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Hi , Does anyone know how to disconnect and reinstall the rod coming off the vacuum actuator leading to the heat riser on my 75 ?? I changed the TVS switch and thermostat, however when she warms up it still does not open..I hear sounds coming from the actuator so I am thinking that is the final part that is not working .. If I pull off the rubber hose on the actuator then the heat riser opens. As always
thank you
disconnect it with a right angle grinder or sawzall. wire the heat riser open or better yet replace it with a spacer block. they usually stick. usually stick shut. unless you live up north and drive the car to work every day it is a waste of space and fuel. unless getting the car judged.
There is a ball and socket with a little spring clip holding the ball on the socket.
It should pop off with little prying pressure from a screw driver.
The Heat Riser shaft has a Male Ball Socket end to it.
The Actuator Shaft has a spring clip installed on the end.
The spring clip simply snaps around the Ball Socket end of the shaft.
I would use a flat head screwdriver and leverage between heat riser plate and actuator shaft AT spring clip to disconnect rod from shaft.
Here is the F/M socket side and spring clip of the actuator shaft...
The noise you hear may be due to the spot welds of the Heat Riser plate to the shaft may have broken loose.
In your 2nd photo the heat riser door is in the open position...
I think if you are getting vacuum after engine hot, retrace vacuum line as something is wrong with the vacuum switch or routing.
The valve should default open without vacuum so it sounds like it’s working.
for now plug the vacuum line leave open at a minimum. Don’t worry it gets hot enough without valve too, just takes a few minutes longer even in winter.
There is a ball and socket with a little spring clip holding the ball on the socket.
It should pop off with little prying pressure from a screw driver.
I think if you are getting vacuum after engine hot, retrace vacuum line as something is wrong with the vacuum switch or routing.
The valve should default open without vacuum so it sounds like it’s working.
for now plug the vacuum line leave open at a minimum. Don’t worry it gets hot enough without valve too, just takes a few minutes longer even in winter.
I just installed NOS TVS switch yesterday . Same thing when motor is hot heat riser doesn’t open unless I pull vacuum line off actuator .. is it possible the vacuum line off the TVS switch is backwards 🤷♂️ I installed the hose the same way I found it
I think if you are getting vacuum after engine hot, retrace vacuum line as something is wrong with the vacuum switch or routing.
The valve should default open without vacuum so it sounds like it’s working.
for now plug the vacuum line leave open at a minimum. Don’t worry it gets hot enough without valve too, just takes a few minutes longer even in winter.
Originally Posted by AKjeff
There is a ball and socket with a little spring clip holding the ball on the socket.
It should pop off with little prying pressure from a screw driver.
hi Jeff is it possible hoses on TVS switch are backwards . The bottom black hose off the F shaped valve is go the heat riser actuator . The upper yellow strip hose is going to the carb
uretor
Thank's for the Photo!
Your EFE TVS switch hoses are CORRECT "If" your replacement switch is correct.
What part number is your replacement switch?
Next question, does your EFE TVS switch have a 3rd or exhaust port like the photo below?
Your vacuum advance hose is blocking the view of that area in your photo is why I'm asking...
Last edited by bmotojoe; Mar 12, 2022 at 03:28 PM.
Thank's for the Photo!
Your EFE TVS switch hoses are CORRECT "If" your replacement switch is correct.
What part number is your replacement switch?
Next question, does your EFE TVS switch have a 3rd or exhaust port like the photo below?
Your vacuum advance hose is blocking the view of that area in your photo is why I'm asking...
The parts catalog does call out that number 3031386 as a replacement switch.
Your EFE TVS switch is connected correctly.
So on a cold start the TVS switch is sending a vacuum signal to EFE actuator closing heat riser door, correct...
Three things I can think of why your NOS TVS switch is not exhausting:
1. Your not reaching Normal Operating Temperature. These switches should exhaust at around 200F
2. Your NOS TVS switch is defective.
3. The exhaust port in your NOS TVS switch is blocked...
I know you have a 75 but digging into the 1977 Assembly Manual there were optional EFE TVS & EGR TVS switches that could have been installed.
Mine is a late 77 but still had the GM #355963 installed.
According to the AIM around 7 of 1976 the part number changed from GM #355963 to GM #3031386 and 3031386 part number is what the Corvette Parts Catalog also shows in Gr. 3.640.
Each of these switches should change state at or around 180* so your good with the switch you installed if it is functioning correctly...
Here is a photo of my Original and GM replacement EFE TVS switch #355963 showing 180*
The parts catalog does call out that number 3031386 as a replacement switch.
Your EFE TVS switch is connected correctly.
So on a cold start the TVS switch is sending a vacuum signal to EFE actuator closing heat riser door, correct...
Three things I can think of why your NOS TVS switch is not exhausting:
1. Your not reaching Normal Operating Temperature. These switches should exhaust at around 200F
2. Your NOS TVS switch is defective.
3. The exhaust port in your NOS TVS switch is blocked...
thank for all the info well appreciated.. know I am moving on to the actuator canister going to heat riser it is making noise while heating up..
I know you have a 75 but digging into the 1977 Assembly Manual there were optional EFE TVS & EGR TVS switches that could have been installed.
Mine is a late 77 but still had the GM #355963 installed.
According to the AIM around 7 of 1976 the part number changed from GM #355963 to GM #3031386 and 3031386 part number is what the Corvette Parts Catalog also shows in Gr. 3.640.
Each of these switches should change state at or around 180* so your good with the switch you installed if it is functioning correctly...
Here is a photo of my Original and GM replacement EFE TVS switch #355963 showing 180*
thank you I appreciated your help 👍 I thought the switch was correct.. Next I am moving into actuator canister, it was making noise while heating up and didn’t open heat riser until I pulled the hose off
Grady, I'll send you the one off my car for the cost of shipping if you want to try it.
Let me know, I'll test it with my vacuum pump before sending it.
Have you tested yours with a vacuum pump? I don't remember.
What I don't understand is your actuator closes the heat riser door correctly on a cold start...
When you manually remove the actuator hose (Simulating Engine Has Reached 180*+) the actuator rod extends to it's normal or home position opening the heat riser door.
No, the actuator should not make any noises but I still think you have a TVS switch not exhausting.
These switches by design are to pass vacuum from the top port to the 2nd port and then to the actuator in it's normal or cold position.
When HOT the TVS switch internally changes state closing off the vacuum flow to the actuator but the actuator and hose leading to it still has trapped energy (vacuum) that needs to exhaust somewhere and that is through the TVS switch exhaust port.
The noise you are hearing at the actuator...
What if:
Your TVS switch was fluttering a vacuum signal between opening and exhausting quickly, but still staying open enough to maintain +- 5 inches of vacuum to the actuator?
Something to try...
Block off the exhaust port of the TVS switch with some tape, rubber cap or something and see if the actuator noise stops...
Grady, I'll send you the one off my car for the cost of shipping if you want to try it.
Let me know, I'll test it with my vacuum pump before sending it.
Have you tested yours with a vacuum pump? I don't remember.
Grady, I'll send you the one off my car for the cost of shipping if you want to try it.
Let me know, I'll test it with my vacuum pump before sending it.
Have you tested yours with a vacuum pump? I don't remember.
Help installing actuator for 75 heat riser
