Lock up Convertor

[SteveMc]

I bought a 87 Suburban with a 6.2 and 700r4 trans about nine months ago. It runs fine and I realy like it. I did notice the convertor was not locking up, so checked out the wiring. From the four connector plug it only has a single green wire going fron the trans to the eng. compartment and stoping. (as in not connected to anything) This leads me to believe there is no lock up convetor installed.

My question is, can I install one and are there any disadvantages to using one on this vehicle
THX

[mhagie]

SteveMc,Check out under hood drivers side you will see where the main wiring harness connections are, about 2" to your left (passenger side)you will see a small wiring harness exit the firewall they are the wires for the TCC, mine has 3 wires 1blue 1blue w/blk stripe 1green they go to a plugin just above hydoboost then on to tranny.
You should definately have TCC lock up with that tranny, it is my guess for some reason it was unplugged for whatever purpose or by accident. :(

[britannic]

With just one wire to the 700R4, it's usually connected to 12v and feeds the TCC solenoid, so that when the pressure switch on 4th is activated, it grounds the other terminal on TCC solenoid.

A quick and safe way of checking, is to connect a continuity meter to ground and the the green wire, then drive and see if you get continuity when in 4th.

After verifying the circuit, if you don't have a TCC computer for some reason, then simply connect the green wire to ignition switched fuse protected 12v power.

[SteveMc]

Well this gives me something to think about. Will take the splash pan from the flywheel and get a number off the convertor for some research. Check for a wire hook up under the hood and a continuty check of the green wire while in forth gear.

There is a sticker showing that the trans was rebuilt by a shop not too far away some years back, so they may be of help.

Would be great if it is only a wire to hook up. Thanks to all
SteveMc

[G. Gearloose]

If the tranny was somehow sourced from a non-diesel anything goes.

The 87 really should not be computer controlled. Signal comes from the 10% throttle switch on the Inj pump, interrupted by a DPST brake switch, and 4wd have an additional wire that inhibits lockup in 4wd unless in fourth.

Some valve bodies are wired common ground. Other are wired common Positive, acuated upon grounding certain wires.

Getting a factory schematic for an 87, as well as dropping the pan to see what you have, might be in your future..

[SteveMc]

I pulled the flywheel cover off and found the number six stamped around the converter. From what I can find it should have been a 4 for a diesel. It also had the letters GO written in yellow facing the engine. I could't read the rest but suspect it is GOOD, as from a junk yard rack.
Ran the single wire coming from the trans connector thru ohm meter and reading did not show continunity in any gear to ground. It appears the wire comes from pin "D" and as I said, it dead ends to nothing in the engine compartment.
Plan to pull the pan this week and take a look inside. I know somewhere on the net are instructions for checking the polarity of the valve body. Nothing like a good mystery!!

[mhagie]

Stevemc, you won't have continuity on the wire to ground as it usually passes through a 4th apply switch,and as mentioned earlier it has wiring on inj pump which I removed from mine because it unlocks tcc when ever you take foot off acc pedal I want tran to help just a little for slowing down.
I still think you should find evidence of a wiring harness exiting firewall.

[wmaster]

I have same problem on mine conv to.
But you should have a positive 12v cable to terminal a on the transm.
I have heard from a friend that the lockup solenoid has a checkball that can be stuck if yours transmition has not been used for a while

[SteveMc]

Mike L.
You may have hit the nail on the head. The vehicle is at the Trans Shop now for its pre trip check out. With 10k mile to tow the camper I wanted to know all was working. Will pick it up tomorrow and let you all know what the sperts say. SteveMc

[SteveMc]

Took the Suburban to the Trans shop for its check out before our camping trip and to check the lockup problem.

You guys had it right. That green wire that came up from the Trans went to the injector pump. I got the wire mixed up there behind the glow plug controller. A wire was off at the brake switch. May have occured when the last owner had a trailer brake controller installed.

We have ten thousand miles to do in the southwest this winter. The trans boys went over the whole system and said it might just make it. Cost me $110 for peace of mind.

Thanks again SteveMc

[SteveMc]

Well the lockup converter is doing just what you guys said it was supposed to do. I drive a lot of back roads and notice it does disengauge each time I slow down for a bend. Mhagie said he disconnected that feature so that the engine would slow the vehicle somewhat.

I was thinking of doing the same via a switch, but was wondering what the purpose of this 10% switch is. Am I changing something that could hurt the trans?

[mhagie]

I don't have a clue as what the 10% switch is for,emmisions? the other half of the switch on the IP goes to the EGR crap. I got rid of that also with the J series intake.
I just installed a bowtie overdrive tranny (700R4) and it is wired 12V to tran, period, with a 4th gear apply switch so the converter locks when shifting into 4th,it'll unlock when tran drops out of 4th.
Mine also has a switch with a wire that bypasses the 4th apply so lockup can be obtained in third and if I am right also in 2nd if so desired. :D

[G. Gearloose]

I suspect the factory didn't want the tranny to slam every downshift upon decel. The complaints would be nonstop. And given the rotational mass of the 6.2, it would chew up the tranny in no time... its not that beefy. They couldn't count on every user dragging the brakes to unlock the TC, besides, the track would make all sorts of 'different' noises whether the brakes were actuated.. and mr public hates 'different'
I suspect you could safely adjust the switch some, but not drasticlly.

Also, they didn't want to lock and chug @ too low an rpm when there might not be enough pump pressure to keep the clutches & bands from slipping, burning the thing out sooner, hence it allows the rpms to come up sooner.
just my therory, I made it up, its all mine...