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I am hoping to get a solution to my driven gear problem. Here are the specs.
Rear diff - 3.08 (not original to the car)
My tire diameter is - 26.85 (215-70-r15) The main case has #3851325
The tail shaft has #3846429 The date code is P0602
Drive Gear 7T 1.76" OD (3708145) (See image attached it looks smaller than the 1.84) (I am also not sure if its a 7 or 8 tooth but I am assuming its a 7 if its original to the trans)
The original was Green (unknown part number) see image attached, it had a 10mph above reading. 60mph but showed 68-70mph.
I took it to the shop and they have it replaced with a 3987920 Blue 20 teeth - which was working for a month (but did not fix the 10mph issue), it eventually gave out. Image below of the damage. Pretty disappointed on the shop.
I swapped it to a 3987918 Brown 18 teeth - and it just didn't work at all. At this point I realized that my drive gear was a 1.76 (teeth unknown I assume its a 7-8) and would require the large driven gear. - I referenced this site. www.stl-vettes.com/65Vette/GearCalc.htm
I am starting to think my diff will not pair up to my 1.76 drive gear. I am leaning on purchasing the 3860345 Green 22 teeth, and live with the 10 mph. This would be the larger diameter and could work. The stl-vettes website does not have options for 3.08 diff.
Here are my options in gears
Driven Gears: 3860341 Brown - 18 teeth 3860342 Natural - 19 teeth 3860343 Blue - 20 teeth 3860344 Red - 21 teeth 3860345 Green - 22 teeth 3860346 Black - 23 teeth 3860347 Yellow - 24 teeth 3860348 Orange - 25 teeth
Any help is greatly appreciated.
Visual of drive gear Reverse went out so they sent me a picture of the trans interior, here you can see green gear when I purchased the car, 10 mph above actual speed. Brown Gear (did not work at all) Blue Gear (lasted 1 month still 10 mph over)
First, without knowing for sure which drive gear is on the tail shaft (by the way, there are NO numbers on a Muncie tail SHAFT, but, there is a casting number on the tail HOUSING), it's difficult to say which driven gear would be compatible.
But, MOST Muncies (depending on rear gear ratio) came with either the 8teeth 1.76in gear or the 8teeth 1.84in gear.
The 1.76 gear is only compatible with the larger 22-23-24-25teeth driven gears.
The 1.84 gear is only compatible with the smaller 17-18-19-20-21-22teeth gears.
Thus, NORMALLY, for a 3.08 rear (depending on tire size), a Muncie would have the large 1.84 drive gear and would use the small 18-19-20teeth driven gears.
Actually, I do not know much about 4spds (mostly Muncies), I've only been rebuilding them for 50+yrs.
Muncie M20 Driven Gear Problem - 3.08 Diff
