| [GMCnet] speedo driven gear change to fix speedometer reading [message #240915] |
Sat, 22 February 2014 21:03  |
KB
Messages: 1262
Registered: September 2009
Karma: 0
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Senior Member |
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Just wanted to report on a part I found recently that worked for us.
Our speedometer was reading low, about 50mph when the GPS said we were at 55mph.
I understand this is a pretty common problem, maybe due to aging magnets in
the speedometer gauge.
After considerable searching, I took a chance on a gear for a 200R4 transmission because it
looked correct, though I couldn't find any references to indicate it would work for us.
(This tranny is also referred to as a 200-4R)
Our stock driven gear is white(ish) and has 31 teeth. The gear I used in its place
is green and has 29 teeth (part number 403999). This is the gear that slips
into the metal sleeve at the end of the speedometer cable on the tranny end.
Other 200-R4 driven gears are available ranging from 26 to 31 teeth.
The 29 tooth gear has done the trick and our oem speedometer now matches
what the GPS says our speed is.
jwid.
Karen
1973 23'
1975 26'
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] speedo driven gear change to fix speedometer reading [message #240950 is a reply to message #240915] |
Sun, 23 February 2014 08:30  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Do you have the original (3.07) final drive? My speedo is pessimistic by about the same amount, that would heal it.
--johnny
'76 23' transmode norris
________________________________
From: KB <kab7@sonic.net>
To: gmclist@temp.gmcnet.org
Sent: Saturday, February 22, 2014 10:03 PM
Subject: [GMCnet] speedo driven gear change to fix speedometer reading
Just wanted to report on a part I found recently that worked for us.
Our speedometer was reading low, about 50mph when the GPS said we were at 55mph.
I understand this is a pretty common problem, maybe due to aging magnets in
the speedometer gauge.
After considerable searching, I took a chance on a gear for a 200R4 transmission because it
looked correct, though I couldn't find any references to indicate it would work for us.
(This tranny is also referred to as a 200-4R)
Our stock driven gear is white(ish) and has 31 teeth. The gear I used in its place
is green and has 29 teeth (part number 403999). This is the gear that slips
into the metal sleeve at the end of the speedometer cable on the tranny end.
Other 200-R4 driven gears are available ranging from 26 to 31 teeth.
The 29 tooth gear has done the trick and our oem speedometer now matches
what the GPS says our speed is.
jwid.
Karen
1973 23'
1975 26'
_______________________________________________
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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| Re: [GMCnet] speedo driven gear change to fix speedometer reading [message #241003 is a reply to message #240976] |
Sun, 23 February 2014 14:09 |
Kosier
Messages: 834
Registered: February 2008
Karma: 1
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Senior Member |
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Karen,
The important thing is the accuracy of your odometer reading. It is a
direct gear reading, while the speedo is magnetically driven.
I like to run ten mile odometer checks while driving on the freeways, if
only to relieve the boredom. In ten miles, every tenth of
error equals one percent. If you get the odometer reading correctly, then a
speedo shop can adjust the magnetism of the speedo.
Finding a speedo shop is not as easy as it used to be, but I know where the
guy lives that retired. I believe United Speedometer
in California is still alive and well. That's about all I know on the
subject.
Oh yes, if you're really obsessive about it, find one of the Stewart-Warner
666 correction gearboxes in the men's mall and I can
change the gears inside to get the odometer exact. I am a little goofy
about those things.
Gary Kosier
77 PB w/500 Cad
Newark, Oh
-----Original Message-----
From: KB
Sent: Sunday, February 23, 2014 11:33 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] speedo driven gear change to fix speedometer reading
I searched the gmc vendor sites first, but never found the gears or any
reference to them. All I found there are the (~$200) reducers/adapters for
the different final drive ratios.
We have a 3.07 final drive.
I got the green 29 tooth gear on ebay for about $15 delivered, though it can
probably be gotten more cheaply elsewhere given part numbers. Here's the
ebay listing for what I ordered; they still have a few:
http://www.ebay.com/itm/151092317132?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Search for 200R4 (also 2004R and 200-4R) speedometer driven gear.
The green 29-tooth gear part number is 403999.
Here's a site that lists part numbers for all the gears (the prices shown
are from 2004):
http://chevelleengineer.home.comcast.net/~chevelleengineer/speedo.htm
Hope this helps.
Karen
1973 23'
1975 26'
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| Re: [GMCnet] speedo driven gear change to fix speedometer reading [message #241017 is a reply to message #241003] |
Sun, 23 February 2014 16:11 |
KB
Messages: 1262
Registered: September 2009
Karma: 0
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Senior Member |
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can't say that I worry much about the odometer reading given that this coach is on at least it's third engine and that the odometer only goes to five digits anyway. I suspect a speedo shop would charge more than $15 to service the speedo too (assuming I could find a competent shop).
Getting tickets for speeding though, that's a different story...
To each his (or her) own.
jwid
Karen
1973 23'
1975 26'
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