1998 GS400, 205K miles, original drivetrain. No trouble codes. Trans fluid was pretty dark when I bought it, so I flushed it all out through the cooler lines. I also dropped the pan and turned the pressure dial to max.

So I’m still trying to figure out why my 1-2 upshift and 2-1 downshift are so smushy. I can’t feel any shift shock whatsoever no matter the throttle. All other gear changes seem ok.

I’ve been researching the crap out of the transmission function. Here’s what I’ve come up with so far:

I initially suspected the no2 shift solenoid, because the engagement into second gear is occasionally kind of jerky, more so when cold. However, downshifting from 3-2 also is kind of jerky sometimes, the shift solenoid 1 is what activates to control that shift.

maybe both solenoids 1 and 2 are sticking? Is it possible for solenoids to leak? That would cause issues without throwing codes.

But maybe since gear 2 is the only gear where both solenoids are active, the extra fluid paths are causing a loss of line pressure? That might mean the line pressure solenoid is bad.


maybs I’ll just say screw it all and put in a junkyard transmission. I can get an entire gearbox for the price of two damn solenoids.

When I bought the car I couldn’t feel any of the gear changes AT ALL. With the pressure dial maxed, I can at least sort of feel all but 1-2.

The thing that worries me most is I drove two other GS4s with similar mileage to mine and their transmissions felt much tighter. I could feel all the gear changes pleasantly and I doubt they’ve messed with their pressure dials.

I didn’t change the filter when I did the dial adjust... I had read from some reputable mechanics that with these screen-type filters, the act of draining the fluid usually dislodges anything substantial from the screen as the fluid falls through.

Although, I could see an obstructed filter causing low line pressure across the board.

But we’re back to square one: if the filter is clogged, something in the tranny is degraded enough to shed that kind of debris, and the whole unit is likely not healthy.

....I hate automatic transmissions.

Oh and also, I didn’t power flush. I flushed by pumping out old fluid via the cooler lines and adding fresh fluid through the dipstick tube. Done it many a time on many a vehicle with no issues.

That was one of the first things I did when I got the car. Couldn’t hurt to do it again I suppose.

OBDII data looks good as well, flow numbers and calculated load all seem to be normal.

Observation: Since the transmission usually ups line pressure when it’s cold, wouldn’t bad clutches slip worse once the trans is warmed up?

Mine tends to slip only when cold, which would indicate that the thicker fluid is having a harder time getting around.