Cruise control advice needed - The 1947 - Present Chevrolet & GMC Truck Message Board Network

56weav · 08-04-2018, 12:55 PM

Hello,
I have a 1986 GMC Sierra Classic short bed.
305v8 automatic. With ac , cruise etc.
When I bought this truck 2.5 years ago many things didn’t work and the p.o. wasn’t much of a wrench. That being said the cruise didn’t work , however,
I replaced all the vacuum lines adjusted the servo rod to the carb and it worked.
It had an issue or 2 but worked.
The issues were and are resume didn’t work and it occasionally wouldn’t hold speed up an incline .
One day while messing with the cruise going down the interstate , i tried getting the system to increase speed and the whole system failed. I replaced the control stalk and it worked again however it was still touchy sometimes it wouldn’t hold speed up an incline
And if you disengaged the system it wouldn’t always reengage .
That being said the system failed completely again.
All lines and the check valve, and servo hold vacuum.
Any thoughts out there ?
I am aware and have had new parts fail ( that’s the ac compressor clutch story it lasted 2 days )
Before I do my normal throw parts at it till it works I thought I’d ask
Thank you

Mattchu60 · 08-05-2018, 07:58 AM

I had various problems with my cruise control - mostly on mine it momentarily cut out and then come back to life. I replaced everything and nothing seemed to help. Then I finally replaced the control module that sits under the dash by the steering column and it worked great afterwards. Not sure thats your issue but its something to look at.

56weav · 08-05-2018, 10:27 AM

Thank You for the mput
I’ll start with that.its would make sense it’s electrical in nature based on my symptoms.
With it holding vacuum everywhere it just didn’t lead to a vacuum issue
I was kinda of guessing the speed vvs that is hooked behind the speedometer
I’ll start with your input
Again thank you

**hatzie** · 08-05-2018, 02:55 PM

The GM Cruise III Service tech training textbook is available in the manuals post.
It may just be a cheap Asian Cruise switch. No way to know without some testing.

56weav · 08-05-2018, 04:34 PM

Thanks for the input
To the poor quality Asian parts I absolutely agree
This isn’t my first time restoring/fixing older vehicles. the quality of the aftermarket parts for these vehicles has been something of which could use improvement

After looking up under the dash I would guess the cruise box is to the right of the steering column and the left of the accelerator ?
Thanks for the manual links I’ll use them !

**hatzie** · 08-06-2018, 12:03 AM

Unfortunately Delco has been sourcing parts in China. They ride em pretty hard but the quality isn't what it was.

08-04-2018, 12:55 PM	#1
56weav Registered User Join Date: Oct 2016 Location: Lincoln illinois Posts: 34	Cruise control advice needed Hello, I have a 1986 GMC Sierra Classic short bed. 305v8 automatic. With ac , cruise etc. When I bought this truck 2.5 years ago many things didn’t work and the p.o. wasn’t much of a wrench. That being said the cruise didn’t work , however, I replaced all the vacuum lines adjusted the servo rod to the carb and it worked. It had an issue or 2 but worked. The issues were and are resume didn’t work and it occasionally wouldn’t hold speed up an incline . One day while messing with the cruise going down the interstate , i tried getting the system to increase speed and the whole system failed. I replaced the control stalk and it worked again however it was still touchy sometimes it wouldn’t hold speed up an incline And if you disengaged the system it wouldn’t always reengage . That being said the system failed completely again. All lines and the check valve, and servo hold vacuum. Any thoughts out there ? I am aware and have had new parts fail ( that’s the ac compressor clutch story it lasted 2 days ) Before I do my normal throw parts at it till it works I thought I’d ask Thank you

08-05-2018, 07:58 AM	#2
Mattchu60 Registered User Join Date: Jan 2014 Location: Swaledale, IA Posts: 485	Re: Cruise control advice needed I had various problems with my cruise control - mostly on mine it momentarily cut out and then come back to life. I replaced everything and nothing seemed to help. Then I finally replaced the control module that sits under the dash by the steering column and it worked great afterwards. Not sure thats your issue but its something to look at.

08-05-2018, 10:27 AM	#3
56weav Registered User Join Date: Oct 2016 Location: Lincoln illinois Posts: 34	Re: Cruise control advice needed Thank You for the mput I’ll start with that.its would make sense it’s electrical in nature based on my symptoms. With it holding vacuum everywhere it just didn’t lead to a vacuum issue I was kinda of guessing the speed vvs that is hooked behind the speedometer I’ll start with your input Again thank you

08-05-2018, 02:55 PM	#4
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: Cruise control advice needed The GM Cruise III Service tech training textbook is available in the manuals post. It may just be a cheap Asian Cruise switch. No way to know without some testing. __________________ 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.

08-05-2018, 04:34 PM	#5
56weav Registered User Join Date: Oct 2016 Location: Lincoln illinois Posts: 34	Re: Cruise control advice needed Thanks for the input To the poor quality Asian parts I absolutely agree This isn’t my first time restoring/fixing older vehicles. the quality of the aftermarket parts for these vehicles has been something of which could use improvement After looking up under the dash I would guess the cruise box is to the right of the steering column and the left of the accelerator ? Thanks for the manual links I’ll use them !

08-06-2018, 12:03 AM	#6
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: Cruise control advice needed Unfortunately Delco has been sourcing parts in China. They ride em pretty hard but the quality isn't what it was. __________________ 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.



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