'77 formula Joe?

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  #1  
Old 11-05-02, 10:26 AM
redneck
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'77 formula Joe?

Anyone out there know what the thingamabob attached to the base of the air cleaner (blue popit looking valve) is called? I believe it is thermo actuated. Engine manifold Vac goes to it then to the valve that shuts the trap door at the snorkel. When the engine is cold vac is supplied to the valve and the door closes--forcing carb to suck air from the exhaust manifold heat riser. When engine is warm vac should be shut off to the valve--allowing carb to suck air from snorkel/hose. Problem is mine sucks air from heat riser all the time! Hence, I need to know what the thingamabob is called so that I can find another one--if they even exist anymore. PS. this is why I usually tear all this "unneeded" crap out! emissions=crap. But, I want to keep this car "stock".
 
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  #2  
Old 11-05-02, 10:33 AM
Joe_F
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If you mean the sensor inside by the air filter, that is called an Air Cleaner Temperature Sensor.

Standard Motor Products or CARQUEST part # ATS2 would be for the 400 from 79 to 77.
 
  #3  
Old 11-05-02, 11:23 AM
redneck
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Yes, it is light blue plastic, and mounts beside the airfilter on the base (inside)of the housing. Not to be confused with the one that mounts to the outside of the air cleaner housing and sticks out to the rear passinger side with two vac lines attached(this one does the opposite by turning on vac as temp rises).
 
  #4  
Old 11-05-02, 02:02 PM
davidf
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Heat riser valve function is to quickly heat up the combustion chamber by passing hot exaust through the cylinder head when the heat riser valve is shut and then when the cylinder head reaches a high temperature the valve opens to allow normal exaust flow from engine exaust outlet through the exaust pipes to the muffler.That is why it is called a heat riser to raise the heat in the cylinder headfor smoother operation and better burn of hydrocarbons.
 
  #5  
Old 11-05-02, 02:56 PM
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Actually it's to heat up the area of the manifold under the carb to promote fuel air mix to atomize. If the manifold was cold the fuel mix would puddle and result in rough running and stalling.

Larry
 
  #6  
Old 11-05-02, 03:38 PM
davidf
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Your right,thanks for jogging my memory.I had a 79 camaro which I kept for twelve years and knew about the heat riser heating under the carb.I remember the cross hatch exaust passages which were visible as raised tunnels like an x and the carb sitting on top of the center on the x.
 
  #7  
Old 11-05-02, 04:10 PM
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Joe is correct on the part name but the system is thermac(which I'm sure Joe knows)stands for thermal air cleaner.Has nothing to do with the heat riser system.The thermac system introduces heated air into the air intake to help lower emission levels and promote better cold engine performance.The vehicles with thermac still have heat risers.It was introduced when emission controls were in their infancy,helping to meet new federal emission guidelines.
 
  #8  
Old 11-05-02, 04:16 PM
davidf
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Doesn't thermac stand for thermal actuator?
 
  #9  
Old 11-05-02, 05:27 PM
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davidf look at an older GM on the snorkel you will find a vacuum actuated motor stamped Thermac.Thermal controlled air cleaner.That is what I beleive the poster was inquiring about not his or her heat riser system.2 different systems.As per your question I'm not familiar with that term unless it's generic or brand specific,sorry.
 
  #10  
Old 11-05-02, 05:49 PM
davidf
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I think the original posting has a mistake in it .He says the carb draws air from the heat riser but what he ment was it draws air from the stove which is a metal shield on the exhaust manifold.The heat riser valve is on the exaust pipe close to the engine actuated by a rod which is connected to an vacuum diaphram.At cold temperatures there is vacuum at the diaphram which moves up with its attached rod which is connected to the heat riser valve.On my camaro the vacuum diaphram was a large metal can with a long rod a couple of feet long down to the heat riser valve on the exhaust pipe.
 
  #11  
Old 11-06-02, 05:40 AM
redneck
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Davo, is right, I was talking about the stove pipe from the manifold--not the valve on the exhaust manifold. The part I was looking for is called the TAC, and a bimetal thermoactuated valve that when above certain temp range shuts vac off to the vac motor on top of the snorkel--the vac motor then opens the flapper valve in the snorkel allowing cool air into the carb instead of the manifold heated air from the stove pipe. I ordered the part from local parts depot--$13. I pulled it and checked it at different heat extremes and it is not functioning properly.
 
  #12  
Old 11-06-02, 09:54 AM
Joe_F
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The part inside the air cleaner is a air cleaner temperature sensor. It is held in with a clip into the air cleaner housing.

The outer snorkel motor is called a Vacuum actuator. That is what is marked ThermAC The "AC" part is that it was designed by GM/AC Delco . Hence "ThermAC" . Davo is right. Most 70's and 80's cars had this. All of my carbed GM's do.

I can't recall if the 77 400 auto cars had the heat riser, but I'm pretty sure my 79 400 4 speed doesn't. It's very light in the emission control department .

Typically the vacuum lines from the air cleaner temperature sensor (at least one of them) runs to the ThermAC motor...that's how most of the GM's I've come across have it.

So which part were you originally looking for, and who was right ?
 
  #13  
Old 11-06-02, 10:17 AM
redneck
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Yup, you were right. My '77 shop manual calls it a TAC, and the "actuator" on the snorkel is called a vacumn motor. As far as a "heat riser" my motor is identical to yours, W-72 4spd, (I owned the exact car you have), I don't think we have one. There is a vac operated valve on the drivers side exhaust manifold--look at yours you got one--not sure what it really does!
 
  #14  
Old 11-06-02, 05:13 PM
Joe_F
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Thumbs up

The 400 is pretty loose in the emission department in all frankness .

No air pump, 2 way catalyst (three way came on in 1980).

Has a catalyst, EGR valve, backpressure transducer, ported vacuum switch in the air cleaner, one on the front of the intake manifold, one in the RH cylinder head. It has the requisite air cleaner controls.

On some 400's, there is a little check valve going to the vacuum advance. It slows retardation of the timing so as to let the emissions stay in check. 1978 W72 400's (even 4 speeds) don't have it, 1979 DOES .

They may have set it up for a heat riser and it's really blank. I'd have to look into it a bit. The key would be to look at your emission decal .

If it's missing, give Osborne Reproduction a call in GA for a new one
 
  #15  
Old 11-07-02, 06:04 AM
redneck
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Nope, no check valve to distributor. Nothing missing off this car 34,000 mile original that has been parked since early 80's. ps. I asked you awhile back about R&R of the heater core. Got it out last night---much easier on a non ac car--took about 1/2 hour. No need to remove fender--although if you had to get to the blower motor the fender would have to come off. Hardest part was getting the nuts off on the engine side of the fire wall. Dremel tool to the rescue again!
 
  #16  
Old 11-07-02, 06:15 AM
Joe_F
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Correct, '77 automatics wouldn't have it. It is a small vacuum regulator valve.

It was missing on my car when I first got it. One of the first things I replaced, along with all the the vacuum lines. Half of them were either plugged or misrouted. All back to stock now. Even the ported vacuum switch in the air cleaner was gone.

All easily rectified in one afternoon.

Good deal on the heater core. I don't buy non AC equipped vehicles, so I also assume the worst .

Sounds like a really nice, original car in need of some TLC. Easily rectified when you are starting from scratch. I have heard stories of cars like that. There was a Macho Trans Am like that for sale once. Turns out the timing was off 180 degrees and it was parked all those years. New timing set and resetting the distributor and it ran like a champ.

Why did it sit so long?
 
  #17  
Old 11-07-02, 09:32 AM
redneck
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Mine is a 4spd, W-72. I bought it from original owner, he just stopped driving it?! I drove it home. Brakes were spongy, radiator was clogged, heater core was leaking, driverside t-top seal was missing, and battery was almost dead. Only thing not original on the car was battery, and shifter knob, and tires, but The original tires (still look good) came with the car. Oh ya, the reverse lockout linkage from the trans to the column is missing, and owner has not located it yet, so if you know where I can find these parts let me know.
 
  #18  
Old 11-07-02, 02:55 PM
Joe_F
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Look up Texas Trans Am sales on the net. They would probably have the needed parts.

His intent was probably to put headers on it at one time.
 
  #19  
Old 11-08-02, 07:04 AM
redneck
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Headers? that is a good idea--they really wake these motors up! The linkage would just get in the way!
 
  #20  
Old 11-08-02, 04:01 PM
Joe_F
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Thumbs down

Which is precisely why the backdrive would be gone...they interfere with most headers for 2nd gen F cars with 4 speeds.

Stay away. Looks hokey, scrapes the ground and makes it into a ghetto-cruiser.
 
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