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3 speed to 4 speed conversion

7K views 9 replies 4 participants last post by  Txbobcat 
#1 ·
Hello everyone! I am wondering if anyone has ever converted a 3 speed manual tranny over to a 4 speed manual? (I am working on a 1964 with a 327 3 speed on the floor) My concerns are if I have to change the or modify the crossmember? Driveshaft? Rear end gears? Bellhousing? I am just toying with the idea and do not want to do anything that could not be easily switched back, it's a very original car, but the un-synched 3 speed sucks sometimes. THANKS for any input!!!
 
#2 ·
All yopu need is a new shifter and a four speed as the three speed is on the tree and four speed is on the floor. Other-wise it a is a straight swap with nothing else on the car changing (assuming you have the same number of splines on the input shaft). I have swapped about twenty Camaro sixes over to BBC four speeds that way (just add decals and instant SS car:noway:)

Big Dave
 
#4 ·
I have a Muncie M20 with a Hurst Comp Plus on it, looks like it should be a breeze if I decide to do it. I'm just not real crazy about the 3 speed, even though it's 'correct'. No one mentioned the driveshaft, so I take it that it bolts right up without shortening it or anything?
 
#6 ·
Looks like the older 3 speeds are indeed different, about 4" shorter than a Muncie 4 gear. I have a 'wanted' ad placed in the classifieds looking for a decent used driveshaft for my application. There is a local company that can manufacture a new one, but it is salty as far as costs. I will go that way if I have to......
 
#7 ·
Sounds like a long tail shaft short tail shaft thing. The factory makes two diferent transmission lengths on automatics a 9" long tail shaft and a short tail shaft that is only 6" long. The long tail shaft is used in B-bodies and pick-up trucks only. Everything else gets a short tail shaft. I have never seen a long tail shaft four speed Muncie before, so I wasn't aware they even existed. Sorry for the bad advise.

Big Dave
 
#9 ·
4 speed is installed!

It is like having a totally new car! Driveshaft had to be shortened by 4", otherwise, it was a breeze. Never fear, each and every original piece is safely stored away. My Dad (the cars original owner) and I talked about this switch over before he passed away last summer, and he was fine with it. He had even said that to do over again, he would have checked the box for a 4 speed on the option sheet in '64, so there was no 'guilt' involved.:noway:
 
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