Car jars when shifting if RPM not high enough
 

Hello everyone. My car currently has a strange shifting problem in which, depending on the RPM when shifting gears, it will either jar violently or shift easily. If the RPM is below a certain amount, it will not shift, and will jar until I release my foot from the gas and press it back on the gas to raise the RPM, which allows it to shift.

I drive a 1999 Chevy Monte Carlo coupe. It is front wheel drive, if that helps. I've checked the transmission fluid a couple times and it's clean and at the level it needs. In march I had the head gasket replaced after a long and annoying period of overheating problems, so it's possible that this might be more aftermath of the broken gasket. I will go into more detail of the problem below.

While in drive, keeping my foot on the gas, the RPM will lower to around 1500. When I try to go faster than around 30 mph, it will only shift if the RPM is above around 1900, so I have to take my foot off the gas and put it on again to raise the RPM in order to shift and go faster. When shifting, I can feel sort of a bump (completely normal, like with any other car), however if the RPM isn't high enough the jarring starts, which feels like the shifting bump happening again and again and again until I take my foot off the gas. Strangely, on days when the air is very humid outside, this doesn't seem to happen very often, and it will sometimes shift easily even when the RPM isn't where it usually needs to be to avoid the jarring.

I know very little about fixing cars and I brought it to my mechanic but he couldn't find what was wrong. I plan on taking it to a specialist but I don't know if this is specifically a transmission problem or something else. If someone knows what is going on, please help me out. If you need more information, just let me know.

What happens when you manually run the gears?

Does disconnecting your battery and waiting a few minutes to reconnect it produce different results in your "tests" ?

So you are saying it stays in 1st gear and never shifts until you run it up over 1900 rpm?

Thanks for the reply sledge.impy.

I played around manually shifting the gears after work, the jarring didn't happen, but I understand very little about how manual shifting works so I don't know if I was putting it through the same conditions as when it's in automatic.

The battery had been changed and disconnected a couple months ago, the problem was happening before and after so I don't think it has to do with the battery.

Yes, it stays in first until I reach 1900 RPM. When I accelerate to the speed limit at first this is not a problem, but if I'm already moving around 30ish mph in first gear and try to go to 40 mph, the gear tries to shift and will only work if it's around 1900 RPM. I know I'm repeating myself a bit but it's hard to explain.

Disconnecting the battery would clear what the computer may have recently learned. A friend had an acura that would act up shifting and he would have to disconnect the battery to temporarily fix it.

Well, manually shifting helped some obviously.

I assume you have a 1-2-3-4-OD? or is it some other combination? 1-2-3-D-OD ?

Does it still happen in 4/D ?

There is probably something happening internally in the transmission. You didn't mention the mileage.