May have lost 4th gear...still drivable on highway?

[marketsons1985]

Evening All,

I don't have a huge knowledge base on cars, so I thought I'd come to the garage to ask for some help.

I drive a 1998 Pontiac Grand Prix SE with 133k miles on it. Today as I was driving down from Northern Michigan (Petoskey) I noticed my RPMs much higher on the freeway than usual, and much lower when the gas pedal released (~1k RPM even at 65+ mph).

I count the shifts from a dead stop and hear the shifts from 1-->2, 2-->3 but I'm not hearing it shift from 3-->4 at around 45-50 mph. In reading the manual, Pontiac mentions an overdrive sensor (I have automatic overdrive) but in reading online I've also seen mention a clutch for 4th gear having some splines on the end going bad. I'm obviously hoping it's the former and not the latter!

I haven't done a transmission fluid check as it was dark by the time I pulled in, but will check that first thing in the morning.

I'm not sure I'll be able to get it in until Friday, and in reading, it seems that 3rd gear is a 1:1 ratio. My RPMs don't go higher than 3300 on the freeway. Am I going to completely wreck my transmission by driving in 3rd on the freeway? I'm looking to have this car last me for at least a few more months until I'm done with grad school, so I'm hoping I can keep driving this car.

 

[iamwiz82]

Theoretically you are fine, but if it was something like a clutch pack then the debris is going to find it's way all over the transmission and will probably kill something else. If it's just a sensor then you don't have much to worry about. I would get it diagnosed, at least.

A fellow Rochester Hillian, woohoo!

 

[MotF Bane]

On the left side of your shifter, you may or may not have a small button. If it is there, try pressing it, you may have previously enabled performance shifting, which involves higher RPM's. As an additional note to this, if performance shifting is enabled, you should see "perf shift" on the left side of the instrument cluster. Also, 45-50 MPH isn't where mine tends to shift, mine goes third to fourth at 55 MPH in non-performance shifting mode, and 60-65 MPH in performance shifting mode - try going faster to check for missing shifts unless your revs are dangerously high already.

 

[bruceb]

As a Pontiac owner (1999 Grand Prix) I had the same issue. The first runs of that trans axle had weak 4th gear clutch hubs and the splines break off. When that happens, no 4th gear. The rebuilds have a 4th gear shaft / hub that are hardened. Time to rebuild or replace the tranny.

http://www.clubgp.com/newforum...69&p=4&tmode=1&smode=1

 

[marketsons1985]

Wiz - I am indeed another rochester hillian, though only on the holidays and occasional weekends (At university in Grand Rapids).

The revs have not been dangerously high at all, but even up above 70 MPH it's still not feeling like it's in 4th gear. I don't have a performance shifting mode, my O/D kicks in automatically.

Bruce, thanks for the info, that's exactly what I'm afraid of (In what i've seen it appears to be the most common problem).

I'm not sure if I'll go through the cost/trouble of getting the tranny replaced or rebuilt as sometime later this year I'm gonna get a new car (sad time for me as this was my first car) and as long as this isn't a safety hazard for me or any other drivers, I might just deal with the higher RPMs and lower gas efficiency until I get a new car.

Thanks everyone!

 

[funboy6942]

Did you turn the OD off by chance? Is there a yellow light saying something about OD off, or the letters OD anything. Hitting off the od button by misstake will do this, caught my wife with this one one day getting in her car, her excuse was she didnt know what it meant so she had been ignoring it 😛

 

[marketsons1985]

funboy - unfortunately as I mentioned above, I don't have a button, it's an automatic OD that doesn't let me turn it off. It kicks in when I push the gas pedal down. No lights, not even check engine.