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determine 18 spline gear ratio while installed?

sam dupont

FBBO Gold Member
FBBO Gold Member
Local time
4:06 PM
Nov 9, 2020
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If I read correctly, there are two possibilities for the gear ratios in my transmission. Never saw the car, but the trans was said to be from a 1970 Challenger 6-Pack.
It replaced a 1966 23 splines and the 18 spline seemed to have longer legs than the 23.
Can it be identified by the VIN?
Yep, two possibilities as there were 6-packs with 18 splines in 1971 too, are there any external markings to identify?
Unfortunatly no. you have to pull the side cover to be for sure. One thing you can look for is if there is a bar on the side cover. If so it is the later scissor style cover and more than likely will have the 2:44 ratio. The earlier ball and detent side cover would have the 2:65 ratio, if no one has been inside of it. 340 or 440 6-pack, I am assuming you mean a big block. The 340 6 pack cars had 23 spline. Post the VIN it may help
Mark input shaft and output put in 4th and rotate input one turn and look at output
full turn or 3/4 turn
Remove the bell dust cover, mark the bottom of the flywheel then, with the shifter in 1st, bump the starter for one flywheel revolution and count the driveshaft rotation. (rear wheels elevated of course)
I will post the VIN on FEBO in case the car didn't get crushed. My car came with a 23, so any 18 would work for me and the original 30,000 mile transmission would be a prize if someone rescued the car. It is a small World. As I remember, it was 6 Pack Challenger that was parted at a shop on North Federal in Denver. That shop had a Superbird they had prepped for Bonneville. They were planning to join the 200mph Club that year.

I will be looking at it this weekend. I think velocityss1985 is correct. Early has a smooth cover and later cover has a raised casting. I looked for photos and found these:
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