Do you need a CPU reflash with gears?

[jerrysta]

I got 3.73 gears installed a couple of weeks ago and was travelling on the highway this week and when I hit around 105 the car started shaking. I realized it was the speed limiter cutting in as I was accelarating. Are the gears tricking my CPU? I have had the shut off kick in before but it was at like 135.

If I need a reflash, are the mail order ones any good?

[94 formula]

Yes, your gears are tricking your car into thinking its going faster than it actually is which not only gives you a false mph but puts miles on your car which are not actually being put on it. A mail order tune would be fine for that or a hypertech should be able to fix it. I'd personally go with the mail order because it is cheaper and you can also get them to do the performance tune to pick up a decent amount more horsepower.

[ExtinctBird]

You do need programming after changing gears. I happily use pcmforless.com with unlimited email updates. Others seem to be equally happy with madz28.

I'm not sure if there is a speed limiter in a TA, unless the car came with a 115MPH speedometer and non-Z rated tires.

[Injuneer]

What gears did your car come with? If it had the 3.23's from the factory, your speedometer is showing 15.5% higher than actual speed. When it indicated 105mph, you were actually going 90mph. Every time you drive 1,000 miles, your odometer shows 1,155 miles. Your computer is also thrown off with regard to shift points.

If your car started with 2.73's from the factory, it gets even worse... a 36.6% error.

When you go to 3.73's or 4.10's it is not unusual to get into vibration problems with the steel driveshaft, due to the fact that it is rotating faster at lower MPH. There is even a factory service bulletin, because the problem was so widespread. None of the V8 cars came with the speed limiter set as low as 105mph. I believe by the later years (with the non Z-rated tires) it was set at 114-118 MPH. There was never a speed limiter set at 138mph either. With the Z-rated tires, it was set at 255mph.... not likely it would kick in....

[jerrysta]

Thanks once again for the advice. I never knew the specifics of when the limiter kicks in, that's just what I thought it was doing. Here's why:


I accelarate to 105 (speedo number)....car kind of shakes as it drops to about 100 however I am still on the gas....accelarates back to 105... repeats the same issue......

It seems that the shaking is a result of the speed lurching back and forth that's why I thought it was the speed limiter.

[jerrysta]

Guys,

I am still having the same issue with the car. It seems just at the point that the car would be going into 4th it shakes as it seemingly cuts the gas off. Has anyone had this happen. I just want to be sure that I don't have a fourth gear issue.

BTW, the car came stock with 2.73 gears, so the speedo is way off.

[Rob B (shoebox)]

Guys,

I am still having the same issue with the car. It seems just at the point that the car would be going into 4th it shakes as it seemingly cuts the gas off. Has anyone had this happen. I just want to be sure that I don't have a fourth gear issue.

BTW, the car came stock with 2.73 gears, so the speedo is way off.

Did you get a tune? If speedo is way off, maybe I guess not. You need to get that taken care of before you do anything else. You might not even have a problem to solve after that.

[jerrysta]

I ordered the tune from MADZ28 today. Thanks for recommending him.

One thing that it seems that I did not make clear about the shaking is that the car will NOT accelarate past that point. When it hits about 105 on the speedo it's done.

Thanks as always guys.

[z28_xxx]

steel rules! order a spohn steel driveshaft!!

What gears did your car come with? If it had the 3.23's from the factory, your speedometer is showing 15.5% higher than actual speed. When it indicated 105mph, you were actually going 90mph. Every time you drive 1,000 miles, your odometer shows 1,155 miles. Your computer is also thrown off with regard to shift points.

If your car started with 2.73's from the factory, it gets even worse... a 36.6% error.

When you go to 3.73's or 4.10's it is not unusual to get into vibration problems with the steel driveshaft, due to the fact that it is rotating faster at lower MPH. There is even a factory service bulletin, because the problem was so widespread. None of the V8 cars came with the speed limiter set as low as 105mph. I believe by the later years (with the non Z-rated tires) it was set at 114-118 MPH. There was never a speed limiter set at 138mph either. With the Z-rated tires, it was set at 255mph.... not likely it would kick in....

[Injuneer]

One thing that it seems that I did not make clear about the shaking is that the car will NOT accelarate past that point. When it hits about 105 on the speedo it's done.

What does it do when your speedo hits 105mph (actual speed 77mph)? Cut off with a "bang"..... simply start to misfire and buck.... continure to run but lose power????? What gear does this happen in, and what RPM is the tach indicating?

[jerrysta]

Fred,

Here is what happens:

"Bucks" would be a perfect description for what the car is doing. When the speedo hits 105 ( not sure of actual speed ) it feels like the car bucks and will not let me accelarate past 105.

I'm not sure of the exact RPM but it is right before a gear change, so it is high in the rev band. You can hear this....and right when you expect a gear change the car starts bucking. The trans works great at all other times. Shifts are still very firm when in performance mode too.

So I would say misfire and buck is what it does.....it does it at a fairly high RPM.....I believe in 3rd gear......will not accelarate past that point......and judging by other cars near me I would say that 77 is prob the right speed.

[Injuneer]

And what is the RPM? Sounds like you are getting another natural consequence of failing to reprogram the correct gear ratio. With an automatic tranny, it screws up the shift points. But at 77mph in 3rd gear, you would only be turning about 3,800rpm. Why would you be expecting it to shift?

Something doesn't make sense with all of this... hard to understand how you didn't notice the speedometer was reading 36% above the actual speed, that you didn't know you have to reprogram for the gear ratio. Are you sure you started with 2.73's?

[jerrysta]

I did notice that the speedo was off. It's been off by a couple MPH since I put in a new gauge cluster. When putting the needles back in I messed up and it is about 5 mph off. When I asked if I needed it done it was more a question about the speed limiter and not so much the sppedo being correct. I was well aware that it was off.....I guess in a way I got used to it. I had just been driving with flow of traffic the past few months.

As far as the RPM's I guess I was just going by the sound of the engine more or less. When the car starts to buck it's really intrusive. I guess I never looked down to check the rpm's. It may not be about to shift....with the new gears the car is turning higher rpm's than what I'm used to from before.

I am positive that I had 2.73's. Checked via the code on the door and also because I had to go through the trouble of ordering the 2 series carrier gear. So, yes, positive.....they were 2.73's.

[Hobbs95]

btw wehat is the formula to get mph its like 336 x trans ratio x rear end ratio/ rpm right correct me if i am wrong