Regear of an automatic

[saand]

Im interested in regearing my automatic transmission.

obviously going to a 5 speed manual would be ideal but that is a big change and im trying to keep the cost down and effort down for changes. I figure i may as well just get a new car if i get to the point where i have to go to a manual.

Anyway as i am stuck with an auto i am interested to know if anyone has or knows how to regear a auto transmission so that i can get lower rpm when im running at 100kph.
Ideally id like to be able to go to the junk yard, find a suitable car with a taller gear that will work in my transmission and swap it in to my transmission.

I have no idea how to get any info on what cars use similar transmissions to mine or if any others have taller gears, i wonder if anyone can point me in the right direction for this sort of information. i am driving a mazda 626 91 GD auto.

[saand]

Ok so no responses yet, so here is a more straight forward question.

has anyone tried to change the gearing on an automatic?

[brucey]

I dont think it will be easy. Other than the final drive (differential gear) it's not as simple as swapping out a gear inside, is my understanding.

It's possible to have different specced gears from the factory, however. In the same transmission. I know that my 4EAT has quite a few, but of course every transmission is unique as far as that goes, you'll probably have to get ahold of some factory service manuals to find out or get on a forum that is well versed in that specific car.

[Zerohour]

The quick and simple answer is no, you most likely cannot change the gearing.

Go look up some rebuild videos of automatic transmissions and you'll get it pretty quick.

Since your 626 is FWD, you most likely cannot change the differential either. It was much different back in the day when there were 3-4 size rear ends used over decades. But modern vehicles all have have their own special casings/gears/etc.

EDIT:
Not FWD, but none the less, it shows some of the internal parts that need replacing with the transmission. You would need to find different versions of these components to change the gearing.

http://www.youtube.com/watch?v=EC_IQ...eature=related

[Frank Lee]

I tried to "gear up" my a/t pickup with taller tires. Then it downshifted all the time.

[saand]

Thanks all, good to know its not worth getting into before i start and research a lot so looks like i will have to give this mod a miss.
I like the idea of larger tires to give a similar effect

[bestclimb]

you would have to have the thing revalved or what ever magic they do in side of an auto to prevent it from down shifting as frank noted is likely.

[comptiger5000]

I put slightly larger tires on my Jeep and corrected the speedo for them. Upshifts happen at a slightly higher road speed (same rpm), and it doesn't downshift any more often (too much low end torque for the current gearing). It seems to have had minimal to no effect on mpg though. If anything, it went up by less than 0.5 mpg on the highway.

Whether or not taller gears will be useful with an auto depends on the vehicle, as well as your driving style. In town, they probably won't help. You may gain a little on the highway, if it doesn't make it downshift a lot.

[Zerohour]

It would really depend on location and route traveled. If you were in something like a Jeep, and drive long trail highway everyday, then changing out the differential would have a big impact. A good comparsion would be my old caprice which had a 2.93 rear ring, it could do 70 on the highway in 4th at 1700 rpm. My buddy with a Monte Carlo has a 3.73. His does 70 on the highway at 2800-3000rpm. Its a huge difference in gas mileage even neglecting differences in motors (carb vs. injection, compression, cams, headers, etc). I could get 18-19 with the Caprice, he gets 13 lol

[comptiger5000]

For exactly that reason, I've considered taller gearing in my Jeep. If a gear-vendors OD weren't so expensive, I'd strongly consider one (although it would make my rear driveshaft pretty short). That 28% drop in rpm on the highway would be awesome.

I'd drop from 1760 rpm at 60mph to just under 1300. That would probably be a bit too low (1500 would be great), but would let me re-gear the axles from 3.73 to 4.10 for better performance when desired, and a better crawl ratio off-road.

With 4.10s in the axles, I'd be at 1930 rpm with the GV disengaged, and just under 1400 with it engaged. It would probably downshift on some hills, which it doesn't now, but the gains would still be well worth it. Plus, I'd have better ratio choices for towing (which I don't do much, but it's certainly capable), as 3rd in the tranny with the GV engaged would be right at 2000 rpm at 60 mph.