speedo drive and driven gear

[Sander B.]

I have a 4 speed borg warner for my 1963
and have the wrong driven gear in it now (green 3.70)

i ordered the correct one a blue for 3.36 rearend

do i also need a other drive gear ? because the blue gear has less tooth and its diameter is smaller so the gears wont reach each other ?

i cant figure it out in the vendor catalogs like CC and Paragon
the only offer 1 type drive gear

thank you Sander,

[Kevin M.]

Re: speedo drive and driven gear

I had to only replaced the one gear.

Kevin

[Mike E.]

Re: speedo drive and driven gear

There shouldn't be a problem between a 3.70 and a 3.36. The best way to check is just stick it in there and rotate the input shaft. If the gear turns, you're good to go.

[Michael B.]

Re: speedo drive and driven gear

Here are two websites with more information than you will ever want to know about speedometer gears. I used these sites for info on an automatic but I think they had manual info too.

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

http://www.tciauto.com/Products/Comp...eter_gears.asp

[Wayne M.]

It may work .....

but theoretically, if your (larger diameter) 22-tooth green driven gear was meshing correctly with your 3708145, 8-tooth drive gear, then (to be correct) you would need to change your steel drive gear to 3708144 to accomodate the smaller diameter 20-tooth blue gear. The difference in the OD's of these steel drive gears is approx. 1.765" vs. 1.850"

I say it may work, as there might be enough interference between the teeth that it rotates the proper amount. However, after wear and/or a heavy speedo cable load, it may eventually start to skip.

[Joe L.]

Re: speedo drive and driven gear

sander-----

If you have a green 22 tooth driven gear currently, then the drive gear used with it is NOT the correct one for use with a blue 20 tooth driven gear.

[nancy charles]

Re: speedo drive and driven gear

what determins what drive gear goes on what main shaft ? is there one drive gear or two ? close ratio or wide ratio ?

[nancy charles]

Re: speedo drive and driven gear

corvette central only shows one drive gear its a ( 8 ) tooth for ( 3:08 - 3:55 ) for 63-67 corvette and it does not say B/W or MUNCIE ????????

[Michael B.]

Re: speedo drive and driven gear

There are three sizes of drive gears for the manual. 1.76, 1.84, & 1.92.

Here is a website that shows GM gears and their compatibility, including GM part numbers.

http://chevelleengineer.home.comcast.net/~chevelleengineer/speedo.htm

[Sander B.]

Re: speedo drive and driven gear

yes thats what i noticed too in there catalog
would that gear be the correct one for 22 tooth blue 3.36 ?

or who sell them

Sander,

[Joe L.]

Re: speedo drive and driven gear

Nancy-----

The DRIVE and DRIVEN gears for 57-63 Borg-Warner and 63-67 Muncies are the same. These also work with most 57-67 Powerglide-equipped cars and most 57-69 3 speed manual applications. While there are quite a few different gears, the VASTLY most popular ones are as below:

DRIVE gears

For use with 18 tooth (BROWN) through 22 tooth (SILVER) DRIVEN gears= GM #3708144 (STEEL). These gear combinations cover MOST 3.08 to 3.55 rear gear ratios.

For use with 22 tooth (GREEN) through 25 tooth (ORANGE) DRIVEN gears= GM #3708145 (STEEL). These gear combinations work with MOST 3.70 to 4.11 rear gear ratios.

For 68-70 Muncies the DRIVE gear is NYLON and retained by a clip to the mainshaft.

For use with 18 tooth through 22 tooth (SILVER) DRIVEN gear= GM #6261794 (LIGHT GREEN).

For use with 22 tooth (GREEN) through 25 tooth DRIVEN gears= GM #6261795 (LIGHT BLUE).

For 71-74 Muncies and 75+ B-W T-10, there is a single DRIVEN gear of GM #3978758. This is a steel gear. It works only with 18 tooth through 22 tooth (SILVER) DRIVEN gears. No 22 tooth (GREEN) or higher tooth count DRIVEN gear can be used with any 1971 or later 4 speed transmission. So, most 3.70 or higher numerical rear gear ratios require a speedometer adapter.

The above DOES NOT cover all possibilities, but it covers the vast majority of 57-81 manual transmission applications and rear gear ratios.

All of the above DRIVE gears are discontinued except the 68-70 GM #6261794. However, I believe they are all available in the aftermarket.

[nancy charles]

Re: speedo drive and driven gear

so whats the difference in the 3708144 & 3708145 steel gear ??????????????

[Michael B.]

Re: speedo drive and driven gear

144 gear is 1.84" OD

145 gear is 1.76" OD

[Wayne M.]

Easier to differentiate by width of gear

Mike has given the OD's but with a dial micrometer, it's easier to measure the width. The "144" is 0.610" thick, and the "145" is 0.531". Both are 8 teeth (but NOT the case with 6-tooth 3845079, which is 1.922" OD and 0.453" thick -- used for 4.56 gears only in the C1-C2 era. Here's a link to the 4.56 set


And here's a still life of drive/driven gears --- Corvette beauty is also internal.

[Sander B.]

Re: speedo drive and driven gear

Thank you Joe
now i get it

so the one Corvette central sells is probably right http://www.parts123.com/parts123/yb....Z5Z5Z50000050B

GM #3708144 (STEEL). These gear combinations cover MOST 3.08 to 3.55 rear gear ratios.

it seems that thats is the one they sell ?

Sander,