recalibrating the speedo? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

beeroh · 09-19-2003, 04:30 PM

Is there something that I can do that will allow my speedometer to tell me how fast I am actually going?

Prerunner1982 · 09-19-2003, 05:24 PM

isnt that what a speedo does? i assume it isnt accurate due to larger tires? there is a certain gear you need instead of the one you have. the other more knowledgable guys around here will know which one or a webpage that shows it. just replace the one in your trans/tcase depending... i think 4x4 is tcase... might try www.73-87.com alot of answers can be found there!

Russell · 09-21-2003, 07:27 PM

Another speedo question, is the gearing going to be significantly different from an 85 MPH to 100 MPH speedo?

gchemist · 09-21-2003, 11:46 PM

No. The magnetics that actually turn the speed are calibrated.

This is the best speedo gear calculator I have found.
Just measure your tire. Then find a combo that gives the closest whole number for a driven gear.

Russell · 09-22-2003, 12:13 AM

So trading a 85 mph and a 100 mph speedo won't affect the accuracy?

79BIG10 · 09-22-2003, 12:39 PM

No not at all. Like Gerado said they're made inside the speedo itself calibrated to the speedo itself. Basically it means the "gearing" inside the speedo is calibrated differently to each 100mph or 85mph speedo.

all4gss · 09-22-2003, 04:36 PM

I second the TCI page... that's the one i used. I had calculated that using a 31inch tire, a drive gear w/ 41 teeth and a driven gear with 17 teeth was pretty darn close. Went to the local GM center and ordered the parts. you can cross reference gear tooth availability on TCI's page for the tranny you're using.

good luck,

Keith

(btw those numbers up there are from memory, may wanna double check it if you've got 31's) :-)

Russell · 09-22-2003, 07:52 PM

Sweet deal

Just gotta lube up that new speedo next time I take apart my dash to rattle can the back a reflective silver to get rid of the bouncing needle sydrome...

09-19-2003, 04:30 PM	#1
beeroh Registered User Join Date: Sep 2003 Location: Atascadero, CA. Posts: 149	recalibrating the speedo? Is there something that I can do that will allow my speedometer to tell me how fast I am actually going? __________________ 84 Silverado,

09-19-2003, 05:24 PM	#2
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,904	isnt that what a speedo does? i assume it isnt accurate due to larger tires? there is a certain gear you need instead of the one you have. the other more knowledgable guys around here will know which one or a webpage that shows it. just replace the one in your trans/tcase depending... i think 4x4 is tcase... might try www.73-87.com alot of answers can be found there! __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call

09-21-2003, 07:27 PM	#3
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	Another speedo question, is the gearing going to be significantly different from an 85 MPH to 100 MPH speedo? __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

09-21-2003, 11:46 PM	#4
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	No. The magnetics that actually turn the speed are calibrated. This is the best speedo gear calculator I have found. Just measure your tire. Then find a combo that gives the closest whole number for a driven gear. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

09-22-2003, 12:13 AM	#5
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	So trading a 85 mph and a 100 mph speedo won't affect the accuracy? __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

09-22-2003, 12:39 PM	#6
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,774	No not at all. Like Gerado said they're made inside the speedo itself calibrated to the speedo itself. Basically it means the "gearing" inside the speedo is calibrated differently to each 100mph or 85mph speedo. __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

09-22-2003, 04:36 PM	#7
all4gss Registered User Join Date: Oct 2002 Location: Rolla, Mo Posts: 46	speedo... I second the TCI page... that's the one i used. I had calculated that using a 31inch tire, a drive gear w/ 41 teeth and a driven gear with 17 teeth was pretty darn close. Went to the local GM center and ordered the parts. you can cross reference gear tooth availability on TCI's page for the tranny you're using. good luck, Keith (btw those numbers up there are from memory, may wanna double check it if you've got 31's) :-) __________________ true power comes from above!!! 1984 C/10 2wd SWB.

09-22-2003, 07:52 PM	#8
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	Sweet deal Just gotta lube up that new speedo next time I take apart my dash to rattle can the back a reflective silver to get rid of the bouncing needle sydrome... __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)



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