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67 Cruise Control - bringing it back to life


RodA67Riv
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Hello everyone. First time posting here. I'm slowly bringing each part of the Cruise Control system back to life on my '67. Started with a dirty activation switch in the speedo. Took it apart, cleaned and lubed the contacts and confirmed that the relay now engages and the cruise light comes on. Next was a badly stiffening diaphragm in the control unit. Dissembled the control unit and soaked the diaphragm in brake fluid for a few days and got it back to life. Confirmed that it would hold a vacuum, installed a makeshift air filter and reinstalled everything. Still no functioning cruise. Next up was confirming that the control unit solenoid worked by jumping it to the battery while the engine was running. Noted a slight movement of the throttle chain and decided that I must have a vacuum leak. Removed the line which connects to the brake switch and held it closed with my finger while again jumping the solenoid to the battery and confirmed that the control unit is working and will throttle up the engine. Yay! So far, so good. Climbed under the dash and traced the brake switch vacuum line and found it torn just after it passes through the fire wall. Now, I could splice the brake switch vacuum line, but it has a spring inside of the hose which makes this a bit more challenging. Question: anyone know where I might find a cruise control brake switch? I think that they are the same from 63-67. The part number is 1598522. Note that the switch has a vacuum line attached to it. When new, the vacuum line comes with the switch. I haven't taken the switch out to see it the whole line can be replaced (it's a pretty tight space where the switch mounts.  Here's what it looks like: 

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Thanks everyone. Hope the steps outlined above might help others bring their cruise control back to life as well.

 

Rod A (ROA member 15162)

Edited by RodA67Riv (see edit history)
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Okay, so I decided to splice the vacuum line to the brake switch rather than search for a non-existent part. Took her out for a test run. Cruise is now working, but oscillating +-3MPH. So, out comes the dash again so I can pull the speedo and clean the contacts. I have to say… pulling the dash completely out is a major PITA! 
 

If you get this far into it, here’s what the cruise contacts area looks like. Look for a spring with a long lead which makes contact with the brass bar shown in the pic. Very (and I mean very) carefully file both sides of the lead and the brass bar where the spring makes contact. Do the same on the brass contact housed in the speed setting dial as well. Reassemble and cross your fingers. Sorry, I didn’t take any additional pics. I’m reinstalling the dash now (after taking the opportunity to clean up the gauges, lens, etc.). I’ll post later if my cruise is now working without the oscillating speed effect.

1D013DCE-EFD4-4573-9BA5-AD00B186C452.jpeg

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12 minutes ago, RodA67Riv said:

Cruise is now working, but oscillating +-3MPH.

 

Have you adjusted all the slack out of the linkage to the throttle? That can cause the speed setting to be erratic.

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I've done this many times. I got real good at R&R'ing the dash. Not something I wanted to be good at though. 😬 I had it down to 15 or 20 minutes but as in your case persistence will pay off.

Before putting speedo back together and instrument panel back in put an ohmmeter across the hair spring contact and make and break it 100 times at different speed setpoints. You want to see less than 1 ohm repeatedly. Otherwise risk intermittent operation. I am pretty sure I did an in depth tech article in the Riview on the 66/67 cruise systems a long time ago. The hair spring contact is the Achilles heel of the system. Very delicate to clean without damaging and sometimes the thin spring gets partially worn through. The Speed Alert option used same hair spring design. On working systems, when not using cruise always good to keep the set point above the speeds you travel to avoid unnecessary contacting of the hair spring.

When these systems working properly they will consistently hold +/- 1mph. Very impressive for the time period.  

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Ok, so I’m still having issues, but this time I’m sure it’s my fault. I get a constant ground out of the cruise contact when measured at the relay/amplifier connector behind the glovebox. There’s a ground wire which attaches to one side of the cruise enable switch (to provide a ground to the Speedo since it has insulated mounting screws. In my haste, sweat, swatting mosquitos and cramped quarters of a hanging dashboard, I’m guessing I grounded the Speedo lead. Urggg! Have to see if I can reach in there and correct it without pulling the dash again. 
 

Anyway, here’s some pics of how to clean up the Speedo cruise contacts. 
 

 

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And just in case someone may benefit from this pic… Here’s the correct connections for grounding the Speedo and the cruise contact lead. There’s a light blue, dbl black stripped wire coming out of the harness (not shown in this pic) which connects to the cruise contact lead.

69CCFD5B-1C78-4386-BF11-4DE413CE82C7.jpeg

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Posted (edited)

Ok… don’t do what I did folks and screw the amplifier lead to ground instead of tying it into the Speedo cruise contact spring lead! 

 

067AF187-636D-4693-A477-0B777DD718C1.jpeg
 

if you do, you’ll need this setup and a very flexible back to crawl under the dash! 
 

F5A21F42-98EE-4C07-AC2B-84ABB7E211D0.jpeg

Edited by RodA67Riv (see edit history)
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Hello Rod, you have a beautiful Riviera and an excellent 1st post here!

 

I temporarily installed a speedo with the "Speed Minder" in my '63 while I fix the Unit with that awful "Transducer". It is on the back-burner for now. So, glad to learn more from your dealings on the '67 unit.

Achilles Heel that spring certainly is! Buick chose to not use the Perfect Circle unit that other GM divisions did. That one measured pulses and sent a Pulse Width (PWM) signal to the vacuum actuator. Buick's "Electro Cruise" measures the position of the indicator and attempts to create a PWM signal with the oscillating spring. Measuring the position of the needle ('63 Speedo) is not ideal but having an electronic system except for that flakey spring, should've named it "Mechano Cruise".

The Spring in my unit is so far out-of-wack (damaged?) that I'm working with a 'real transducer' while maintaining measuring of indicator position, the original design. If successful, it will be 100% electro/pneumatic.

I've tried several PWM controllers but a heated seat controller appears to work best. My attempt might be a long shot but, I'm a sucker for doing things the hard way!

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Posted (edited)

Thanks John B. Interesting setup you are working on. For the layperson, I’ll describe the 66/67 electro cruise as just a set of switches when you boil it down. The engage switch on the dash energizes a solenoid within the relay. Once the engage switch it released, one set (of 2) contacts within the relay keeps the relay solenoid enabled while the second set of contacts turns on the cruise light and provides positive power to the solenoid on the “power unit” (aka the vacuum diaphragm). The function of the power unit solenoid is to open a vacuum valve which pulls the diaphragm, chain and throttle. On the negative side of the power unit solenoid there is a simple transistor circuit (aka the “amplifier” as GM called it) which also acts as a switch. If the speedo cruise control contact spring is closed (speed is less than the cruise setting) the contact spring grounds the base lead of the transistor which allows current to flow thru and this in turn, grounds the power unit solenoid, opens the vacuum and pulls the throttle until the desire speed is achieved. Once the speed is met, a lever on the speedometer dial (shown in the photos above) pushes the spring and breaks the grounding contact. Once the spring ground connection is opened, the ground to the transistor is also opened and current to the power unit solenoid is removed  - thus acceleration stops. The vehicle speed slows and the spring once again is grounded starting the acceleration cycle again. This repeated deceleration/acceleration cycle happens so quickly that it isn’t noticed by the driver and speed is “maintained”.  The on/off cycle produces a pulse width signal to the transistor, but if you’re not a tech person, just think of it as a rapid series of on/off signals which ultimately open and close the vacuum in the “power unit” at a rate which controls the vacuum and therefore throttle tension. 

 

Pressing the brake opens the positive side of the circuit (via the cruise control brake switch) and the relay is released cutting positive power to the cruise light and power unit solenoid. The cruise control brake switch also opens a valve to rapidly release any vacuum in the power unit thus immediately removing throttle link tension.

 

Cheers!

 

 

Edited by RodA67Riv
corrected/clarified the description for future users (see edit history)
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Ladies and gentlemen… drum roll please…

 

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Thanks everyone for your advice, tips and suggestions! 
 

That was the last of my accessories repairs. Every option is now functional (including the R12 based A/C)!
 

Next up… rear end bushings. I did a complete front end rebuild (including the steering gearbox) just after I bought her, but the rear end seems more challenging to me for some reason. Or, maybe I just don’t like working underneath 2 tons of steel with jack stands anymore. ;)

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On 7/26/2021 at 9:37 AM, Ronnie said:

 

Have you adjusted all the slack out of the linkage to the throttle? That can cause the speed setting to be erratic.

Hi Ronnie, thanks for this tip. At lower cruise control speeds, I was still getting an oscillating symptom (although not as pronounced as before cleaning the speedo contacts). Tightened the chain slack to 1/8 inch longer than where the coupler meets the throttle linkage (per the GM service guide) and that solved the issue. Great advice!

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On 7/27/2021 at 6:58 PM, RodA67Riv said:

Hi Ronnie, thanks for this tip. At lower cruise control speeds, I was still getting an oscillating symptom (although not as pronounced as before cleaning the speedo contacts). Tightened the chain slack to 1/8 inch longer than where the coupler meets the throttle linkage (per the GM service guide) and that solved the issue. Great advice!

 

Happy to hear that solved your problem.

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On 7/27/2021 at 12:30 AM, XframeFX said:

I temporarily installed a speedo with the "Speed Minder" in my '63 while I fix the Unit with that awful "Transducer". It is on the back-burner for now. So, glad to learn more from your dealings on the '67 unit.

 

 

On 7/27/2021 at 12:30 AM, XframeFX said:

Hello John B. Not sure where you are located, but I wouldn't mind taking a look at your '63 Electro Cruise speedo. I'm confident that the setup is exactly the same as the '66-67 and it's just cosmetic differences for the 63-65 vs. 66-67 speedo. I'm thinking that I'll do a full write-up on the Electro Cruise operation and repair for all model years where it applied. I'm in the Chicago area. 

 

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Rod, I believe they were the same also. I like the tumbler speedo and it would be conducive to implementing Buick's Electro-Cruise. However, the 1st generation Rivieras were blessed with round instrument pods in an era where longitudal speedos prevailed. This lends well to full custom digital gauges such as Dakota Digital. Not for me though. I simply want to restore function of my accessories. Maybe modify if a bad design or if a simple modern solution is available.

I tested all components of my Electro-Cruise and the only deficient items were a leaky diaphragm, bad hose with the spring inside and that flakey hair-spring. The latter is so archaic and is just plain terrible. When not using the cruise, set the pointer high out of the way to save wear and tear. Basically a poor design in the transducer department. Again, my spring appears to be messed with long nose pliers, totally NG.

If successful, I'll post images that will pertain to 1st gen Rivs only. Perhaps the 1966 - 67 speedo might be easier to mount my transducer.

You are centrally located, not me. Edmonton Alberta.

Thanks for responding,

JB

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21 hours ago, RodA67Riv said:

I'm thinking that I'll do a full write-up on the Electro Cruise operation and repair for all model years where it applied.

 

I'd love to see that article in the Riview;)

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