99 GT, 99 OB 4EAT, TCU incompatibility?

[Tbird Man]

I just finished putting a 99 OB 4EAT in my 99 GT, everything seems to work ok (except for a front seal that leaks like a sive, i know, i should have replaced it) but it seems to be slow to shift and hang in 3rd. when it does shift to 4th even a small amount of throttle will make it downshift. Initally i assumed it was from low fluid since it is a PITA to keep the level up with a leaky input shaft seal, but i wondered if it could be an imcompatibility with the TCU? the reason i say this is I recall hearing somewhere (maybe the service manual?) that the OB torque converter has a higher stall speed then the GT which if i understand AT's correctly would throw the shift points off, no? if so, since I have to pull the trans to change the main seal ill put the GT TqC back on.

[idosubaru]

If the TC is leaking like a sieve then I would fix the known issue first before guessing on others.  Fluid loss will mean pressure loss which will effect lines pressures, valve body, etc.

 

TC and TCU shouldn't be the issue, but keeping the TC with the vehicle is a good idea.

 

That being said the TCU is super easy to replace so not a big deal to find out.

 

Though 99's are an oddball year with Phase II engine and trans changes.

[ivans imports]

Stall is the same 2100rpm. Only impreza and 2.2 legacy had high stall. Was wire harness exact same pins ? trany same ratios ? any AT light ?

[idosubaru]

any AT light ?

 

 

that's the million dollar question.

or check engine lights?

Edited April 16, 2014 by grossgary