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Old 05-11-2018, 10:14 AM   #1
willy12844
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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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Old 05-11-2018, 10:26 AM   #2
davepl
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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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Old 05-11-2018, 11:19 AM   #3
andrewpclayton
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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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Old 05-11-2018, 01:43 PM   #4
willy12844
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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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Old 05-11-2018, 02:12 PM   #5
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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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Old 05-11-2018, 02:16 PM   #6
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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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Old 05-11-2018, 02:58 PM   #7
willy12844
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Re: Speedometer/Transmission Gear

Question, am I still dealing with a 700R4 transmission?? Or something else?
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Old 05-11-2018, 03:33 PM   #8
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Re: Speedometer/Transmission Gear

Quote:
Originally Posted by andrewpclayton View Post
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
Just like mine!
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Old 05-11-2018, 04:14 PM   #9
Bigdav160
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Re: Speedometer/Transmission Gear

Quote:
Originally Posted by willy12844 View Post
Question, am I still dealing with a 700R4 transmission?? Or something else?
Try here
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Old 05-11-2018, 04:17 PM   #10
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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...
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Bill
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Old 05-11-2018, 08:59 PM   #11
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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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Old 05-11-2018, 09:51 PM   #12
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Re: Speedometer/Transmission Gear

Quote:
Originally Posted by willy12844 View Post
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
Just remove the stewart warner box (or whatever mfgr it is) and connect directly to the trans - then see how far off you are. You might get lucky. And remember to only determine your actual speed with a GPS if possible.
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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Old 05-16-2018, 04:27 PM   #13
BCOWANWHEELS
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Re: Speedometer/Transmission Gear

those gears in that little box are swapable
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Old 05-17-2018, 12:44 AM   #14
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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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Old 05-17-2018, 01:46 AM   #15
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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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Old 05-19-2018, 07:55 PM   #16
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Re: Speedometer/Transmission Gear

Quote:
Originally Posted by zosoppp View Post
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
Great Link Provided. I had one of those on my truck but removed it and changed the tranny gears to get it closer.

Bill
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