Need help diagnosing 700R4 lockup issues..

[fanmanj]

I'm having some trouble... My '86 has a 700r4 that when I bought it, someone had cut the vacuum switch off. I have since found a switch in the junkyard, hooked it up, still no lockup... Should the wiring going through the brake switch and vacuum switch have 12v whenever the key is on? Can I apply 12v directly to the TCC solenoid wire and lockup the tranny just to make sure the solenoid is good? HELP!!!
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[beamn7]

There are multiple wiring setups for the 700R4. When I built mine, I configured the pressure switches on the valve body so that when the ecm would apply ground for lockup, it went through an external relay I installed that would close when the 4th gear pressure switched opened up which tells the ecm to reduce egr flow therefore only allowing lockup in 4th. Stock it would apply in 2nd....
How many wires do you have going into the transmission at the 4 pin connector (usually 3 or less wires) and what are their colors? On mine one is + that is interupted by stepping on the brake, one is a ground that is applied by the ECM once predetermined values are met and a lock up signal is given and the other is a signal wire back to the ECM. Like I said though, there are multiple configurations depending on ESC or no ESC, C or K, trans code (stamped on pass side of trans at back just above pan), etc.... My 85 has no vac switch....

[fanmanj]

Well my tranny has a yellow, light blue, and green wire, it's a c series, and it had ESC.
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[fanmanj]

Also, im getting 12v with the key on all the way to the vac switch, and through it with vacuum
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[Desert1957]

I think you misunderstanding what the vacuum switch does.
If its the 2 wire switch on the firewall with 1 vacuum hose to it. This switch senses slight vacuum loss under partial throttle load and DISENGAGES the TCC , it does not apply it.

During high engine vacuum the switch stays closed completing voltage to the TCC , under acceleration , engine vacuum drops, causing the switch to open, this stops the voltage to the TCC and almost feels like a partial down shift.

Desert

[beamn7]

ok good. Disconnect the harness from the trans and verify which wires go into which terminals. Each terminal will be labled A, B, C or D. "C" will not be used. "A" should be positive with the key on and drop when you step on the brake. "B" is the ground signal back to the ECM to tell it to reduce EGR flow and "D" is the ground supplied by the ECM to lock up the converter. Looking at the transmission from the drivers side the terminal are: 2 inboard pins are "B" and "C", "B" being the front one and "C" being the back one. The 2 outboard pins are "A" and "D", "A" being the front one and "D" being the back one.

But................there were 11 different wiring configurations so this could be wrong. If you can get the model code of the trans (pass side of case at the back just above the pan bolts) it would help. Should be 2 or 3 letters and some numbers.... example would be: YNM or MFM or TW, etc....

[fanmanj]

Thanks Desert, I thought the switch engaged it!
Beamn, I'll check the connector and tranny code tonight. Thanks guys!
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[fanmanj]

Beamn, does your truck have the California emmissons equipment? If so, it has the CCC quadrajet carb and computer controlled timing. If that's the case your truck is wired COMPLETELY different than mine. I dont believe my truck has an ECM to control lockup.

[beamn7]

Correct, mine does have CA emissions so it will be wired differently however the pins in the connectors will mostly have the same function. "A" will always be hot and drop with brake depressed. The rest is what changes depending on ECM or no ECM, etc. You can have a 3rd gear normally open pressure switch that closes upon the transmission reaching 3rd and then applies power to a TCC solenoid that is grounded to the case OR a ground that is run through a pressure switch that then completes the ground once the vehicle has reached second gear and there is a 4-3 downshift pressure switch on the positive side that momentarliy releases the TCC upon a 4-3 downshift, etc. The best thing to do would be get the previously mentioned model numbers off the trans and I can match it up with the schematics. Like I said, there are 11 different possible wiring configurations....
Here is the MOST likely scenario: (keep in mind that in schematic the plug on the harness and the plug on the transmission is inverted) "A" is light greeen, "B" is light blue and "D" is yellow. Circuit 383 (lt blue) is power feed, goes through splice 383 and to low vac switch, assuming engine is not in a low vaccum scenario, power will pass through the switch into the trans to the N.O. (normally open) 4th clutch switch. Once the vehicle reaches 4th gear the switch closes and provides power to the TCC solenoid which is grounded to the valve body. The converter clutch will now be engaged. At the same time, the TCC switch now closes providing a ground signal back to the EGR bleed solenoid that is already receiving power from circuit 383 (lt blue wire) and allows for a reduction in EGR flow in order to reduce the opportunity for pre-ignition / detonation / pinging since now you have a direct coupling rather than a fluid coupling which would have allowed for some runaway. I would verify that you have power to the light green wire at the transmission with the Key on and foot off the brake. IF so, then take the truck on the highway, obtain a steady speed and throttle pedal and once you have reached 4th gear lightly depress the brake pedal without taking your foot off the gas and listen. If you have a tach, you should see approx 200-400 rpm increase. (give or take depending on load). IF not, most likely you have another issue. (pressure switch, tcc solenoid, sticking apply valve in the valve body, etc)
Below is the schematic and a flow chart for testing the electrical side of the system. The "test plug" is an orange plug that is under your dash near the fuse panel....

Hope this helps....

[fanmanj]

After testing voltages, and tracing wires, I found that my light green is actually my power feed, which is working fine and intact. HOWEVER... My light blue and yellow had been cut and stuffed inside the looming. I dug out the yellow, grounded it properly, and I HAVE LOCKUP!!! Thanks for the help!
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[beamn7]

Awesome! Glad to hear it! You are correct, Lt Green should be power feed. (forgot to mention it changes from Lt blue after leaving the low vac switch but it certainly is pin "A".)
Amazing how many PO's disconnected or cut the wires to the TCC because they didn't like it or the way it felt. Many fo them didn't realize that 700R4's can actually overheat in 4th due to no lock-up........ Glad you got it handled!

[fanmanj]

Yeah my PO was a real dips**t... I believe he removed the Tcc lockup switch because he thought it was emissions equipment. My truck also had the ESC tip in switch removed, the vacuum reservoir removed, and countless wires cut and vacuum hoses misrouted or missing... The joys of owning a 25 year old truck that a kludge owned... Lol
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[fanmanj]

Sigh... My lockup worked for approx. 20 miles.. Truck was in 3rd gear, locked up, then unlocked, and went in/out of lockup about 5 times, and hasn't locked up since... Argh...
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[made2drag]

I have a 86 700r4 that seems to have a bad 4th since it doesn't ever shift from 3rd to 4th. I think the last guy might have messed it up some how. I read that 4th can go after a rebuild or if someone doesn't have their TV cable right.

If I run the 700r4 in "D" instead of "OD", will it let me get by without having the lockup cable hooked up? I have heard that 85 and up will not burn up, if you run without lock up, but I wish I knew for sure. I like it how it is and it drives like a turbo 350, but I am wondering about excessive heat and wonder if that excessive heat is only when TC spins in 4th? My solenoid only clicked once and is probably bad, which is another reason im fine with no 4th.