th400 kick down switch

[mike rust]

I'm swapping a 5.3l vortec in my 87 c10. It has a th400 from the factory, and my understanding is that the TBI ecm controlled the kick down (spade terminal on driver side of trans). What's the best way to trigger this wire in my swap? Should I mount an earlier th400 kick down switch on the gas pedal? What would happen if I didn't hook anything up to this terminal?

 

[Arkansas_V8]

It wont hurt anything, that I know.

Some of my off road buddies haven't had it connected for years, they just manually downshift in some places. (Yes they daily some of these rigs).

 

[Rickf]

If it was up to me I'd put the switch on the accelerator pedal, but I'm still running carburetors. I don't think the th400 will downshift w/o a switch. I put an intake/carb mounted switch on my '54 with an inline six.

 

[Arkansas_V8]

If it was up to me I'd put the switch on the accelerator pedal, but I'm still running carburetors. I don't think the th400 will downshift w/o a switch. I put an intake/carb mounted switch on my '54 with an inline six.

Looks cleaner on the pedal. I am almost 90% sure it will still downshift on it's own(switch is only for WOT downshifts pretty sure). Ask a buddy later when they all wake up.

 

[Arkansas_V8]

I'm swapping a 5.3l vortec in my 87 c10. It has a th400 from the factory, and my understanding is that the TBI ecm controlled the kick down (spade terminal on driver side of trans). What's the best way to trigger this wire in my swap? Should I mount an earlier th400 kick down switch on the gas pedal? What would happen if I didn't hook anything up to this terminal?

If it was up to me I'd put the switch on the accelerator pedal, but I'm still running carburetors. I don't think the th400 will downshift w/o a switch. I put an intake/carb mounted switch on my '54 with an inline six.

You will be fine.

It will still downshift just fine, just not past a certain speed.

Buddy said that speed varies car to car, just not by much. He cant remember what is.

He said just manually downshift if you need to.

Hope that helped.(he knows way more about transmissions than me)

He also said buy an aftermarket switch if you are that worried about it. (Very quick, angry overview, I texted before his coffee so he is GRUMPY)

 

[Preston]

That’s true mine downshifts without the switch just do not have passing gear

 

[Frankenchevy]

The trans will only downshift below 35ish mph. The vac modulator can only do so much.

Do the pedal switch. Orange wire from case connector to either spade and switched 12v + to the other side. Easy as can be. Then you just need to set the switch for your pedal travel.

 

[mike rust]

That’s true mine downshifts without the switch just do not have passing gear

Thanks for the response......so just to clarify.....when you come to a stop it downshifts back to 1. But when you hammer the throttle in 2 or 3 it doesn't downshift a gear?

 

[mike rust]

The trans will only downshift below 35ish mph. The vac modulator can only do so much.

Do the pedal switch. Orange wire from case connector to either spade and switched 12v + to the other side. Easy as can be. Then you just need to set the switch for your pedal travel.

What year vehicles will have the pedal switch? And was this only a th400 feature?.....or do other transmissions use the switch as well?

 

[Frankenchevy]

What year vehicles will have the pedal switch? And was this only a th400 feature?.....or do other transmissions use the switch as well?

Th350 uses a kickdown cable and 700r4 uses tv cable. Th400 is electronic.

They are proud of those switches. They’re around $50.

 

[K201979]

That’s true mine downshifts without the switch just do not have passing gear

Ive been dailying mine like this for like 2 1/2 years, no problems. Not by choice, just havent had the time to mess with it, aside from chasing the wires and making sure they were hooked up. I did get my gas gage to work when i did that tho. Sadly it has quit again since then. Bad ground somewhere. Another project, low on the priorety list. Anyway, id do the switch if i were you. If you have the time, and youre working this part of the project, just do it right. A passing gear is nice to have

 

[K201979]

Thanks for the response......so just to clarify.....when you come to a stop it downshifts back to 1. But when you hammer the throttle in 2 or 3 it doesn't downshift a gear?

Yes

 

[K201979]

Id say any pre-tbi(87) vehicle with the th400 would use the gas peddle switch.

 

[Merlin3e9]

Hi everyone,

I just completed a TBI to Holly 650 swap on my 87 R10 and I'm experiencing a similar situation as the OP. I can shift just fine, but when I put my foot into it, I don't get passing gear.

I didn't put two & two together when I made the swap. I might search Summit Racing or Jegs for the gas pedal switch.

 

[K201979]

Yep, get a switch er grab the shifter n yanker down

Hi everyone,

I just completed a TBI to Holly 650 swap on my 87 R10 and I'm experiencing a similar situation as the OP. I can shift just fine, but when I put my foot into it, I don't get passing gear.

I didn't put two & two together when I made the swap. I might search Summit Racing or Jegs for the gas pedal switch.