Thread: TH 400 Kickdown Switch

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Some top of the line station wagons of the early '60's ran 400 small blocks backed by TH400's. To my knowledge Chevrolet put automatics behind all 400 small blocks. That should help you expand your search.

Even those are getting hard to find in the yards. I haven't found a 400 small block in a long time. The big difference in the pedal that used the pedal mounted switch is in the vertical accerator arm. On late 60s to early 70s passenger cars it's inside the firewall and on trucks it's outside. Not sure about the G van but car stuff would take a lot of work to change. If it ever dries out around here I will have to take a trip to my favorite yards and see what I can find.

Tom

I haven't run into that yet. I think that they just figure that nobody else is stupid enough to buy the junk I take off so it's all profit.

It's been awhile a since I updated this thread and I work slowly but tonight I got it in gear and made the parts I needed. I bought a B&M switch kit from Summit. It is a pull on switch with the parts to connect it to the Holley throttle arm. It still requires a bracket on the carb or intake so I made one. Now I can use the stock wiring ro connect to the trans and it was a lot cheaper than the Lokar cable deal.

First thing I did was get familiar with how the switch worked. It has a rod that pulls on a spring that pulls the switch on. It is supposed to be full on a little before the carb is wide open. The spring allows the carb to go wide open after the switch is all the way out. The rod is adjustable so the bracket can be close and be good enough.

Next I measured and triple checked my sketch to be sure things would line up. I found that the switch needs to be mounted higher than the carb linkage so the rod will be pulling near horizonally at wide open. Now I transferred my measurements to poster board. Bending the poster board to shape showed me how the bracket would fit.

Then I cut out the 1/8 steel to shape, bent the tabs and drilled the holes. I was amazed that the bolt holes on the manifold actually lined up perfect. We all know how that usually goes.

The attached pictures show the bracket in process and the whole thing mounted and adjusted. Now I need to take it off to clean it up and paint it.

One last one.

Hi 39Deluxe I know this is an old thread but I am in need of this brack for my aplacation on my truck can you please send me the templet I whould sure apreciate it thanks in advance.

JulioG, first welcome to the site.

The last posting I see from 39Deluxe was in 2015. You could try to e-mail him directly by clicking on his username (in blue) above and then select "e-mail" member. I'd be amazed if he still had a template from 2009. But you could follow his methodology and make a template from cardboard using the pictures as an example.

I'm still around. I should stop in more though.

The thing with the bracket I made is it is designed to fit the two vertical holes in this Offenhauser 360 degree intake. A different intake would require a different configuration. You might need to use the intake bolts for your bracket. Once you have the switch in hand and a piece of poster board you can judge where the switch will work best and where the mounting legs will need to go down for attachment. It's easy to keep modifying your paper template until you get everything where you want it. You will notice that I mounted the switch slightly high because once the throttle is wide open and the throttle shaft linkage pin rotates forward it also raises to the point that the switch is now inline with the pull. Make sure your steel is thick enough that it doesn't flex under full throttle.

FWIW, what's your opinion of the Offy 360º ?

Well, I've read a lot about them over the years and the theory makes sense. I got a chance to buy this one cheap on Ebay so I did. The engine is fresh. I finished it a couple of years ago but haven't lit a fire in it yet. I want to get it rolling and stopping first. It's a 355 with 9.3:1 compression,1.94 iron heads milled, port matched and street ported, and exhaust ports/chambers polished and cc'd. Cam is a GM Performance 214/224 with .442/.465 lift. My 69 short stepside has a THM400 and 3.73 gears so I expect it to be pretty strong off idle up to 5500 or so. Carb is an original Chevy Holley off of a '66 L79 327 I had restored be Bob Kunz in St. Louis. It will hit cruising speed right in the sweet spot of the cam so everything is well matched.

Don't you run this intake?

Tom

Originally Posted by 39Deluxe

Well, I've read a lot about them over the years and the theory makes sense. I got a chance to buy this one cheap on Ebay so I did. The engine is fresh. I finished it a couple of years ago but haven't lit a fire in it yet. I want to get it rolling and stopping first. It's a 355 with 9.3:1 compression,1.94 iron heads milled, port matched and street ported, and exhaust ports/chambers polished and cc'd. Cam is a GM Performance 214/224 with .442/.465 lift. My 69 short stepside has a THM400 and 3.73 gears so I expect it to be pretty strong off idle up to 5500 or so. Carb is an original Chevy Holley off of a '66 L79 327 I had restored be Bob Kunz in St. Louis. It will hit cruising speed right in the sweet spot of the cam so everything is well matched.

Don't you run this intake?

Tom

I ran it, it's in the garage, on a 400 I had in a 62 1/2ton. Stock 400 with a 650dp and headers and it was fairly stout for what it was. The Offy 360º is a single plane manifold with a split plenum and IMHO it gives you the best of both worlds. I also have it's brother, a dual quad, which I might run on my Vett someday.
I was curious with what you thought of the manifold.