Transmission Issue ??

[RoryH19]

Good thread as I too have issues when my 83 k5 goes into 4th.
I thought it was a quadrajet issue not supplying enough power and lugging the engine.
I'm going to check vacuum, and the tcc by unplugging the cable.
May also try the instant shudder fix.
If no change, I'll go back to my original thought of the carb. It's been sitting for several months.

 

[C10MixMaster]

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Brandon this is the switch and the delay valve you're looking for. mine is not in the factory location. I think they were on the fire wall between the engine and brake booster. The switches I have tested open and close around 3.5-5 inches of vacuum. when i added the delay valve ,the black and blue check valve thing, my cycling went away. To test the function of the switch an ohm meter will confirm continuity and a vacuum hand pump will cycle the switch and let you know at what vacuum. if you dont have a vacuum pump you can suck on it to cycle the switch (it will click)and verify its not leaking. Also T in a vacuum gauge to manifold vacuum and see what you vacuum reading are when your truck is lunging, if it's not in that 3-5 inches of vacuum range you might have a different problem. You can also unplug the vacuum switch ( for testing ) that would eliminate the lock up converter, if you still have lunging then you have eliminated or confirmed the lock up converter as the problem.

 

[Read]

Ben--Is this the switch? It is located on my fire wall. Forgive me in advance for all the questions.

What does the delay valve do?

Using the Ohm meter will tell me if switch is good or not?

Is it ok to drive with vacuum switch unplugged? Does that prevent lock up from engaging? How is that different from unplugging lock up connector wire?

Why would this issue only occur with warm temps? If it was the lock up converter, wouldn't it be a constant issue?

Thanks for your help!

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[C10MixMaster]

Ben--Is this the switch? It is located on my fire wall. Forgive me in advance for all the questions.

no thats a different sensor i believe it part of the computer controlled carb set up


What does the delay valve do?

acts as a buffer for the vacuum signal


Using the Ohm meter will tell me if switch is good or not?

yes should have infinite resistance and then have little to no ohms resistance with vacuum applied


Is it ok to drive with vacuum switch unplugged? for testing yes
Does that prevent lock up from engaging? yes
How is that different from unplugging lock up connector wire? it accomplishes the same thing

Why would this issue only occur with warm temps? If it was the lock up converter, wouldn't it be a constant issue?
Not sure? possible scenario, heat reduces engine power so you are on the gas harder which also lowers you vacuum signal.

Thanks for your help!

You must be registered for see images attach

Ben--Is this the switch? It is located on my fire wall. Forgive me in advance for all the questions.

no thats a different sensor i believe it part of the computer controlled carb set up


What does the delay valve do?

acts as a buffer for the vacuum signal


Using the Ohm meter will tell me if switch is good or not?

yes should have infinite resistance and then have little to no ohms resistance with vacuum applied


Is it ok to drive with vacuum switch unplugged? for testing yes
Does that prevent lock up from engaging? yes
How is that different from unplugging lock up connector wire? it accomplishes the same thing

Why would this issue only occur with warm temps? If it was the lock up converter, wouldn't it be a constant issue?
Not sure? possible scenario, heat reduces engine power so you are on the gas harder which also lowers you vacuum signal.

one other thing there is a temp switch in the transmission that will prevent the lock up from engaging before it reaches operating temperature.

Thanks for your help!

 

[Read]

Where should I look for that switch?

 

[C10MixMaster]

Where should I look for that switch?

seems to me they are located near the brake booster.

 

[Read]

Couldn't find another switch except the one pictured earlier. Is it possible it is missing the switch?

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[C10MixMaster]

Couldn't find another switch except the one pictured earlier. Is it possible it is missing the switch?

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after looking at the wiring diagram for the 85. it looks like that vacuum sensor is for the computer controlled carb and the computer also controls the lock up on your trans. Im not familiar with the CCC systems and probably not going to be the best of help on this system.

 

[Read]

Thanks for you efforts! Are you thinking this switch/sensor in the pic is the one for both carb and lock up?

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[Read]

Also if it controls both carb and lock up that could explain why I am also having a stalling issue at similar times with warm weather?? Truck will stall while driving as if there is a fuel problem. Pull over and will start back up in minutes.

 

[C10MixMaster]

Also if it controls both carb and lock up that could explain why I am also having a stalling issue at similar times with warm weather?? Truck will stall while driving as if there is a fuel problem. Pull over and will start back up in minutes.

yes that sensor feeds manifold pressure info to the computer then the computer controls the carb and lock up

As for the stalling thing i would instal the 3 port fuel pump before doing any other diagnostics.

 

[AuroraGirl]

Any noise? What does the fluid look and smell like? Is it downshifting if you change the gears manually any difference? If you take your foot off the gas does it make a difference ? Or does it just happen while accelerating?

my manual trans fluid smelled like melted beaver and it came out in two different consistencies, one a wet oil like soy sauce and the other marginally faster than molasses, one was clear and one was black.


Not related OP just wanted to share.

 

[79Scott]

Hey guys,
Been following this thread for a bit, I had started another thread with a similar problem (just the shuttering, no stalling). once I unplugged the switch on the side of the transmission the problem went away. My question is what is the module that is supposed to be located on the fire wall called? I took a quick glance on my '86 Silverado and didn't see one. was going to following the wire leads tonight. I would like to rule out the module. Thanks

 

[Wonder Bob]

This is the Distributor Thermal Vacuum switch, also known as a tip in switch. Here is a previous thread.

Whats this vacuum switch do?

On my 84 K10 I have it has a vacuum switch on the passenger side firewall that looks like the tc lock up thats on the driver side. When I got the truck I was surprized it would even start or move after I saw what was unplugged under the hood. the switch has a 2 pin plug in and should have a...

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