'76 C30 Cruise Control Help... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chaseman17 · 08-03-2025, 12:47 PM

Hi. I am in need of some assistance diagnosing the cruise control on my '76 C30. It has worked perfectly ... three times...in the short time I have owned it. That tells me that the issue is likely something simple???

It has the single button actuator on the turn signal post. Simple on / off only. No resume, accelerate, etc.

There is a switch down by the brake pedal that I believe is part of the cruise. It has a vacuum line to the switch. The switch makes a hissing sound when the brake is engaged and no hissing sound when the brake is not engaged. (that makes sense to me)

The vacuum hissing sound at the switch by the brake pedal does not happen all the time when the brake is applied, but I feel like it should...??

The vacuum lines show no signs of leaking.

If anyone can provide some insight on what they think and how to test, I would really appreciate it. The cruise is the only thing on this truck that doesn't work properly and I want to get it dialed in.

Thanks in advance!

Dead Parrot · 08-06-2025, 05:47 PM

Not an expert but that vacuum switch is designed to dump the vacuum in the pot holding the throttle open when the brake is applied. Very likely that if the cruise isn't engaged, there is no vacuum to dump, thus no hiss.

I think some cruise systems also had a 2nd electrical brake switch that cut power to the cruise unit to turn it off. If you have one and it is not adjusted correctly, might not let the cruise turn on.

**hatzie** · 08-06-2025, 08:34 PM

Download the Cruisemaster manual in the manuals post.

chaseman17 · 08-07-2025, 06:50 AM

Thank you, I will look into that. That would be very helpful!

08-03-2025, 12:47 PM	#1
chaseman17 Registered User Join Date: Mar 2010 Location: Holland, MI Posts: 150	'76 C30 Cruise Control Help... Hi. I am in need of some assistance diagnosing the cruise control on my '76 C30. It has worked perfectly ... three times...in the short time I have owned it. That tells me that the issue is likely something simple??? It has the single button actuator on the turn signal post. Simple on / off only. No resume, accelerate, etc. There is a switch down by the brake pedal that I believe is part of the cruise. It has a vacuum line to the switch. The switch makes a hissing sound when the brake is engaged and no hissing sound when the brake is not engaged. (that makes sense to me) The vacuum hissing sound at the switch by the brake pedal does not happen all the time when the brake is applied, but I feel like it should...?? The vacuum lines show no signs of leaking. If anyone can provide some insight on what they think and how to test, I would really appreciate it. The cruise is the only thing on this truck that doesn't work properly and I want to get it dialed in. Thanks in advance! Attached Images __________________ 6T7 C10

08-06-2025, 05:47 PM	#2
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,809	Re: '76 C30 Cruise Control Help... Not an expert but that vacuum switch is designed to dump the vacuum in the pot holding the throttle open when the brake is applied. Very likely that if the cruise isn't engaged, there is no vacuum to dump, thus no hiss. I think some cruise systems also had a 2nd electrical brake switch that cut power to the cruise unit to turn it off. If you have one and it is not adjusted correctly, might not let the cruise turn on.

08-06-2025, 08:34 PM	#3
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 5,049	Re: '76 C30 Cruise Control Help... Download the Cruisemaster manual in the manuals post. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

08-07-2025, 06:50 AM	#4
chaseman17 Registered User Join Date: Mar 2010 Location: Holland, MI Posts: 150	Re: '76 C30 Cruise Control Help... Thank you, I will look into that. That would be very helpful! __________________ 6T7 C10



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