Home » Public Forums » GMCnet » Speedo question
| Speedo question [message #186854] |
Wed, 10 October 2012 11:23  |
biggreen
Messages: 347
Registered: June 2011
Location: Northeast Florida
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I think I know the answer to this but, I'm planning to redo my dash and would like a gps speedo instead of the cable driven oem that is way off now that I changed out the final drive ratio. I know I can get an adapter from Jim K. (one did not come with my final drive), but I hear they are not all that accuate anyway.
Question is, if I delete the speedo, will my cruise control ever work? (It doesn't work now, but thats also in the plan.)
Thanks.
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| Re: Speedo question [message #186859 is a reply to message #186854] |
Wed, 10 October 2012 12:22  |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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I think the speed control uses forward motion to derive a set point for the cruise. Newer vehicles use a VSS to do this. As long as you remove only the analog speedometer, it should not defeat the use of the cruise feature. GPS would give you an accurate speed reading.
If you remove the entire speedometer cable down to the transmission, the analog GMC OEM cruise will not function. You would need to convert to a VSS enabled cruise. Kevin Henderson and others have done interesting stuff with later model electo-motive cruise controls from newer GM vehicles. I'm slowly collecting parts to follow in his foot steps.
Will a GPS speedometer pass vehicle inspection, if one is required?
Tom,
mS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] Speedo question [message #186861 is a reply to message #186859] |
Wed, 10 October 2012 12:26 |
Ronald Pottol
Messages: 505
Registered: September 2012
Location: Redwood City, California
Karma: -2
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Depends on the state. 20 years ago, the only vehicles required to have a
speedometer in California were school busses.
Ron
On Oct 10, 2012 10:22 AM, "Thomas Phipps" <tph1pp5@yahoo.com> wrote:
>
>
> I think the speed control uses forward motion to derive a set point for
> the cruise. Newer vehicles use a VSS to do this. As long as you remove
> only the analog speedometer, it should not defeat the use of the cruise
> feature. GPS would give you an accurate speed reading.
> If you remove the entire speedometer cable down to the transmission, the
> analog GMC OEM cruise will not function. You would need to convert to a
> VSS enabled cruise. Kevin Henderson and others have done interesting
> stuff with later model electo-motive cruise controls from newer GM
> vehicles. I'm slowly collecting parts to follow in his foot steps.
> Will a GPS speedometer pass vehicle inspection, if one is required?
> Tom,
> mS II
> --
> 1975 GMC Avion, under forever re-construction
> Vicksburg, MS. 3.7 miles from I-20
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| Re: [GMCnet] Speedo question [message #186868 is a reply to message #186854] |
Wed, 10 October 2012 12:59 |
emerystora
Messages: 4442
Registered: January 2004
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On Oct 10, 2012, at 12:24 PM, "R.D. Hart" <regor5556@yahoo.com> wrote:
>
>
> I think I know the answer to this but, I'm planning to redo my dash and would like a gps speedo instead of the cable driven oem that is way off now that I changed out the final drive ratio. I know I can get an adapter from Jim K. (one did not come with my final drive), but I hear they are not all that accuate anyway.
They are extremely accurate if they are set up with the right gears. There are many combinations of gears that will give fractions of a mph change. When I got one I then measured my mileage with the odometer for a hundred miles and also the mileage with the highway mileage and also with my GPS. T markers and the GPS were within 0.2 miles. The odometer was off about 1-1/2 miles. I gave the shop the odometer and the GPS readings and the calculated the ratio of the gears in the box and put in new gears and then it was exactly the same as my GPS. Of course wearing of the tires will change it a little bit anyway so it's hard to keep it 100% accurate.
> Question is, if I delete the speedo, will my cruise control ever work? (It doesn't work now, but thats also in the plan.
Yes, the cruise control would work anyway even without the speedometer head connected.
Emery Stora
77 Kingsley
Frederick, CO
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| Re: [GMCnet] Speedo question [message #186880 is a reply to message #186863] |
Wed, 10 October 2012 15:21 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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| WD0AFQ wrote on Wed, 10 October 2012 10:37 |
I look at no speedometers in my vehicles. The new hybrid does have a nice digital one but it is not accurate. With the gps I know I wont get a ticket if I have it set at speed limit. I blow up the speed numbers so I can see them on my Lowrance gps units. I also like the altitude feature in the GMC. It tells me why my vacuum may be falling or rising. In the GMC I have the Rostra cruise and it works great. Was an easy install too. We have the updated final drive and the speedo corrector. Not even close to accurate.
Dan
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Dan, Like me, you are running oversized tires (you; 245/75s, me; 255/70s). my speedo is not accurate either, but I suspect it would be a lot closer if I were running 225/75 size tires, in spite of the 3.70 final drive and the speedo corrector.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Speedo question [message #186893 is a reply to message #186854] |
Wed, 10 October 2012 17:46 |
Gail Marks Cruiser
Messages: 125
Registered: August 2009
Location: Gold Coast, Australia
Karma: 0
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G'day,
We have all after market instruments, which includes an electric speedo.
It replaces the second half of the cable, screwing onto the cruise control speed sensor.
It was easy to calibrate, drive 55(used GPS) record noted speed on the speedo, go to the provided chart, and set the required combination on the back- done.
We have found the speedo very accurate and still have an odometer.
I have also noted our GPS displays slower speeds in hilly areas, I put it down to the GPS reading on 2 planes not allowing for the extra distance travelling up and down. Has anybody else noticed this or do I have a dodgy GPS.
Mark Bennett
Gail & Mark's Cruiser
Gold Coast, Australia.
Motorhoming Lifestyle.com
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| Re: [GMCnet] Speedo question [message #186895 is a reply to message #186893] |
Wed, 10 October 2012 17:53 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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My GPS tells me"You are exceeding the speed limit." when we are on a ferry
boat between Kingston, Wa. and Edmonds, Wa. Ms GARMIN has led us on some
FINE EXCURSIONS.I wouldn't trust her to tell me how fast I am driving.(grin)
Jim Hupy
Salem, Or
78 GMC Royale 403
On Oct 10, 2012 3:46 PM, "Mark Bennett" <mark.bennett.58@gmail.com> wrote:
>
>
> G'day,
> We have all after market instruments, which includes an electric speedo.
> It replaces the second half of the cable, screwing onto the cruise
> control speed sensor.
> It was easy to calibrate, drive 55(used GPS) record noted speed on the
> speedo, go to the provided chart, and set the required combination on the
> back- done.
> We have found the speedo very accurate and still have an odometer.
> I have also noted our GPS displays slower speeds in hilly areas, I put it
> down to the GPS reading on 2 planes not allowing for the extra distance
> travelling up and down. Has anybody else noticed this or do I have a dodgy
> GPS.
> --
> Mark Bennett
> Gail & Mark's Cruiser
> Gold Coast, Australia.
> Motorhoming Lifestyle.com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Speedo question [message #186898 is a reply to message #186893] |
Wed, 10 October 2012 18:30 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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The GPS speed will always be off in hilly country. It calculates based on times between places on a flat earth.
Mac in OKC
Sent from my iPhone
On Oct 10, 2012, at 17:46, "Mark Bennett" <mark.bennett.58@gmail.com> wrote:
>
>
> G'day,
> We have all after market instruments, which includes an electric speedo.
> It replaces the second half of the cable, screwing onto the cruise control speed sensor.
> It was easy to calibrate, drive 55(used GPS) record noted speed on the speedo, go to the provided chart, and set the required combination on the back- done.
> We have found the speedo very accurate and still have an odometer.
> I have also noted our GPS displays slower speeds in hilly areas, I put it down to the GPS reading on 2 planes not allowing for the extra distance travelling up and down. Has anybody else noticed this or do I have a dodgy GPS.
> --
> Mark Bennett
> Gail & Mark's Cruiser
> Gold Coast, Australia.
> Motorhoming Lifestyle.com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Speedo question [message #186929 is a reply to message #186886] |
Wed, 10 October 2012 21:39 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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| WD0AFQ wrote on Wed, 10 October 2012 14:09 |
I really do not understand why folks care about what the speedometer says today. I mean with gps stuff you are as accurate as the cops' radar. I bought a 355 gear and speed corrector. The best I can figure, using the tach, I got a 370 gear with a 355 adapter so mine is not even close. Smaller tires would help but I am into the biggest fattest tires I can get stuffed into the fenders on all of my vehicles. The more rubber between me and the pavement the better.
Dan
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The only reason I worry about the speedometer is because my nervous passenger wife keeps the GPS on her side of the coach (so it doesn't distract the driver...me). I check with her once in a while to see how fast we are actually going. Then it gives me a point of reference on my speedometer. It seems to be off about 6%.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Speedo question [message #186938 is a reply to message #186854] |
Thu, 11 October 2012 05:40 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| biggreen wrote on Wed, 10 October 2012 09:23 |
I think I know the answer to this but, I'm planning to redo my dash and would like a gps speedo instead of the cable driven oem that is way off now ...
... if I delete the speedo, will my cruise control ever work? (It doesn't work now, but thats also in the plan.) ...
|
I personally would not depend on GPS as the only way to know my speed. While they are much better than they have been in the past, you need to have a signal and they do average the speed over a period of time. Others have mentioned issues with GPS speed displays.
As for the OEM Cruise, it is ran from the same cable as the speedo, but the CC is driven first and the cable to the speedometer head is connected to the cc unit. (I know this because my OEM CC was causing an error on the speed displayed on my speedometer.)
_If_ I was going to replace my speedometer with a new unit, and all I had was the OEM CC unit, I would replace BOTH with electronic units. Why would you modernize with to a nice new accurate speedo and leave the old analog cc?
To get rid of all the cables, you can get a speedometer take off "bullet" that fits in the governor that does NOT have a cable... only wires. See the top item in this picture: <http://www.gmcmhphotos.com/photos/junk-yard-cruise-control/p35186-dsc01759.html> I found some in Pontiac Fiero's.
You MIGHT have to condition the output with a 4-out buffer, (see Spiffycar's, Junk yard cruise control album) but it should provide outputs for the speedo, cc and fuel injection computer... if you have one.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Speedo question [message #186941 is a reply to message #186898] |
Thu, 11 October 2012 08:19 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| k2gkk wrote on Wed, 10 October 2012 19:30 |
The GPS speed will always be off in hilly country. It calculates based on times between places on a flat earth.
Mac in OKC
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This statement is completely and totally device dependent.
Even if that were the case, the error would be very small.
Case:
15% grade (8.5°)
Cosine is 0.989
Therefore, a true 60.0 MPH on the road would indicate....
....59.34 MPH....
More likely what you are seeing is either update rounding or an algorithm problem caused by the navigator being forced to change references (satellites) because of the vehicle motion.
My better GPS (actually for inshore navigation) can report velocity with a resolution of 0.01 knot. If I have it on in the coach (I used to use it as the GPS for SA3), I can see the variations with a one second update rate. If I am in a car, and I am paying attention to keeping the needle in the same place, then the reported velocity also does not vary enough to notice.
Yes, I do go places with hills. There are none close by here.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Speedo question [message #186959 is a reply to message #186854] |
Thu, 11 October 2012 14:07 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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The cable to the opriginal cruise control goes first from the transmission to the control module, and the second cable goes from the module to the existing speedo. Just leave the second one off and blank the connection on the module with a threaded cap of the proper size to keep dirt out of it. It will work fine whether the speedo is there or not.
--johnny
'76 23' transmode norris
\'76 palm beach
From: R.D. Hart <regor5556@yahoo.com>
To: gmclist@temp.gmcnet.org
Sent: Wednesday, October 10, 2012 12:24 PM
Subject: [GMCnet] Speedo question
I think I know the answer to this but, I'm planning to redo my dash and would like a gps speedo instead of the cable driven oem that is way off now that I changed out the final drive ratio. I know I can get an adapter from Jim K. (one did not come with my final drive), but I hear they are not all that accuate anyway.
Question is, if I delete the speedo, will my cruise control ever work? (It doesn't work now, but thats also in the plan.)
Thanks.
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Speedo question [message #186996 is a reply to message #186895] |
Fri, 12 October 2012 07:01 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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My Georgraphy Professor buds at Ms State tell me the basic problem with GPS is the mapping. The coordinates will be dead-nu8ts accurate... but the makers buy the absolutely cheapest maps they can find, and those are often inaccurate. I agree with them.
--johnny
'76 23' transmode norris
'76 palm beach
006 Garmin Nuvi
From: James Hupy <jamesh1296@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Wednesday, October 10, 2012 6:53 PM
Subject: Re: [GMCnet] Speedo question
My GPS tells me"You are exceeding the speed limit." when we are on a ferry
boat between Kingston, Wa. and Edmonds, Wa. Ms GARMIN has led us on some
FINE EXCURSIONS.I wouldn't trust her to tell me how fast I am driving.(grin)
Jim Hupy
Salem, Or
78 GMC Royale 403
On Oct 10, 2012 3:46 PM, "Mark Bennett" <mark.bennett.58@gmail.com> wrote:
>
>
> G'day,
> We have all after market instruments, which includes an electric speedo.
> It replaces the second half of the cable, screwing onto the cruise
> control speed sensor.
> It was easy to calibrate, drive 55(used GPS) record noted speed on the
> speedo, go to the provided chart, and set the required combination on the
> back- done.
> We have found the speedo very accurate and still have an odometer.
> I have also noted our GPS displays slower speeds in hilly areas, I put it
> down to the GPS reading on 2 planes not allowing for the extra distance
> travelling up and down. Has anybody else noticed this or do I have a dodgy
> GPS.
> --
> Mark Bennett
> Gail & Mark's Cruiser
> Gold Coast, Australia.
> Motorhoming Lifestyle.com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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