Tranny/gears problem?

[LETZRIDE]

Ok...so as some of you may remember a few months back I swapped in 3.90 gears into my car...I think I may have a problem in third gear but I am not sure.

If I go to one of the gear calculation sites and input the info on my car...96 camaro A4, 3.90 gears, 245 50R16 tires
I come up with 1st gear shifting at
1st: 59 km/h
2nd: 115 km/h
3rd: 179.2 km/h
4th: 250-260 km/h or somewhere around there...

When I am at the track, I am redlining third and shifting at about 150-155km/h

what could cause this?

Also, the gear calculator puts my rpms on the highway 120 km/h at around 2500....in reality I am actually going around 3100rpm

I know these calculators are just estimates, however the original 3.08 gear calculations were correct, and the calculations on the 3.90's are correct for gears 1-2, which leads me to believe I must have some sort of problem...especially because the third gear is seemingly short....

[Skinny]

Re: Tranny/gears problem?

Gear calculators work great for manual trannies, but not for automatics. There's no way to account for torque converter slippage because it would depend on what kind of converter you have. If your TC is locked in 3rd (which it shouldn't be at WOT) then it might be close but still probably a little off.

Also, is this a 10bolt? If so, where'd you get 3.90 gears for it?

[LETZRIDE]

Re: Tranny/gears problem?

yea its a 10 bolt...I think they started making the 3.90's for us a year or so ago, IRC I believe I got them off of the summit racing site....I have a stock TC
I understand it should be a little off...but 3rd gear is shorter then my 1st gear lol....

how would I know if my TC is slipping, or how would I be able to check?

[Skinny]

Re: Tranny/gears problem?

how would I know if my TC is slipping, or how would I be able to check?

The torque converter SHOULD be slipping. That's how it works. ;) Maybe "slipping" isn't a good word for it, but that's basically the action.
The gear calculators account for direct movement only. For a manual transmission, the clutch engages the flywheel and turns the input shaft, which when mated with whichever particular gear provides X.XX ratio to turn the output shaft, which turns the driveshaft that rotates the pinion gear to turn the ring gear at X.XX ratio. The ring gear directly rotates the carrier to turn the axles which move the wheels, that are XX.XX diameter, etc etc etc.

With an automatic transmission, it's all about fluid dynamics in the torque converter. The input shaft and output shaft of the transmission itself should rotate in direct ratios with each other, but the problem that the calculator cannot account for is the fact that the input shaft of the transmission is NOT directly rotated by the engine. Depending on the efficiency of any given torque converter at any given engine RPM, the difference in rotation will vary by a percentage.

With all that being said, if you lock the torque converter in 3rd gear, the engine flywheel, transmission input shaft, and the transmission output shaft WILL all be turning at a 1:1 ratio, and then I bet your calculator will be pretty close.

[LETZRIDE]

Re: Tranny/gears problem?

I see....makes sense for the most part

however, I am still stumped as to why my third gear is shorter then my 1st gear....

also when is the TC supposed to lock, when you are at cruising speeds?

[Skinny]

Re: Tranny/gears problem?

Here's a great article on how torque converters work:
http://www.automedia.com/Torque_Conv...cr20050401tc/1

Yes, lockup is supposed to only happen at cruise. Most factory programming will release the lockup clutch when you're anywhere near WOT. You can force a lockup with some scan tool/programmers.