3 speed overdrive with an HEI distributor

[cwcarpenter98]

So I've been doing a lot of research on the stock wiring for a 3 speed overdrive trans, but I'm confused on how to make it work with my HEI dizzy. I want my trans to work just as GM intended, but I don't want to swap back to my points dizzy.

It makes sense to me that the coil is grounded out when the kickdown switch is pressed to take the load off the trans so the solenoid can pull it out of overdrive. What I am confused on is how to wire it to the HEI without burning up anything.

Please let me know if y'all have any suggestions, thanks

[ray_mcavoy]

As you know, the stock system momentarily grounded the negative side of the coil to make the ignition cut out just long enough to take the load off the trans and allow it to drop out of OD. It's my understanding that grounding the negative side of the coil with HEI has the potential to damage the module.

So instead, you could momentarily interrupt the power feed to the HEI. That could be accomplished by adding a relay into the HEI power feed wire (connected through the normally closed contacts). Then trigger the relay to open during kickdown by using the "ground-out" wire from the OD trans wiring that would have originally connected to the coil.

Now, I can't say for sure that momentarily interrupting power to the HEI will be 100% safe for the module. But it's much less risky than grounding the coil.

[cwcarpenter98]

Thanks Ray, that's extremely helpful. If I can't figure out anything to ensure that the module won't be damaged at all, I'll wire it up this way

Is there any way to keep the module from firing without cutting the power to it? Seems to me that doing it that way would ensure that the module doesn't burn up

[ray_mcavoy]

You're welcome!

About the only other option I can think of would be to interrupt the signal from the HEI pick-up coil to the module. That could also be done with a relay. However, the pick-up coil wires are located inside the distributor, and there isn't room in there for a relay. So tapping into that circuit would probably involve drilling a hole in the distributor housing, inserting a grommet, an running wires to a relay mounted nearby.

Since this would be interrupting a relatively "low level" signal input to the module, I would think it would have a low probability of damaging the module. But it might have the potential to introduce noise/interference that could result in misfires. Although using a quality relay, terminals, etc. and keeping the added wire length relatively short (and away from the spark plug wires) should minimize the chances of that happening.

[cwcarpenter98]

Yeah, I think that will be a bit of a challenge to make it work. I'm probably going to just add a relay into the power wire that opens when the kickdown switch is pressed.

My truck had an OD in it from the factory I think, because it has the relay still bolted on the fender and the lockout cable in the dash. I got another relay with the trans I got, so do you think I could use that for the power wire to the HEI? Not sure if that will work, but it would look a lot better than a new, plastic relay

[ray_mcavoy]

Unfortunately, I don't think one of the original OD relays will work for this. The OD relays have normally open contacts and one side of the coil internally connected to the contact that's on the +12V input side. So the contacts only close when the other side of the coil circuit is completed to ground. You basically want the opposite (normally closed contacts that open when one side of the coil is completed to ground) to temporarily interrupt power to the HEI.

When I wired up the 3-speed OD trans we swapped into Dad's 66 C10, I didn't want to use an "out of place looking" modern plastic case relay either. The original OD relays I found were rather pricey and there are some horn relays that look similar but don't have a continuous duty rated coil. So I ended up looking through an old Standard Motor Products catalog I had and found a metal case relay with the required coil/contact configuration. I think it ended up being a relay that was normally used for a heater blower (and other applications) in some late 70's / early 80's GM vehicles. Something like that should also work for interrupting power to the HEI and still look right at home under the hood of a 60's truck.

[cwcarpenter98]

I had a feeling that relay wouldn't work. At lease I have a spare!

Thank you so much for all this info. Now I know what I need to make it all work. I want to get everything together before I swap the trans because I'm still driving the truck All I have left to find is a relay for the HEI that works and looks good, and find a kickdown switch. Those are the only parts I'm missing

[CRUZN66]

Originally Posted by cwcarpenter98

All I have left to find is a relay for the HEI that works and looks good, and find a kickdown switch. Those are the only parts I'm missing

Might check here:

http://www.fifthaveinternetgarage.co...rive_parts.php

[curvedglass]

I had a similar question. Unfortunately the trans is still on my garage floor but the answers on this thread may help

http://67-72chevytrucks.com/vboard/s...d.php?t=725779

[cwcarpenter98]

Originally Posted by CRUZN66

Might check here:

http://www.fifthaveinternetgarage.co...rive_parts.php

Thanks for that link, looks like some good stuff there. I didn't see the GM kickdown switch though. I don't think anyone repops that

[cwcarpenter98]

Originally Posted by curvedglass

I had a similar question. Unfortunately the trans is still on my garage floor but the answers on this thread may help

http://67-72chevytrucks.com/vboard/s...d.php?t=725779

Thanks man, I read through that a couple months ago, but completely forgot about it! I would like to get the trans in before I have to go back to school in January, but not sure if that is going to happen

[ray_mcavoy]

Originally Posted by cwcarpenter98

Thanks for that link, looks like some good stuff there. I didn't see the GM kickdown switch though. I don't think anyone repops that

Yeah, I don't think the GM kickdown switches are being reproduced. For Dad's 66 we used a replacement switch meant for a Studebaker. Look for part number 529479 on ebay by member stude4x4. It's a quality US made Cole Hersee switch that looks similar to the ones originally used by GM. The biggest difference is that this one has screw terminals instead of round pin terminals ... which actually makes it easier to hook up if you're making your own wiring harness and don't have the OE type connector for the GM switch.

[cwcarpenter98]

Thanks Ray for that part number. I'll look into that as a potential option. I have the wiring harness, but the kickdown switch plug is in poor shape. I would need to replace the plug if I use the GM switch anyways.

Edit: After discussing it with my dad, we are going to go with the Studebaker switch because of the cost of finding a GM switch. It just makes sense to go the cheaper route since I'm not restoring this truck to factory specs. I just want to drive the wheels off of it

One other question Ray: Would you happen to have the part number for the relay you used on your dad's truck? Thanks for all your help on this. I really appreciate it!

[ray_mcavoy]

You're welcome!

I looked at a number of different relays, but I think the one we finally ended up using was a Standard Motor Products RY-12.

It is a common 5-terminal relay with both N.C. (normally closed) and N.O. (normally open) contacts inside a metal case with a built-in mounting tab. However, the terminal numbering isn't the same as a typical plastic case automotive relay. This one has terminal #1 as the common contact, #2 is the N.C. contact, #3 is the N.O. contact, and #4 & #5 are the coil. It has 1/4" wide blade terminals that will accept Packard/Delphi 56-series connectors for a factory installed look, or can be used with generic 1/4" quick connect terminals.

[cwcarpenter98]

I just looked at one, and I like the looks of it a lot better than the plastic ones, thanks.

Just so I make sure to get it right, how should I wire up the relay? I'm still new to wiring stuff, and I definitely don't want to get it wrong and screw something up

[ray_mcavoy]

Originally Posted by cwcarpenter98

Just so I make sure to get it right, how should I wire up the relay? I'm still new to wiring stuff, and I definitely don't want to get it wrong and screw something up

To use the RY-12 relay for interrupting power to the HEI for the overdrive kickdown, you would want to make the following connections:

• Disconnect the power feed wire from the HEI distributor and re-connect it to terminal #1 on the relay.
• Run a wire from the relay terminal #2 to the HEI power terminal. (*)
• Connect a short jumper wire between the relay terminals #1 and #4. (**)
• Connect the overdrive "ground-out" wire (that originally went to the negative coil terminal) to terminal #5 on the relay.
• Leave terminal #3 unused.

(*) Note: Make this wire the same gauge (typically 12ga) as the one originally feeding the HEI.
(**) Note: This will result in 2 wires connected to the #1 terminal. To avoid a splice joining the 2 wires, there are special Packard/Delphi terminals available that will allow 2 wires to be crimped together into the same terminal.


And I know you're using an original overdrive relay, but for anyone else interested, to make use of the RY-12 as a substitute for the original OD relay, the connections are:

• Connect the fused power feed wire to terminals #1 and #4. (***)
• Connect the overdrive solenoid's power wire to terminal #3.
• Connect the control wire from the kickdown switch to terminal #5.
• Leave terminal #2 unused.

(***) Note: This double wire connection is not necessary with the original OD relay because it already has an internal connection between the relay's contact & coil.

[cwcarpenter98]

Thanks again Ray. This is some great information that I have been lacking this whole time. Once I get everything together, I'll be swapping transmissions as soon as possible. I can't wait!

[Wrenchbender Ret]

Hook the interrupter wire to the tach term. on the HEI. I had test equipment that shorted cyls. for comparison & that's the way it hooked up. I checked with the equip. manufacturer & they said it worked that way. I did it many times & never had any failures.
George

[cwcarpenter98]

Originally Posted by Wrenchbender Ret

Hook the interrupter wire to the tach term. on the HEI. I had test equipment that shorted cyls. for comparison & that's the way it hooked up. I checked with the equip. manufacturer & they said it worked that way. I did it many times & never had any failures.
George

Didn't think about doing it that way. Since I've already ordered the relay, I'll try that first, and if it burns up the module, I'll try this. Thanks for your input

[ray_mcavoy]

Connecting the overdrive kickdown "ground-out" wire to the HEI "tach" terminal is the same as connecting it to the negative side of the coil (as was originally done with the points ignition).

As I mentioned earlier, I have heard that can potentially damage the module, but that could very well be one of those old wive's tales.

[cwcarpenter98]

If you're like me and don't want to spend a fortune on the GM kick down switch, the Studebaker one from Stude4x4 on Ebay is a great option. Thanks Ray for that suggestion! The switch has some weight to it, definitely not plastic on the insides. I haven't used it yet, but it feels like a quality part. It was easy to change the wiring harness to work with the new switch, and I wasn't upset about that because my GM plug was busted up pretty bad.

Here's a pic of the switch with the bracket that I just finished up making (more details of that on my build thread)

[NewBayColony]

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[cwcarpenter98]

Update: I have been driving the truck a good bit since I completed the swap. I have not had any issues with the trans or the wiring. The kickdown switch and the wiring for the HEI works great. I think I have put at least 500 miles on this trans since I put it in. Hard to tell though, since I don't have an odometer

[cwcarpenter98]

Well it's been about a year since I got everything working right with the overdrive. I'm happy to say that I haven't noticed any negative affects from wiring the HEI this way. I've driven the truck a good bit, even as my daily driver for a couple months and the overdrive has allowed me to get almost 16 mpg on the highway. Not bad for a little 283 and my lead foot lol

[NewBayColony]

Do you have any pictures of where and how you mounted the lockdown switch? Thanks