A-904 Interchange

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vynn3

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Really enjoying my 273-powered 1967 Dart Convertible, but I've realized that I miss part-throttle downshift from my previous (newer) Mopars from the 70's.

I have access to a 904 from a '74 318 Charger, but I vaguely recall something about a flexplate or torque convertor change between '67 and later years.

What's the easiest way to get part-throttle downshift with the parts that I have? Will the later trans swap as they are, or can I rob the valve body and/or other parts from the '74 trans into my current trans?

-vm
 
There was a difference in the cases right in front of the low reverse band servo, so make sure the case matches up in that area, and doesn't uncover/cover any holes. There was a front converter snout dimension change along with the crank pilot hole, also an input spline change about the same time. Problem is, these trannsss have been swapped around over the years and so you don't really know what you have until you take it apart. The crank could have been changed, the whole motor, the input shaft; sometimes they even run the small snout converter in the big hole crank...
 
The easiest would be the A&A Part Throttle Kickdown kit, around $100.00-I think. That was what I did on my 67 Dart. Well worth the effort! The car is much more enjoyable to drive with the part throttle kickdown.
 
The easiest would be the A&A Part Throttle Kickdown kit, around $100.00-I think. That was what I did on my 67 Dart. Well worth the effort! The car is much more enjoyable to drive with the part throttle kickdown.

That would be easiest. I did some looking around, and A&A only lists this kit for the 727 trans. I've emailed them to ask if it will work on the 904, but I'm not optimistic.
 
Really enjoying my 273-powered 1967 Dart Convertible, but I've realized that I miss part-throttle downshift from my previous (newer) Mopars from the 70's.

I have access to a 904 from a '74 318 Charger, but I vaguely recall something about a flexplate or torque convertor change between '67 and later years.

Assuming that it has the original engine the 74 transmission has a larger front hub so it wouldn't work but you may want to be sure it's the original engine. A lot can happen to a car in 50+ years.
 
Will do. The car seems to be original/unmodified, so if it's a 318, it's still dressed as a 273. It also seems to be a fairly low-mileage car for it's age.

I'll probably just live with until the future 5.2 Magnum swap (someday). But this little motor won't die – it just runs better and better the more the car is driven.
 
The A&A kit installed in my original 904 in my 273-2 barrel Dart. The valve bodies are interchangeable.
That would be easiest. I did some looking around, and A&A only lists this kit for the 727 trans. I've emailed them to ask if it will work on the 904, but I'm not optimistic.
 
Not all valve bodies interchange. There were changes in the cases and in the valve body castings to work with them. I know folks just slap different valve bodies around as long as they bolt up to the case, but there are differences that effect pressure and exhausting. That A&A kit sounds like it would work.
 
What I meant to say was that same year 727 and 904 valve bodies will interchange, might not be programmed right, so at least I thought.
 
Not all valve bodies interchange. There were changes in the cases and in the valve body castings to work with them. I know folks just slap different valve bodies around as long as they bolt up to the case, but there are differences that effect pressure and exhausting. That A&A kit sounds like it would work.
Tell more about the effecting pressures and especially the exhausting please does it involve the converter exhausting thanks
 
It's something I'm very careful about. If a trans comes in with a mismatched vb/case I don't get involved with it unless the customer is willing to bring in the correct vb. If you look up in the case in the triangular shaped hole right in front of the reverse servo, some cases have an exhaust hole and some don't. I don't know all the effects of using a mismatched vb; that's one reason that I don't do it. I can't afford to use my customers as guinea pigs.
 
The A&A kit installed in my original 904 in my 273-2 barrel Dart. The valve bodies are interchangeable.

I (re)confirmed with Rob at A&A Trasnmissions that the kickdown works with 904's as well. Thanks for the head's up!
 
I have installed that PT kit on several pre-71 904vbs so, AFAIK, that PT valve can be retro-fitted right down to 67.
Having said that, if you get your governor set right, the KD will work pretty slick without the PT valve..
 
"Having said that, if you get your governor set right, the KD will work pretty slick without the PT valve.".[/QUOTE]
What modifications do you recommend for the governor? I modify every TF id rebuild by enlarging holes in the separator plate as per the TransGo instructions, plus I block the accumulator with a 1/2" piece of pipe within the spring, but I'd really like to do a governor mod to all of them if I could improve the KD.
 
to @CudaFactHackJob
Bottom line;

That was the mid to late 70s so I can't tell you what exactly I all did or in what order, but the end-result was, IMO, pretty slick
===============
As for the governor:
This story begins in about 1976, and I was 23 and totally ignorant of autos.
But I was working as a manual-trans rebuilder, and was friends with all the team of other specialists, so I jumped right in, expecting that they could bail me out if I screwed up.
I had just bought this 69 Barracuda and just replaced the oil-burning pig in it. The car had 2.76s and a 225, so it was a bit of a turd IMO. I wanted to keep the hi-way gears, and since I worked at this rebuild shop, the owner made me a deal on what was at that time called, a "Dirt-Jerker" TC; which turned out to be a 2800 behind my new slanty.
And I rebuilt the A904, with HD parts and a TF-III/full-manual shift kit.
But I got real tired of having to shift all the time so converted it to TF-II/semi-automatic status right quick.
Of course with 2.76s in the back the governor pressure did not match what the TC was doing. Since this was a hiway car, the 2.76s were staying.
So I had to learn about governors, and how to fine-tune them to make them do what I wanted it to do.
What I learned was that line pressure and governor pressure are always battling for supremacy. If the governor wins, you get a shift. If line pressure is augmented with throttle pressure from the KD adjuster, then the governor loses..... for a while, until the driveshaft speed bumps the governor back up into supremacy.
So really all I had to do was get the Governor flyweight into the ballpark, so the KD mechanism could be adjusted for the right Throttle Pressure.
You probably know all about this part.
At this time I had never heard of a PT downshift valve.
So you can guess how that went.
I could get the system to work pretty good over a narrow throttle setting, but the trans would often downshift one gear, when I really didn't need or want it to.
So then I started playing the line-pressure off the throttle pressure; but quickly discovered that the line-pressure adjustment range was very limited. And it was too easy to make the trans bang into gear with too much pressure when stopped, and I didn't like that; remember I'm 23, just shacked up/engaged/or married ( can't recall), and this is my first real job, so no future to speak of, and I better not break this trans.
(BTW, for those who want to know; I didn't get saved or baptized until 1993 so shacked up was not a big deal to me at that time.)
So that wasn't gonna be the best solution for me.
I really needed that PT valve, but hadn't yet heard of it.
The way I figured it, that KD mech should have been designed differently, with the first portion dedicated to throttle pressure and the second portion to KD; so I set about to see what I could do in that direction.
of course the miles are piling on, time is ticking, and the boys in the shop are rebuilders not Hot-Rodders or not into Mopars, so no help coming from them.
By this time I had figured out that I didn't like the Accumulator defeated so I hunted up a few springs from the shop trash bin and found something I liked, then moved on.
What I ended up doing is; I disconnected the KD mech from the throttle-arm, then tied the KD lever back about 75% of the resistance range NOT the travel-range, then worked on the governor until I got that working the way I liked it. Then clipping the tieback and reinstalling the KD, and voila.
Now I could floor it and get 4500rpm automatic upshifts,
or I could signal an earlier upshift by lifting, or
I could still hold it to 5000 with a manual shift, or,
Not at WOT, I could let the trans do it's thing, albeit with slightly higher rpm automatic upshifts than might be considered normal.
Then I happened one day, to be driving my buddy's babysitter home, a young boy, just old enough to have a driver's license, and he freaked out and was very keen to have this car.
Well I knew he had no money.
but I knew he had recently totaled his 340 Duster,
So I made him a deal for parts, and that "Warm-Rod" went down the road.

I liked that Dirt-Jerker so much I went and got me another for my next car, a 73Swinger 318/904/ and you guessed it 2.76s. But those were very soon replaced with an 8.25 with 4.10s. And this car, had the PT valve in it Now we're getting into the 80s.
Bottom line;
That was the mid to late 70s so I can't tell you what exactly I all did, or in what order, but the end-result was pretty slick ....... IMO.
 
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Oops, sorry, I fell asleep about halfway thru, woke up in a cold sweat from a nitemare; remembering a hazy day from the seventies; when I didn't know where I was or where I parked my car..
 
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