Hitman's Pontiac Trans Am Forum
Trans Am Information => Trans Am Tech => DriveTrain => Topic started by: Dinero on March 15, 2019, 10:57:26 PM
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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.
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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.
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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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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.
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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
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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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Ok, if only one button on the turn signal lever then it’s 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 I’m not as familiar with.
As far as the vacuum, yes you’ll 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 won’t 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 “clunk clunk” as you push it all the way in and “clunk clunk” as you let it out. Let me know if you do or dont hear that.
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Brian, did exactly as you posted. No Thump-Thump...
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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 you’ll 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.
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OK, to what setting do I set the voltmeter to? thanks
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One of the DC volt setting. There’s 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.
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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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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. (Don’t let the wire from the positive battery terminal touch anything else while it’s hooked up to the battery or you might get a spark and smoke show lol.) If it does go “clunk” you know the transducer solenoid is engaging at least. Not out of the water yet but it’s a start. When you’re 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 it’s grounding fine try the following
#1, there could be a break in the wire somewhere but that’s probably not likely so we’ll 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 didn’t come unplugged somehow. That’s the plug to your cruise button on the turn signal stalk. I can’t 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 that’s blown. It would be an in-line fuse and not part of the fuse block. I say “may be” because there is a reference to a fuse in the manual and I’ve heard other people mention it but my 77 does not have a fuse that I’ve found nor does an extra Wiring harness I have.
#3, if that’s plugged in and the fuse is good (or not there) then I’d 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.
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And the ignition was on when you tested for voltage right?
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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
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Ignition was on
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Ok those are good things so far then I think. The two switches with the plungers, one is the electric switch i mentioned that activates the brake lights and disengages the cruise. You could test that by unplugging the connector on that switch for the cruise control which should expose two terminals on the switch. Connect your multimeter to the terminals using the ohms setting. There should be continuity (should be a reading) with the pedal not pushed. When you push the brake pedal, you should lose continuity. I think the brake light wires for my 77 are green and red. Yours may be different.
The other switch with the plunger is a vacuum dump valve. Its so when the cruise is engaged, and is pulling vacuum on the servo, when you press your brake the electric switch cuts off power to the transducer and the vacuum dump valve opens and allows the vacuum to escape which allows the throttle to return to the closed position.
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I was thinking, while you're there at that switch, you could test to see if youre getting power to the switch. i dont remember what the colors are but one of the terminals on that connector should have 12v with the key on. Put the positive tester lead on one wire on the connector and the negative lead on a good ground and test for voltage. If none, test the other wire.
let me know
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ok, on the brake switch there are 2 terminals, one has a white/orange and the other has a brown, pink and black. which one do I test? the orange/white connector the is one closest to the plunger. the vacuum dump connector where the hose goes to is also stopping the white orange connector from coming off.
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White and orange should be for the brake lights. I think the colors of the wires are different between 77 (my car and the manual i have for it) and your 80. Youll have to pull that connector with the brown pink and black off and test each of those for 12v with the key on. I'll try to do some more digging in the meantime and see what i can find. Itll probably be the brown wire if i had to guess. Are you sure there are 3 wires on that plug?
Are you able to post a picture of it by chance?
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BTW, I found the bracket part that holds the threaded part of the switch and the dump switch not holding them in good. they were pushed out so i push both switches up against the bracket. not sure if this was throwing off the adjustment. wish there was a way to test to see if that was the problem without having to drive the car
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actually 2 brown wires, one comes in from the firewall bundled in with the vacuum dump hose, the other brown wire comes from a connector. so those 2 brown wires come together into one wire into one of the spades and then there is the pink wire. so these 3 wires make the 2 wire connector to the switch, that switch looks to be easier to come off to test
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will try to get a good pic. will have to send as attachment
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1st 3 pics are switches and the last is the transducer. hope they show up clear for you Brian. thanks
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2nd pic
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3rd
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transducer itself
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question, what actually grounds the transducer? is the that little thin copper wire?
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so i put the meter to ohm's. put the meter wires on and just got OL, then switch meter wires and get a reading of 0.00. also put a test light to it and got a good light. thanks
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ok, switched meter to V. got a reading of 0.15. also that 3 brown wire that goes into the brake switch comes from the connector that goes to the turn signal lever. that brown wire goes with the blue and green coming from the transducer
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BTW, I found the bracket part that holds the threaded part of the switch and the dump switch not holding them in good. they were pushed out so i push both switches up against the bracket. not sure if this was throwing off the adjustment. wish there was a way to test to see if that was the problem without having to drive the car
You don't have to drive the car. Unplug the connector thats for the cruise, put the multimeter on the terminals on the switch set to ohms. There should be a reading with the brake pedal not pressed. when you press it your multimeter should read OL meaning the contacts inside were opened (supposed to be like that) If the opposite happens, meaning OL when the pedal is not pressed but you get a reading when you press the pedal, those are for the brake lights then. Check the other set of terminals.
If, now that you adjusted that switch, you have continuity with the pedal out and a zero reading with the pedal pressed, plug the connector back in and go back to the beginning and retry the steps i had you try with the plug on the transducer and pressing the button with the key on and see what you get.
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question, what actually grounds the transducer? is the that little thin copper wire?
Yes. it connects the case to the bracket that bolts to the inner fender. I dont know if someone added it to mine or if it was factory at one point (i think someone added it) but mine has a wire going from that nut where the copper wire is to a bolt that holds the inner fender in. You could do that if you wanted but since during the ground test earlier you said the ground seemed good on the transducer I wouldn't worry about it.
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so i put the meter to ohm's. put the meter wires on and just got OL, then switch meter wires and get a reading of 0.00. also put a test light to it and got a good light. thanks
I think (since i'm not familiar with your digital multimeter) OL means open line meaning no continuity. That would be correct if you were testing the two terminals connected to the brake light wiring (orange and white). When you said "switch meter wires" if you meant you tested the other two terminals where the cruise connector was connected and got a reading of 0.00 with the pedal not pressed that would be right too and that's the important one to get the cruise to work. If that DIDNT happen before you adjusted that bracket, then that's probably what your problem was.
ok, switched meter to V. got a reading of 0.15. also that 3 brown wire that goes into the brake switch comes from the connector that goes to the turn signal lever. that brown wire goes with the blue and green coming from the transducer
As far as that, I think you want to test for voltage on the pink wire and a good ground. Again, the colors are different on your car vs my 77 but voltage should come from that pink wire into the brake switch. When the pedal is not pressed it allows voltage to pass from the pink wire to the other wire(s). I only have two wires at my connector, not the extra brown one you have. I'm wondering if maybe the extra one is for resume type cruise control (which started in 1980 i think). Maybe it was easier for them to install the same harness regardless of what kind you have and just not use the extra wire if you have non-resume.
Either way, test for voltage between the pink wire and a ground. If that works, plug the plug back in on the switch and retry the test with the key on where you switch the plug on the transducer so the "engage" wire is plugged into the "hold"terminal only. Press the set button and see if you get the transducer to clunk.
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transducer clunks ok. good reading on ground. well, will hit the road tomorrow for test after I get instrument panel and all other stuff back on. I rarely use the cruise but it bothers me that it is not working. I appreciate all your help. I am grateful. Will keep you posted. thank you
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Ok, just for the record, I was wrong about resume cruise. That didn't start until 1981. So that extra brown wire isn't for that. I found an 80 wiring diagram that shows both brown wires but its not clear as to where they go. One has to go to the button on the turn signal lever for sure. Where the other one goes, i'm not sure honestly. But I think we can still get you rolling so be sure to update when you can.
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transducer clunks ok. good reading on ground. well, will hit the road tomorrow for test after I get instrument panel and all other stuff back on. I rarely use the cruise but it bothers me that it is not working. I appreciate all your help. I am grateful. Will keep you posted. thank you
Awesome! Must have been that switch not being aligned right. Let me know when you try it out what happens.
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Brian, does the Thumping and clicking mean that the transducer is working like it should? No chance to test yet. Had storms almost every night. Streets still have water on them. Hopefully monday. thanks
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Not 100% no. It’s possible it could clunk and something else might not work right. Does your speedometer work though? If so, and it’s clunking now I’d say there’s a pretty good chance it can work. In the meantime there a couple more tests you could do to make sure the vacuum portion is working correctly. You’d have to run the engine to do so unless you have a vacuum pump.
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OK, I do have a vacuum pump
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One thing you could do is unplug the two hoses that come off that 4 way “T”. One should go to the servo (diaphragm) and the other goes to through the firewall to the vacuum dump valve on the brake pedal. Hook up your pump to the one that goes to the brake pedal and make sure it pulls a vacuum without leaking off. If not you may need to adjust the valve or replace it. If it holds a vacuum without leaking press your pedal and make sure it releases the vacuum.
The next thing you can do is attach the pump to the hose that goes to the servo and pull a vacuum on it. Make sure it pulls on the throttle without binding and holds a vacuum without leaking. If so you’re good so far.
At that point, again assuming your speedo works and isn’t really bouncy or anything, you could take it for a drive and test it. Remember there is a low speed mechanism built in so you should be above 30mph at least for cruise to work. Maybe faster. That’s slightly adjustable if necessary. Could try above 40 to be safe.
If you try it out and it doesn’t seem to work don’t give up. There’s another thing that can be adjusted.
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oK, diaphragm hose holding. linkage moves ok and diaphragm is been sucked good. Vacuum holds. Now the hose going to brake pedal is not holding at all. Waiting on wife to pull vacuum on it while I get underneath to check for leak or hear it. Will try a smaller hose and hook up straight to it to see if the main hose is bad. If it holds ok with the short hosem then hose might be bad. If vacuum does not hold with either hose, is the vacuum dump thingy bad? Stand by.
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ok, put different hose straight to vacuum dump valve and it does not hold vacuum. But would a bad vacuum dump valve stop the cruise from working? thanks
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update,,made sure that both brake switch and vacuum dump plungers were flush against the brake pedal bracket. after that did vacuum test again on valve and it is holding. Once i step on brake the vacuum releases.
Can't figure out why the switches are been pushed out that is causing the plungers not to stay all the way in and flush with the brake bracket. I just push both of them in and they go flush again. OK so now that I have good vacuum, I am ready for a test. Will keep you posted. Thank you Brian
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ok, put different hose straight to vacuum dump valve and it does not hold vacuum. But would a bad vacuum dump valve stop the cruise from working? thanks
Yes. If that doesn’t hold vacuum cruise will not work at all.
No problem though. And sorry I’m not sure why the valve and switch are moving on you so I’m little help there.
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as soon as I get the instrument cluster back in I will take a test drive. Will keep you posted. Thank you
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Sounds good
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Brian, I want to thank you for all your help. Finally got to do a test drive and the cruise control was spot on. So in the end it ended up been the vacuum dump switch not been properly adjusted. After setting it flush with the brake pedal is work. I did learn a l lot from you and I appreciate all your help. Live on.
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No problem at all. I’m glad it works and I was happy to be able to help.