81 Tranny Wiring.

1954 Views 13 Replies 4 Participants Last post by skd81shark, Apr 9, 2007

skd81shark

Discussion Starter · Mar 24, 2007

Okay here's the deal.

My 81 originally had an electronic lockup THM350c. (I know, because it is sitting on the floor of the garage right now). Lol...one local tranny shop said there was no such thing as an electronic lockup THM350C he was upset when I showed it to him.):smack

I am installing a THM700R4. Got the Croos member and kit, along with shifter mod (Thanks Bowtie Overdrives and Shiftworks!)

Now, in this little adventure I discovered something odd.

The 350c has a two prong wiring receptacle for the harness pigtail.
The 700R4 has a 3 prong one. (Identical, same shape/size)

The car has a 4 prong pigtail. Said 4 prong pigtail allowed THM350 to shift just fine and dandy.

Anybody know if 81's were prewired for a 700R4? Maybe a production delay kept them out, or maybe my car is a late 81, so has 82 crossover parts?:WTF

Just wondering if said harness will actuate and release the lockup in the 700....would save a buttload of time, and eliminate extra wires.

Anybody done this before? The parts in the Bowtie kit (I bought the brake pedal switch kit) look identical! The plug, the Switch (I just bought a new Brake light switch from GM about 5 months ago. EXACT same switch, just in GM white, instead of Bowtie Overdrives Black. Same config, same # of prongs, etc....then there is that harness pigtail......any clues?:huh:

Steve

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sensei

· #2 · Mar 24, 2007

Steve, I just installed the BTO 700r4 in my '81 and you can just plug in the stock plug from the th350c and it will lock up in 4th, but it will not unlock from the brake pedal. I have been studying the wiring and have figured out how it works, I just need to figure out how to emplement the mod needed to get it to unlock with the brakes. With a 4th gear only lockup, the only problem with no brake unlock is that if you slam on the brakes and lock up the rear tires while in fourth gear, the engine will stall. This is a possible but unlikely scenario. I will come up with a fix sometime soon and will post it for you if you want. In the mean time, save yourself some time and trouble and just plug in and go.
By the way, did you get their TV made EZ kit? I you have not installed it yet, you might try not using it. After I installed it, which required cutting off the riveted stud from the carb linkage, I realized that the only advantage it had over the stock kickdown cable was an extremely small amount of adjustment that seemed to make no noticable difference in my shift timing at all. I would be interested is seeing if it was really needed at all, or if the stock linkage would be fine as is. Either way, you don't need their mounting plate (the one that goes under the carb), your stock mount will work fine.
Hope I am of some help. For a full rundown on my install, check this:
http://forums.corvetteforum.com/showthread.php?t=1645988&highlight=700r4+install+begins

God bless, Sensei

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sensei

· #3 · Mar 25, 2007

Here's an update; the only reason mine was not unlocking with the brakes was that my brake pedal switch was mis-aligned. Fixed it last night and all is well. So, bottom line, an '81's wiring will plug right in and work for a 700r4. God bless, Sensei

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sensei

· #7 · Mar 26, 2007

TimAT said:
The TH350 cable WILL NOT work with a 700. The 350 uses the cable for kickdown shifts and the 700 uses the cable for line pressure modulation- upshifts, downshifts, kickdown, everything. If you don't have the correct cable you WILL be rebuilding the tranny. The line pressure will be low and you'll be cooking clutches.

:cheers:

While the function of the cable on the 350 and 700 are different, the cables themselves are virtually identical! All you have to be sure of is that your pressure rises instantly with any throtle movement, so the stock kickdown cable should work fine.

I had BTO custom build my tranny so it came with the right gears installed.

The shiftworks conversion has issues, but you will need a bracket for mounting the shift cable at the tranny. It would be very difficult (percise cutting and welding) to modify the stock one. Theirs had to have a chunk removed to fit, but it was easy with a dremel tool and cutting wheel. The bracket in the car was the real problem. Don't bother with it. It did not fit right and needed modification to work at all, and in the end, I still do not have first gear. I could have left the stock bracket and had the same thing.

I used my stock speedo cable, and no mods whatsoever concerning the ECM.

God bless, Sensei

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sensei

· #10 · Mar 27, 2007

Sorry, I was talking about the shifter bracket in the console. I thought it was obvious I meant I can't manually select 1st gear. It does start in first. God bless Sensei

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