79 cruise control
Thread Starter
Racer
Joined: Mar 2015
Posts: 306
Likes: 20
From: Greenville SC
79 cruise control
I have had my car about 2 1/2 years. I have slowly gotten most everything working that I would like to work except for the cruise control. Initially the cruise would not hold a set speed. It would engage but the throttle went faster and faster. I now have a new transducer new switch at brake pedal and I think the vacuum diaphragm is pliable and seems to operate ok.
The car never had a vacuum valve(also located in the brake pedal). Now the cruise doesn't engage at all. The valve is listed in the Willcox instructions for trouble shooting cruise issues but I don't see where any one makes a repro. Is the valve a must for the cruise to operate?
The car never had a vacuum valve(also located in the brake pedal). Now the cruise doesn't engage at all. The valve is listed in the Willcox instructions for trouble shooting cruise issues but I don't see where any one makes a repro. Is the valve a must for the cruise to operate?
Melting Slicks
Joined: Dec 2009
Posts: 3,235
Likes: 658
From: Thunder Bay
Get a wiring diagram and check for power at the transducer. IIRC power is supplied to the transducer though the switch on the brake pedal. If that switch is out of adjustment, there won't be power to the transducer. As I recall, the switch is designed to disengage the cruise by cutting power to the transducer when you step on the brakes, and to release the vacuum at the same time. When I put the TKO 600 in my '79 I installed a second switch on the clutch pedal and my cruise wouldn't work. Turned out the clutch wasn't returning high enough to engage the switch and there was no power to the cruise.
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
No.
Is it required for the cruise control to operate safely?
Yes.
You can temporarily disable the brake vacuum switch for testing. Look in the vacuum line leading to the servo that drives the throttle. Look for a "T" with the branch leading through the firewall. Disconnect the line and plug the fitting.
IMPORTANT! The cruise control has a fail safe design and disengages electrically and/or via vacuum. If it fails to cancel when testing with the vacuum portion disabled, just turn off the ignition for a moment.
Is it required for the cruise control to operate safely?
Yes.
You can temporarily disable the brake vacuum switch for testing. Look in the vacuum line leading to the servo that drives the throttle. Look for a "T" with the branch leading through the firewall. Disconnect the line and plug the fitting.
IMPORTANT! The cruise control has a fail safe design and disengages electrically and/or via vacuum. If it fails to cancel when testing with the vacuum portion disabled, just turn off the ignition for a moment.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
No.
Is it required for the cruise control to operate safely?
Yes.
You can temporarily disable the brake vacuum switch for testing. Look in the vacuum line leading to the servo that drives the throttle. Look for a "T" with the branch leading through the firewall. Disconnect the line and plug the fitting.
IMPORTANT! The cruise control has a fail safe design and disengages electrically and/or via vacuum. If it fails to cancel when testing with the vacuum portion disabled, just turn off the ignition for a moment.
Is it required for the cruise control to operate safely?
Yes.
You can temporarily disable the brake vacuum switch for testing. Look in the vacuum line leading to the servo that drives the throttle. Look for a "T" with the branch leading through the firewall. Disconnect the line and plug the fitting.
IMPORTANT! The cruise control has a fail safe design and disengages electrically and/or via vacuum. If it fails to cancel when testing with the vacuum portion disabled, just turn off the ignition for a moment.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
I have had my car about 2 1/2 years. I have slowly gotten most everything working that I would like to work except for the cruise control. Initially the cruise would not hold a set speed. It would engage but the throttle went faster and faster. I now have a new transducer new switch at brake pedal and I think the vacuum diaphragm is pliable and seems to operate ok.
The car never had a vacuum valve(also located in the brake pedal). Now the cruise doesn't engage at all. The valve is listed in the Willcox instructions for trouble shooting cruise issues but I don't see where any one makes a repro. Is the valve a must for the cruise to operate?
The car never had a vacuum valve(also located in the brake pedal). Now the cruise doesn't engage at all. The valve is listed in the Willcox instructions for trouble shooting cruise issues but I don't see where any one makes a repro. Is the valve a must for the cruise to operate?
I finally paid thru the nose, and got a NOS GM unit. Works perfect, but now my speedo is jumpy.
There is a set of gears in there that strip out where the cable shafts are driven. POS design. Good luck.
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Thread Starter
Racer
Joined: Mar 2015
Posts: 306
Likes: 20
From: Greenville SC
79 cruise
If you use a test light to see if the switch (at break pedal) is getting power, when would the switch get power? When you depress the button on the turn signal lever or when the brake is applied???
If the switch isn't positioned correctly the brake light would not function. Correct???
Does the transducer receive power all the time or when the cruise button is depressed.?
If the switch isn't positioned correctly the brake light would not function. Correct???
Does the transducer receive power all the time or when the cruise button is depressed.?
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
The white wire at the transducer should get +12V only when the button is pushed and the brake is NOT pressed. Pressing the brake should kill the power. The switch for this is another set of contacts in the brake light switch; its' wires are pink (12V ignition power) and red (switched power).
The brown wire at the transducer has an integral section of 40 ohm "resistance wire" and will have a small voltage whenever the ignition is on and brake is NOT pressed. The purpose of this is to give just enough voltage to KEEP the solenoid closed after a momentary pulse from pushing the switch has done the job of actually closing the contacts.
In '79 the only other wire at the transducer is a ground that connects in the fender well.
Pressing the brake switch cuts off ALL power to the cruise system which via the solenoid in the transducer cuts off the supply of vacuum to the servo. A separate vacuum switch on the brake pedal opens the servo to the atmosphere which also disengages the cruise.
The brown wire at the transducer has an integral section of 40 ohm "resistance wire" and will have a small voltage whenever the ignition is on and brake is NOT pressed. The purpose of this is to give just enough voltage to KEEP the solenoid closed after a momentary pulse from pushing the switch has done the job of actually closing the contacts.
In '79 the only other wire at the transducer is a ground that connects in the fender well.
Pressing the brake switch cuts off ALL power to the cruise system which via the solenoid in the transducer cuts off the supply of vacuum to the servo. A separate vacuum switch on the brake pedal opens the servo to the atmosphere which also disengages the cruise.
Thread Starter
Racer
Joined: Mar 2015
Posts: 306
Likes: 20
From: Greenville SC
Thank you SBMIKE for taking the time to give me such detailed instructions. Now I can track down my problem.
BTW, do you know if anyone makes the vac. valve that attaches to the brake pedal? I never had one.
BTW, do you know if anyone makes the vac. valve that attaches to the brake pedal? I never had one.
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
Here's a great Cruisemaster Technical Bulletin
I'm looking and looking but have struck out with the "vacuum release valve assembly". I find it mentioned in the assembly manual but no part number is given
I'm looking and looking but have struck out with the "vacuum release valve assembly". I find it mentioned in the assembly manual but no part number is given
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
The part number appears to be 3885302
The ONLY place I show availability is in Doc Rebuild's print catalog from 2008. Here's his website: www.docrebuild.com
Be VERY cool when calling/contacting. Great products and an interesting character. DO NOT disagree with him in any way! DO NOT mention "other" part suppliers!
Presuming it's sold out (I bet it is) try salvage. I was used in millions of GM cars from the late 60s through early/mid 80s.
The ONLY place I show availability is in Doc Rebuild's print catalog from 2008. Here's his website: www.docrebuild.com
Be VERY cool when calling/contacting. Great products and an interesting character. DO NOT disagree with him in any way! DO NOT mention "other" part suppliers!
Presuming it's sold out (I bet it is) try salvage. I was used in millions of GM cars from the late 60s through early/mid 80s.
Thread Starter
Racer
Joined: Mar 2015
Posts: 306
Likes: 20
From: Greenville SC
Cruise issue
Sorry to revive this thread, however I have just located a vacuum valve that attaches to brake pedal. Releases vacuum to cruise. After further digging into this, is it possible this valve was required ONLY on cars with manual trannys
??????/
??????/
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
No. They all have them. Now could the part numbers be different? I don't know.
Melting Slicks
Joined: Oct 2000
Posts: 2,144
Likes: 196
From: Englewood FL
If your car has a manual transmission, then someone added the cruise control, and did not install the valve on the brake pedal.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Sounds to me like you need to adjust the brake and clutch pedal switches properly so the system will work. All those switches do is pass 12vdc power to operate the system until either the clutch or brake pedals are depressed. Activating either pedal cuts power to the system and cruise is dropped. The switches are easily adjustable (turned IN or OUT via the threaded body).
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
Sounds to me like you need to adjust the brake and clutch pedal switches properly so the system will work. All those switches do is pass 12vdc power to operate the system until either the clutch or brake pedals are depressed. Activating either pedal cuts power to the system and cruise is dropped. The switches are easily adjustable (turned IN or OUT via the threaded body).
Thread Starter
Racer
Joined: Mar 2015
Posts: 306
Likes: 20
From: Greenville SC
my car is an auto. It seems to me that the vacuum valve is redundant. There is already a switch that attaches to the brake pedal that goes out to the transducer. This elec. switch is suppose to shut down the cruise control when pedal is pushed down. I can't locate an additional vacuum line under the dash that the valve would attach to.
I'm going to the regional NCRS meet here in town tomorrow. Maybe someone with a 79 will let me look under the dash.
Thanks for all the replies. I am some what mechanically disadvantaged.
I'm going to the regional NCRS meet here in town tomorrow. Maybe someone with a 79 will let me look under the dash.
Thanks for all the replies. I am some what mechanically disadvantaged.
