Lock up switch?

[czarcaustic]

Quick question for the minds of the board ...

I just bought my lil' '72 GMC Short Fleet. The PO had placed a 350sb and some unknown (to me) automatic transmission in it. To this point the most I have ever done to any vehicle of mine is change the oil and replace a battery. Now I have a whole new wonderful greasy world to explore and I am a bit overwhelmed.

My truck has a little nondescript toggle switch intalled in the dash ... I have flipped it while idle and while the engine was off and nothing changes. The widow of the PO I bought it from didn't know what it was. I was talking to an old timer here in town and he said it was most likely a "lock up switch." Unfortunately our conversation was only in passing and I was unable to ask him what it was, what it did, and if it was necessary.

Can anyone explain what a lock-up switch is and if I need it? Furthermore, If it isn't a lock up switch, any ideas of what it could be.

[tecky11]

im gonna take a stab in the dark here. since it is an auto with a 350 i would say it has 1 of three trannys. th350,th400 or 700r4. easy way to test said switch take a drive get to about 40 or so and flip the switch and see what happens, if notheing well then i dont know

[retodd7711]

Could have been for fog lights or such.
Are there any wires on the switch?

[Jacfourteen]

if you have a 200-r4 or a 700-r4 they have a lock up converter and in a stock vehicle they lock up automatically (like when you have the clutch out in a manual) when you are driving down the road, but when you stop the converter needs to disengage or the engine will stall. My guess it that if it is a lock up switch and it was in the locked position when sitting still in drive the engine would stall out. As far a knowing for sure what it is you would need to trace where the wire goes and see what it is attached to. If you don't know what tranny you have maybe post some pics and someone can help you out. Good luck!

[Longhorn Man]

no trannys lock up on there own. They need an electrical source.

This old guy, does he know anything about the truck? Or is he just rambling nonsence? Listening to someone who knows absolutly nothing about your truck guess at what the switch is, seems a little silly to me. He coulda said flux capaciter.
Crawl under the dash, and follow the wires. Untill you do this, then we'll all just be guessing.

[czarcaustic]

Thanks for the preliminary help/guesses guys. I will trace the wires from the toggle today when I get out to the garage and report back.

Is there an easy way to distinguish what transmission I have? I am guessing there won't be a neat placard on it informing me.


"He coulda said flux capaciter"
- Now THAT would be worth writing about!

[cdowns]

catalogues from places like speedway motors summit jegs normally have pics or illustrations of what the drain pans on the different trannies look like thats about the easiest way to ID an automatic tranny

[KEL]

http://www.lmctruck.com/icatalog/cb/full.aspx?Page=11

[mclairmo]

That toggle switch could be for anything. Might not be hooked up at all anymore. I have two under my dash with no labels, one for the amplifier and one for the electric fan overide switch just in case the temp probe blows out and the fan won't turn on. Have to trace the wires.

[czarcaustic]

It is the REVERSE LIGHTS!!!!

what the hell?

I thought there was a switch on the transmission for that?

[vectorit]

There is one, but it is a b!tch to get to. So someone just did some Mac Gyver'n to make em work, albeit the manual way of do in it.

[Longhorn Man]

thats how both of mine are too. When on a toggle, they double as work lights

[cdowns]

backup switch is located on the steering column with the neutral safty switck on automatic tranny trucks