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Over-Drive Concern

brandonl2000

brandonl2000

New member
I just got my Grand Prix GT running on Labor Day and been driving it as a DD. There is absolutely NO slipping of any kind and it shifts beautifully (has 155K, assuming stock tranny). My only hang up is that when on the streets, it doesn't want to slip into overdrive. The RPMs will fluctuate SLIGHTLY and you can tell it's attempting to shift to overdrive, but it's not very noticeable. I had to really be watching and paying attention to even notice it. Typically, going about 40mph the RPMs are around 2K or a little over (assuming it's in 4th gear). However, when it DOES go into overdrive, which I can get it to do if I speed up and kinda let off the gas a little, the RPMs are like 1.5-1.7K just estimating.

On a side note, when on the interstate, I don't see any problems with it going into overdrive-maybe that helps identify the culprit. The RPMs on the interstate (assuming overdrive IS in) going about 70mph are appx. 2.25K RPM. That seems about normal to me in overdrive.

My question is: Is this common and is there an easy electronic fix or is it fluid change?

My plans so far are to drop the pan and drain the fluid, change the filter, and put new fluid back in it along with some type of Lucas tranny treatment.

My dad has 2 gallons of dexron III and said he wanted to put that in it. Since I'm on here, I recommended dexron VI to him. But we agreed that since I just paid $164 for tags and $109 to fix the a/c that we should just use what we have (Dexron III) and upgrade fluid later.
Will doing this most likely fix the problem?
Is Dexron III fine for now? I know GM recommends it but that was also 11 years ago. I will do dexron VI later..

Thanks guys, I appreciate all your help and all advice is appreciated; just want to make sure I'm headed in the right direction here. :th_winking:
 


I use amsoil in my trans the gm dex one. 4th gear only happens at a certain speed, throttle position, temp etc...

a common problem with 97-02 cars are the 4th and there isn't anything you can do unless you have a tuner and make changes to 4th gear. Do you have a tuner? A good way to tell if there is in fact something wrong would be, pull the bin file on the car, and look and see what parameters 4th sets into, usually at 45 mph and with throttle position of 40% or less, scan and see what the car is actually doing. Most likely the 4th clutch is stripping itself, it happens to the best of us. Gm fixed the problem with heat treated 4th clutch in the 03 cars.
 
while driving in the city with speeds under 50 mph, have the car in 3rd, that way it will never have a chance to think about going into 4th gear.

That is what I do, then when you hit the freeway just wait till you at your speed and move the shifter up and bam 4th gear, crusing time.
 
99prixgt said:
I use amsoil in my trans the gm dex one. 4th gear only happens at a certain speed, throttle position, temp etc...

a common problem with 97-02 cars are the 4th and there isn't anything you can do unless you have a tuner and make changes to 4th gear. Do you have a tuner? A good way to tell if there is in fact something wrong would be, pull the bin file on the car, and look and see what parameters 4th sets into, usually at 45 mph and with throttle position of 40% or less, scan and see what the car is actually doing. Most likely the 4th clutch is stripping itself, it happens to the best of us. Gm fixed the problem with heat treated 4th clutch in the 03 cars.
Click to expand...

yea, i've heard of that 4th gear problem. :( i hope it's not messing up i really do love this car and have no money for tranny replacements/fixes.
i do not have a tuner so i can't really do much about it. i did planned on getting a tune pcm. would that help out?

but for starters, definitely gonna do a pan drop and add something extra to help out.
 


and idk if anyone knows, but does it have an exact speed in which it goes into overdrive? maybe i'm just expecting it too early idk.
maybe typical RPMS..?
 
brandonl2000 said:
yea, i've heard of that 4th gear problem. :( i hope it's not messing up i really do love this car and have no money for tranny replacements/fixes.
i do not have a tuner so i can't really do much about it. i did planned on getting a tune pcm. would that help out?

but for starters, definitely gonna do a pan drop and add something extra to help out.
Click to expand...

pan drop and filter change wouldn't hurt. A tuned pcm would help if there is adjustments made to 4th gear and some other parameters,...like making changes to your tcc table and commanding to downshift into 3rd from 4th at around 30% throttle, since 4th gear is weak and you shouldn't stress it, and commanding to from 3rd to 4th at 30% throttle so this way your not stressing going into 4th, also, i don't know how fast you drive but, don't ever be WOT going into 4th, the car will shift into 4th at around 135-140 (somewhere in that range), I made adjustments to have my car shift at 49 mph, this way its not going into 4th driving around town. Id look into getting a trans cooler as well, helped me out. I got the desert fox kit that 3800 performance has, no leaks, awesome quality :th_thumbsup-wink:

brandonl2000 said:
and idk if anyone knows, but does it have an exact speed in which it goes into overdrive? maybe i'm just expecting it too early idk.
maybe typical RPMS..?
Click to expand...

around 45mph, if your pcm has factory settings, it will be 45. Automatics don't really shift by rpm range, the car shifts by rpm, mph and throttle position. normal driving it will shift by mph and throttle position, on the other hand going WOT the car will shift by rpm and mph.

when your 4th gear is completely shot, you will know it. Al ot of guys do the 03 trans and 03 pcm swap. I looked into doing the swap but instead i just bought a built trans from our local vendor Dave (TEP).
 
tps and shift speed
0 6 12 19 25 31 37 44 50 56 62 69 75 81 87 94 100
45 45 46 52 62 76 88 102 112.......................etc.
 
okay. 45 mph then. in that case, i believe over drive is shifting fine then. seems the tranny is doing okay.
over 99% of the time i will not be going WOT, theres no sense in it. i dont drive crazy i drive average i guess. little more than babying, a little less than aggressive, but i most definitely take care of my vehicles.

is it a good chance my tranny may hold up and do fine as is??
the car will never be raced, it is going to be a reliable daily driver.
 
I know this is old, but I'm pretty sure your car is going into overdrive. Your TCC just isn't locking up right away. Overdrive and 4th are the same thing. My car is around 2500 going 55 or so in 3rd, about 2200 going 55 in 4th (overdrive) before the TCC kicks in, and 1700 once it kicks in. If you're still having trouble, I recommend seeing if a transmission shop will check for codes on your TCC.
 


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