Converting 4sp 915 to a 5sp???

[samjepperson]

What are my options for converting my original 72 915 4sp into a 5sp? What parts do I need? Is it just easier to find a 5sp and install and keep the #'s matching tranny on the shelf? Any help would be great!

Thanks,
Sam

[coldstart]

I am in the same boat with my 72 and would also like a taller final gear ratio in the five speed for highway driving.

From what I have read, we need to replace our transmissions and the shifter to get a five speed. Supposedly, any tranny from 1973 to 1977 will be compatible without getting new CV axles, etc. The later 915 transmissions will work but require some modifications.

That said, there is nothing wrong with the four speed transmission. Mine shifts very well and is a blast to drive, except for long distances over 70 mph (~120 km/hr).

[MBruns]

If I remember correctly, the 4 speed had a couple of spacers in the place of the 5th gear set, other than the ratios set up for 4 instead of 5 I bet you could find some stock 3rd - 5th ratios fairly cheap and make it a 5 speed, the slider for 5th/rev should be the same and never used for 5th, shifter may be different maybe not but easy to find
Mike Bruns

[jkarolyi]

They can be converted, but you will not get any taller final gear ratio unless you go with a $$$ new non-stock gear. A lot of work for not much gain.

The 5sp is just a closer ratio version of the 4 speed ratios...1st is the same ratio in both gearboxes, and 4th in the 4spd is the same ratio as 5th in the 5-speed.

[samjepperson]

Thanks everyone for the response! To be honest I have not driven a 4sp box (currently restoring the car now), but have heard that 4th gear is not highway friendly cruising at 70mph (over 3,500 rpm), which is why I would like to convert to a 5sp. Of course budget is always in mind, so it looks like I might be stuck with the 4sp for now...