1987 700R4 Converter not locking up - Hot Rod Forum : Hotrodders Bulletin Board
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Old 04-03-2011, 05:39 PM
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1987 700R4 Converter not locking up

I just finished rebuilding a 1987 700R4 transmission in a corvette. Everything seems to be working fine but I can not detect the converter locking. I read all the how to info on setting the tv cable and am sure it is set correctly. It shifts 1,2,3,4 in OD and shifts 1,2,3 in D. It down shifts real nicely but I just can not see that rpm change going into lock up. When I am driving 70mph and hit the brake peddle I see no rpm change like the book mentions. The original problem leading to the rebuild was it had no 3 and 4 gear. The rebuild showed to be this clutch pack was toasted. I did play it safe and put in a remanufactured torque converter.

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Old 04-03-2011, 06:14 PM
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The ecm grounds the lockup solenoid when conditions are met. Power flows through the brake light switch to the solenoid,it cuts the power to the solenoid when the pedal is depressed.Maybe one or the other is not there. If you have a scanner you should be able to see what is happening, otherwise you will need to track it down with a test light.
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Old 04-03-2011, 06:56 PM
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Do mean the 700R4 trans should shift 1 2 3 4 then lockup? That would be a 5 speed.

Intresting, my truck has a TH350C and my lock up is on a switch , energizing the brake lead wire 12 volts to disengauge the TCC. The TH350C is misleading because it shifts 1-2-3 then lockup about another 250 rpm at 65mph . 4 RPM Gear drops on lockup, from a 3 speed auto.
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Old 04-03-2011, 07:15 PM
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Thanks for a starting point. I will check the brake circuit and so on. Yes this is a 4 speed plus a converter lock the best I can tell.
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Old 04-03-2011, 08:36 PM
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More Info, requirements for Lockup>> http://tech.oldsgmail.com/trans_TCC.php
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Old 04-04-2011, 05:47 PM
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What sends the positive power to the solenoid or the brake switch and when do you get this power? Ign on or drive or does the car even need to be running to check this positive power being present?
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Old 04-05-2011, 03:29 AM
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Ignition On.
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Old 04-06-2011, 01:59 PM
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As stated above, with the key in the "RUN" position, and the brake pedal not depressed, you should be able to probe the 4 pin connector (car side of harness) and find a constant 12+ source. If the source is present, you should then test the ground wire (supplied by computer) to see if the computer is commanding lock-up. You could do this by tapping into the wire from the PCM that provides the ground, and then driving the car while probing the wire with a multi-meter. If ground is present from the PCM at the correct time, then the lock-up solenoid may not be working inside the transmission, the internal wiring harness may have a short, or open, or the torque converter may have a problem internally, or one, or more, of the pressure switches inside the trans. is faulty-or the temperature switch is no good and not allowing the circuit to close.

There is a way (if you know how to do it) that you can apply both a ground, and a 12V source to the pins at the connector on the trans, and get it to lock-up. Because of the internal pressure switches, the car will have to be driven while you are providing a (-), and a (+) to the pins.. This would help diagnose in that if it locks up with your "dummy" wires, you will have proven that the converter, lock-up solenoid, and internal wiring harness, and pressure switches are all good.
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Old 04-06-2011, 04:05 PM
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This problem is narrowing down to a 4 prong connector problem. I ran the voltage test and I am getting 12 volts to my wire harnes plug. The problem seems to be in the 4 prong connector that I replaced during the rebuild. The wire harness male plug has the plastic clip broken so it does not secure down tightly anyway. I got to looking and these 2 item are not actually plugging together. The original connector in the trans. was a dull white plastic and had one of the 4 holes blank (this old connector broke while I was removing it). The new one is black and has 4 holes with 4 female pins. It looks like it is just different enough the 2 will not plug together all the way. What to do now? I need a new harness repair plug anyway and I am thinking that if I just get the matching harness plug to match this black one, I might be better off. Has anyone made this mistake and do you know if the inside is compatible? The best I can recall the inside harness seemed to plug in just fine.
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Old 06-11-2011, 05:20 PM
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ive had a similar problem with that plug on an 88 700r4. Just go down to any junkyard and take it off one of the transmissions there. The way I do it because I dont want to even seperate the connector from the bottom piece is I cut the harness on the junkyard car going to the trans (3 or 4 inches above the connector) and then theres a flat tab on the connector going into the transmission, just pry that up and that whole bottom piece of the connector will come out without ever seperating the 2 pieces of the connector. Every one ive seen has 3 terminals and 1 blank.
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Old 06-11-2011, 06:01 PM
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also, my lockup literally JUST stopped working after that last post...weird I know haha...I pulled out the end of that 4 pin connector going into the trans and the harness inside the transmission that connects to that connector fell off. I figured out a way to get it on the connector without dropping the pan so if thats the same problem your having let me know and ill give you detailed info on how I got it to work. good luck
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Old 06-17-2011, 04:52 PM
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Thanks for the info. I went ahead and ordered the correct white connector body for the 700R4 and everything is working now. I learned the hard way to order the white one and not the black one.
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