Speedo Gear Size/color needed

[Bill C.]

hey -
quick question.

1967 4spd
stock profile tires with 3.36 gears - what tooth count/color is the 4spd transmission gear?

Thanks Bill

[Leif A.]

Re: Speedo Gear Size/color needed

Bill,
I believe a 20 tooth blue gear.

[Joe L.]

Re: Speedo Gear Size/color needed

Bill,
I believe a 20 tooth blue gear.

Leif and Bill------


Yes. GM #3987920.

[Bill C.]

Re: Speedo Gear Size/color needed

hey -

reason i was asking....
i have to rebuild the clutch pack in the posi and was going to R&R the rear too.
car currently has 3.70 gears and they kinda are miserable on the HWY.
thought I switch to 3.36

but - i found out from reading archives that i also have to switch the DRIVE gear and i don't wanna tear into the tranny too.

so - just gonna go with pain A, and not switch gears.

thanks for the input...

Bill

[Joe L.]

Re: Speedo Gear Size/color needed

hey -

reason i was asking....
i have to rebuild the clutch pack in the posi and was going to R&R the rear too.
car currently has 3.70 gears and they kinda are miserable on the HWY.
thought I switch to 3.36

but - i found out from reading archives that i also have to switch the DRIVE gear and i don't wanna tear into the tranny too.

so - just gonna go with pain A, and not switch gears.

thanks for the input...

Bill

Bill-------


Yes, to go from 3.70 to 3.36 you'd also have to change the drive gear.

However, there is another option: use a speedometer adapter. A good speedometer shop can fix you up one.

The 3.36:1 is a much better rear gear ratio for all-around driving.

[Gary R.]

Re: Speedo Gear Size/color needed

I'm pretty sure I didn't change the Drive gear between 336 & 370's, just the plastic driven gears when I did my 69 over. In fact the 69 Muncie I just did I replaced the plastic drive gear with a 8 tooth steel and Silver plastic driven gear for a 336 to 373 swap.

[Joe L.]

Re: Speedo Gear Size/color needed

I'm pretty sure I didn't change the Drive gear between 336 & 370's, just the plastic driven gears when I did my 69 over. In fact the 69 Muncie I just did I replaced the plastic drive gear with a 8 tooth steel and Silver plastic driven gear for a 336 to 373 swap.

Gary-------


If you go FROM a 3.36:1 TO a 3.70:1, then you can use the 22 tooth SILVER DRIVEN gear with the existing drive gear. The 3.36:1 uses the "large" DRIVE gear in combination with small series DRIVEN gears (18 tooth to 22 tooth SILVER).

However, if you go FROM a 3.70:1 TO a 3.36:1 it doesn't work out to be so easy IF the application is a 1970 or earlier. Pre 1971 3.70:1 applications used the "small" DRIVE gear in combination with the large-series DRIVEN gears (22 tooth GREEN to 25 tooth). The 1963-1970 3.70:1 applications used the "small" DRIVE gear in combination with the 22 tooth GREEN DRIVEN gear. There is no 20 tooth gear, used with 3.36:1 applications which is compatible with the "small" DRIVE gear.

GM did not release the 22 tooth SILVER DRIVEN gear until 1971. It would have been well if they had introduced it MUCH earlier.

[Gary R.]

Re: Speedo Gear Size/color needed

Thanks Joe, I didn't realize the silver gear wasn't sold till '71.

[Joe L.]

Re: Speedo Gear Size/color needed

Thanks Joe, I didn't realize the silver gear wasn't sold till '71.

Gary-------


I believe the reason for it was this: beginning in 1971, all Muncie transmissions had only one speedometer DRIVE gear available. This was a steel gear of the "large" OD, compatible only with the "small" OD series of DRIVEN gears (18-21 tooth prior to 1971). So, in order to accommodate rear gear ratios of up to 3.70:1 with the single available DRIVE gear, the 22 tooth SILVER DRIVEN gear was added to the "small" OD series. This enabled GM to avoid having to use speedometer adapters in most cases. Speedometer adapters are expensive.

22 teeth is the only tooth count DRIVEN gear which is represented in BOTH series of DRIVEN gears. The "small" OD series is the SILVER gear; the "large" OD series is the GREEN gear. Each gear is compatible ONLY with the DRIVE gear for the specific gear series.

[Gary R.]

Re: Speedo Gear Size/color needed

Great info Joe.

[Wayne M.]

Re: Speedo Gear Size/color needed

...22 teeth is the only tooth count DRIVEN gear which is represented in BOTH series of DRIVEN gears. The "small" OD series is the SILVER gear; the "large" OD series is the GREEN gear. Each gear is compatible ONLY with the DRIVE gear for the specific gear series.

Here's a side-by-side for the two 22-tooth gears. I would call the silver gear gray.




c

[Joe L.]

Re: Speedo Gear Size/color needed

Here's a side-by-side for the two 22-tooth gears. I would call the silver gear gray.




c

Wayne-------


"Silver" is GM's description of the gear. I've always wondered why they use that description.