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| | | | Joined: Sep 2015 Posts: 6 New Guy | | New Guy Joined: Sep 2015 Posts: 6 | I recently replaced my original instrument cluster, as none of the gauges worked, with one i bought from classic Industries. After installing a new wiring harness(for the whole truck) we hooked up the cluster and the speedometer reads about 30 mph's faster than the correct speed. Any suggestion how i can calibrate this or at least get it closer to correct speed?
The Truck has a 350 small block with an automatic transmission that replaced the original 6 and 3 speed (this was done before i bought the truck).
| | | | | Joined: Feb 2002 Posts: 12,029 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Feb 2002 Posts: 12,029 | the problem is the speedo drive in the trans, you need to find a different speedo gear for it or use something like a GPS to figure out the accuracy and live with it .... if it's a "steady" 30 fast at all speeds you might move the needle down
Bill | | | | | Joined: Mar 2010 Posts: 10,279 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,279 | Have you checked to see if the odometer is as far off as your speedometer? Mine doesn't register speed nor miles accurately, and by different percentages.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Oct 2002 Posts: 4,066 Bolter | | Bolter Joined: Oct 2002 Posts: 4,066 | boy, that would drive me crazy if I was using a mile marker for a check and did not know my odometer was off.. I dont have nor know how to use a gps.. I am falling behind in my old yrs.. sometimes I do check how fast cars are going in my block by a mental time/count
and using certain aids. I have previous timed them with my count and speedometer, clever, huh. This would be when I am out side watching them go back.. it is a 25 mph zone and most dont even come close to it..wife thinks I am crazy when I point one out and tell her..
Last edited by joker; 06/17/2016 2:48 AM.
Redryder pixMy HotrodA veteran - whether active duty, retired, national guard, or reserve - is someone who, at one point in his or her life, wrote a blank check made payable to The 'United States of America', for an amount of "up to and including my life."I am fighting cancer and I am winning the fight | Pain is part of life; misery is an option. | | | | | Joined: Sep 2010 Posts: 1,706 back yard wrench turner | | back yard wrench turner Joined: Sep 2010 Posts: 1,706 | I have a speedometer app on my phone. I used it to determine my speedometer was reading 10 mph slow. I moved the needle and it's very close now.
Wayne1938 1-Ton Farm TruckStovebolt Gallery Forums1989 Silverado 1996 Mustang GT convertible When I die, I hope she doesn't sell everything for what I told her I paid for it! | | | | | Joined: Jun 2016 Posts: 236 DLBrooks | | DLBrooks Joined: Jun 2016 Posts: 236 | If the speedometer is in working order, I was told it needs to spin 1000 rpm for 60 mph. I am not sure what trans you have probably a 350 turbo or 700r4 you need the gearing to match your rear gears and tire diameter. There are calculators on the web. You may need only a diff speedo gear but it could be a housing and gear as Flxible said above. http://www.tciauto.com/tc/speedometer-gear-calculator/As Carl and Wayne said above --check actual speed with a garmin, tomtom or a phone app for a sanity check. I would guess you are now running a 4.10 gear and the trans was set up for a 2.73, 3.08, or 3.42 or so. If I am thinking correctly.
Last edited by 42465967; 07/09/2016 3:20 AM.
| | | | | Joined: Jan 2013 Posts: 1,384 Shop Shark | | Shop Shark Joined: Jan 2013 Posts: 1,384 | Using the odometer to calculate the is the easiest way to determine where the problem. The odometer is gear drive and the speedo is magnetic drive.
If the problem is the trans drive gear (most possible) the error will be a ratio.
Drive some miles 10 is best, 2 is about minimum, checking the mile markers. Then compute the error. Lets sau it's 10% low, then when the steedometer is reading 20mph you will be going 22, 60 indicated will be 66 actual. Change the gear accordingly or add a ratio adapter. Moving the needle can't help this.
If the mileage check is a perfect 1:1 then move the needle. | | |
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