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Old 12-13-2020, 07:33 AM   #1
1979 GMC Sierra
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700r4 vacuum hose and 2 wires for lock-up?

Hey guys, i just got my 700r4 tranny fixed (we took it out of the truck and brought it to a shop). It's an early model (82-84) that i had in my 76. So when installing it back into my 76, there's a vacuum hose and 2 wires for lock-up...not sure where they go correctly? Any info would be appreciated. Thanks.
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Old 12-13-2020, 07:41 AM   #2
Corts60
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Re: 700r4 vacuum hose and 2 wires for lock-up?

I believe only the t400 had vacuum? 700R4 should have a TV cable.
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Old 12-19-2020, 02:22 PM   #3
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Re: 700r4 vacuum hose and 2 wires for lock-up?

No vacuum hose on any of my 700r4's There is a kit for the lockup.
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Old 12-19-2020, 05:21 PM   #4
kwmech
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Re: 700r4 vacuum hose and 2 wires for lock-up?

Are you sure you don't have a T350C
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Old 12-20-2020, 03:13 PM   #5
hatzie
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Re: 700r4 vacuum hose and 2 wires for lock-up?

TH700R4 & 4L60 have TV cables not vacuum modulators.
If you have a hose on a TH700R4 transmission it's a vent.
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Old 12-22-2020, 01:06 PM   #6
Desert1957
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Re: 700r4 vacuum hose and 2 wires for lock-up?

This is the only thing I've ever seen controlling anything on a 700R4 , It has a single vacuum line and a two wire harness that controls torque convertor lockup (TCC).

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Old 12-22-2020, 06:13 PM   #7
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Re: 700r4 vacuum hose and 2 wires for lock-up?

All 700R4's do have one electrical plug located on the left side of the trans that I know of which is for converter lockup. While the trans doesn't have a vacuum modulator like the 350's and 400's it does have a vacuum switch to unlock the converter under load which is located by the brake booster and looks similar to the one pictured by desert. The one he showed though is actually a vacuum tip-in switch for the later ESC distributors. I attached a wiring diagram from a factory manual (Note RPO MD8 is for a 700R4) I believe there is a non-egr one that exists too but is very similar. Hope that helps!
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Old 12-22-2020, 06:23 PM   #8
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Re: 700r4 vacuum hose and 2 wires for lock-up?

Found a picture online, this is the vacuum switch and plug for the TCC
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