97 Park Ave Ultra - shf

I have a supercharged 97 Park Ave Ultra with 190,000 that has a shift problem when it is driven 1-1 1/2 hours. It starts to shift hard into overdrive first and then begins in all gears. I can always tell when it will happen because the supercharger will kick in 100% of the time. Also, occassionally (only with the hard shift points) the transmission will start to chatter when it is kick down into passing gear. The only way to make the problem go away is to shut the car down for 1-10 minutes, start it back up and the problem is gone. It may or may not start up again in a couple of hours. The car runs perfect and the tranny fluid was flushed and filter was changed at 160,000 miles. This has been happening for the last 30,000 miles or so. I have been told it may be a electrical or solenoid problem cause by heat. How do I fix this, what is the cost.

I've read post's from over at www.bobistheoilguy.com and www.auto-rx.com about using auto-rx in your transmission to help clean up the gunk.
From what I read in your post the fluid has only been changed once in 190K.
Try some auto-rx.

I've used it in my crankcase in 3 of my vehicles and have seen great improvements in all 3.

Big mistake getting it flushed with 160K miles. :shakehead

It may be rebuild time. However, it is best to get it scanned with a trans capable scanner to see if any tranny related DTC(s) are stored which may lead you to a solenoid or valve body related issue. Many do not give a SES/CEL light.

Additives are only a band-aid fix and may not work at all.

I bought the car with 161,000 and drove it only short trips to work with no problems. Only after month and a couple of longer trips did I notice the hard shift. The car was serviced on a regular basis and tranny was flushed once around 100,000. The past year the car was driven 30-200 mile trips with hard shift problems only 3 to 4 times. This mainly happens in the summer time when the weather is warmer. (I live in Northern MN) I am currently traveling for my job and drive the car 400 miles to the job site and 60 miles back and fourth to the hotel. The only time I have problems is on the trip out, it may act up once or not at all.

After I flushed the system at 160,000 the problem has been better but still there. I normally have to drive it 100-200 miles before it starts. I was thinking about flushing the system again and using Amsoil which I know has cured shift problems in high mile tranny's for a couple of buddies. If it is soleniods are they easy to change/ cost? I had the car scanned and no codes show up. This problem is more of an anoyance then anything, I just like to figure out what it is.

Does the scanner read GM extended DTCs like P1XXX/P1811 which is a PCS - pressure control solenoid problem which causes harsh upshifting. When the harsh shifting occurs what does it do when you manually downshift?

We have an illustration of the 4T65E autotransaxle that shows solenoid location which is under the side cover assembly and on the valve body. See link below located at Buick Tips & Maintenance. To replace you have to drop the engine and tranny intact on the subframe and tilt. But other items have to be removed first such as hub and axle shaft, etc. Not exactly a DIY job but it can and has been done DIY.

http://www.automotiveforums.com/vbulletin/showthread.php?t=760735

I tried the manual down shift last night, it harsh down shifting too.

From all indications although you may not be getting any DTCs it sure sounds like a line pressure problem specifically the Pressure Control Solenoid - PCS.

I had the car scanned and no codes show up. From all indications although you may not be getting any DTCs it sure sounds like a line pressure problem specifically the Pressure Control Solenoid - PCS.
I agree, but don’t forget about the vacuum modulator, it controls line pressure, and in turn, shift firmness! If you do not have a hand vacuum pump, find someone who does and see if the modulator will hold vacuum. If you have a major diaphragm leak, you may be able to see trans fluid in the vacuum hose connected to the modulator. A new modulator runs in the range of 15-65 bucks, depending on the brand.

I agree, but don’t forget about the vacuum modulator, it controls line pressure, and in turn, shift firmness! If you do not have a hand vacuum pump, find someone who does and see if the modulator will hold vacuum. If you have a major diaphragm leak, you may be able to see trans fluid in the vacuum hose connected to the modulator. A new modulator runs in the range of 15-65 bucks, depending on the brand.

:confused:

You got me confused Bo. Not a bad suggestion assuming he has a 4T60E autotransaxle. Last time I checked the '97 PA Ultra was delivered with the 4T65E-HD GM RPO code MN7 autotransaxle, therefore there is no vacuum modulator. The PCS via the PCM module controls all line pressure electronically.

Thanks Bob, sorry I missed the year! Long day at work viewing the PC for 10 hrs and my eyes are blurry! :uhoh: Maybe you can help me find my Visine too! I hate getting old! :frown:

Hey guys just wanted to thank you for the help! Whats a ball park price to get this fix labor, parts? Cost of rebuild/new tranny? Just trying to decide if I should have the tranny rebuilt (because of high miles)or just try replacing the PCS. Are there any other solenoids, modules that are recommended to be replaced as long as the tranny is out. I don't want to spent a whole lot of money because is a secondary/work car.

Based on your mileage a rebuild may be in order. :dunno: But just for a PCS, of course cost will vary, around $600 for part (PCS) and labor at for example AAMCO/Cottman's. A thorough rebuild could cost in a range of $2000-$3000 dollars. Other alternative would be to get a serviceable used or reman. Reman cost as low as around $700-$800 with core exchange and with labor to install around $500. I had success with just a PCS replacement done DIY and waived the rebuild. Good luck and let us know how it turns out.