4:11 Speedo Gear What Color?

[Mark A.]

I Am Rebuilding My Muncie From My 71 Lt-1. The Car Has 4:11 Gears, Which Uses The Small Transmission That Plugs Into The Tailshaft. It Has A Red Plastic Driven Gear. Is This Correct For This Ratio? Stock Firestone Tires. The Speedo Never Worked When The Car Was Running, So I Can't Verify If The Speedometer Would Read Correctly.thanks, Mark

[Joe L.]

Re: 4:11 Speedo Gear What Color?

I Am Rebuilding My Muncie From My 71 Lt-1. The Car Has 4:11 Gears, Which Uses The Small Transmission That Plugs Into The Tailshaft. It Has A Red Plastic Driven Gear. Is This Correct For This Ratio? Stock Firestone Tires. The Speedo Never Worked When The Car Was Running, So I Can't Verify If The Speedometer Would Read Correctly.thanks, Mark

Mark------

If by "...small transmission that plugs into the tailshaft" you mean the speedometer adapter that threads onto the speedometer fitting on the extension housing, then, yes, your application does require an adapter. It was originally GM #6477965. It had a ratio of 0.8333:1

The speedometer DRIVEN gear used for your application and in conjunction with the above was, indeed, a RED gear of 21 tooth count and of GM #3987921.

For 1971+ 4 speed applications with 4.11:1 rear gear ratio, it is not possible to achieve proper speedometer calibration without the use of an adapter.

[Mark A.]

Re: 4:11 Speedo Gear What Color?

Joe,
Yes that is the adapter I am talking about. Thanks for the confirmation on the red gear! Mark

[Paul O.]

Re: 4:11 Speedo Gear What Color?

Mark how early is your 71 mine was #1914 also 4:11 rear and it used a 70 driven speedo gear not the normal 71 gear. The 70 is a much larger driven gear then the 71. Just slightly smaller then the opening in the tail shaft.
Paul 18046

[Dick W.]

Re: 4:11 Speedo Gear What Color?

If you have problems finding an adapter, HD truck dealers have been a good source. The adapter is now made by SS White Company.

[Joe L.]

Re: 4:11 Speedo Gear What Color?

Mark how early is your 71 mine was #1914 also 4:11 rear and it used a 70 driven speedo gear not the normal 71 gear. The 70 is a much larger driven gear then the 71. Just slightly smaller then the opening in the tail shaft.
Paul 18046

Paul------


It's possible that early 1971's used 1970 transmissions. If so, it's very easy to tell the difference. 1970 transmissions will have an extension housing casting number of 3857584. 1971 transmissions will have extension housing casting number 3978764. These numbers are very prominent and easy to see.

One can NEVER use the "large" OD speedometer driven gears (i.e. 22 tooth GREEN through 25 tooth ORANGE) in a 1971-74 transmission (i.e. with a 3978764 extension housing). These gears will fit in the fitting and extension housing orifice but they are not compatible with the 71-74 DRIVE gear.

[Wayne M.]

Re: 4:11 Speedo Gear What Color?

Mark how early is your 71 mine was #1914 also 4:11 rear and it used a 70 driven speedo gear not the normal 71 gear. The 70 is a much larger driven gear then the 71. Just slightly smaller then the opening in the tail shaft.
Paul 18046

Paul, Joe, Mark -- I shouldn't even mention this, because my parts books only go to Rev. Jan 1970, but for the 1970 MY, whether or not you had an adapter with a 4-speed Muncie depended on whether your trans was close or wide ratio, in combination with your axle ratio. I assume that with 4.11 final drive, Paul's trans would be close ratio.

For instance, WIDE ratios from 3.55 final drive up to 4.11 used the adapter that Joe mentions and the red 21-tooth plastic driven gear that Joe mentions. If 3.08 or 3.36 -- no adapter with natural or blue driven gears, respectively.

CLOSE ratio flipped the situation; only 3.08 and 3.36 used an adapter # 6477966 with black and orange driven gears, respectively. 3.55 and up used NO adapter.

All the above assumes F70 x 15 rubber. Caveat: this may have all changed for the 1971 MY.

[Joe L.]

Re: 4:11 Speedo Gear What Color?

Paul, Joe, Mark -- I shouldn't even mention this, because my parts books only go to Rev. Jan 1970, but for the 1970 MY, whether or not you had an adapter with a 4-speed Muncie depended on whether your trans was close or wide ratio, in combination with your axle ratio. I assume that with 4.11 final drive, Paul's trans would be close ratio.

For instance, WIDE ratios from 3.55 final drive up to 4.11 used the adapter that Joe mentions and the red 21-tooth plastic driven gear that Joe mentions. If 3.08 or 3.36 -- no adapter with natural or blue driven gears, respectively.

CLOSE ratio flipped the situation; only 3.08 and 3.36 used an adapter # 6477966 with black and orange driven gears, respectively. 3.55 and up used NO adapter.

All the above assumes F70 x 15 rubber. Caveat: this may have all changed for the 1971 MY.

Wayne------


It did change for the 1971 model year. For 1971+, there was only 1 DRIVE gear available. That drive gear was compatible with only the 18 thru 22 tooth (SILVER) driven gears. So, an adapter was required for any application that would have otherwise required a 23-25 tooth driven gear.

Of course, any 1971 that was originally fitted with a 1970 transmission could have used a 1970 speedometer gear/adapter configuration such as you described.

[Mark A.]

Re: 4:11 Speedo Gear What Color?

Guys,
Just to reference, my car is a very late car, build date of July 71. It is a close ratio tranny. Mark