Higher overdrive gear on a manual?

[Dusty T.]

I swapped from 3.08's to 3.55 gears a couple months ago. I am really happy with the way they handle in city driving and the light offroading I do, and with acceleration, but the engine RPM's turn a bit higher on the highway than they used to. When I used to turn 2400 RPM at 75, I now turn 2800 RPM, which is okay but I'm worried it's sucking down my mileage.

I have the Mazda M50D tranny with "overdrive" as 5th gear. It's final drive is .79, but I'm wondering if a higher (i.e. a .68 ratio) could be swapped in? I'm going to need a new clutch eventually, and the tranny whines a bit in overdrive as it is. I figure why not do this during a rebuild?

Does such a gear exist?

Thanks.

 

[Mud Bug 94]

they have overdrive units but i dunno about a single gear.

 

[chbtech]

Unless you can find the same make/model transmission that has the gear sets you want, you are probably out of luck.

As an example, for 60's Chevy's you could get an M21 Muncie with 2 different 1st gear ratios. One was a 2.20 to 1.00 "close ratio" for road racing use and the other was somewhere around 2.54 to 1.00 which was the standard ratio. I assume that one could interchange the gears but I never tried it myself.

Try looking up the specs for an M5OD and see if they came from the factory with more than one OD gear ratio. Maybe someone out there knows of an aftermarket supplier of various gear sets for that transmission....I guess that was your initial question.

 

[RangerX]

Can't help ya with the OD, but as to your MPG concerns, be sure to change the speedo cable gear before computing your MPG with the 3.55s.

Welcome to the forum.

 

[briwayjones]

My manual in 5th turns 2500RPM at 75. Could your RPM gauge be off some? My RPM was determined by my guage and a scangauge.

 

[Dusty T.]

Can't help ya with the OD, but as to your MPG concerns, be sure to change the speedo cable gear before computing your MPG with the 3.55s.

Welcome to the forum.

Thanks!
I did change out the speedo gear after the regear, and it's within 2 or so MPH I'd say. I've checked it against several friend's vehicles and it reads pretty dead-on.

As for the tranny ratios, I think they only had two different ratios for these Mazda transmissions, but only in gears 1, 2, and 3. It looks like 4th and 5th (OD) are the same all the way around. So I'm guessing they threw in different tranny gears between 2wd and 4wd Rangers?

Hah, I'm thinking I could have just rebuilt the tranny and had them swap in the lower gears when I had the old 3.08's.