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#1 |
Registered User
Join Date: Jul 2015
Location: Gilberts, illinois
Posts: 102
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Speedometer/Transmission Gear
My speedo reads 10MPH slower then I'm going. The cable go into a small box maybe 2x4” that is bolted on to the 700R4 tranny. Ive never encountered this box in previce times of changing speedo gears. Do i need to open it up to get to the little gear hat he speedo cable goes into???
Thanks, Bill
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The pessimist is one who feels bad when he feels good for, fear he'll feel worse when he feels better |
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#2 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Speedometer/Transmission Gear
Does the cable actually run to the transmission or just to the "box" which is then connected only by wires?
If that's the case, what you've got is an electronic box driving the speedo cable, and it needs to be recalibrated. But you'll need to know brand and model before you can do much. Fortunately, there are only a couple out there.
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#3 |
Registered User
Join Date: Aug 2017
Location: Eugene Oregon
Posts: 128
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Re: Speedometer/Transmission Gear
Ha i have the same problem in my TH350 except its 10+mph faster.. I buried the needle this am as I drove with the speed of traffic on the freeway lol
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1977 SWB (c20 conversion) SBC350 Springfield Oregon Instagram: @nevernotchevy |
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#4 |
Registered User
![]() Join Date: Dec 2012
Location: Vancouver, Washington
Posts: 1,644
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Re: Speedometer/Transmission Gear
Just like mine!
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1968 Chevrolet C/10 LWB - 327, TH350 - 4/5 Drop |
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#5 |
Registered User
Join Date: Jul 2015
Location: Gilberts, illinois
Posts: 102
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Re: Speedometer/Transmission Gear
Thanks Dave,
There are no wires coming to this box just the cable. There is some printing on it (Stewart-Warner. Made in USA. 666F. 1.0500. There is a group of wires entering the side of the tranny about 10” towards the front of the tranny.
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The pessimist is one who feels bad when he feels good for, fear he'll feel worse when he feels better |
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#6 |
Registered User
Join Date: Mar 2014
Location: Lincoln Park, NJ
Posts: 189
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Re: Speedometer/Transmission Gear
I think that's a mechanical converter.
One side rotates at the transmission speedometer output gear speed, then goes through some reduction gearing to the output to the cable to the speedometer. http://garbee.net/~cabell/stewartwarner.htm
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#7 |
Registered User
Join Date: Mar 2014
Location: Lincoln Park, NJ
Posts: 189
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Re: Speedometer/Transmission Gear
That 1.0500 might be the "correction ratio"
See the right-most column near the bottom of this page. http://garbee.net/~cabell/december/datcon/~hpa0002.jpg
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#8 | |
Registered User
Join Date: Jul 2013
Location: LI, NY 11801
Posts: 1,140
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Re: Speedometer/Transmission Gear
Quote:
Bill
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1970 C10 8' Fleetside, L6 250, 3 on the Tree. The most basic of pickup trucks! |
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#9 |
Registered User
Join Date: Jul 2015
Location: Gilberts, illinois
Posts: 102
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Re: Speedometer/Transmission Gear
Question, am I still dealing with a 700R4 transmission?? Or something else?
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The pessimist is one who feels bad when he feels good for, fear he'll feel worse when he feels better |
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#10 | |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: Speedometer/Transmission Gear
Quote:
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My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#11 |
Registered User
Join Date: Jul 2015
Location: Gilberts, illinois
Posts: 102
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Re: Speedometer/Transmission Gear
Hey OregonNed,
That is one Dyn-o-mite looking 68 C-10. Would you be kind enough to send me the paint code of that blue paint. I have a 72 C-10 and it has what looks link that blue you have on years. I would greatly appreciate it, and it just might help me a ton... Thanks, Bill
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The pessimist is one who feels bad when he feels good for, fear he'll feel worse when he feels better |
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#12 |
blood type; Retumbo
Join Date: Jan 2004
Location: next to my reloading bench
Posts: 10,269
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Re: Speedometer/Transmission Gear
I just swapped out the TH350 in Lefty for a 700r4. The speedo was off quite a ways. My nephew ordered new gears from some speedo gear place based on the recommended parts from bowtieoverdrives. Thankfully the guy called and asked where he got the gear numbers. He said bowtieoverdrives has been wrong for so long.
He got them from www.laspeedometergear.com
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Man rule #77...if you own a 67 stepside with a caddy 472 you will never be in danger of loosing you man card |
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#13 | |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,964
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Re: Speedometer/Transmission Gear
Quote:
If eliminating the SW box makes things worse, then you will need to swap the speedo gear on the transmission (where the cable goes into your 700R4). |
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#14 |
Registered User
![]() Join Date: Nov 2006
Location: KINGSPORT,TN.
Posts: 3,035
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Re: Speedometer/Transmission Gear
those gears in that little box are swapable
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I BELIEVE IN JOHN 3:16 |
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#15 |
Senior Member
![]() Join Date: Mar 2003
Location: Colfax-California
Posts: 8,549
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Re: Speedometer/Transmission Gear
First off, you cannot be off 10 mph at any speed. It works off a percentage. If your speedo says 60 and you are doing 70--you are off 14.3%. From there you can do the math with the gears you have, and what is available. If it doesn't work with the factory parts then you can get a box to make up the difference
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#16 |
Cluster King
![]() Join Date: Nov 2012
Location: Junction City, OR
Posts: 5,263
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Re: Speedometer/Transmission Gear
If you are seeking to get the correct transmission gears for your speedometer to read correctly, don't be concerned with needle position such as 60 or 70, etc.
Find a road where you can drive a measured mile and see what your odometer reads. If it moves 1 exact mile to the measured mile driven there is no need to change trans gears. If it is different, some basic calculations and a visit to a good trans shop, will get you the right gears. If your trans gears are correct but your GPS does not match your giving speed, 60 or 70 mph, etc, then your speedometer head is out of calibration. I hope this helps anyone confused about how the trans gears are determined. Odometer movement in a measured mile. Tom
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Contact me on all of your gauge cluster needs. I specialize in restoration, repair and parts sales for 67-72 Chevy and GMC trucks. email me at tbonegarris@yahoo.com I am also a dealer for Counterpart for gauge cluster parts only. Also see my facebook page, CG&C |
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