How is 700r4 lock up controlled in a 1984?

[5akman]

Rebuilding a basket case 1984 K20 with the 700r4 sitting in the bed. How was lockup controlled in this era truck? Trans shop said a simple computer deal behind the glove box but i don't remember seeing anything back there when I did the heater core R&R.

 

[Old Painless]

I'm not sure what years, but I believe earlier ones controlled lockup via vacuum or line pressure switch and later ones were computer controlled?

If the trans has a 4 pin connector on it, then there is a +12v wire connected to your brake switch, and 2 ecm wires (one is ecm ground to tcc solenoid). Otherwise I believe they are internally controlled, and the only outside influence it has is via the TV cable. I know some companies make internally regulated lockup kits.

Either way, your computer should be more above the glovebox than behind it; pop your glovebox open and look through the hole where the metal piece that the latch connects to - should see it back there.

I'd say check the connections on that thing - if it's got that 4 pin plug driver's side near the tail housing (only 3 are actually used) then it's likely electronic and you can manage it a few different ways. There are lots of lockup kits for fairly cheap online that'll achieve this; check out summit or jegs for kits.

Sorry I'm not more help, hoping this hones you in a little on the thing or at least gets a true 700r4 guy to shed some light. I had one with my 6.2 diesel before the swap - gave me lots of issues when I first resurrected the thing, but eventually worked like a dream after adding about 90 quarts of atf and adjusting the TV cable.

While the thing is out of the truck maybe check out the governor - dome-shaped cover driver's side by the tailhousing (by that 4 pin connector if you've got it), pop the cover off and it slides right out. Wacky little device that has a set of counterweights on it, make sure those open and close fine and the needle in there is free. Mine was fine when I checked but i've heard they can get sticky or worn and impair trans performance.

 

[5akman]

"Old Painless", its at the trans shop now for beefed up rebuild along with them going through my np208 transfer case. Thanks for the info, I'll look up the kits you referenced.

 

[1987 GMC Jimmy]

The TBI and CCC cars and trucks use the ECM to control torque converter lockup. That's gonna be '81 and on California square bodies. All the other carbureted, 49 state ones use the solenoid and switch in the transmission, which have their power fed to them by a four pin style connector above the pan, and the vacuum switch, brake light switch, and WOT switch control TCC functions. Does this have an E4ME Quadrajet? It should if it originated from CA and will need to pass emissions. You will have an ECM, and it should control the lockup. Here's the wiring to the four pin connector.

 

[1987 GMC Jimmy]

So in the likely chance you have the computer controlled carburetor, you more than likely had a TH350C or 700R4 in it from the factory. There aren't all the pieces outside of the transmission like in 49 state carbureted trucks so it shouldn't be that hard to get going if my assumptions aforementioned are correct. Just in case, here's the pinout for the Computer Command Control ECM. You shouldn't need to rewire unless your truck has been hacked to high heaven or if it somehow didn't have factory lockup. I would heed the fellow's suggestion above in finding your ECM. My Caprice has the same system, and its computer lives in the hollowed out and compartmentalized passenger side kick panel. It's pretty cool, actually.

 

[5akman]

"1987" I'll have to check the options sticker under the hood to see if it was originally a 700r4 truck. I'm thinking so as I believe I've seen a 4 prong plug hanging down under the transfer case shifter.

 

[1987 GMC Jimmy]

"1987" I'll have to check the options sticker under the hood to see if it was originally a 700r4 truck. I'm thinking so as I believe I've seen a 4 prong plug hanging down under the transfer case shifter.

Okay. Well, the TH350C was operated exactly the same way, too. What's your carburetor situation? You've got the E4ME Q-Jet, all the wiring for the sensors, the sensors, the ECM, and all the wires that plug into it?

 

[5akman]

The carb that was on it when I got it was a Holley 4150. I've since had "Quadrajet Power" rebuild me a Qjet so I'll have to compare numbers.

 

[1987 GMC Jimmy]

I gotcha. I don't know if the higher GVWR trucks escaped Computer Command Control in California so at this point if you had the feedback carburetor and all the sensors in there, you should have an ECM, but if it didn't you should have the vacuum-electric system I mentioned earlier. Just let me know what you find out. If you have an emissions sticker still, that's a good source of information on what you had from the factory.

 

[5akman]

1987 Jimmy, it has the vac switch next to the brake booster and 4 prong plug at the tranny. Current carb on it is a non smog/computer/elec Qjet.

 

[HotRodPC]

I'd say someone probably converted the 87 Jimmy to carb and did the vac switch addition too. So it sounds like they did it right instead of a hack job. Otherwise is should have been controlled by the OBD 1 TBI ECM.

 

[HotRodPC]

Being that it's a K20, I don't think it would be an OEM 700r4 truck. Also being a K20 with a higher GVWR I don't think this would be a CCC (Computer Command Control) truck even if it were an OEM Cali emissions truck. Do you even have a Cat Converter on this truck Lance? Fuel Gauge say Unleaded Fuel Only on it? I take it that it's an original gas truck and not a 6.2 Diesel truck?

Another member here is building an OEM Diesel truck to avoid needing smog tests, and he's running a gas engine now since emissions requirement is detected or lack there of, by the VIN #. If the VIN # designates a 6.2 Diesel engine, Cali computer kicks it out of needing emissions testing. This is the only reason I've kept my 85 K10 and converting it to K20 springs and axles. It was originally a 6.2 truck, so if I ever move back to Cali, this truck will not require any smog testing even though I'll biggo nasty smoggy gas engine in it.

 

[5akman]

Being that it's a K20, I don't think it would be an OEM 700r4 truck. Also being a K20 with a higher GVWR I don't think this would be a CCC (Computer Command Control) truck even if it were an OEM Cali emissions truck. Do you even have a Cat Converter on this truck Lance? Fuel Gauge say Unleaded Fuel Only on it? I take it that it's an original gas truck and not a 6.2 Diesel truck?

Another member here is building an OEM Diesel truck to avoid needing smog tests, and he's running a gas engine now since emissions requirement is detected or lack there of, by the VIN #. If the VIN # designates a 6.2 Diesel engine, Cali computer kicks it out of needing emissions testing. This is the only reason I've kept my 85 K10 and converting it to K20 springs and axles. It was originally a 6.2 truck, so if I ever move back to Cali, this truck will not require any smog testing even though I'll biggo nasty smoggy gas engine in it.

It was originally a CA emissions truck based on decals under the hood. The drivers side fender decal does say something about "heavy over drive transmission" or something to that effect. The Vin makes it a gas engine also.

 

[HotRodPC]

I had heard that there were some 700r4's in 3/4 tons but it was very rare. That must be the rarity. Cali trucks, maybe even Cali trucks only, or maybe just Special Order trucks only.

So you still have to have it smog tested, but being a K20 and highter GVWR, I'd imagine it's pretty easy to pass. Does it even have a Catalytic Converter? 49 States 3/4's didn't have Cats until 1987. Do have EGR though.

 

[5akman]

I had heard that there were some 700r4's in 3/4 tons but it was very rare. That must be the rarity. Cali trucks, maybe even Cali trucks only, or maybe just Special Order trucks only.

So you still have to have it smog tested, but being a K20 and highter GVWR, I'd imagine it's pretty easy to pass. Does it even have a Catalytic Converter? 49 States 3/4's didn't have Cats until 1987. Do have EGR though.

Its currently in CA but headed to AK (where I registered it when I bought it a few months ago) so no smog needed forever and ever!