What's up with the acceleration!?

October 23, 2006 6:55 PM

What's going on with my girlfriend's car?

In the past two weeks, we've noticed that instead of changing gears when it used to (around 2000-2,500 RPM,) it's changing gears around 3000 to 4000 RPM. This only seems to happen so drastically when going from 2nd to 3rd gear, although we can't be sure as it's an automatic. It's very jerky up until about 45 MPH, when I assume it won't change gears for until you go much faster. Lastly, when it hits around the 45 MPH mark, it smooths up considerably.

And please God, let it not be something expensive, we're not in the position to pay even a couple hundred right now.

(I just changed the oil and the front brakes were replaced last July)

posted by InsanePenguin to travel & transportation (16 comments total)

Check the fluid in the transmission reservoir, first off. Sounds like it may be low.
posted by Dipsomaniac at 7:00 PM on October 23, 2006

I was going to fill it up this week, I was thinking that might be it. The fluid level on the dipstick wasn't very low, about halfway between Full and Low, but I figure I'll buy acouple quarts, throw one or two in, and see if that helps.
posted by InsanePenguin at 7:03 PM on October 23, 2006

What kind of car? How many miles? If money is tight, I would start by just getting the transmission fluid changed. That might fix it, it might not, but it's not a bad idea anyways. If the fluid is dirty, it could cause issues similar to this.
posted by ninjew at 7:04 PM on October 23, 2006

It's a 2001 Hyundai Accent GL, with around 95,000 miles on it. I'll do the fluid change first thing tomorrow, because I have no idea if it's ever been changed.

Although, I would assume they do that when they fix other stuff, but who knows with mechanics sometimes.
posted by InsanePenguin at 7:11 PM on October 23, 2006

Well, looking around seems to indicate that the transmission fluid should be changed every 42000 kilometres or so. You may be far past the recommended interval.

If a tranny fluid change hasn't ever been listed on any of your invoices, then it wasn't done.
posted by Dipsomaniac at 7:15 PM on October 23, 2006

Make sure you get the transmission filter changed as well. A clogged up trans filter will screw up yer trans quick. Avoid going to those quickie-national-we-change-all-kinds-of-fluids-kinda-places. Have an actual mechanic do it.
posted by Bighappyfunhouse at 7:16 PM on October 23, 2006

A thorough transmission flush may help. A friend was told that they had to replace their transmission at a very high cost. Took it to my favourite mechanic who flushed the transmission about four times before the fluid stopped coming out black. After this it ran like new.
posted by tomble at 8:08 PM on October 23, 2006

Just make DOUBLE sure they put fluid back in it.

One place I brought my car to 'forgot' to. Thats a bit detrimental to the car.
posted by SirStan at 8:22 PM on October 23, 2006

Premature torque converter lockup for the lower gears (if it has locks for the lower 2-3 gears) for the jerkiness; as for why it would decide to wait until high rpm to shift, have a mechanic hook that car up to OBD-II. The computer might have its reasons. I can't think of any good ones.

Just guessing, you need to see a transmission mechanic.
posted by attackthetaxi at 8:42 PM on October 23, 2006

InsanePenguin writes "The fluid level on the dipstick wasn't very low, about halfway between Full and Low, but I figure I'll buy acouple quarts, throw one or two in, and see if that helps."

Generally the difference between Low and Full on a transmission dipstick is only one pint. A full quart would be four times to much.
posted by Mitheral at 8:46 PM on October 23, 2006

This is based on similar experiences with my car ('95 Neon):

The "smoothing out" at 45mph is probably the torque converter locking. Basically, it's going from transmitting power via the transmission fluid to a direct mechanical connection. If it's jerky before locking up, then it sounds like something wrong with the fluid (which essentially runs the entire transmission except when it's locked up, as far as I know).

I had a similar shifting-at-high-RPM problem that I traced to a sticking throttle kickdown linkage. There is a connection between your gas pedal and the transmission so that the transmission knows how hard the pedal is being pushed. That lets it shift down (kickdown) when you want to accelerate and are pushing the gas pedal harder. Mine was stuck, so the transmission basically thought I was constantly flooring it, and wouldn't shift up until high RPM (and conversely would shift down far too soon). So that's something to check. I ended up just disconnecting mine and getting it re-stuck in a position where it thinks I'm always barely pressing the gas. Since that's how I drive, I'm fine unless I really need the most acceleration I can get at some point.

So you might have an issue with your kickdown cable/lever/whatever-you-have. If you can find your kickdown linkage, check it for sticking. On mine, there's a cable from the gas pedal to the throttle body controlling the butterfly valve in the throttle, then a cable from that to the transmission. It's free for you to check (if you can find it), and it can't hurt.

Otherwise I generally agree with the low/bad transmission fluid thoughts. My (uneducated, mind you) understanding of automatic transmissions is that the whole thing is controlled by a ridiculously complex hydraulic system, and the transmission fluid is essentially running a lot of the "logic" of the transmission in addition to whatever else it does.
posted by whatnotever at 9:05 PM on October 23, 2006

Do you have a "turbo/overdrive" button anywhere on your shifter or dashboard? And might it have accidentally been engaged? My parents' old Camry had an "Overdrive" button that caused it to assume a totally different (more aggressive) driving profile.
posted by misterbrandt at 9:51 PM on October 23, 2006

This could also be a problem with the engine. If it's not developing normal horsepower and torque, the symptom you describe could occur. A fouled injector, or a fouled plug could do just this, but you haven't given enough information.
posted by kc0dxh at 7:19 AM on October 24, 2006

your transmission should still be covered under warranty, if the car was purchased new. you got 5000 miles left.
posted by lester's sock puppet at 7:51 AM on October 24, 2006

You are checking the fluid level with the engine running, yes? After starting the car, shift to Drive and Reverse briefly, then put it in Park and check the fluid level.
posted by Kirth Gerson at 7:58 AM on October 24, 2006

IMPORTANT: If you add fluid or have the fluid replaced, USE SP-III FLUID. This is not available at many auto parts stores such as Pep Boys or AutoZone, but may be purchased from Hyundai, Kia and Mitsubishi dealers.

Failure to use only SP-III will almost assuredly result in the demise of the transmission.

And 95,000 miles is way too long to wait.

People who are much, MUCH smarter than I in the ways of Hyundais are available at ElantraClub.com, a forum I belong to. I would greatly recommend you sign up and ask for advice there. Although that forum is focused on the Elantra, there is a lot of knowledge of other Hyundai models on that board from Hyundai technicians that are members there.
posted by Doohickie at 8:28 AM on October 24, 2006