Need help very confused

[78Malibu496bbc]

One other way to determine what you have for a T-box is to take your cell phone and re-attach it to that long stick again. Then moving around the car to the passenger's side, slide/stick the phone and home brew selfie stick under the car so it is focusing on the rear of the t-case near the crossmember. If it is a TH350C, what you should see via the camera on the phone is a cylindrical object attached to the case beside the tailshaft housing with a nipple/hose attached to the rear face of it.. That is your modulator valve and it is vacuum controlled. The hose will be attached to a vacuum fitting that is either located on the base plate of the carb or more commonly screwed into a port on the intake behind the carb. Most of that line will be a shaped steel tube with only short sections of rubber tube at either end to complete the connection top and bottom.

Should the modulator valve not be present, then you likely do not have a 350 of any kind; it is more probable that you would have a TH200R4 or the Th200-4R or one of the variations on that theme.

The biggest immediate distinction between the 350's and the Th200R4 and the 700R4 is the 350's use engine vacuum to decide shifts, whereas the 200/700's use internal pressure and the TV cable to make that decision.

If all you have to look at is the ends of the cable, then the TV cable has a little plastic oval shaped cap on the end which snaps onto and over a mushroom shaped pin on the lower ear of the throttle shaft lever.

The 350 cable will likely display a long thin metal blade with a slot cut in it. It drops over the same pin but uses a metal clip or an E clip to retain it, or possibly even a cotter pin.

The two shots of the service manual instructions pretty much cover the install and adjustment if you do get to deal with the TV cable. I did post a detailed description of the whole process last summer so the resident search engine for this board ought to able to locate and retrieve it for you.


Too bad your driveway is a lake. That kind of puts a crimp in getting some proper shots of the case and what is hanging off it.



Nick

explained beautifully! 100%

 

[TimothyOnTop]

explained beautifully! 100%

Is this the vacuum modulator?

 

[78Malibu496bbc]

Is this the vacuum modulator?

yes, located on the right rear corner above pan

 

[TimothyOnTop]

yes, located on the right rear corner above pan

I was able to grab a screen shot from video I made does that mean it's a th350?

 

[78Malibu496bbc]

I was able to grab a screen shot from video I made does that mean it's a th350?

yes. the th400 vacuum modulator is located more to the front/center above pan

 

[TimothyOnTop]

yes. the th400 vacuum modulator is located more to the front/center above pan

And someone said if it was a th250 the pan would have an x instead of being flat as long as it still had the original pan on it? So is the th350 a better transmission than the th200c that came stock in my car?

 

[TimothyOnTop]

And when I rebuilt the carburetor there was a small hard line going into the middle rear of carb is this the vac line from transmission? Because I couldn't figure out where it was coming from or if it was possible a secondary fuel line

 

[69hurstolds]

And when I rebuilt the carburetor there was a small hard line going into the middle rear of carb is this the vac line from transmission? Because I couldn't figure out where it was coming from or if it was possible a secondary fuel line

Usually that's for power brake booster vacuum with a brass adapter to a pipe thread steel tubing. You will need to follow the vacuum line from the modulator back to the vacuum source on the intake manifold or carburetor. Since your stuff isn't original, who knows where it will go.

If you don't have the adjusting screw, then you have a version of the TH350. The TH350 or even a TH350C is much stronger than a plastic-gutted (I exaggerate to clarify) 200C. As I understand it, even the 350C has plastic washers in it. The TH350 does not.

The "passing gear" is what the kickdown cable is used for. It's not absolutely required to operate the transmission, and that's why your transmission isn't the unicorn 200C you thought it was. Typically, in contrast, the TV cables that are left unhooked eventually cause the transmission to fail because of a loss of internal pressure control based on load. TV cables are very important in the lives of these types of transmissions. The TH350 does not require it to work normally, except without the kickdown cable hooked up, you have no "passing gear".

If you have a TH350C, you should see a plastic electrical plug on the driver side of the transmission (circled in pic below) for an electrical connection for lockup converter signal. If this is unplugged, no big deal, you just won't have lockup. Converters are different between the 350 and 350C as well. Spline engagement is different and you will tear up a 350C if you just put a regular torque converter in it. If no electrical plug is there, then you have a "regular" 350. The regular TH350 best choice for sturdiness out of anything that's not a TH400 right out of the box.

 

[CopperNick]

Yes to the high probability of your t-mission being a TH350. As depicted in the picture above the "C" variant does come with the lockup provision. The plug for that socket has only two wires, and, as already noted, if it is disconnected or the harness is gone altogether, no biggie., the box will move from gear to gear without issues. I will leave it to a manual to explain exactly how the lock up works.

In the world of the first gen SBC's, starting around the middle 60's, the 350 was about as common and prevalent in GM's Chevrolet line of cars as pepperoni is on pizza. There is actually a whole subindustry attached to them in terms of parts and service and rebuild/performance products.

As for tracking the vacuum line, from the modulator valve it will proceed up to parallel the case and follow the shape of the case forward and upward to the seam between the t-case and the back of the engine block where the two bolt together. From there, depending on its source for vacuum, it can take a path to either side of the distributor and plug in to a vacuum port screwed into the intake manifold just ahead of the dizzy.

That port fitting has many shapes and sizes as it can possess as few as one port or as many as four or more, dependintg on many subsystems located in the vehicle make use of vacuum to operate.



Nick

 

[TimothyOnTop]

Yes to the high probability of your t-mission being a TH350. As depicted in the picture above the "C" variant does come with the lockup provision. The plug for that socket has only two wires, and, as already noted, if it is disconnected or the harness is gone altogether, no biggie., the box will move from gear to gear without issues. I will leave it to a manual to explain exactly how the lock up works.

In the world of the first gen SBC's, starting around the middle 60's, the 350 was about as common and prevalent in GM's Chevrolet line of cars as pepperoni is on pizza. There is actually a whole subindustry attached to them in terms of parts and service and rebuild/performance products.

As for tracking the vacuum line, from the modulator valve it will proceed up to parallel the case and follow the shape of the case forward and upward to the seam between the t-case and the back of the engine block where the two bolt together. From there, depending on its source for vacuum, it can take a path to either side of the distributor and plug in to a vacuum port screwed into the intake manifold just ahead of the dizzy.

That port fitting has many shapes and sizes as it can possess as few as one port or as many as four or more, dependintg on many subsystems located in the vehicle make use of vacuum to operate.



Nick

Thank you Nick good information I appreciate your help