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They call me, Hugh Huffner
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Discussion Starter · #1 ·
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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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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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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They call me, Hugh Huffner
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584 Posts
Discussion Starter · #4 ·
Cool info! Thanks!

Well, Trans is in...
Did your stock TV cable work with the additional length of the 700R4?

They are pulling apart the rear end today..for complete rebuild. Driveline get picked up tomorrow.

On an interesting note, I noticed you had problems with the Shiftworks shifter conversion. Did you get these straightened out?

How does she run now?
Also.. need to figure out the Speedo gear thing...my Trans did not come with the gear that drives the Speedo/odo. What did you use? I need the gear and the bracket thingy to allow the cable to mount, also, did your stock speedo cable work?
What was the deal about the wire on the ECM? Do I need to worry about that?
Steve
 

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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:
 

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They call me, Hugh Huffner
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584 Posts
Discussion Starter · #6 ·
Thanks for the advice!

Anything else I should watch for? the shakedown is about 3 days away. As soon as the rear gets buttoned up, and the top end of the motor is buttoned up, its RUMBLE TIME! whoohooo!
 

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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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No 1st gear? Trans doesn't start out in first gear? you can't manually shift it to 1st? More detail is needed here. Manual linkage misadjusted, TV valve stuck, governor stuck, 1-2 servo stuck, Line pressure too high, long list-
Throw some more info out here please!!

:cheers:
 

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They call me, Hugh Huffner
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584 Posts
Discussion Starter · #11 ·
:D Got it. Not too worried about it selecting first, (though would be nice) think that could be fixed later. As long as it shifts and doesn't chew itself up, and unlocks when it is supposed to, that is the major checkpoint.

Got the driveline back today...all balanced and pretty with new U joints, Rear end drops tomorry. They should have that done in one day. Praying for the speedo thingy, and the gear. If they have it locally.......I will be................

ALMOST THERE! WHOOOOOOOHOOOOOOOOO!!!!!!!!!!!!!!!!!
 

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They call me, Hugh Huffner
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584 Posts
Discussion Starter · #13 ·
Found the Speedo thingies. (The nubbis looking speedo housing, the gear, o ring and the clamp)

Finally, the mechanic has the %@$% rear end out and apart, found out the rear end was about ready to explode, the clutch packs were working out, one of the keepers was disintigrated, and the others were working their way out.

Good thing I bought all that junk already. Everything is cleaned and he will have it reassembled tomorrow (We are now 5 days late getting back to body shop...NOT Happy!!)

Then reinstall into car, do TV, Do Shifter, Button up engine, THEN we can figure out if she works or not. JHC, I am going nuts!

:thud:
Steve
 

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They call me, Hugh Huffner
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584 Posts
Discussion Starter · #14 ·
FINALLY
Mechanic has Rear end in Car...should fire tomorrow...JHC what a nightmare. Had to replace ignition switch. If I ever meet the stupid designer who thought it was a really great idea to put the ignition switch where it is, and make it nearly impossible to get to....they get a free kick in the junk. Maybe two, depending how foul a mood I am in that day.

Update on the Tranny. The Shiftworks kit works Great! It selects all gears including first! Their carb plate, is not needed, use the TV cable from Bowtie OD, and plug it into the stock bracket, you need it for the throttle cable and the vaccuum diaphragm on the 81 anyway.

This has been a fun, though fustrating adventure....what started as a "freshen up the Engine" has turned into nearly a frome on resto. Only 6K overbudget! Lol.

Car should be painted in the next two weeks, saying of course I don't have another disgusting emergency. Lol. I think I need to kick my car's last owner in the cajones a few times as well. Poor vette was ABUSED!

Steve
 
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