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#1 |
Registered User
Join Date: Aug 2009
Location: Simi Valley, CA
Posts: 193
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Speedometer adjustment
I have checked the odometer and it is very accurate, but the speed is off about 10% at 65 mph. So it shows 60 but I'm actually doing 66.
So I know I don't need to change the gears in the transmission but is it possible to calibrate just the speed? This is in a 1967 C20 2wd. Thanks! |
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#2 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,594
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Re: Speedometer adjustment
If your speedo is off 10% then your odometer is too!
To correct it you need to change the driven gear or use a ratio adaptor. Look here. http://www.transmissioncenter.net/sp...n_______va.htm |
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#3 |
Truck and auto performance nut
Join Date: Feb 2007
Location: McKinney,Texas
Posts: 3,848
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Re: Speedometer adjustment
what trans? should be able to change the speedo gears in the trans?
__________________
Kurt - '68 GMC short step - NIB '09 LY6 6.0L crate motor w/mods, NIB '12 crate 4L85e w/billet 3k stall Circle D, 3.73 posi 12 bolt, DynaTech f-swap headers, 3/4 drop, handling mods, etc. - my toy '72 Chevy LWB C-10 Highlander - 350/350 ps/pb/tilt/ac - not original but close '06 Chevy TrailBlazerSS - LS2/4L70e - little black hot rod SUV - my DD '18 Kia Sorento - wife's econo-driver '95 Chevy S10 - reg cab shortbed, LS, 4.3, auto... my '68's powertrain and chassis build -links broken A surprise phase - carb to efi -links broken |
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#4 |
Registered User
Join Date: Aug 2009
Location: Simi Valley, CA
Posts: 193
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Re: Speedometer adjustment
I verified with GPS that the odometer is only off .1 miles over 50 so the gears are correct, it's just the magnetic part of the speedometer that needs adjustment.
The transmission is a TH400. |
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#5 |
Registered User
Join Date: Aug 2009
Location: Simi Valley, CA
Posts: 193
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Re: Speedometer adjustment
So it turns out you can adjust your indicated speed relative to your odometer.
I took the speedometer out, and if you look at the shaft where it goes into the cup where the magnets are, there is a metal piece that bridges the gap and the spring that returns the needle is attached to it. All you have to do is rotate that piece of metal, either to decrease the spring load, which increases indicated speed, or increase the spring load, which decreases the indicated speed. I use a drill with a small screwdriver for a bit and used it to spin the speedometer before and after adjustment. Just adjust until the speed you want to show does and it should be fine. Anyway, just thought this might help somebody in the future. Remember, this is only necessary if your odometer is accurate but your speed isn't. |
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#6 |
Registered User
Join Date: Oct 2011
Location: Bloomington Indiana
Posts: 322
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Re: Speedometer adjustment
Thank you for the info on adjusting the speedometer. Mine is off just a little, so I am sure this will correct mine. I was about to start swapping the gears around,and that would not have solved the problem. Nice to have people on the forum that take the time to help each other out.
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#7 |
Registered User
Join Date: Feb 2012
Location: Smyrna TN
Posts: 1,153
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Re: Speedometer adjustment
Great post!
__________________
1971 Longbed BB Cheyenne Super 1972 Longbed SB Cheyenne Super 1972 Longbed Highlander Custom Deluxe 1975 K5 4x4 full convertible Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=645165 Greg Smyrna TN |
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#8 |
Registered User
![]() Join Date: Dec 2012
Location: Chandler AZ
Posts: 1,149
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Re: Speedometer adjustment
Tk, you didn't happen to take pics did you?
__________________
1970 Longhorn, Front Disc, 350/4 bolt, 882 heads, HEI, Edelbrock, 700R4, HO-52/4.11. 1996 Corvette, Collector Roadster, LT4, 396, 450RWHP, 6sp, 4.11/Dana44/posi 5 point roll bar And let us not grow weary of doing good, for in due season we will reap, if we do not give up. Gal 6:9 |
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#9 |
Registered User
Join Date: Nov 2010
Location: Carlsbad, CA
Posts: 1,584
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Re: Speedometer adjustment
Good info here, thanks.
__________________
- Jim - My Daily Driver is a 1969 Chevrolet Custom/20 Fleetside 350/TH400/Eaton H052 4.10 and its Project thread is here http://67-72chevytrucks.com/vboard/s...d.php?t=456911 |
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#10 |
Registered User
Join Date: Nov 2009
Location: Rudyard, Michigan
Posts: 125
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Re: Speedometer adjustment
A couple questions:
Do you remember which way to turn to speed up or slow down the speedometer? About how many turns did you need to adjust your 10 mph? Thanks for posting! |
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#11 |
Registered User
Join Date: Aug 2009
Location: Simi Valley, CA
Posts: 193
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Re: Speedometer adjustment
I didn't take any pics so I stole this one from OldGold's trip odometer post, I hope he won't mind. It shows the adjustment bar pretty well and I added text to show it.
To add 4 mph I only had to move it about 1/8" clockwise (looking from the back). It's pretty sensitive so you just rotate it a little then check, rinse and repeat until you get what you think you need. |
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