904 Won't Pull

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demon322

demon322

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I need some guidance here as I admittedly know very little about transmissions. Sorry that this is long but I am trying to include all the details I know of to paint the best picture about what is going on.

68’ 904 behind a 360 in my Demon. Ran fine but always seemed to have some trouble shifting. The 2nd to 3rd shift always seemed to slip and I don’t think the passing kick down was working properly.

Realized my reverse lights weren’t working due to the incorrect ‘rooster comb’ so the valve body was swapped out with one from a ’78 904. Same shifting issues and this is really when I noticed the kick down issue so I can’t be certain if it was always a problem or after this swap.

This summer I swapped a 340 in for the 360 with the same 904. Same shifting issues the little I got to drive it but now the problem is it won’t pull hardly at all in forward gear. Reverse seems to work ok. It just sits until the revs come up quite a bit and at that point will creep forward enough to move but never with much force.

Possible problems: The transmission is a bit overfull. After a nightmare of a time breaking and then replacing transmission cooler lines (and adding a bottle of Lucas) it is too full. Could this be it?

Could the convertor be the issue? It seemed to work ok before but I probably ran the car too long low of trans fluid while the lines were off but we were working on getting the motor to run. Also, the dust shield was bent and rubbing the converter bolts for a while before I realized it.

Or, is there any way incorrect or out of adjustment linkage could be the culprit?

Thanks for taking the time to read this. Please let me know if I have left anything out that might help diagnose the problem. A little note, if this fix turns from something simple into big bucks – I probably will just try to find a 727 to use for the time being. My whole goal was to continue to use the 904 since I already had it running while I save money/find parts for my planned 5 speed swap.

Thanks all!
 
Most likely just needs a rebuild from the description you gave of the symptoms, but it's possible it could also need hard parts.
You just never really know but a look in the pan can give some pretty good clues as to what you might be in for.
If there is a teaspoon of little metal bits in the pan like gold dust stuck in a little pile of mud and black flakes laying around it is probably ok and just needs a rebuild.

Ok, so a tablespoon of little metal bits since you were trying to make it go anyway. :D

Inspection and assessment is where the real answer lies.
 
I see what you are saying. I will see what I can find but if it needs a rebuild I think it's the end of the road for the 904, at least for my uses. I think I have enough pieces around here for a 727 swap to get me moving while I wait for the 5 speed. Thanks again.
 
As Tony said more than likely you killed it by driving it with the kickdown (actually throttle pressure) linkage not working and adjusted correctly. It controls hydraulic pressure to the front band and both clutches. If not adjusted right it'll smoke the trans pretty fast
 
demon322 said:
I see what you are saying. I will see what I can find but if it needs a rebuild I think it's the end of the road for the 904, at least for my uses. I think I have enough pieces around here for a 727 swap to get me moving while I wait for the 5 speed. Thanks again.
Click to expand...

You are welcome.
Keep in mind only a 727 converter works in a 727.
 
And the kick downlinkage needs to be adjusted correctly on a 727
 
fishy68 said:
As Tony said more than likely you killed it by driving it with the kickdown (actually throttle pressure) linkage not working and adjusted correctly. It controls hydraulic pressure to the front band and both clutches. If not adjusted right it'll smoke the trans pretty fast
Click to expand...

This does make sense. This means it was something that happened over time and would have happened with or without the motor swap. I just worried that overfilling the trans after the cooler line issue and running it low a bit might have caused it. Even though the 904 was in the car for quite some time, it only ran about 300 miles total. Maybe it was just time to fail due to the linkage issue. Next time I will ask for advice on the linkage to try to avoid this issue.
 
TrailBeast said:
You are welcome.
Keep in mind only a 727 converter works in a 727.
Click to expand...

I for sure have a couple of 727 converters. Other than the trans itself, what all would I need for the swap? I know the driveshafts are different between 904/727. Is a Dart driveshaft the same as a Demon? I think they have a different wheelbase. Transmission mount?

My uncle has offered to let me borrow his 727 and driveshaft from his 70 Swinger which is sans motor at the moment if it would work. If so, should I also look to borrow or find some new linkage? Wasn't sure if they were the same between the transmissions.
 
Dart has a 3 inch longer wheel base..so the driveshaft will be longer...the trans X member is in same place and use the same X member..tranny mounts are interchangeable.
 
It's not helping that the wrong terminology is being used. That linkage is the Throttle Rod. Mopar does not call it the kickdown linkage anywhere although it does serve that purpose.

The important part of the throttle rod adjustment is that it not only controls shift timing and feel, but also line pressure. So, if you don't make the simple adjustments that Mopar outlines and that are described in detail on the internet, you risk burning the clutches right out of it. If it won't pull in low gear, you really smoked it.
 
IIRC, the 78vb does not fit the 68 case properly. Check the area around second gear apply and release. I ran into this issue once; but I forget the vb year.
If reverse works but manual low does not then the forward clutches are probably cooked. Chrysler calls this clutch the rear clutch,cuz,well,it is the rearmost one.And with insufficient operating pressure, it is the most likely one to get cooked first.
I wouldn't give up on that sweetheart; she just needs some TLC and a few upgrades.
 
70aarcuda said:
Dart has a 3 inch longer wheel base..so the driveshaft will be longer...the trans X member is in same place and use the same X member..tranny mounts are interchangeable.
Click to expand...

Good to know. So I need to be looking for a shaft from a duster/demon/dart sport with small block/727/8.75?
 
TylerW said:
It's not helping that the wrong terminology is being used. That linkage is the Throttle Rod. Mopar does not call it the kickdown linkage anywhere although it does serve that purpose.

The important part of the throttle rod adjustment is that it not only controls shift timing and feel, but also line pressure. So, if you don't make the simple adjustments that Mopar outlines and that are described in detail on the internet, you risk burning the clutches right out of it. If it won't pull in low gear, you really smoked it.
Click to expand...

I learn something new here most every time I log on. I never knew that linkage played that important a role in keeping line pressure. I have begun to research a bit and will for sure pay attention to get it adjusted right when I get it back together. Thank you.
 
AJ/FormS said:
IIRC, the 78vb does not fit the 68 case properly. Check the area around second gear apply and release. I ran into this issue once; but I forget the vb year.
If reverse works but manual low does not then the forward clutches are probably cooked. Chrysler calls this clutch the rear clutch,cuz,well,it is the rearmost one.And with insufficient operating pressure, it is the most likely one to get cooked first.
I wouldn't give up on that sweetheart; she just needs some TLC and a few upgrades.
Click to expand...

This seems to be the case. The rod that goes down to the trans hasn't seemed to work correctly since the new vb was installed. I fear that you are correct and she is cooked. I'm sure it could and should be repaired but I don't want to put any more $ in the 904 since it isn't my permanent solution. I hopefully can borrow a 727 for the time being but will be sure to have everything adjusted correctly before I make the same mistake again. Thanks for the reply.
 
No, the external linkage should be the same. It is possible that the wrong ratio throttle pressure arm was installed on the VB, but otherwise the rest is how it is engaged by the carb. The 2bbl rod,and the 4bbl rod,(The top rods) are different, and if this is not corrected then the VB will never receive the correct command from the carb. And if you use this same wronk linkage on the 727, then it too will cook.
The 904 can easily be beefed up for a hot streeter. It gets pricier as you approach 400hp, but 300hp is nothing more than a good kit, and some tuning, and adequate cooling.
 
IF it was still moving, even somewhat, you might luck out and only need a soft rebuild. Bands and such. But that depends on how much it was moving, the more the better. Every time you drove it when it was slipping you killed it a little more. You've definitely cooked the insides. Who knows though, might luck out. I don't think its expensive for a shop to look at it.

904's are nice cause they are lighter weight internals. Less rotating mass and friction, therefore more power makes it through them. They can be built very strong and work excellently behind small blocks. Just a thought. However if you have a 727, they are basically bulletproof behind almost any small block, even with mid-level mods. I would always suggest a stage 2 shift kit and if the motor has any real work to it, a custom converter. You will know the difference. You will appreciate the difference. Your transmission will appreciate the difference as well.
 
There's a mighty slim chance that you could take up the slack in low/reverse band, and the "kickdown" band, and drive it until you make the swap for the 5er.
Read the factory service manual on band adjustment, and sorta wash over the micro-torque and backing off so much after stuff.
When you check the actuator, moving it by hand as the hydraulic servo would, you will see/ feel a certain amount of movement, most likely too much as a result of friction material wear. You want to DECREASE the amount of "slop" in the band, while still leaving a reasonable amount of actuator movement to hold AND release with minimal hydraulic action.
 
" Per post #1;Reverse seems to be working".So the L/R band "seems"to be doing it's job.
For it not to move in Drive or manual Low, the problem has to be in the RearClutch.Or the TC, but then reverse would be sluggish too.
If that clutch is cooked, the fluid will reek, and not be it's usual pretty red color.It will be darker and more towards the Burgundy end of the scale, perhaps even blackish.
 
Update: Decided to move on from the 904. Going with a 727 for now. Deciding on whether to try to make the throttle rod work with this one or opting for a lokar or similar cable.

Going to swap in a different rear end at the same time. Going from an open 742 with 3.23 to a 489 with 3.91s.

Will I be able to use my 904 driveshaft with the 727 if I have it shortened? That seems to be the part that I might need to find if not.
 
Going to a different center section in the rear may require a different U-joint, depending on what the new center section came from! There are solutions out there though, like the offset U-joint with the 7260 yoke on one side and the 7290 on the other! So, the answer is yes, you can shorten your existing driveshaft for the 727, but you will need the 727 front yoke, as the 727 and 904 tailshaft splines are different!
 
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