1985 Chevy Silverado transmission/engine swapping

Asked by Feb 20, 2015 at 05:51 PM about the 1985 Chevrolet C10

Question type: Maintenance & Repair

Ok guys, really desperate here. I've
been fighting with this ever since I did
an engine swap. I switched it from the
305 to a 350(355). Boared 40 over.

Long story short, was my first swap
with my brothers help.

After swapping engines, It took a few
weekends of "tuning" to get to where I
am now. Recently rebuilt the Quadra-
jet carb. Also! I swapped his
distributor over too, which is an
aftermarket distrib. Now after driving
it , it's not shifting automatically. I
believe it's a 700r4 electric tranny.
The '77 Chevy the 350 came from was
vacuum tranny. So I've just plugged
that hole now. However as stupid as
is sounds, Idk where the wires coming
from the driver side of the tranny plug
into on this block to. I believe the
wires I speak of are the torque
converter lock up wires? (Two wires,
yellow and blue) into a male plug, two
small circle inputs.  

I have managed to find out the 4
pronged wire that comes out on the
left side of the distributor from the
firewall plugged into my old
distributor. I don't think it does the
same to the new distributor.

Side note : after the snow fall and
freezing temperatures, I couldn't even
get it to manually shift to 3rd. It's
stuck in second.

15 Answers

I was driving it like it is a good bit, because I could still manual shift it to third. Without the two pronged wire that comes from the tranny, (torque converter lock up wires?) And the 4 pronged that plugs into the distributor. Have I ruined the torque converter, or transmission? It worked great before the engine swap


It sounds like you have a 4l60e trans which will require a seperate control mod to work properly, Jegs or summit will have one. What distributor do you have?

The current one is the aftermarket 6500 watt. My old one which I have is stock

Thank you btw, I really don't have money to take it to a professional. While I'm also trying to better my knowledge. I appreciate your help, keep asking questions lol


@CamaroCollector the 4l60e has a large multi-pin connector, from what he is describing it sounds like a 700r4. @Jason. The original TH350 tranny has the vacuum modulator and a separate kick down cable. The newer 700r4 only has a cable but it does the job of both the vac and kick down. It is called a T/V (throttle valve) cable and must be set to the right travel or the transmission will be seriously damaged, it is the most overlooked feature of that tranny (compared to the older units) and causes a lot of failures. You will need to ensure that you are using the correct cable bracket and linkages at the carb, the correct stroke/cable pull is critical. Search 700r4 T/V cable setup for instructions. Try this and see if your tranny is still good. If you still have issues you can test the line pressure before ripping into it. Personally I have destroyed 4 of these (700r4/4L60) and I will not use one again unless it is built, tested and warrantied. I prefer the TH350, then the 4L60e (e requires an electronic module to operate). As for the T/C lockup wiring I would have to look into that. I would concentrate on the T/V cable first. The T/C lock-up will only help your economy once the rest of the tranny works!

Best Answer

Im about to look over all this now. Thank you guys , I've had no luck researching.


http://www.cpttransmission.com/tech_tvcable.htm This is good info. Just need to ensure you are using 700r4 brackets and links on the carb.

I used the original bracket off the 305 that was originally in here and it shifted fine until we swapped motor

1 out of 1 people think this is helpful.

I'm still having a problem locating where this wire that comes off the driver side of the transmission case goes, as I said I think it's torque converter lock up wires. Two small wires, a splice half way, goes into the firewall on driver side, then the other splits off into a small blue and yellow wire with a red connector, two small circle prongs. I'm determined it goes back on the firewall somewhere.

1 out of 1 people think this is helpful.

Currently swapping distributors and connecting the 4multipin plug, then double checking tv cable and brackets.


If it's a 700r4 it is a 4spd tranny. If it is in good shape and not damaged it will run through all of the gears normally without the lock-up connected. The T/V cable is the main issue and must be addressed first. If it is not shifting correctly you may damage (or already damaged) the tranny. Is the carb you used on the 350 from the original 305. You must use the correct linkage to operated the the cable. On a 2 wire 700r4 the TC lock-up is controlled by the brake switch in the cab. One pin is ground and the other is power from the switch (enable). Once the correct line pressure in 4th gear is achieved the TC can lockup (internal pressure switch). It is possible that the previous owner modified the TC wiring to delay lock-up? Trace the wires on the other side of the firewall. Maybe there was a toggle to disable? On the EFI vehicles there is a third pin to allow the ECM to control the lockup.

We seen we're it goes in the firewall, to the brake switch in the cab. But we can't find where the other end that splits off, into a two pin plug somewhere under the hood, when comes from the tranny. We are using the exact carb I had on my 305, we rebuilt this one. Both Rochester Quadra jets. We're back at it today, just opened the hood. We're going over the tv cable and brackets. I'm almost sure it's correct. The tc wire is now the only thing not hooked up. I'm scared I already ruined the tranny. The 4 multi pin is plugged into the carb properly.

We just backed off the torque converter a screw driver width double checked it's in properly, now we've adjusted the tv cable again. I'm pretty sure it's stuck in second, I don't feel it shift from first to second. And now it's not even going to third. Is it sounding like I've already destroyed it from driving it and having to manually shift it. (That lasted a week,) the new engines been in two weeks now.

Edit: two messages ago, the 4 pin multi plug is now in the old distributor I put back in. Significant improvement in cold starts.

Someone help lol... I feel like we're overlooking something. Or the tranny is shot

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