WTB speedo gears

[Longhorn Man]

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?

[Palf70Step]

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.

[bandit37388]

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

[bandit37388]

Also, I can probably dig up many of the part numbers for the different gears. Most are still available from GM

[bandit37388]

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

[Longhorn Man]

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.

[70GMCer]

Longhorn....this is how I did mine.......gives you gear colors and all.

http://novaresource.org/speedo.htm

[Palf70Step]

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

[bandit37388]

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.

[454_72_4X4]

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.