Author Topic: 1980 T/A transducer vacuum for cruise control  (Read 2436 times)

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Offline Dinero

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1980 T/A transducer vacuum for cruise control
« on: March 15, 2019, 10:57:26 PM »
I am curious, where does the vacuum get created at for the cruise control, at the transducer or at diaphragm? the cruise on my 80 T/A quit working. I have checked all hoses, all ok, no leaks. There are no hoses going to the block or carb for vacuum either. When I squeeze the diaphragm the moves the linkage at the carb ok. So when I pull the hoses off the transducer I do not hear or feel any vacuum been created. So does that mean that the transducer is faulty? Thank you
p.s. the cruise control used to work ok before and if I remember,  when I would pull a hose off the transducer the car idle speed would roughen up like a vacuum leak. when I put the hose back on it would go back to smooth idle.
Desi Dinero

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Offline Dinero

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #1 on: March 25, 2019, 09:00:06 PM »
OK...update. did not have hose at transducer plugged into engine block vacuum source. I had replaced the brake booster and brake cylinder and had disconnect all hoses at transducer and did not make not of where hoses went. Once I got hoses in right sport. cruise control started working.
Desi Dinero

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Offline Dinero

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #2 on: May 25, 2020, 09:25:36 PM »
update: got all hoses in right place but cruise still does not work. I know there is one hose that goes to the vacuum source but do all hose's have vacuum to them though? thanks
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Offline b_hill_86

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #3 on: May 25, 2020, 11:11:01 PM »
Do you have resume cruise or non resume? I think resume was a new option for 80 Or 81.  If non resume I can probably help you problem solve it.
-Brian-

1977 Trans Am 400 4 speed hardtop

Offline Dinero

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #4 on: May 26, 2020, 08:46:41 PM »
Do you have resume cruise or non resume? I think resume was a new option for 80 Or 81.  If non resume I can probably help you problem solve it.

Brian, Not to sure what type of transducer I have. It is just a one button on the lever. What do I check to see what type I have? There are two wires, red and green to transducer. thank you
Desi Dinero

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Offline Dinero

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #5 on: May 26, 2020, 08:49:32 PM »
Brian, BTW, should there be vacuum to all hoses?  I only have vacuum to the vacuum source hose going to the block There is no vacuum to diaphragm or to brake hose. Do not know what starts or makes the vacuum to these lines. Thank You
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Offline b_hill_86

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #6 on: May 26, 2020, 09:57:03 PM »
Ok, if only one button on the turn signal lever then itís non-resume. That makes things easier for me to help with. The resume type transducers are the same but have an added piece or two attached that Iím not as familiar with.

As far as the vacuum, yes youíll only have vacuum present on the hose that goes from your vacuum source to port B without cruise engaged. Once the cruise is engaged there is a solenoid inside the transducer that energized and basically connects the B port to the A port which allows vacuum to be pulled on the diaphragm (servo).

Is your transducer new or old? Step one is to look at the plug on the top of it. On the transducer near the terminals it should say HOLD and ENGAGE. With the car and key off, unplug the plug and turn it so the wire that was on the ENGAGE terminal is now on the HOLD terminal. The other wire wonít be plugged into anything for now.

Now turn your key on so the ignition is on but the car is not running and press the button on the turn signal lever. You should hear ďclunk clunkĒ as you push it all the way in and ďclunk clunkĒ as you let it out. Let me know if you do or dont hear that.
-Brian-

1977 Trans Am 400 4 speed hardtop

Offline Dinero

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #7 on: May 27, 2020, 12:54:07 AM »
Brian, did exactly as you posted. No Thump-Thump...
Desi Dinero

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Offline b_hill_86

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #8 on: May 27, 2020, 04:36:49 AM »
Ok. Do you have a multimeter or a test light? If so stick the positive lead in the plug end for the engage terminal and put the negative lead on a good ground and press your button. See if you have voltage when you press the button. It should show voltage with the button about halfway in. Or as you press it in youíll see the voltage go up then drop off as the button is fully pressed. As you release it voltage will come up then drop off once fully released.
-Brian-

1977 Trans Am 400 4 speed hardtop

Offline Dinero

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #9 on: May 27, 2020, 12:42:52 PM »
OK, to what setting do I set the voltmeter to? thanks
Desi Dinero

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Offline b_hill_86

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #10 on: May 27, 2020, 01:47:58 PM »
One of the DC volt setting. Thereís probably a 10 or 50 or something. Those just select the range of the scale. Mine is analogue so it has a needle so for example, if i select the 10 volt scale and give it 12 volts The needle will peg to the right. If I select the 50 volt scale the needle would only raise about a fifth of the way.
-Brian-

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Offline Dinero

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #11 on: May 27, 2020, 02:31:43 PM »
i have one of those fancy auto detect meters. SO i set it to DCmA and I get zero reading, put it one DC10A an also get a zero reading, there is also a 10 MegOhm input DCV but thee I get all sorts of numbers up and down, What do you think? Thank you
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Offline b_hill_86

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #12 on: May 27, 2020, 03:01:19 PM »
Well, just confirming you tested the wire that went to the engage terminal right? If so there could be a couple things.

Before I get into the wiring, if you have some extra wire and clamps or an extra set of hands run a wire from a good ground or the negative battery terminal to the case on the transducer. Then run the other wire from the positive battery terminal to the engage terminal on the transducer and see if it clunks. (Donít let the wire from the positive battery terminal touch anything else while itís hooked up to the battery or you might get a spark and smoke show lol.) If it does go ďclunkĒ  you know the transducer solenoid is engaging at least. Not out of the water yet but itís a start. When youíre done with that, before you move on to below, also take your multimeter and set it to measure resistance (ohms). Touch one lead to a known good ground or the negative terminal on the battery and touch the other end to the case of the transducer to make sure the transducer is grounding okay. If you get a reading on your meter move on to below. If it reads zero you might have two problems at once.


If the transducer clunks with the test above and itís grounding fine try the following

#1, there could be a break in the wire somewhere but thatís probably not likely so weíll skip that for now.

 #2, look under your dash for a small black connector. It should have some pretty tiny wires coming out of one side that are stuck together so to speak. It makes them look like one flat and wide wire but if you look close theres actually 3. Assuming the colors are the same for 1980 they should be blue black and brown. Make sure that didnít come unplugged somehow. Thatís the plug to your cruise button on the turn signal stalk. I canít post pictures here but I can try to find you a picture and maybe email it to you if need be.

#2.5, there may be a fuse around there thatís blown. It would be an in-line  fuse and not part of the fuse block. I say ďmay beĒ because there is a reference to a fuse in the manual and Iíve heard other people mention it but my 77 does not have a fuse that Iíve found nor does an extra Wiring harness I have.

#3, if thatís plugged in and the fuse is good (or not there) then Iíd move on to the brake pedal switch. The switch on the pedal doubles to activate the brake lights when you press the pedal and it also breaks the circuit feeding power to the cruise so when the cruise is engaged it disengages when you press the brakes. That switch could be out of adjustment (though not likely if your brake lights work okay) or maybe the plug for the cruise cane off for some reason.

Let me know.
-Brian-

1977 Trans Am 400 4 speed hardtop

Offline b_hill_86

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #13 on: May 27, 2020, 03:21:03 PM »
And the ignition was on when you tested for voltage right?
-Brian-

1977 Trans Am 400 4 speed hardtop

Offline Dinero

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Re: 1980 T/A transducer vacuum for cruise control
« Reply #14 on: May 27, 2020, 03:30:38 PM »
It does thunk. get good ohm readings. ground ok. I see wire you're referring to. Green and blue going into firewall, then it picks up a brown wire(ground) I suppose and turns into a connector. then i see the wire coming from the turn signal lever, plugged in ok. Fuse good. Ok so I have the instrument cluster out and steering pull down. i can see 2 switches with plungers that go against brake pedal. I see a vacuum hose plugged into one switch. When I press the brake pedal I hear a clicking sound but can't tell which switch is clicking. Can't see how these switches could go out of adjustment and I cannot tell if either is out  of adjustment. When  I do press the brakes, the lights do come on.
OK, so I also had the rear up on jacks to test the transducer without having to test drive. 2 fllor jacks and 3 jack stands. Don't know if this is a good way to test but I did not get the transducer to engage.
Is thers a way to telll if switch with vacuum hose can be tested? Thank you
Desi Dinero

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