Yea, I don't think 4th gear/od at 28 is a normal shift either. My Lumina shifts to 4th at about 38. There's a AC Delco certified shop right across from the trans shop I went to and a Chevy dealer right across the street from where I work. I'll have one or both of them check into it. Maybe it's the PCM or something else forcing the shift? I don't know. If I get an answer I'll post it.

 

I visited the dealer yesterday and they said that it's the PCM that controls the shift points. I asked about reflashing the PCM, but they didn't seem to think that would accomplish anything. Told them I'm hesitant to pay an $85.00 dx fee for them to state everythings ok, so the serv mgr said try resetting the PCM and see if that changes anything. Instructions were to disconnect the battery cables, clamp them together for a while, (memory will be lost) hook cables back up and go. Also heard you could disconnect the positive cable only and ground it to engine/alt/etc to disipate residual power with the same effect. I'll give it a try this weekend. Anyone ever use this technique with any success? The trans is "adaptive" and the PCM can make adjustments to compensate for wear of clutches, springs, seals, bands etc, so resetting the PCM restores the settings to base level.

 

Yes, i've done this, and it will reset your PCM, but you need to wait a while before all memory will be lost. How long exactly, IDK. I waited a good hour. But I THINK it only takes like half and hour.

In any event, it is worth a try.

 

Well, trying to reset or clear the PCM did not alter my shift points. Neither the dealer nor the trans shop see any issue with this car pulling fourth gear from 28 mph. I think my next step, if not too expensive - is to pull a PCM from a similar car - junkyard and see what happens. There's also a ebay seller that has this PCM for $65 including vin specific reprogramming. (spareecm is the seller)

 

Update (lengthy) - I was about to pull my pcm and ship it off to NY to a "pcm tuner". No one locally would touch it - 3.8 liter montes are apparently not good enough for the local "tuner" folks. Screw 'em. Plan was to have the shift points reprogrammed. Almost everyone I talked to (except MAMONTE !) - dealer, transmiss shop, other owners of this model, would tell me that a 3-4 shift at 28 mph was normal. I was told that this was a factory setting, it was used to increase MPG, etc. As a last ditch effort to dx this issue, I pulled out the factory (GM) service manual. Wouldn't you know the diagnostic section included the topic of "high or low upshift or downshift speed", and they were kind enough to include the specified shift speeds at various throttle positions. Minimum upshift speeds for my 3.8/4T65E at 12% throttle are approx 16, 25, and 48 mph (+/- 3 to 5 mph depending on which shift it is). Per the manual, there are only two things that could cause an "outside of the calibrated range" shift - misadjusted/faulty TPS or an incorrect calibration in the PCM. So, I was right, going into 4th gear at 28 mph is NOT normal. Now with my factory specs in hand, I guess I'll stop by the dealer and see if I can convince them as well. To be continued .......

 

Yea, I knew 28 MPH was WAY to low. I think 35 MPH is the absolute MINIMUM most trannies will go into OD, and even 35 MPH is low. 40-50 MPH is normal for OD, all depends on the specific transmission. But your 48 MPH sounds pretty normal.

Keep us updated!

 

I'm reopening this post about shift points because I have more info. I thought my 99 Monte's 4T65E was shifting into 4th at under 30 MPH. The tranny shop I deal with let me hold and view their scan tool while they drove. Turns out that what I thought was a 4th gear shift was actually the torque converter locking up in third at 27 mph. The tranny shifts into 3rd at 23 MPH then the TC applies at 28 MPH. The service manual does state that the TC will apply at about 30 MPH in third, but should I feel it? Should it apply so strongly that I mistake it for a shift? 4th gear then comes in at about 45 MPH. I've read that the TC on this tranny is designed to "allow slippage" so that the application of the TC is almost imperceptible. Thoughts, anyone?

 

I can feel mine engage.

 

Matt, so you can feel the TC lockup in 3rd gear? Does it sound/feel like the other shifts? Because my 3rd gear TC lockup feels just like a shift. Do you also get the 3rd gear lockup at about 30 mph under light acceleration? I took this car to the Chevy dealer last week, told them what I was feeling, and they recommended replacing the transmission (it has only 4,000 miles since the rebuild at the shop that just explained to me that the TC lockup is normal). Yes, the dealer wanted to install a new tranny for $3,500. They said that they don't rebuild them or repair them, they just replace them. Oh, and when I told the dealer that the tranny was a rebuilt unit w/ only 4,000 miles on it, they said "we wouldn't have known that, the tech drove it and scanned the computer, he wouldn't have looked at the transmission itself". The chevy dealer justified the need for a new tranny by telling me that it "shifted hard".

 

Sounds like the dealer was looking to get your money. I never take vehicles to the dealer unless its under warranty.

I can feel mine, it feels like a shift. It doesnt hit or clunk or anything, you can just feel it engage. Im not sure exactly when it engages but its between 3rd and 4th under light acceleration so 30 sounds about right maybe alittle higher for me because of the different gearing used for the LQ1.