My car hasn't been shifting correctly. It takes to long to shift into 2nd gear and hits the rev limiter before shifting, but only under wide open throttle. I have been to aamco and to the dealer. The fluids are fine. Aamco says it is not a tranny problem. The dealer wasn't sure, and thought maybe when I changed the gears from 2.59 to 3.33 that this may have screwed up the computer. They recommended a custom chip taking into account the new gear ratio. I already have a high perf. computer chip, but it doesn't account for the new gears. I was thinking that if it was the computer it would happen every time, but when the car is cold it usually shifts OK. Also, it has gone for a month with no problems shifting, and then just recently started happening again. I didn't own the car before the gears were installed, so I don't know whether it was happening before. Any Ideas? What about adjust the transmission cable. Whats it called the detent cable or something? :confused:

 

Yep, custom chip should do it (If the tranny is a 4L60E, not sure about the '92).

What's happening is that the 3.33 causes the car to accelerate faster than what the pcm believes the vehicle it doing. It's therefore waiting to shift causing you to hit the rev limiter.

Your speedo is probably off too.

It's probably shifing wrong at part throttle, it's just not very noticeable.

 

Thanks a bunch! Just wanted confirmation before spending any more cash! Hopefully an Ed Wright chip will have me back at the track! :yesnod:

 

I'm not so sure about this. I have heard that problems can occur with gear swaps (before correcting with correct speedo gears and sensor) but I didn't notice any difference/problems. I just went from 2.59's to 3.75's and drove for almost two weeks before I could install the new speedo gears and speed sensor. The "only" difference I saw was that under WOT (at high speeds) when the car shifts into OD, it would occur a bit early, I have to manually hold the gear and shift myself.

Please notice that these are just my observations. You can contact 18Carfan (Jeff Kopp) here on the forum and he'll be able to set you up with the correct parts (pretty cheaply too) to correct your speedo. I hope this helps.:flag

Eric

 

I swaped out my 2.59's for 3.54. Changed speedo gear & sending unit. No problems at all ! ! ! :yesnod: :yesnod: :yesnod: :yesnod:

 

The only thing a chip will effect on a 92 or a 93 is torque converter lock up. Your shifts are controlled by the govoner and the TV cable.

 

YEP! I agree with that.

 

My Speedometer is way off, so I am guessing that the sending unit was never changed as well. What is a sending unit?

 

If that is the case, now what? I paid for two diagnostics so far and neither place knew what the problem was. So if it isn't the computer chip, I guess the TV Cable needs adjusted? :confused: :confused: :confused: :U

 

Don, when you changed from 2:59(or 2:73) to the new ratio, you should have changed the little gears in the tranny and the VSS, to get the speedometer to read correctly. As someone stated above, give Jeff Kopp a call and he'll set you up with the correct parts. :cheers:

 

That's what I wasn't sure of. I wasn't sure when the electronicly controlled transmission was made available.

 

Nobody has been able to answer this question accurately. First off the wrong speedo gears aren't going to cause the problem or fix it.
I have the same problem, I just went from 2.59 to 3.45 gears.

Since your '92 and my '93 are speed density cars, a simple gear change can affect it.

Here's a quote from Charles Probst in his last book "Corvette Fuel Injection"

Everyone I ask can't help me with this, they all tell me to change the speedo gears(which I did at the time of the switch), but that isn't going to help my situation since it's a computer problem not a speedometer problem.

 

dscottr,
I changed from 2.59 to 3.54 in a 92 just like you. this is in the dana 36. along with the gears you need 3 parts for the transmission side. these are the correct combination for 3.54 gears in a 700R4 auto trans 92 Vette.

25513050 - 43 Tooth speedo gear
8642620 - 15 Tooth drive gear
10456089 - Speed Sensor (3-series)

as others mentioned get a hold of Jeff he is the one i got these from. at first the guys who did mine did not change the Speed Sensor (VSS). bad idea. the VSS in a car that came with 2.59 gears is a 2-series. you now need a 3-series. that will throw your speedo off. and if you are unlucky like i was it will also break. and you'll know if it does because the computer will get very upset... if you had the G92 option, 3.07 gears, then there is no need to change the VSS because you have the right one.

as for the chip. nope. i ran the factory chip and my speeds read correct with the above parts. and the car shifts very nice. jumpy from 1st to 2nd but easy from 2-3-4. the chip makers will tell you that on the 700R4 they do not control your shift points. it is not computer controlled. the 4L60E(sp?) auto is computer controlled and your shift points can be programmed. i have since converted to an Ed Wright Fastchip and it makes no difference in shift points at all.

mrmojo,
i'm wondering, if you went to the dana 44 with an auto trans, then you replaced the whole carrier from a dana 36. the ring gear is bigger in the dana 44. would it be possible that the same 2 speedo gears that i used for my setup will not work correctly for yours? just a thought...

i made an Excel spreadsheet with 2.59, 3.54, 3.75 gears for my auto in both D and OD using the standard gear calculation. then watched my tach in D (3rd) and OD (4th) and my speeds and rpms are correct.

graham

 

Graham, I used the same part #'s you listed.

 

That is weird. I reread that article you pasted into your response. From that description on MAP vehicles then you would expect the computer to be all screwed with the various mods people make. I've gone to cold air with k&ns, cut shroud, stock and aftermarket chip, muffler changes. Those may have affected the way the computer adjust fuel/air mixture. That would make sense. But how it gets your speedometer to read wrong makes no sense to me at all. You figure with all the changes we've all made in our cars they would all be screwed up and not read correctly. I still think something is wrong with your VSS or the signal the computer is getting.
Good luck. If you ever figure it please post the answer.
Graham

 

My Speedo reads fine, and actually today, I didn't have any problems at all at the track. I still think heat has a lot to do with my problem also. I am running a tranny cooler.