1986 chevy c70

[mountaintrace]

i have a 1986 c70 with 366 in it with 5 speed it is popping in 3rd gear found a 4 speed that came out of a old bus cheap just wondering what would be different than5 speed w. would it be slower top end,not pull as good bottom end use more gas 'dont have 2 speed rearend so jus looking for pros and cons thanks

 

[rarefish383]

We had a 78 Ford F600 brand new and it kept popping out of 3rd gear. You actually had to ride down the road with your hand holding it in gear. Turned out to be a minor adjustment and all was well. If that's your problem, I'd check out adjustments to the original 5 spd before swapping out. Your truck obviously has many more hours on it than our new Ford, but the problem might be similar and just be adjustments to wear, Joe.

 

[brisawyer]

If it is making a popping sound it is time to rebuld/replace. If it is popping out of gear I would track down a shop manual and try to remedy before I replaced it. If your 5 speed is not overdrive you will have bigger steps between gears and same top speed. If the 5 speed is overdrive you will have about the same steps between gears and less top speed. Personally I like every gear I can get on a heavy truck.

 

[Rftreeman]

your answer depends on the gear ratio of the two different transmissions, if I had to guess I'd say the are the same except the 5th gear is more of an overdrive where the 4th is probably 1 to 1 ratio...