Cruise Control Issue

[MR. T.]

I took our 77 on its first significant trip so far, about 250 miles last weekend. Ran like a top and handled well, but and there is always a but, the cruise did not work, it would engage but then is surged and would not hold the proper speed. I am thinking it is likely a vacuum leak, cause it appear the system operates off of vacuum, but I have no idea where to start. Any suggestions? Thanks

 

[78IndyPace]

First step is to check all vacuum hoses connected to the transducer.

On my 78, surging was caused by the transducer. Surging was accompanied by the speedometer needle bouncing a bit. Removed the transducer, inserted the tang of a small round file in the socket where the speedo cable from the transmission connects, and spun it. Could hear and feel something rubbing inside. Disassembly is simple. Just be careful when removing the nut holding the coiled copper spring to the case, and while pulling off the sensor plate.

On mine it turned out the rotating disk, driven by the speedo cable from the transmission, was rubbing slightly against the sensor plate just forward of the rotating disk. Using a small hammer, I carefully tapped the rotating disk rearward on its shaft a bit, then reassembled the transducer and checked it by spinning it again. Repeated the tapping-reassembly-spinning process until no more rubbing was heard or felt. Then I cleaned up the transducer interior and parts, sparingly lubricated all friction points, reassembled, and reinstalled. The system works fine now. Rock steady holding speed and no more bouncing speedo needle.

Sorry that I did not take photos, but the transducer is pretty simple.

Hope this helps.

Good luck!
Jerry

 

[Art Jett]

If it turns out that you need any parts, I have an entire cruise control setup (minus the steering column lever) out of my 77. Transducer is new and diaphram is good. I would part with all or any for a reasonable price.

 

[MR. T.]

If it turns out that you need any parts, I have an entire cruise control setup (minus the steering column lever) out of my 77. Transducer is new and diaphram is good. I would part with all or any for a reasonable price.

I will try and check it out tonight, and if I need parts I will contact you. Thanks for the offer

 

[MR. T.]

Well, I pulled it apat and did a little adjustment as you suggested and I know have a cruise that is working for the most part. I still have a very tiny surge, but it is just in the rpm not in the speedo, so perhaps I have a wee vaccum leak. Funny thing is the speed neddle bounce more now at lower speeds. Thanks for the help so far.

 

[78IndyPace]

Probably time to check your speedometer cables. Do a search on this forum and others for "speedometer+cable+lubrication". The longer cable from the transmission to the cruise control transducer is more likely to be the culprit than the short cable from the cruise transducer to the speedometer. The forum searches will yield suggestions on removal, checking cable condition, and lubricants.

Hope this helps too!
Jerry

 

[Elliott]

I've got a 79 and am told I need a new servo; is that the same as the tranducer? The problem with minie is when activated is surges to full speed. What do you want for your parts? Dave

 

[78IndyPace]

Servo vs. Transducer

The servo is mounted on the top left rear of your motor and connects to your carb's throttle linkage. The unit is merely a spring loaded diaphragm that responds to a modulated vacuum signal from the transducer to open & close the throttle and maintain constant RPM.

The transducer is mounted on the inside rear of the driver's side wheel well in the engine compartment below the power brake booster. It interprets changes in vehicle speed via the speedometer cable and provides modulated output vacuum to the servo.

IMHO, since your car surges to full speed when you engage your cruise control, the servo is certainly functioning. But it seems to be receiving full vacuum from the transducer instead of properly modulated vacuum that will adjust the throttle to maintain speed. Thus I suspect your transducer is malfunctioning rather than your servo.

Before you start changing out your servo or transducer, make SURE all your vacuum hoses and connections to and from servo and transducer are correct with NO leaks.

Good luck!
Jerry

 

[Mike Boggs]

If it turns out that you need any parts, I have an entire cruise control setup (minus the steering column lever) out of my 77. Transducer is new and diaphram is good. I would part with all or any for a reasonable price.

How much is a reasonable price? I need the Servo and Transducer Thanks Mike

 

[Art Jett]

How much is a reasonable price? I need the Servo and Transducer Thanks Mike

Sold about a year and a half ago. Sorry