i honestly thought that the bonneville had 5 gears <4 + overdrive> yet have only found evidence of 4 gears. sources:

http://www.carfolio.com/specificatio...ls/id/?car=307

http://www.globalcar.com/datasheet/P...Bonneville.htm

i am assuming that 4a means 4 speed automatic. what else could it mean?

somebody prove me wrong please

4 speed auto with TCC lockup.

what does TCC stand for any way? torque converter clutch?

Prior to the 4T65E (440-T4, 4T60E, etc..) FWD Bonneville transmissions were 3 speeds plus an OD or 4th gear.
With the 4T65E (1997+ for L67 cars, and 1998 for L36 cars) it is a true 4 speed automatic trans -no OD.

Hmm: http://www.chevrolet.com/montecarlo/specifications/ says:

RPO: MX0/M15 (4T65-E)
Type (Supercharged SS): 4-speed automatic, heavy-duty, electronically controlled with overdrive

http://www.gmcanada.com/english/vehi...tml#Mechanical
Says: "Transmission - 4-speed automatic with overdrive"

Is there not an option to 'turn off' overdrive in 97+? Maybe I'm just confused haha :P

Before I explain what I am pretty sure OD is, someone tell me what OD is if it is not a gear.

OD is a gear, its designed purely for fuel economy. Thats why it shifts out of it the second you press more than like 25% throttle.

Mine holds on longer.

I believe OD simply refers to a gear with a ratio lower than one. So the output spins faster than the input.

prolly my tps settings then

There are four geared ratios plus a lockup (2 speed) torque converter. Since one of the ratios is less than 1:1, it is called an overdrive (yes, Virginia, there are underdrive gears as well, 1st: 2.921 and 2nd 1.568 ).

The 1-2 and 3-4 are very smooth shifts since not much happens 2-3 OTOH tends to get interesting particularly under light throttle. These are real gears though planetary ones just like in a F*rd model T (except it just had one).

The lockup OTOH essentially locks the input of the torque converter to the output and is good for about a 500 rpm drop and about 2% increase in efficiency (aren't churning the fluid any longer).

The 440T4 is capable of lockup in both 3rd (1:1) and fourth (.705:1) so you really have six apparent gears. Is easy to tell when lockup is applied: the rpm does not vary with throttle movement, only with speed.

Now before you calculate speeds from the above ratios you also need to know the number of teeth on the chain gears and the output gears but just to simply matters these are usually 2.84:1, 2.97:1 or 3.33:1 I have also seen 3.06:1 mentioned but not the application.