: Weird transmission behavior - any ideas?



ejguillot
05-28-09, 12:43 AM
I'm beginning to wonder if the transmission in my STS is flaking out...

Background: Bought the STS in Sep 2006 with 91K miles. Changed trans fluid at 102K, used the then new Dexron VI (GM OEM fluid) Fluid was a opaque dark red (with a tinge of brown) when changed. Got all the old fluid out of the trans by removing one of the radiator cooler hoses and feeding in new fluid until the old one had stopped coming out (new fluid was clear bright red). Car currently has 133K miles.

Symptoms: I've noticed that over the last few months, the torque converter is taking longer to reach full lockup (or not locking up all the way). Way I can tell is that I have a regular stretch of road that I always set the cruise control at the same speed every time (60mph). The indicated RPM's seem to settle at about 100RPM higher than they used to (about the 2000RPM zone). If i slightly press the accelerator to gain 1-2MPH then let go, the RPM's will settle into the normal region while the car is coasting and stay there.

Today, accelerating out of a right hand turn in 1st gear (merging into traffic) at about 3/4 throttle (but not WOT), the transmission acted like it missed the 1-2 shift at first, bouncing hard against the 6500RPM limiter before doing the gear change.

Like I said, weird... any thoughts/ideas? Should I start thinking about transmission work? (If so, i'll get a junkyard trans and rebuild it in my spare time... and see about installing a higher stall torque converter while i'm at it.)

AJxtcman
05-31-09, 08:35 PM
Look for a leak by the left axle.

AJxtcman
05-31-09, 08:38 PM
This would be a sign of a bushing failure and the main internal lubrication circuit is restricted or just the one to the 3rd clutch housing I guess.

ejguillot
05-31-09, 10:05 PM
AJ,

Thanks for your input. No leaks at all, and this weekend the transmission behaved normally. Still weird... and does not inspire any confidence in the powertrain. I had to replace a leaking water pump 2 weeks ago. It's pretty bad when I have a loss of coolant and am relieved to find the leak source around the waterpump housing... meaning that my headgaskets haven't failed yet. (Since replacing the pump, no coolant leaks and normal temps.)

ejguillot
05-31-09, 10:07 PM
Given the symptoms, should I start budgeting for a transmission rebuild/upgrade in the next year or 2?

AJxtcman
06-01-09, 08:05 AM
AJ,

Thanks for your input. No leaks at all, and this weekend the transmission behaved normally. Still weird... and does not inspire any confidence in the powertrain. I had to replace a leaking water pump 2 weeks ago. It's pretty bad when I have a loss of coolant and am relieved to find the leak source around the waterpump housing... meaning that my headgaskets haven't failed yet. (Since replacing the pump, no coolant leaks and normal temps.)

The transmission electrical connector is just below the water pump. They get coolant into them and then the trans shifts funny

ejguillot
06-01-09, 08:53 AM
That explains a lot - i'm sure it got drenched by coolant when the pump was swapped. Thanks!

tateos
06-02-09, 06:23 PM
The transmission electrical connector is just below the water pump. They get coolant into them and then the trans shifts funny

Excellent insight AJ!