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Cruise vs non cruise, different speedometer head?

Started by TJ Hopland, October 30, 2015, 11:05:19 AM

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TJ Hopland

Was talking about cruise controls on another forum mainly 1970's GM stuff where you had the little gearbox unit inline with the speedometer cable.   Question came up does it matter which direction the cable turns?   With no cruise it would turn one way,  with a cruise (at least in this era) the gearbox unit reverses it so it wound turn the other way.   If the speedometer only works one direction this means that you would have to have a different head unit or speedo gears in the trans for a cruise vs non cruise car.   Can anyone confirm this by looking at parts books?   Did the pre 70's cruise units also reverse the rotation?

On one of my cars, an 81 Buick I was unable to get the the original cruise system working so I gave up and bought an aftermarket system.   The original unit has gears in it so essentially it reverses the rotation of the direction.   The aftermarket sensor is straight inline so no change in direction.  Originally I thought this would be a problem but did a quick search online and found a Corvette forum that said it does not matter which direction the cable turns.   I went ahead with my installation and all has been well for a couple years now. 

Talking to another guy on a forum he says that on his 70's era GM cars the speedometers don't work in reverse so changing the direction of the cable by removing or adding a cruise would give you a non working speedometer. 

So whats the deal here?   I just get lucky?   Seems unlikely that some head units work in both directions and others don't?   Seems more likely that at some point the feds mandated that the work in both directions so it would be harder to roll back the miles.  If that was the case when was that?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

76eldo

Why would the cruise unit change the direction of the rotation of the cable?  There's no way that GM would have a different speedo head to account for a reversed cable direction coming off of the cruise unit.

Back in the 70's Lincolns and Caddys with cruise had a cable coming into the unit from the Trans and then back to the speedo head.  If you disconnected the cable going to the speedo such as if you rented a town car for the weekend it did not register the miles. Not that I would have done such a thing.

Brian
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

TJ Hopland

The gearbox does change the direction but now I'm wondering if the fact that the cables go in and out the same side cancels that out so the cable is actually turning the same direction with the gear box in place as it would if the cable was direct?    IF the cables were connected in an inline direction the result would be reverse but the other way no change?

I will have to sketch it out or mock it up later to see if my new theory is correct.     That almost has to be the deal.   If it did cause issues with the speedometers you would think they would have designed the box differently just to keep the rest the same. 

StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

TJ Hopland

Had to figure this one out and I did.    It is the direction the cables are attached that makes it so the rotation of the cable does not change.



Picture is how the cables turn when attached to the little cruise gearbox on the fender.   Now imagine you take those to cables and stick em end to end?   Result they still turn in the same direction.   So nothing is different other than the cables for a cruise vs non cruise car.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

bcroe

Quote from: TJ HoplandOn one of my cars, an 81 Buick I was unable to get the the original cruise system working so I gave up and bought an aftermarket system.   The original unit has gears in it so essentially it reverses the rotation of the direction.   The aftermarket sensor is straight inline so no change in direction. 

Talking to another guy on a forum he says that on his 70's era GM cars the speedometers don't work in reverse so changing the direction of the cable by removing or adding a cruise would give you a non working speedometer. 

No the feed through cruise doesn't change the speedo cable  rotation.  However, those
things don't last; I always replace them with a straight thru cable (that always works). 

I think the FWD 66 Toro and perhaps some other cars actually had an extra output from
the trans to drive the cruise.  That cable would be turning the other way, the cruise didn't
care. 

I once had a problem with an 81 cruise.  I had converted it from a 5.7L diesel to gas.  It
turns out they are wired differently, and after checking the manual I was able to get it
working.  Bruce Roe

The Tassie Devil(le)

I just hooked up a speedo cable to a spare transducer I happen to have, and even though the input and output are turning in opposite directions, when it comes to the correlation of the transmission end, and the speedo head, the ends of the cable are actually spinning in the same direction.

Yes, I couldn't believe it, until I used a short piece of inner cable and inserted it into one end of the transducer, then as I was spinning it, I turned the battery drill over, and put it up against the output hole, and lo-and-behold, the output hole was spinning in the correct rotation to go to the speedo head.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

TJ Hopland

I had trouble wrapping my brain around it too till I drew that picture.   If the picture is the face of both cables and you stick em face to face the cable is still turning the same way.   If they had the gears and the cables coming off opposite ends it would be backwards.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Jeff Rosansky CLC #28373

Dealers would install cruise. No way to change the speedo head in the field. They would have to set the miles and then certify it.
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

bcroe

Quote from: TJ Hopland
I'm wondering if the fact that the cables go in and out the same side cancels that out so the cable is actually turning the same direction with the gear box in place as it would if the cable was direct?   

Now you have got it.  In line gear boxes have 2 gear stages.  Bruce Roe