I have an '84 FBody with carbureted 2.8L and 700R4. I have finally gotten to a point where I'll be replacing the carb/distributor with components from an S10 which means I'll be losing the TPS input to the ECM and subsequently it will not be controlling the TCC lock-up.
I've researched a number of threads here going back many years and came up with a potentially simple approach to dealing with this common issue. While I don't have a problem with spending a little extra $ on a 'kit' - it seems they are (understandably) as much about retrofitting 700R4s to earlier cars as about dealing with losing ECMs control in newer cars (such as 3rd gens) which already have most of the 'stuff' on them for controlling 700R4s.
I'm not going for performance here - but rather functionality, economy and longevity.
I'll reference just two posts: Apeiron
lists several solutions in this excellent post including: https://www.thirdgen.org/forums/carb...c-control.html (TCC Control)
| Alternate/optional parts for homemade kit |
P/N 71V 1-6 inHg adjustable vacuum switch $43.00
P/N 71V2 6-22 inHg adjustable vacuum switch $43.00
P/N 71 7 inHg fixed vacuum switch $49.00 (use with connector below)
P/N 71-2 4 inHg fixed vacuum switch $49.00 (use with connecor below)
P/N 71X Vacuum switch connector with pigtail $24.00 (for above fixed vacuum switches, also works with GM vacuum switches above)
P/N 71XX Vacuum switch connector without pigtail $8.00 (if you're really cheap and you don't mind crimping the pins yourself)
P/N 71W External connector with pigtail (don't need this if you didn't butcher your factory wiring)
Then in this excellent tech article by Ed Maher
There is a suggestion to wiring a switch into the F port on the ALCL. I was already familiar with the 'F' port on the ALCL from when I had to debut my TCC (was the brake switch) some years ago. So here is yet another possible solution: Why not simply install an NO vacuum switch such as the #71V or #71V2 to the F connector on the ALCL and then ground the vacuum switch and run a vacuum line to it? That's it!
(Universal adjustable vacuum switch)
The vacuum switch could be installed on the firewall, grounded to the body and a wire run under the dash and spliced to the wire leading to the 'F' connector on the ALCL. A vacuum hose run to probably the same source as the (yet to be installed) vacuum advance source with a plastic 'T'.
This would allow all the stock wiring to stay in place and require a minimal amount of effort and cost. Even without a functional ECM - I believe this should
Lockup would occur in high vacuum conditions when the switch closes (grounding 'F') and and it would unlock in low vacuum conditions when the switch opens (ungrounding 'F').
Same as the various kits - this would lockup even when cold - the factory setup keeps the TCC unlocked when cold to help with faster warm-up of drivetrain. No biggee - I think that function will be lost regardless of approach. Question:
Will this work? Or did I miss some gotcha?
What advantages does a kit such as TCI P/N 376600 $79.88
have over a simple vacuum switch grounding the 'F' connector on the ALCL?
I'm thinking the kits just lockup 4th. This approach would lockup 2nd thru 4th under low throttle. Remember I'm not going for performance with a 2.8L. But I'm not sure how this would affect driveability.
Again - I don't have a problem spending extra for a kit if there's some functionality or other design aspects worth considering.