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#1 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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WTB speedo gears
I'm needing the drive and driven gear for a TH400 and 3.07 rear gears.
Anyone parted out a truck with that combo lately? Anyone know what color/tooth count gears I need for this? Price to 43228 if you got them? |
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#2 |
State of Confusion!
![]() ![]() Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 46,845
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Re: WTB speedo gears
Andy, does this help? I save this off TCI Automotive's website a while back, but can't find their site anymore.
I don't have any, but maybe this will help. TH400 Speedometer Gears Drive Gears 7 teeth - red 8 teeth - black 15 teeth - brown or gray* 16 teeth - orange 17 teeth - red 18 teeth - yellow or blue 19 teeth - yellow or white 20 teeth - green 21 teeth - black Driven Gears 16 teeth - (truck) 17 teeth - (truck) 18 teeth - (truck) code H 19 teeth - (truck) code J 20 teeth - (truck) code K 21 teeth - (truck) code L 22 teeth - (truck) code M 34 teeth - light green 35 teeth - pink 36 teeth - white 37 teeth - red 38 teeth - blue 39 teeth - brown 40 teeth - black 41 teeth - yellow 42 teeth - green 43 teeth - purple 44 teeth - dark gray 45 teeth - light blue Notes: Two aluminum housings are available for driven gears with 34 or more teeth. One fits gears from 34 - 39 teeth and the second one fits gears from 40 - 45 teeth. The driven gear housings go in the case just forward of the tailhousing. Andy if I figure this right with the calculator they provided, using a 3.07 and 29" tires you'll need a 8 Drive gear and a 17 driven gear or a 17/36 or a 18/38 for a 31" tire it will be 8/16 17/34 18/36 Again hope this helps ya and I think my figures are correct. Oh yeah, I don't know why some of the driven gears mention turcj/code, but no color.
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Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! Last edited by Palf70Step; 01-20-2008 at 10:55 AM. |
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#3 |
Registered User
Join Date: Dec 2007
Location: tullahoma, tn
Posts: 23
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Re: WTB speedo gears
Lot more than just that needed for it to be correct. Have to take into account tire size also. And do lots of math.
1. First determine the Circumference of tire in inches. 2. Second divide that into 63360 (number of inches in a mile). This tells how many revolutions your tire makes in 1 mile. 3. Third multiply that by your rear axle ratio. This determines how many revolutions your drive shaft makes in 1 mile. 4. Finally find a ratio of availabe drive and driven gears that will cause your speedometer cable to turn 1000 revolutions per mile. If you need any more help with this feel free to pm me. I used to have a spreadsheet I created for doing this. Can't seem to find it right now, but can certainly recreate if needed. Steve |
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#4 |
Registered User
Join Date: Dec 2007
Location: tullahoma, tn
Posts: 23
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Re: WTB speedo gears
Also, I can probably dig up many of the part numbers for the different gears. Most are still available from GM
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#5 |
Registered User
Join Date: Dec 2007
Location: tullahoma, tn
Posts: 23
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Re: WTB speedo gears
I. Gm drive gears (gear on end of cable)
Part Number No. of teeth 3987917 17 3987918 18 3987919 19 3987920 20 3987921 21 3987922 22 3987923 23 II. GM driven gears (the gear in the transmission that drive the Speedometer cable gear) Turbo 350 Part Number No. of teeth 6261783 8 6261782 9 8629547 15 Turbo 400 Part Number No. of teeth 8629549 18 9629547 15 8440055 8 |
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#6 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: WTB speedo gears
ok, the stock speedo gears in my GMC were for a 3.07 rear gear, and I had 275/60's on the rear. The speedo was off by one MPH at 60... which is within GM's specs, and mine too.
My burb is about to get a 3.07 rear, and I'll be installing 275/60's in the back. |
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#7 |
Senior Member
Join Date: Apr 2005
Location: Joppa, Maryland
Posts: 4,408
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Re: WTB speedo gears
Longhorn....this is how I did mine.......gives you gear colors and all.
http://novaresource.org/speedo.htm
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1997 GMC Sierra Ext 1965 Mustang |
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#8 |
State of Confusion!
![]() ![]() Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 46,845
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Re: WTB speedo gears
Andy according to calculations, you tire is 28"
you'll probably need to use a tranny gear of 8 and speedo gear of 17 other combos that come close are 15/33 or 18/40
__________________
Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! |
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#9 |
Registered User
Join Date: Dec 2007
Location: tullahoma, tn
Posts: 23
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Re: WTB speedo gears
If the tire size is 28" Diameter. You need to use a 9 Drive and 20 Driven gears. that gives you a driveshaft cable rotation of 995.04 revolutions per mile. 1000 is what your speedometer is designed for. 995.04 is as close as you will get without a ratio adapter. Check around for a 1.004978303 ratio adapter if you want the exact 1000. However you will probably be less than 1 mile per hour off without it.
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#10 |
Registered User
Join Date: Apr 2004
Location: N.E. MO
Posts: 1,749
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Re: WTB speedo gears
I've got a collection of speedo gears, but they came out of th350 and 700r4's.
The drive gear won't work for ya but the driven gear should. When ya figure out what color ya want, if I have it it's yours. I'll dig 'em up and see what colors I have.
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