The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 10-29-2009, 08:25 AM   #1
mabu
Registered User
 
Join Date: Oct 2009
Location: Rancho Cucamonga, CA
Posts: 6
Speed switch

I have searched but cannot find anything, can someone please tell me where the speed switch is located? (Not speed switch solenoid)
mabu is offline   Reply With Quote
Old 10-29-2009, 08:42 AM   #2
68 TT
Still plays with trucks
 
68 TT's Avatar
 
Join Date: Jul 2009
Location: Spokane, WA
Posts: 3,556
Re: Speed switch

I haven't hear anybody talk about a speed switch before. Are you talking about a part of the cruise control system?
68 TT is offline   Reply With Quote
Old 10-29-2009, 08:53 AM   #3
mabu
Registered User
 
Join Date: Oct 2009
Location: Rancho Cucamonga, CA
Posts: 6
Re: Speed switch

Truck is a 1980 originally 6 cyclinder now has a 350 but missing a bunch of things. Including the speed switch solenoid. It is a California truck so I need all the smog junk to be on the truck. In the wiring diagrams it shows a speed switch with wiring going to the speed switch solenoid located on the carburetor.
mabu is offline   Reply With Quote
Old 10-29-2009, 11:23 PM   #4
mabu
Registered User
 
Join Date: Oct 2009
Location: Rancho Cucamonga, CA
Posts: 6
Re: Speed switch

Anyone?
mabu is offline   Reply With Quote
Old 10-30-2009, 03:18 AM   #5
TravisMartin
Curmudgeon of Poor Means
 
Join Date: Jan 2009
Location: Lubbock, Texas
Posts: 113
Re: Speed switch

The only solenoid I can think of on an '80 carb would be a fast idle solenoid to compensate for the air conditioning compressor. But I'm not sure if that's what you're talking about. On my 3/4 ton '82 with the HD emissions 350, they had a vacuum operated fast idle with a solenoid valve to provide manifold vacuum to it when the compressor runs.

I bought an '80 new but it's been way too long from me to remember that detail.

Where did you get the diagram you're working from? Can you scan it and post it? I have a factory shop manual for an '82 but it's loaned out right now; I can look when I get it back and see if the '82 had something similar.

Travis
TravisMartin is offline   Reply With Quote
Old 10-30-2009, 03:24 AM   #6
TravisMartin
Curmudgeon of Poor Means
 
Join Date: Jan 2009
Location: Lubbock, Texas
Posts: 113
Re: Speed switch

I just had another thought; perhaps it was TCS (transmission controlled spark) that you're looking at. I don't recall whether an '80 would have that or not; perhaps someone else will clarify.

In a nutshell, it's a system where a switch on the transmission closes in high gear and turns on a solenoid mounted on the intake near the carb that switches vacuum ports to the distributor's vacuum advance.

This system was installed commonly on the '70 Chevelles I used to fool with but I don't remember whether it was still around by '80.

Another possibility...I definitely remember the '80 having a lockup torque converter, in fact I think '80 was the first year for it, and it was controlled by a vacuum operated switch on the firewall.

But to my knowledge none of these were labeled a "speed switch" so more info would sure be helpful.
TravisMartin is offline   Reply With Quote
Old 10-30-2009, 08:29 AM   #7
mabu
Registered User
 
Join Date: Oct 2009
Location: Rancho Cucamonga, CA
Posts: 6
Re: Speed switch

Wiring diagrams from a post on this site:
http://67-72chevytrucks.com/vboard/s...wiring+diagram

http://www.73-87chevytrucks.com/tech...80_SBC_eng.jpg
also haynes book shows the same.
If it is only related to the ac or cruise control it would be nice, I could ignore it for now.
mabu is offline   Reply With Quote
Old 10-30-2009, 09:37 PM   #8
mabu
Registered User
 
Join Date: Oct 2009
Location: Rancho Cucamonga, CA
Posts: 6
Re: Speed switch

?Anything you see?
mabu is offline   Reply With Quote
Old 10-31-2009, 02:01 AM   #9
TravisMartin
Curmudgeon of Poor Means
 
Join Date: Jan 2009
Location: Lubbock, Texas
Posts: 113
Re: Speed switch

I really don't know what to make of it; don't recall ever seeing such a thing.

The schematics you found do tell me this much: the "speed switch" is drawn as a relay that is connected to the tachometer output of the HEI distributor. That would imply that it changes state at some engine RPM. You can see that its contacts are connected to the "speed switch solenoid" so the solenoid activates either above or below some RPM; it doesn't indicate which.

Now the mystery, at least to me, is...what the heck does it do? And is it necessary?

My best guess is it's something to do with emissions controls of the day, but that's only a guess. Maybe EGR? When did EGR become required?

Unless someone comes up with better information, I'd ignore it for now.

Travis
TravisMartin is offline   Reply With Quote
Old 10-31-2009, 02:19 AM   #10
TravisMartin
Curmudgeon of Poor Means
 
Join Date: Jan 2009
Location: Lubbock, Texas
Posts: 113
Re: Speed switch

I looked at the drawings for all the engines that were posted and notice that all have this "speed switch" except the 250CID six; even the 292 has it.

The more I think about it, the more I'm betting it's EGR control. EGR is the big vacuum operated valve on the intake manifold that bleeds some exhaust gas into the intake for reduced emissions. If I'm right, the "speed switch solenoid" will be a solenoid operated vacuum valve mounted on the intake somewhere. It'll have a couple of vacuum lines coming from it, one to the EGR valve and the other to the carb. There should be a vacuum hose schematic drawing on the air cleaner. But if your truck was originally a six, you'd need to look at someone else's drawing.

I know where there's a '78 454 truck parked that's still pretty much original; I'll go look at it and see if it tells me anything. The drawings you posted say they are for '77 to '80 so we'll see. I'll try to have some more info in a couple of days. Might even have some pictures if it looks like they'll help.

Travis

Last edited by TravisMartin; 10-31-2009 at 02:29 AM.
TravisMartin is offline   Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 09:27 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com