400 turbo won't kickdown

[LipRipr]

I just bought a 1984 K20 Scottsdale that has almost been untouched. Everything is stock except the crate engine. I test drove it around the guys neighborhood & never really got test very much. It drove & stopped & was priced right so I bought it.

Now to my issue. I can floor the gas pedal & nothing happens. The engine gets louder but that's it. No kickdown & no power. The fluid level is correct, the switch on the gas pedal rod is working, I do have voltage down to the orange wire coming off the drivers side if the tranny, the vac line is clear. I pulled the mod off the passenger side & it had some fluid in the tranny end but none coming out the other side. It does shift firmly from park to R to N to D to L2 & L1.

I'm going to try a new mod in the morning. Any other ideas?

 

[76chevyc20454]

 

[foamypirate]

Could possibly be the kickdown solenoid itself. I have no idea how hard it would be to change it though, never done one.

 

[76chevyc20454]

i have the same problem, every great once in awhile when im try to overtake a car it will kick down but most of the time it will stay in 3rd.

 

[DoubleDingo]

i have the same problem, every great once in awhile when im try to overtake a car it will kick down but most of the time it will stay in 3rd.

I never thought of that, but yes, mine does that too if I am going 55 mph or faster, the TH400 will not kick down, just the 4 barrels kick in. My guess is to keep the engine from revving too high. But below 55 it will kickdown, the 4 barrels will kick in and it will accelerate above 55 before it shifts back into 3rd.

 

[LipRipr]

I took it out on the highway tonight. It does shift through all of the gears, 1-3. I stomped on it once & it took off like it should. Then every time after that, it was doggy like before. I can get a solenoid for around $30, a pan gasket & fluid. Looks like the solenoid would be easy to replace. I'll get one & keep you posted.

 

[chengny]

You can check detent solenoid operation without even dropping the pan. A properly stroking solenoid will emit an audible clicking sound in time with a 12 VDC that is applied and removed.

Just lay under the transmission. Have your assistant turn the ignition switch to RUN and then simulate a series of WOT's by jamming the accelerator to the floor.

If the solenoid valve is shuttling fully - from open to closed - there will be no doubt in your mind. It is loud enough that, if you know what you are listening for, you don't even have to climb under the truck. It is usually sufficient to just kneel down and kind of stick your head under the rocker panel.

If you can't hear the solenoid valve snapping open and closed be happy - it's an electrical issue.

Replacing the solenoid (or repairing the associated wiring) is the easiest solution to this problem. Nearly every component within the transmission control section is involved in a Detent 3-2 Downshift.

Here is the diagnostic chart for no 3-2 detent. Below that is the flow diagram for that operation:

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If you do find the solenoid to be non-operational - it is an easy fix. The valve and coil are under a little cover that is visible as soon as you drop the pan. It is secured to the valve body base plate with two bolts.

If you have extremely good luck - and find that there is something amiss with the internal section of the control lead - just repair it. The wires on either side of the transition plug can be pulled off if necessary. It will look like this:

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But, on the other hand, if you determine that the detent solenoid is working properly and you still don't get a 3-2 kickdown - the other fixes are more involved. The TH400 in my truck has a fully functional detent solenoid but still will never kickdown. Other than that it works great - and that's the way it will stay.

 

[LipRipr]

I found out that the truck has been sitting longer than the guy told me. It does kick down now, solenoid is working great. I dropped the pan, cleaned it up, new filter, fluid & etc.

I also installed a drain plug. My pan is 3" deep. The valve body in the forward corner on the passenger side hangs down 1.5" . That's where I put the drain. Not hitting or in the way of anything, works great. https://www.youtube.com/watch?v=BvcZyJnoArQ