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Diagnosing 700R4 (electronic) Torque Converter NOT locking up...

My '84 GM F-Body 2.8L V6 w/ 700R4 as of yesterday didn't engage the TC lock at cruise like it normally does. Basically as I'm cruising in 4th I'm running an extra 500rpm or so. It is stock and has worked fine up until the other day.

What should I start looking at to diagnose the issue and what are some of the easier, more basic problems to check out? Is it likely the solenoid itself? The wiring? The computer? or some sending unit or other that triggers the computer logic to engage it? Again just looking for some 'common' or 'typical' starting points to look at on a

700R4 of this vintage and application.

I looked at the Haynes wiring diagram such as it is and it shows 2 wires going to the computer, 1 for 4th gear discrete and 1 for TCC. It shows a 3rd wire but doesn't show where it goes...? I also don't see any any relays etc in the circuit but again my diagram isn't that good.

How do I determine if mine is one of the '84 700R4s that will overheat or not w/o the TCC engaged?

Any simple way to wire up the TCC to engage directly and bypass the computer?

thanks

Reply to
loadhawg
Loading thread data ...

======= ======= ok........here goes......pay attention......don't read fast...cuz i type reeeeeeeeeeeeeelly slow.!!!

(this is ALL based on YOUR post..so don't get mad at me if YOU ....HAVE....led me to believe YOUR wording is correct, and what you've led me to believe is correct..get pss'd at yerself...not me)

here we go.........

it happened for the first time yesterday....no lockup.

fk it...........

what are you worried about....??

man......i go days without take'n a crap..but i don't go histeric and phone the Doc every fk'n time it happens.

fact......not fiction.

~:~ MarshMonster ~tranny tech~ ~fact..not fiction~ ~:~

Reply to
Marsh Monster

This is from working on my wife's Beretta with a TH125, so it's not quite the same, but it may help.

The TC will only lock up if all of the following conditions are met:

2nd or 3rd gear. engine warmed up. speed > 25 MPH (or 35km/h I forget) brakes are NOT applied.

Any of these conditions being set will cause the TC to unlock.

you should be able to disconnect the wires from the transmission and set up a test with a switch where you can lock and unlock the tc at will. If it doesn't lock no matter what, it's either the solenoid or the guts of the transmission.

My guess is the solenoid has failed, but I only have the fact it's done that twice on the wife's car as my guess. (On the Beretta what starts to happen is the TC will fail to unlock when you apply the brakes - the solenoid sticks in the ON position.)

Ray

Reply to
Ray

Yeah it's meeting all those - (drive the same highway commute everyday)

My diagram shows:

1) tan/black wire going to the ECM TCC output 2) purple wire going to ??? (not shown on my diagram) 3) lt blue wire going to the ECM '4th gear discrete'

I'm presuming it grounds through the transmission but maybe not...

I'll have to experiment w/ the wires above and figure out which would be the hot and which the ground and hook up a switch...

OK - thanks. Can these be serviced from underneath w/ the pan off? Again mine's a 700R4

Also did yours just fail suddenly? Mine gave no particular warning - it just refused to work one morning and hasn't come back since... tranny appears to be functioning great otherwise...

thanks

Reply to
loadhawg

on a TH125 you service the TCC solenoid via a side cover. Honestly don't know much about the 700R4.

And no, it started failing gradually - it would intermittently not unlock or unlock/lock very rough until eventually it just stuck on even after turning the car off. This was spread over a couple of months before it became more regular - at first it was once a week, so it was hard to troubleshoot - you'd notice a rough shift and then it was fine - and it was the middle of winter, so I chalked it up to temperature...

Sorry I can't be of more help.

Reply to
ray

Easy access with the pan off. Stay out of 4th with the converter not locking. The trans WILL overheat without the converter locked up.

Reply to
Steve Austin

Cool - thanks! I'd read online precisely that - the 82, 83 and early

84 700R4s should not be run in 4th withOUT the TC engaged or they'll overhead...

Well once I figure out if the TCC solenoid is it I'll be doing a fluid change early this time 'round - thanks again

Reply to
loadhawg

=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D

if yer gonna persist in break'n this otherwise good tranny....

then here...... scroll down to the perty pictures...

formatting link

YOU SHOULD.....do two things.... do a google for "thirdgen" and go to the site....lots of Fbody stuff.

and..BUY A REPAIR MANUAL...if yer gonna persist in breaking that nice ride of yours.

~~a last note.....~~ If you look under the dash, find the ALDL conector, aka diagnostic connector, for the computer.....you can, if you want to, as a quick test, jump the "F" and "A" terminals togeather while driving the car....to see if the rpm's drop. Connecting those two terminals turns on lockup. I would suggest using a couple long wires and a switch...yer gonna look funny driven down the road try'n to touch those two terminals togeather use'n a paper clip.

:)

anywhoooo...... there yee go... there yee have it... there yee arrrrrrrreee.....

~:~ MarshMonster ~trannytech~ ~sips his crownroyal.....wonders if he shudda told you to jest run some juice to the purple wire.......................nah....... he'll figure it out~

Reply to
Marsh Monster

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