We're swapping the transmissions in the shop truck. It's a late 80's GM 1/2 ton. The 700R4 had an electrical plug on it. I have no idea what it was all used for. I have to assume, speed sensor, neutral start and/or reverse switch, converter lockup etc.

The TH350 we're installing is basic. It's for a yard truck with limited street use. We don't need a speedo etc.

Will the ECM still allow the engine to operate properly without the tranny plug hooked up since it won't be getting a vehicle speed sensor signal?

 

The connector on the 700R4 is for TCC lock-up. If it's a non lock-up turbo 350, just swap in a non locking converter. The truck should run fine.

 

Some 700R4s have 2 plugs and others just one. The 2-pin is for the speedo sensor at the tailshaft. If it had a mechanical speedo then this one isnt there. The 4-pin plus is as described above and for the TCC clutch lockup. Some TH350s have a lockup converter but most do not. IDK if there were any electronic speedo TH350s. Either way your OK

 

There connector is more than a 4 pin. That's why I'm concerned. Although I never saw the old tranny, it's possible it was a 4L60E.

 

I put a Th350 in my '84 GMC 1/2 ton, which had a 700R4.

The 700R4 plug is for lockup, and high/low switch. The VSS is derived from the green module in the dash. Your truck (unless its post 87) should have a cable driven speedo. If its a VSS driven speedo, your in trouble.
I'm not sure if you can get a VSS from a 700R4 to work on a Th350. You're gonna lose some functionality in the ECM - EGR, some throttle follower stuff, etc.

The reverse is at the end of the column, and the neutral start is integrated into the switch assembly within the column.

-- Joe

 

As I mentioned above, we don't need a speedo. It's mostly a yard truck with limited street use. We don't even need the detent cable. Just a vaccum line for the modulator.

Well we got the tranny in today. Filled it full of oil and fired the engine up. That's the good part

When my foreman reved the engine up, smoke came out the tranny dipstick tube! Fluid level is fine. We don't have the linkage hooked up yet but the truck is up on jack stands so we manually put it in gear. Nuthing. No gears.

Well at least the used tranny was free. All it cost us was a filter, oil and some time. Now that we have a core, we'll go pick up a rebuilt one that we know will work. The tranny will be more than the truck is worth, that's why we tried a used tranny.