ltmonson

Hello,

I joined because I'm looking to contribute and find answers to my issues. I'm running out of hair to pull out trying to figure out why my 71 Cutlass Convertible will not upshift. I'm quite certain it is vacuum related and have been tracing down vacuum lines to ensure everything is hooked up properly. I have discovered that on the passenger side of the intake manifold there once was a plate bolted to the manifold that had two tubes coming out of it, this is broken/ gone/ not around anymore. Is the absence of this item contributing to my shift issue? Where do I find this part for purchase? Do I have to make one if I need it? (I hope I don't have to make it)

Someone told me the plate with the two tubes was heat for the choke mechanism on the carb but I don't know if that's accurate either, isn't that what the heat riser coming off the exhaust is for? I've referenced other threads on this site for most of the vacuum tracing but I have not found anyone addressing the mysterious plate with two hard lines coming off of it which was bolted to the manifold on the passenger side, next to the carb. Anyone that can offer any suggestions is going to be my Cutlass hero. Thank you,

-Ltmonson

rocketraider

It's the choke hot air tube. It sits in the exhaust crossover passage in the manifold. One end is connected to the carb choke thermostat housing, the other to a port at the top back of the carburetor. There is a vacuum port inside the choke housing that draws air thru the tubing where it picks up heat to relax the choke coil and allow the choke to open.

The heat riser in the exhaust manifold closes off to direct more exhaust gas thru the crossover passage for quicker choke warmup. Once it reaches operating temp its spring relaxes and allows the flapper valve to open. At that point exhaust gas thru the intake passage is minimal.

So no, it's not related to the transmission vacuum modulator at all. Look underneath the car, passenger side, and you'll see a round thing with a vacuum line attached to the transmission. That is your vacuum modulator. Follow the steel tube up the back of the engine to where it ends. At that point it should have a section of rubber tubing going to a manifold vacuum port, usually toward front of the intake manifold.

If the choke stove is missing and not blanked off with some type of cover plate, you're bound to have a dead exhaust leak unless the crossover ports in the heads have been filled.

ltmonson

Okay, I appreciate the info. When I had the carb rebuilt last year I had them add an electric choke so the "choke stove" that you are referring to is no longer in use. I'm guessing I should block that portion of the intake manifold off? I guess I'm not sure what a dead exhaust leak means, so it's just an exhaust leak and not contributing to a vacuum leak I'm assuming. I went out and followed that hard line down to the transmission and the end at the transmission is not connected to anything, there's just a small piece of rubber hose on the end of the steel line and it is not connected to anything. There is so much crud from fourty years of grime that I can't really tell where it is supposed to go...I'm going to jack the car up and try get a better look. Any more info you may have is hugely appreciated, thank you very much for the response.

ltmonson

So I think I see where the hose is supposed to be hooked up, it's a nipple sticking straight up on the pass. side of the trans. While under there I noticed an electrical connector with two wires running to it that is unplugged?! Is this a sensor or some sort of connection for the transmission? That connection I'm not able to tell where it is supposed to be hooked up...

Thanks again.

boese1978

The rubber hose conects to the vacum modulator. not sure how I imbed a link but try googling it. it is a small "horn shaped" thing, hold the line where it would look normal and it should be right there.

ltmonson

It shifts!!! Thank you gentleman, I'll be posting more when I tackle the next issue. The wire I found laying on top of the trans I'm guessing must be a power source for a console shift car (not equipped on this car, shifter is on the column)? Just a thought because I can not find anywhere it would connect to on the transmission.

rocketraider

My guess is the car has had the transmission replaced at some point with an incorrect application and people may have gotten sloppy in the changeout. There's a square metal tag attached to the trans that gives the code and year built. Give us that code and we can tell you whether your transmission is correct for your car.

I'm pretty sure that electrical plug is for the Transmission Controlled Spark system, which you're better off if you don't have anyway. The TCS prevents vacuum advance to the distributor until transmission is in high gear and coolant temp is above 120 or so. It was an emissions thing that looked good on paper, but in practice made the cars perform like dogs.

Allan R

The electrical connector. If it has 2 female inlets - it goes onto the TCS at the front of the intake. That's used to avoid overheating at idle, and when the engine sees heavy vacuum - like pedal to the metal. The TCS upper has an electrical and a vacuum port. There are also 3 ports on the lower portion. They measure vacuum draw and allow check valve movement to adjust the advance timing. What kind of carb are you running? Doesn't sound like a q jet. Maybe an Edelbrock?

ltmonson

I'm pretty sure it's the original carb. The electrical connector I was referring to is under the floor and was laying up on the transmission. Looks like it's one female connector with two wires running to it, I think they were black and green. The TCS upper is all connected now, thanks.

Allan R

Great! Is your car a 455 with a TH400?

ltmonson

Its a 350 and I have yet to positively ID the trans. My great uncle bought it brand new and my uncle owned it after him, I'm the third owner with all the paperwork. I'm fairly confident it's equipped with the original trans, but I don't know which one it is yet. I think that car with a 350 came with 2 or 3 different trans options.

1969w3155

If it's the original trans to your '71, and as you have pointed out an automatic, then it's the th350.

OLD SKL 69

Welcome to CO!