Previous owner of my '81 put in a nice new crate motor and removed the computer. The trans is the original with a lockup converter but the lockup doesn't work. Is this controlled by the computer and is there another way to make it work?

 

Bowtie overdrives has the info you need

 

You can install a check ball in the valve body and it will automatically lock up around 45 mph. Any good trans guy will know how to do the mod. My trans is being rebuilt now, but I elected not to do it that way since my lockup still works. Don't ask me where in the valve body it goes, but my friends who know th350's inside and out informed me.

 

This diagram shows how they made the lockup converter function on the non-computer controlled '80.

 

Thanks guys. Looks like a fun project.

 

Simple toggle switch works for me

 

B&M sells a simple pressure switch that goes into the 4th pressure tap.

 

This will be easy on an '81 as all the electrics are in place (unless they've been ripped out?). If the electrics are unmolested then all you need to do is emulate the computer by fitting a switch in the cabin. The computer used to connect a wire to ground when it wanted lockup, so run a wire from this switch to a good ground & connect the other terminal of the switch to the wire the computer was grounding. This is a black/tan wire (which is probably dirt grey by now!). You can find it under the centre console by removing the d.side cover (3 screws). It's a wire with a hard black plastic test connector in it. It's a rectangular thing about 3/4" long & there's a partially exposed spade terminal on one side of it (and only 1 wire entering/exiting it). It should be about level with the ashtray, just hanging in the mass of wires in that area). This is the TCC diag connector & is in the wire that the computer grounds for lockup. Cut this wire & join it to the terminal of your new switch (the end that runs to the firewall).
If the wiring has been ripped out it's still an easy job. The stock setup used a relay (the computer grounded a wire that caused current to flow that switched the relay. The circuit that was then switched on/off controlled both the EGR & TCC functions). Assuming the EGR stuff has also gone then I'd wire it up without the relay (mounted on a bracket on the firewall directly in front of the driver, along with an AIR relay & MAP sensor). Here's how I'd do it (& have done similar with my Th200-4r, but without the manual switch):

Fit a toggle switch in the cabin & find the black/tan wire with the test connector in it. Cut this wire & join it to one side of the switch (the part heading to the engine bay!). On the other side of the switch run a wire to a good ground. This is where the fun now starts! Running up from the trans is a harness that goes to a connector hanging somewhere behind the rear of the d.side valve cover. Find this connector & you should see that 3 terminals on it are wired up: A (pnk/blk), B (tan/blk) & C(don't matter it's not used!). The pink/blk is a permanent 12v with ign on & the tan/blk goes to the TCC/EGR relay (& gets switched to earth when the computer earths another tan/black wire - the power through the trans uses a circuit in the relay that is connected between pins A & E when a circuit on pins B & C is energised by the computer - but you don't need to worry about that unless you're trying to fault find on the stock setup). Next find the EGR/TCC relay. It's got connectors A - E on it & is easy to spot as terminal D has no wire to it (unlike the other relay there (AIR?)). On pin C you will find a ppl wire. This is the wire that comes from the TCC switch on the brake pedal. Somehow join this wire to the wire on terminal A of the connector to the trans (removing the existing one & taping it up/whatever as it's live). You now have 12v going to the trans which gets cut when the brake pedal is pressed. Next, find terminal B on the relay. The has a black/tan wire on it & it's the wire that runs to the computer & has the diag connector in it (& should now go to your switch). Cut this wire & join it to the wire on terminal B of the connector to the trans. How you do the cutting/connecting is up to you (you can just cut the relay completely out & mask up the old wires, or you can do it so that it could be converted back to NCRS standard in the future), but what you need is the ppl wire connected to pin A to the trans & the black/tan connected to B & then heading off into the cabin to your grounding switch). Throwing the switch will then lock/unlock the converter.
NB. Just to confuse things, for some reason the wire on terminal B of the connector on the trans harness actually runs to pin D on the trans (wtf?!!!!). This can cause major confusion when looking at things saying connect to pin D on the trans. Pin C does sweet FA. I wasted a bunch of time pulling the pan off of my trans as somebody said it was used. It isn't. There's nothing connected to the C terminal in the trans (on mine, at least).
Another NB: Better check (with an AVO) that the black/tan wire from the engine bay to your switch doesn't branch off anywhere else (remnants of the EGR system? I'm pretty sure it doesn't, but can't say 100% as I didn't use it on mine) & that you've got the correct wire (as well as there being 2 different black/tan wires in the TCC circuit, all the wires on mine were the same color (grey), so an AVO is useful here).
Hope this all made sense! It sounds techy/tricky but really is easy (once you've summoned up the courage to cut the wires to 2 connectors on the advice of a complete stranger on the Net ). The converter will lock in 3rd gear if 12v is passing through the trans (there's a pressure switch in the internal circuit that, I'm told, prevents lockup in low gears or low speed). By connecting the ppl wire to pin A you're giving it 12v, that will be cut when you brake (a safety feature), & fitting the black/tan wire on pin B to ground allows current to flow, giving lockup. Fitting a manual switch in this wire lets you manually override lock up.

 

UKPaul - what a marvelous description of the potential solutions!!!
Thank you for making things so clear. Now I will have a good reason to avoid lawn mowing this weekend.

 

I have a 1980 with L48 350 Auto trans

How can I tell if my lock up converter is working?

Darrel

 

When cruising you just spike the gas slightly, if the rpm's shoot up then it is locked, the t/c always the eng to free rev slightly, when it is locked it does not

 

Do you have to have functioning cruise control to have the convertor lock up or just have a steady foot? My cruise system was removed sometime ago by the previous owner.

 

You can order a TC lockup from Summit that will lock your TC in 4th gear. I'd rather have this than my TC locking at 45 MPH. That would suck if you were racing.



PRF-60109 $129.88


Brand: Painless Wiring
Product Line: Painless Performance 700R4 Converter Lock-Up Kits
Manual Override Switch Included: No
Speedometer Sender Style: Electronic
Indicator Light Included: No
Quantity: Sold as a kit.

Torque Converter Lockup Kit, Electronic Sender, GM 700R4, Kit
These converter lockup kits from Painless give you an inexpensive way to automatically lock up the torque converter in 4th gear, when retrofitting a GM 700R4 transmission into an early non-computer controlled vehicle. The kits include everything you need for an easy installation, and you don't even need a speed sensor!

http://store.summitracing.com/partde...5&autoview=sku