I have a '99 Pontiac Montana van (3.4L) automatic. I bought it with 25,000 miles on it, and presently has 84,000. It has regular service always. The transmission has started an intermittent “hard shift”, which subsides when you stop somewhere for a break and turn off the engine for a few minutes. Then it drives like new. Any ideas?
You might want to change the fluid if you not done so since 25k miles. The fluid should be red, if it’s brown change it, and the filter if applicable. Follow Pontiac’s prescribed method of changing the fluid, whether it be drain and fill or flush.
I changed the fluid twice since I have owned it. All required maintenance has been accomplished.
Does it shift hard through all gears? Does it do it when it’s cold and or when it’s warmed up? Has the CEL come on?
I’ve been out, but am back. Yes, it will “bump” when shifting no matter if cold or not, but not every time you start out. No check engine light has appeared. It seems to be random. Like I said, once you stop and turn off the engine while shopping or on a break, the van shifts normally after a re-start.
It occurs intermittantly whether cold or warmed up. No check engine lights.
Take it somewhere and have the computer scanned for codes. Most local auto parts stores will do it for free. When the computer picks up a problem, one of the first things it will do is to max out the transmissions line pressure to protect it. This will cause harsh shifting. Have the computer scanned and post back with the trouble codes if there are any. We’ll go from there.
Montana’s are famous for transmission failures. Transman’s advice is best. I fear your Monatana’s transmission is nearing the end.
My '99 Montana is doing this very same thing. Wonder if two years later anyone has come up with a conclusive explanation?