Changing OD gear questions

[M4s73r]

I cant seem to find the answer to my question.
First, where would I find a different 4th gear for my 97 Auto GST tranny? I'm wanting to change it out when i put in my LSD (since ill be in there already) to something that will allow me to drive a lower rpm on the hwy at 70-75 mph. What size gear should i look at putting in? Searched high and low and not sure if im just calling it the wrong thing, or what. Any help would be appreciated. Thanks

 

[undefined0000]

Subscribed. Wanna see where this goes. With the planetary setup of auto trannies, it would only make sense that changing gear ratios would be impractical.

 

[M4s73r]

Well no idea what you mean by planetary. Just saw the manual guys talking about putting in a evo 5th gear. Went and bought a 2g tranny from the scrap yard (20 bucks!) so i can learn how to rebuild one. just the taking apart and putting it back together side before I do my built one that's in my car. Haven't really started tearing into yet. Called Royal Transmission and they quoted me 2000 to put in a LSD. PSH F that noise. Ill teach myself and save 1150 bucks. Was just thinking that it would be really sweet to put a little taller (shorter?) gear on my 4th

 

[undefined0000]

Hm, interesting, tis why I am lurking, because it sounds like something I would like to try. HATE how big auto tranny gears are, but love the shift speeds. From what I know and have seen, auto trannies are a planetary gear system with a center sun gear and planet gears around it, then some magic happens and power is sent to the output shaft.

 

[M4s73r]

Mmmm Magic.

Got on a calculator and at 8k rpm with the OD gear being 0.685:1 you would mathematically top out at 203 mph at 8000 rpm on 205/55r/17 tires. So i guess the real question is can you find a 0.658:1 gear (tops out at 211mph@8k or 70 mph@2650k) to replace it with. Wonder what material the gear is made out of. or if you could use the 5th gear from a Jetta to do this.

 

[slo2spool]

Well, if you haven't discovered already, since you have an auto you are kinda SOL. For a maunal trans fwd, switching out 5th gear for one from an awd 5 spd or evo 5 spd would work. BUT, these auto trannies use planetary gearsets instead of helical gears which manual transmissions use. A planetary uses what is called a sun gear, a ring gear and typically 4 or 5 planet gears. the amount of teeth that all of these teeth have are determining factors on your gear ratios.