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[GMCnet] Speedometer too slow by 3-4mph [message #321362]

Sun, 30 July 2017 22:47

Olly Schmidt

Messages: 1265
Registered: February 2014
Location: Germany and Scottsville, ...

Karma: 8

Senior Member

As you may notice, I have some spare time at Camp Walmart :-D

I noticed that the speedometer shows 50mph when the GPS shows 54mph.

I was always under the impression, the speedometer from the factories
should show faster than you actually go.

What could be the reason for this?
--
Best regards

Peer Oliver Schmidt
PGP Key ID: 0x83E1C2EA

'76a Eleganza II, CA
'73 Sequoia, VA

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Best regards

Olly Schmidt
PGP Key ID: 0x18a9 3a1f 4196 bf22
'76a Eleganza II, VA
'73 Sequoia, SH, Germany

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Re: [GMCnet] Speedometer too slow by 3-4mph [message #321363 is a reply to message #321362]

Sun, 30 July 2017 23:24

emerystora

Messages: 4442
Registered: January 2004

Karma: 13

Senior Member

Tire size.

Emery Stora
77 Kingsley
Frederick, CO

> On Jul 30, 2017, at 9:47 PM, Peer Oliver Schmidt GMC wrote:
>
> As you may notice, I have some spare time at Camp Walmart :-D
>
> I noticed that the speedometer shows 50mph when the GPS shows 54mph.
>
> I was always under the impression, the speedometer from the factories
> should show faster than you actually go.
>
> What could be the reason for this?
> --
> Best regards
>
> Peer Oliver Schmidt
> PGP Key ID: 0x83E1C2EA
>
> '76a Eleganza II, CA
> '73 Sequoia, VA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

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Re: [GMCnet] Speedometer too slow by 3-4mph [message #321364 is a reply to message #321362]

Sun, 30 July 2017 23:28

Olly Schmidt

Messages: 1265
Registered: February 2014
Location: Germany and Scottsville, ...

Karma: 8

Senior Member

Emery
> Tire size.

I have 16.5 tires atm. Is there an easy fix to calibrate the speedo, or
is the easiest fix to use the brain to just add some 5mph to whatever I see?

--
Best regards

Peer Oliver Schmidt
PGP Key ID: 0x83E1C2EA

'76a Eleganza II, CA
'73 Sequoia, VA

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Best regards

Olly Schmidt
PGP Key ID: 0x18a9 3a1f 4196 bf22
'76a Eleganza II, VA
'73 Sequoia, SH, Germany

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Re: [GMCnet] Speedometer too slow by 3-4mph [message #321369 is a reply to message #321362]

Mon, 31 July 2017 00:05

<rallymaster

Messages: 361
Registered: May 2014

Karma: 2

Senior Member

or final drive ratio

On Sun, 30 Jul 2017 22:28:12 -0600 Peer Oliver Schmidt GMC
writes:
> Emery
>> Tire size.
>
> I have 16.5 tires atm. Is there an easy fix to calibrate the speedo,
> or
> is the easiest fix to use the brain to just add some 5mph to
> whatever I see?
>
> --
> Best regards
>
> Peer Oliver Schmidt
> PGP Key ID: 0x83E1C2EA
>
> '76a Eleganza II, CA
> '73 Sequoia, VA
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

Ron & Linda Clark
North Plains, ORYGUN
78 Eleganza II

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Re: [GMCnet] Speedometer too slow by 3-4mph [message #321371 is a reply to message #321369]

Mon, 31 July 2017 00:33

Hal StClair

Messages: 971
Registered: March 2013
Location: Rio Rancho NM

Karma: -12

Senior Member

Or if the speedo cable doesn't have the correct gear installed.
Hal

"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane." 1977 Royale 101348, 1977 Royale 101586, Diesel powered, 1974 Eagle Bus 45',w/slideout, Rio Rancho, NM

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Re: [GMCnet] Speedometer too slow by 3-4mph [message #321373 is a reply to message #321364]

Mon, 31 July 2017 05:59

emerystora

Messages: 4442
Registered: January 2004

Karma: 13

Senior Member

Often it's caused by the use of radial tires instead of the original 8.75 x 16 originals. Or as Rallymaster says possibly the final drive ratio. Whatever is causing it, record your odometer reading over a distance (such as 50 or 100 miles) and at the same time record your gps distance reading.
This will give you an accurate amount of correction. Then you either change the speedometer gear in the governor box or install a small speedometer speed correction box between the governor and the end of the speedometer cable. Jim Kanomata has heard or the speed correction boxes. Bring him the odometer/gps distance reading and he can get your speedometer reading correctly.

Emery Stora
77 Kingsley
Frederick, CO

> On Jul 30, 2017, at 10:28 PM, Peer Oliver Schmidt GMC wrote:
>
> Emery
>> Tire size.
>
> I have 16.5 tires atm. Is there an easy fix to calibrate the speedo, or
> is the easiest fix to use the brain to just add some 5mph to whatever I see?
>
> --
> Best regards
>
> Peer Oliver Schmidt
> PGP Key ID: 0x83E1C2EA
>
> '76a Eleganza II, CA
> '73 Sequoia, VA
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

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Re: [GMCnet] Speedometer too slow by 3-4mph [message #321380 is a reply to message #321364]

Mon, 31 July 2017 07:41

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

KISS principle; add 5 mph!

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Peer Oliver Schmidt GMC
Sent: Monday, July 31, 2017 2:28 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Speedometer too slow by 3-4mph

I have 16.5 tires atm. Is there an easy fix to calibrate the speedo, or is the easiest fix to use the brain to just add some 5mph to
whatever I see?

Best regards
Peer Oliver Schmidt

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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

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Re: [GMCnet] Speedometer too slow by 3-4mph [message #321388 is a reply to message #321362]

Mon, 31 July 2017 08:30

jhbridges

Messages: 8412
Registered: May 2011
Location: Braselton ga

Karma: -74

Senior Member

Every one I'vs seen including mine reads slightly slow. A couple of guys at the recent show at Redwine with 70s GMC products fitting what looks like the same cluster say the same. I suspect 40 years of aging and wear are what's responsible. The Mac Dash one in my current coach is dead nuts on speed according to my GPS. It's mechanical, running 16" tires, a 3.70 differential and a Manny supplied reduction gear on the transmission.

--johnny

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

[Updated on: Mon, 31 July 2017 08:30]

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Re: [GMCnet] Speedometer too slow by 3-4mph [message #321403 is a reply to message #321362]

Mon, 31 July 2017 10:14

k2gkk

Messages: 4452
Registered: November 2009

Karma: -8

Senior Member

If you are expecting the speedometer to indicate FASTER than true speed, you must have been driving BMWs in the past! Typically, 120 mph indicated was more like 110 or less true speed. This experienced in my 1971 BMW 2800 sedan. The same is generally reported by BMW motorcycle owners.

Believe your GPS!

D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com

________________________________
From: Gmclist on behalf of Peer Oliver Schmidt GMC
Sent: Sunday, July 30, 2017 22:47
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Speedometer too slow by 3-4mph

As you may notice, I have some spare time at Camp Walmart :-D

I noticed that the speedometer shows 50mph when the GPS shows 54mph.

I was always under the impression, the speedometer from the factories
should show faster than you actually go.

What could be the reason for this?
--
Best regards

Peer Oliver Schmidt
PGP Key ID: 0x83E1C2EA

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Unsubscribe or Change List Options:
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Re: [GMCnet] Speedometer too slow by 3-4mph [message #321404 is a reply to message #321362]

Mon, 31 July 2017 10:18

Olly Schmidt

Messages: 1265
Registered: February 2014
Location: Germany and Scottsville, ...

Karma: 8

Senior Member

Mac,
> If you are expecting the speedometer to indicate FASTER than true speed, you must have been driving BMWs in the past!

I rarely drove BMW. One BMW 1800 for a year or so until I gave it away,
a 320 as a company car, that I totalled driving too fast on a snowed in
Autobahn, and a 325. I like the comfort of the 1800, but didn't like the
3-series with the 6-cylinders at all.

In Germany *all* cars read too high. This makes it easier for you to
stay within the speed limit.

--
Best regards

Peer Oliver Schmidt
PGP Key ID: 0x83E1C2EA

'76a Eleganza II, CA
'73 Sequoia, VA

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Best regards

Olly Schmidt
PGP Key ID: 0x18a9 3a1f 4196 bf22
'76a Eleganza II, VA
'73 Sequoia, SH, Germany

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