Transmission downshift switch for Turbo400

[Bruce D.]

My automatic big block 74 will not downshift above 1500 RPM by using the gas pedal. I am told there is a switch inside the pan that can be changed while pulling the pan and doing a transmission filter change.

Can anyone give me more info on this switch and verify that this could be the downshift problem? Any info about where this part is available and what it is called? Thanks

[Clem Z.]

Re: Transmission downshift switch for Turbo400

My automatic big block 74 will not downshift above 1500 RPM by using the gas pedal. I am told there is a switch inside the pan that can be changed while pulling the pan and doing a transmission filter change.

Can anyone give me more info on this switch and verify that this could be the downshift problem? Any info about where this part is available and what it is called? Thanks

make sure the switch under the dash operated by the gas pedal is fully engaged. i have slipped a piece of rubber fuel line over the projection on the switch to make the downshift engage

[Bruce D.]

Re: Transmission downshift switch for Turbo400

Thanks Clem. It seems to engage fine below 1500 RPM, but not at higher speeds. I will check for that in any case.

[Joel A.]

Re: Transmission downshift switch for Turbo400

There is a solenoid inside the pan that controls the kick-down/passing gear. If you remove the pan you'll see it on the driver side, bolted to the case, just behind the shift linkage. Two 7/16" head bolts hold it on(some had 3/8" head bolts). If yours is original, it will be shaped like an oval can. The replacement are square shaped, and fully interchangeable. However....the older, can style solenoids use a thin sheet metal gasket under them that is NOT used on the newer square solenoids. The new solenoids have a built in gasket. Using the sheet metal gasket on the square solenoid can cause a no passing gear.

You should check for voltage at the accelerator switch first, as Clem suggested. It is the same switch that operates the cowl induction door in the hood, so if the hood door works, there is power to the switch. Also be sure that the wire to the trans is actually connected to the trans. The outer sheathing for the connector gets hard over time, and it can actually cause the wire to fall off the trans connector.

In regards to using the rubber hose on the switch pin, I've done that too. The pin/plunger is actually adjustable, tho, so the hose trick is basically the quick way to fix it. If you push the plunger toward the firewall really hard, it will click forward, and set. Then, pushing the pedal all the way to the floor will re-set the switch plunger properly.

hth

In response to your second post, the trans will downshift off of the vacuum modulator at lower speeds, so you may still have a solenoid/wiring issue...

The solenoid is called a kick-down solenoid. You should be able to get one at most parts houses...prolly around $20 or so.

[Edward J.]

Re: Transmission downshift switch for Turbo400

Bruce, Clem is right with the hose over the end of switch. one note is that there is a limited on the kick down, its also operates on govener pressure so after about 40-45mph the kick down will not work. the only other way to extend the kick down is to install a shift kit.

[Richard G.]

Re: Transmission downshift switch for Turbo400

On can usually verify the solenoid function with a 12 volt power supply from the battery. Attach to the kick down wire connector at the transmission. Usually one can hear the click when the solenoid is energized. If you use a battery charger for this test don't forget the ground. Just complete this test in a quiet place. Lots of other things to go wrong but I have tested my share of the solenoids and they rarely fail.
Rick

[Russ S.]

Re: Transmission downshift switch for Turbo400

If you guys are talking about the transmission control switch which is activated by the accelerator when you kick the gas pedal down to get downshift which I think you are referring to, I assume by putting a hose on the switch rod you are trying to get more travel so it kicks down. There is no need to do this as the switch can be reset as per the service manual. I realize you are talking about a 74 and I have a 73 but I believe they are the same. To reset the switch, press the plunger forward as far as possable. This presets the switch for adjustment. The switch will then adjust itself with the first wide open throttle application of the accelerator pedal. Russ