# 1977 F150 transmission swap **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [June 24, 2012, 6:52am UTC](https://community.cartalk.com/t/1977-f150-transmission-swap/73199 "2012-06-24T06:52:02Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![dwbat](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@dwbat](https://community.cartalk.com/u/dwbat)\ **Post date:** [June 24, 2012, 6:52am UTC](https://community.cartalk.com/t/1977-f150-transmission-swap/73199/1 "2012-06-24T06:52:02Z")
New truck new questions. I’m now driving a rebuilt 1977 F150 with the 390. The question being, am I able to switch the 4 speed out with a 5 speed? If so, what would be the best route to go? I’m ok with losing a bit of power in order to increase my fuel economy. Thanks for the help ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [June 24, 2012, 5:05pm UTC](https://community.cartalk.com/t/1977-f150-transmission-swap/73199/2 "2012-06-24T17:05:43Z")
You might compare the mating surfaces, lengths, output shaft splines, speedometer drive and input shaft/pilot bearing length and diameter. It might be much simpler and cheaper to swap for a taller geared chunk. ---
**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\ **Post date:** [June 24, 2012, 8:52pm UTC](https://community.cartalk.com/t/1977-f150-transmission-swap/73199/3 "2012-06-24T20:52:04Z")
All a 390 needs is a 3-speed…Putting a 5-speed behind it is loves labor lost…You will not notice any improvement in fuel economy…5-speeds were never offered in 352/360/390 pick-up trucks…So installing one now might be quite a challenge, a very expensive challenge… You might investigate what your rear axle gear ratio is. It’s stamped on a tag attached to the third-member or back cover. If it’s 3.73, 3.92, 4.11 then there might be room for improvement…If it’s 3.23, 3.52 just leave things alone…