd run those and take up the slack elsewhere at the pump or between the front and rear shaft.

 

[Duster Captain]

Thats good news.

I also realized that .059" min thickness is for 727 thrust washers. These are fine for the min thickness for 904 washers, so Im reusing them.

 

[Duster Captain]

Making steady progress.

Question:

Am I missing something for my kickdown servo assembly?

Im pretty sure this is everything that came out of the kickdown bore during disassembly. The rebuild book and pictures online show a piston? Did I lose a part?

Is this just how they are for 1971? Is this a "load controlled" vs "non load controlled thing"?

 

[KickDown]

That is just the guide plate & pin you have pictured there. The piston is probably still in the bore. The piston pushes the pin to actuate the apply lever to apply the intermediate band for 2nd gear. You can remove the piston with a pair of expanding snap ring pliers. I've never come across a controlled load servo piston in a 904, only the later model 727

 

[Duster Captain]

That's what I figured, I'm hoping the piston is still in the case and I just overlooked it...

I will report back later once I've had a look.

 

[Duster Captain]

Ok so I was just being a dummy and forgot to remove the kickdown piston, it was in the case.

On to my next questions for the counsel:

Does the pin on my output shaft look ok? Looks a bit rough around the edges like it was broken... is it replaceable?

These are the sealing rings that are on my governor assembly. Is it supposed to be a combination of 1 normal sealing ring and 1"interlocking" sealing ring? Also, that top normal sealing ring looks awful big but thats the one that was on it....

The sealing ring on my accumulator broke in half when I tried to remove it. My rebuild kit did not come with a new steel one, so Im looking for a source for a new one. Might just get a variety pack if I can find it.

On the topic of sealing rings, what is this? It is flexible plastic (teflon?) and has tapered ends (scarf cut?) that mate together. They came in various sizes in my rebuild kit. The internet is telling me they are also sealing rings. Are they meant to replace steel sealing rings (both simple and interlocking steel rings)? Should I use one on my accumulator?

So there are three types of sealing rings:
-standard steel
-interlocking steel
-plastic bendy (teflon?) with tapered ends as in the pic

I have many plastic rings in my rebuild and not many steel rings. Should I be replacing all steels with the plastic scarf cut ones?

 

[TrailBeast]

Ok so I was just being a dummy and forgot to remove the kickdown piston, it was in the case.

On to my next questions for the counsel:

View attachment 1715220557
Does the pin on my output shaft look ok? Looks a bit rough around the edges like it was broken... is it replaceable?

Seen way worse that reused without issue, as that pin just basically aligns the gear train shafts at their meeting point.
The planetary gear set takes care of the aligning once it's back together
The thrust washer that goes on that pin is important though, and you may even need a different one for endplay concerns but can cross that bridge when you get to it.

View attachment 1715220558
These are the sealing rings that are on my governor assembly. Is it supposed to be a combination of 1 normal sealing ring and 1"interlocking" sealing ring? Also, that top normal sealing ring looks awful big but thats the one that was on it....

Usually they are both the same, but someone was in that trans before for sure.
It really wouldn't make any difference though since both type rings doo the same job anyway.
(Factory was two open ended rings, that you had to be careful not to snap off when reassembling)

View attachment 1715220556
The sealing ring on my accumulator broke in half when I tried to remove it. My rebuild kit did not come with a new steel one, so Im looking for a source for a new one. Might just get a variety pack if I can find it.

Teflon rings are more commonly in newer transmissions, but if done correctly they can also be used in older transmissions.
I like the metal rings myself, but I do have to admit the Teflons do work even though they look like they would leak fluid badly.
Over bending the ends a little and heavily lubing then in place making sure the ends don't get cut off on assembly is the main PIA about Teflon.
They make rubber D rings as a replacement for the metal ring, because the rubber rings seals better.
If the Teflon ring fits right there shouldn't be a problem, but a better seal will mean better holding pressures on the second gear (kickdown) band.
Teflon wears on the metal surfaces more that steel rings also believe it or not, but I have to admit I have used them (and specifically as on an accumulator piston)


View attachment 1715220559
On the topic of sealing rings, what is this? It is flexible plastic (teflon?) and has tapered ends (scarf cut?) that mate together. They came in various sizes in my rebuild kit. The internet is telling me they are also sealing rings. Are they meant to replace steel sealing rings (both simple and interlocking steel rings)? Should I use one on my accumulator?

So there are three types of sealing rings:
-standard steel
-interlocking steel
-plastic bendy (teflon?) with tapered ends as in the pic

Yep, "scarf cut" it is.
I think I covered the main stuff about them up there.

I have many plastic rings in my rebuild and not many steel rings. Should I be replacing all steels with the plastic scarf cut ones?

I replied within your post for simplicity.

 

[Duster Captain]

I replied within your post for simplicity.

Thanks for the good info.

I think I will try to find some replacement metal rings for my accumulator and go with the teflon rings if I cant find any.

I am almost done with everything but the valve body. Getting into that this weekend hopefully.