Sunday, February 23, 2020

Kick Down! Fixing the TH400 shifting issues

It seems that the PO did some deletions to the transmission to get rid of the kick-down feature on the RV. Not sure why except some think that it's annoying when you floor the pedal and then the RV shifts down a gear (and on a 3 speed that can be somewhat disconcerting!). When climbing hills or trying to pass something (also up a hill) you may need that kick-down option.

Now, this later Chevy has the activation switch near the gas pedal (accelerator) instead of a switch and cable setup found on early Chevy's where the switch was near the carburetor. Basically the idea is that once you floor the go pedal, a switch is flipped that allows for activation of a solenoid in the transmission to shift down one gear for the time you have the pedal depressed that far.

I looked under the dashboard to see what I had near the accelerator and there was that GM kick-down switch! I pushed the pedal down as far as I could with my hand and could not activate that switch. It would take considerable pressure on the pedal by my foot to get that switch to move! First issue found. The other one is making sure the wiring is hooked up to that part of the transmission to allow the voltage to activate the solenoid. Have not checked that yet but I recall a wire hanging loose near there.

This is the Allegro's setup with the switch set in a way that you have to REALLY punch the gas to get it to move. Purple wire is 12V source and orange goes to the shift terminal on the TH400. 

Stock photo showing a shiny plug in the place of the terminal lead to activate the shift solenoid that's accessed by dropping the transmission pan. Hope that part is still there and working!!!
Here are pics of the gas pedal switch, wires and a stock photo showing where the plug should be on the transmission. This plug photo works better showing the location than almost any one with the terminal lead on the dirty and grimy transmissions.

I'll update this once I get the connections adjusted, including putting a section of hose around the switch post to get it to activate a bit sooner... tip I found on-line!

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