904 third gear flare

[Charlesvolare]

I have a 904 behind a mild 360, probably around 350 hp and 325 ft/lbs I'm guessing. I built the trans with beefier clutches, and had it behind a stock 360 magnum for a bit as well. Has about 8,000 miles on it total, and I drive the thing hard. Stoplight to stoplight, there's never really much of a chance to get into third gear quick, but merging on the highways third gear has always been great. Second time I took the car to test & tune I noticed engine rpm would flare up on the 2-3 shift, so I messed with the kickdown cable (lokar cable, set up correctly as per instructions and internet for 7,000 miles prior) and it didn't do much so I put it back. A couple weeks later it started flaring on the street as well. Today, i discovered I can no longer drive on the highway due to the fact it won't stay in 3rd gear anymore.... there's a sweet spot in the pedal where it'll stay in gear, anymore and it'll downshift (not entirely onto second though, it's weird) any less and I'm just coasting. Not good for driving the highway with 3.55 gears. Whenever it would stay in gear, it'd hold. Pulled hard in third too. 65mph is right at the start of the good stuff at 3200 rpm, pulled to 90 in about .000001 seconds it felt like. The first 904 I built was for the original slant six, and that started doing the same thing; when I pulled that apart after the engine swap the front clutch pack was a disaster. I haven't touched the bands since I built it but every other gear is strong with hard shifts. Fluid is good. I'm just trying to come up with any reason it'd do this other than the front clutch pack is toast, any thoughts?

Here's a video of a pass, notice the 2-3 shift we're I let off the throttle for it to go into gear:



It WAS like this, today is wouldn't even stay in gear...

 

[oldkimmer]

Is this tranny all stock or is it modified? If so what was done to it? The bands usually have to be check/reset after awhile. What parts did u use ? What clearances did u have? Mire info=more help. Kim

 

[Charlesvolare]

Stock valve body
Rebuild kit I used: Performance Automatic Max Performance Kits PAKT12700
Front band used: TCI Red Lined Flex Bands 125600
Stock converter
Rebuilt to stock specs, no special clearances or anything. Replaced every seal in the thing.
'73 case and inners, '80 tail housing (from previous /6 904, didn't want to mess with changing bushing and seal when I had basically new ones all ready installed in the other housing.)

Again, this transmission has worked flawlessly up until now.

 

[CudaFactHackJob]

Third gear is the weak spot on this trans. Low fluid level will do it. I'm amazed by how many folks don't know they have to check fluid level in neutral. But this direct clutch frailty makes you always check the inside of the drum for ring wear; can't have any surface imperfections whatsoever. I also limit end play to about .015-.020; otherwise that drum can wobble easier; wearing out the rings; losing pressure. Loose clutch pack clearance will lead to premature wear. The bushing has to be good or the drum will wobble. Can't have any wear on the pump surface where the drum bushing rides. Oh, and a stock valve body sometimes has too much overlap on the 2-3 shift that will fry the band and the direct clutch. Gotta have some type of shift kit.

 

[Sterling]

I rebuilt my brother's 904 years ago, got a Fram rebuild kit. High gear was flaring soon after. Pulled it back apart, and put stock Chrysler clutch disks in. That fixed it. Didn't like the look of the Fram disks , but didn't know enough about transmissions then.

 

[Charlesvolare]

Think I'd be okay with just replacing the clutch disks if everything else looks okay, and leaving everything else alone?

 

[CudaFactHackJob]

Check the inside of the direct drum for ring scoring; it has to be perfectly smooth. Check end play; if it's loose that drum will be allowed to wobble on its bushing. bushing might be bad; journal on pump might be bad; check the piston seals. Oh, and the rings will get side slammed if the drum is busy going front to back and wobbling. Replace the two direct rings.

 

[70aarcuda]

Last weekend our 71 Dart had the 3/4 gear flare up almost 500 rpm .....readjusted the front band changed the fluid and clean out the pan.....4 passes today and no flare .....

 

[CudaFactHackJob]

Last weekend our 71 Dart had the 3/4 gear flare up almost 500 rpm .....readjusted the front band changed the fluid and clean out the pan.....4 passes today and no flare .....

What was in the pan?

 

[70aarcuda]

the usual crap....disc and band crap......

 

[CudaFactHackJob]

Reverse usually gets a hesitation in it when the third gear clutch wears down. Pretty common but it's easy to drop out the pump and just freshen up the band and the clutches in the two front drums without getting into everything in the back. Too often guys want to take everything completely apart and omg it turns into a huge cf.

 

[Charlesvolare]

I haven't had time to mess with it much, but heres a few more things I've figured out that may or may not help:
1) Shifts perfect when engine is cool. I can start the car in the morning and drive the few miles to class with no problems shifting into third.
2) My allergies have cleared up enough for me to smell again. Fluid is so burnt it smells like a campfire.

I'm no expert by any means, but bad fluid would result in loss of pressure/density of fluid, which is needed for shifts, and since it does fine cold (thicker) maybe a fluid change would fix it.

If I remember correctly, reverse has higher line pressure than direct, so that's why reverse is fine. I can still break tires loose backing it up, cold and hot.

When I can get the chance, I think I going to drop the pan and check it out. If it looks okay (aka not too much clutch material in it/metal in it) I'm thinking about just adjusting everything and doing a fluid flush, possibly a shift kit while I have the pan off. Does anyone recommend I do this first or does then bad trans fluid mean bad internals and necessitate pulling it apart?

 

[TrailBeast]

I haven't had time to mess with it much, but heres a few more things I've figured out that may or may not help:
1) Shifts perfect when engine is cool. I can start the car in the morning and drive the few miles to class with no problems shifting into third.
2) My allergies have cleared up enough for me to smell again. Fluid is so burnt it smells like a campfire.

I'm no expert by any means, but bad fluid would result in loss of pressure/density of fluid, which is needed for shifts, and since it does fine cold (thicker) maybe a fluid change would fix it.

If I remember correctly, reverse has higher line pressure than direct, so that's why reverse is fine. I can still break tires loose backing it up, cold and hot.

When I can get the chance, I think I going to drop the pan and check it out. If it looks okay (aka not too much clutch material in it/metal in it) I'm thinking about just adjusting everything and doing a fluid flush, possibly a shift kit while I have the pan off. Does anyone recommend I do this first or does then bad trans fluid mean bad internals and necessitate pulling it apart?

If you put new fluid in a trans with burned fluid it will probably do it in.
New fluid has new detergents and will soon eat up what's left of the burned clutches.
Save your time and money for a rebuild or replacement.

 

[Charlesvolare]

If you put new fluid in a trans with burned fluid it will probably do it in.
New fluid has new detergents and will soon eat up what's left of the burned clutches.
Save your time and money for a rebuild or replacement.

How? The frictions

If you put new fluid in a trans with burned fluid it will probably do it in.
New fluid has new detergents and will soon eat up what's left of the burned clutches.
Save your time and money for a rebuild or replacement.

How? Frictions are designed as a wearable component, so it's not like a non-wearable camshaft with engine oil additives. Most atf additives and detergents are for anti-wear and stability under temp. Burnt fluid is worse off for the tranny id imagine since thes extra additives are obviously broken down and no longer doing they're jobs leaving the fluid to deteriorate on the molecular level, resulting in property changes that should actually be way more detrimental than new fluid.

 

[CudaFactHackJob]

Dirty fluid is thicker so pressure is higher. Just change the filter and dump the old fluid back in; minus the chunks. New fluid you'll probably lose third even when cold. It would be interesting tho.

 

[Charlesvolare]

Dirty fluid is thicker so pressure is higher. Just change the filter and dump the old fluid back in; minus the chunks. New fluid you'll probably lose third even when cold. It would be interesting tho.

Dirty fluid might possibly be thicker, but shouldn't burnt fluid be thinner? The fluid should break down resulting in it being less viscous (=thinner).

It's not old fluid with 100k miles, it's fluid with about 7,000 miles in car that's been driven hot and hard. That seems to exhibit problems only when it's warmed up.

 

[Charlesvolare]

Dirty fluid might possibly be thicker, but shouldn't burnt fluid be thinner? The fluid should break down resulting in it being less viscous (=thinner).

I'm not trying to argue, just understand. I don't have too much first hand knowledge but I've taken materials and fluid mechanics classes so I know how things should theoretically work for the most part. Whether they do or not, that's what I'm trying to figure out.

I know engine oil may sludge and thicken when not changed or used but I'd imagine ATF behaves completely different especially in this circumstance.

 

[CudaFactHackJob]

Install new fluid and report back. Don't forget to drain the torque converter. At least this will flush the converter should you decide to reuse it. But the contamination in the converter went in there as fine dust particles that would pass thru a filter; however, it will come out in chunks that will clog the new filter.

 

[TrailBeast]

How? The frictions

The new detergent will eat the friction adhesive and the friction material because it has been cooked.
It isn't the same material that it normally is, but has changed "molecularly" as you say.
Do it and see, because all you have to loose at this point is the time and money.

They will usually work a little better for a short time, and then get WAY worse fast as the new solvents break down the material that is left.

You will need a new or good used converter, as well as flushing out the cooler lines to and in the radiator really well.
Flushing converters doesn't cut it as some would like to think.
If using the same converter it needs to be cut open and cleaned/inspected.

 

[CudaFactHackJob]

I learned all about flushing converters on a th400 I rebuilt. The clutches were all fried but the converter wasn't worn. About every twenty miles the new filter would clog with material that had been lodged in the converter and the pump would start to whine from drawing a vacuum. I had to change the fluid and filter three times but it was fine after that. A worn direct clutch as stated would probably only put about one fourth or a fifth as much material as that th400 converter had in it. Trying to flush a converter outside the car is futile, but in the car it can definitely be done but the th400 I did was definitely not worth it. Now I decide based on the level of wear found within the trans. If a torqueflite comes in with both clutches and a band destroyed I say no way, but if just the direct is half gone I reuse it. The problem is that a lot of the 904 converters are cracked anyway; they just haven't exploded within the pump yet. But a high dollar stall converter would be worth saving by changing the fluid several times. If you have a viscosity tester, I would be interested in test results comparing your old fluid to new fluid (at the same temperature).

 

[transman]

The new detergent will eat the friction adhesive and the friction material because it has been cooked.
It isn't the same material that it normally is, but has changed "molecularly" as you say.
Do it and see, because all you have to loose at this point is the time and money.

They will usually work a little better for a short time, and then get WAY worse fast as the new solvents break down the material that is left.

You will need a new or good used converter, as well as flushing out the cooler lines to and in the radiator really well.
Flushing converters doesn't cut it as some would like to think.
If using the same converter it needs to be cut open and cleaned/inspected.

Guys who think flushing a contaminated converter will get all the crud out, have obviously never seen one apart. Clutch material will get caught up in the vanes of the pump(hub part of the converter), and also in the turbine. Think of the centrifugal force these oils are splashed against the internals. Putting solvent or the like in the converter and sloshing it around for a while won't loosen this crap up very much. Years back, transmission shops used to have a converter flusher that kinda worked. I'm sure you've seen them T.B. and if you worked in the industry, you know that for the most part they were a joke.
Get a rebuilt converter or get yours cut open, cleaned and rebuilt at the same time.
My opinion on used converters of any kind remains the same: they're great door stops.

 

[transman]

I learned all about flushing converters on a th400 I rebuilt. The clutches were all fried but the converter wasn't worn. About every twenty miles the new filter would clog with material that had been lodged in the converter and the pump would start to whine from drawing a vacuum. I had to change the fluid and filter three times but it was fine after that. A worn direct clutch as stated would probably only put about one fourth or a fifth as much material as that th400 converter had in it. Trying to flush a converter outside the car is futile, but in the car it can definitely be done but the th400 I did was definitely not worth it. Now I decide based on the level of wear found within the trans. If a torqueflite comes in with both clutches and a band destroyed I say no way, but if just the direct is half gone I reuse it. The problem is that a lot of the 904 converters are cracked anyway; they just haven't exploded within the pump yet. But a high dollar stall converter would be worth saving by changing the fluid several times. If you have a viscosity tester, I would be interested in test results comparing your old fluid to new fluid (at the same temperature).

What is cleaning the crap out of the converter, as well as the transmission lines and the cooler is the hot ATF(normal operating temperature). Hot ATF is the best cleaner for this purpose.
Also the item that cracks the most on both 904 and 727 converters is the hub.