So we rebuilt the 904 in my Dart a few months ago, and finally ran the car in another LeMons race in Colorado last weekend. Unfortunately, we had to shift with the 2 and D buttons all race because we could not get the kickdown to behave properly. Or is it fortunately? It actually worked surprisingly well and didn't break all weekend. And we won our class race, which is awesome. I'll link to the full race write-up by Judge Phil once it's been posted.
But anyway, I would like to get the thing to behave properly when you just leave it in Drive. Currently, it will shift from 1 to 2 at about 20 mph, with very little variation based on throttle input OR kickdown lever adjustment. This is too slow, in my opinion- maybe 2000 RPM in 1st. Depending on where you set the kickdown adjustment, it will either stay in 2nd way too long (and possibly never upshift unless you let off the throttle), or it will upshift into 3rd and never downshift again unless you come to a stop. At its current setting, it will actually do both: It will stay in 2nd forever with the throttle pressed to the floor, but once in 3rd, it will never downshift again.
This is very different from its behavior prior to the rebuild, wherein the upshift and downshift points were fairly close no matter the throttle position. The only gripe I had with it before is that I couldn't get the shift points high enough even with the lever fully actuated. Now it seems I have the opposite problem, but only on the upshift. It also seems like the shift behavior will sometimes change from one drive to another. Maybe it's dependent on temperature.
All this taken together makes me wonder if there's maybe a clog in the valve body. The behavior doesn't seem 100% reproducible, so that might suggest some debris that's moving around, or maybe something in the governor assembly is hanging up. We didn't touch any of this during the rebuild, and my understanding of how it works is not very good either.
A guy posted the following comments on our LeMons team Facebook page: "Did you use the factory service manual? They're very well written. You can run an oil pressure gauge temporarily to the test ports on the side of the trans and compare what you get to the chart in the manual. Try the governor port first. All those spools need sharp edges. Rounding them off with sand paper, or getting nicks in them when rebuilding could cause erratic behavior...
With the oil pressure gauge hooked up to the governor port, you should see it steadily increase as vehicle speed increases, and decrease with speed. When hooked up to the throttle pressure port, you should see it steadily increase and decrease with throttle movement. You may be able to do this manually by moving the linkage back and forth in drive and idling with the brakes on. Could narrow it down to valve body or governor."
Any thoughts? We'd like to get this operating well before our next race. Shifting with the buttons worked fine in Colorado, but I'm paranoid that pushbutton mechanism is going to break with all the abuse.
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