This is probably a dumb question but I don't really know what's the difference between overdrive and regular drive. I drive a '91 Camaro RS with the lo3 305 with an automatic transmission. I'm not trying to turn this thing into a racecare. It's my daily driver and it's going to remain stock for the most part. For gas mileage, what the best to use driving around town and on the highway? I apologize if this has been covered before. I tried searching and came up empty.

when goin down highway its best to use overdrive if ur in town u dont want to use overdrive cause it will wear out your tranny from all the shifting back and fourth. will save u lots of gas if u use it going down the highway

OD is 4t gear

I disagree here, just put the shifter in OD and GO. In 3rd you are engaging the over-running clutch pack and that increases the engine braking, hurting your gas mileage. Just us OD or Drive, unless the transmission is shifting/hunting excessively. The original "weak" 700r4 in my 1983 G20 Van behind its equally "weak" 305 lasted nearly 200K miles before being replaced when I put a decent engine in front of it. When I pulled it out, it was still operating smoothly and quietly. The clutches/band were definately showing wear though.

I like to have my tranny in third around town because the lock up starts hunting around (on and off) at about 40 MPH and I find that very annoying. The only bad thing is I sometimes forget to put it in 4th when I hop on the freeway

yo im saying if ur in town with a lot of stops where u never get over 40mph if ur tranny keeps trying to shift back and fourth through the gears then it wont last long i know have had to replace three of them cause of that!!

I know what you are saying, but I've had MULTIPLE vehicles that have not had your issue. Even in city driving, its best to stay in OD. Some cars/trucks do not lock the converter unless it is in OD and some do not route fluid to the cooler if the TCC is unlocked. 3rd and no lockup OVERHEATS these transmissions very quickly. The OD in my van kicks in at about 39 mph and stays in it until the speed drops below 35 mph at real light throttle. The current transmission has 50K on it and I had to go into it on a non-related issue. It was near immaculate, looked like it did when I put it together. Here is the reason I like to run OD while coasting around town, datalogging the S-AUJPv4 code, in 3rd running 1,700 rpm @ 40 mph I show 12 mpg, running in OD @ 1,100 rpm, I show 22 mpg! There is no way with as much city, traffic driving that I do, that I would give up that extra steady state fuel economy.

i think o/d is wonderful if your not towing something.

Some people may think I am loonie, but I even use it while towing, as long as its not over 3K lbs or so. I pull the boat to the lake in OD.

so i guess some cars have Drive as well as 3rd gear to select from, so on our cars, would using 3rd gear apply engine braking already? also, is TCC lockup applied in OD & 4th gear only, or, when selected OD, would i also have lockup 1st through 3rd gear?

lol when i race i through it in first and do it manually shifting at 5,000 rpm then 2 ,3,OD works greatly but hurts the tranny badly that y i only do in races..

When I rebuilt my 700r4, I used MANY HD components, especially when it came to the Transgo Shift Kit. It also comes with extra strength release springs that keep the clutches from applying above 5,500 rpm. It shifts smooth and hard, when I run it hard, I shift about 5,800 and it completes the shift by 6K. Its not all that much harder on the trans than a normal 5,500 rpm upshift.

mine when it does it by itself shifts at 4200 GAY

On our cars, the only "gear" allowing a free roll is OD.

Here are the 88-92 fbody settings that are controlled by EBL, should be the same for the ECM.

TCC-lock enable CTS -- 51.50 C°
TCC-forced lock -- 100 MPH
TCC-LoGr max TPS% coast unlock -- 1.96 TPS
TCC-LoGr MPH ok to lock -- 34 MPH
TCC-LoGr min TPS% coast unlock -- 1.57 TPS
TCC-LoGr MPH to unlock -- 32 MPH
TCC-HiGr max TPS% coast unlock -- 1.57 TPS
TCC-HiGr MPH ok to lock -- 44 MPH
TCC-HiGr min TPS% coast unlock -- 0.87 TPS
TCC-HiGr to unlock -- 40 MPH

TCC-TPS% opening/closing delta -- to many # to write
TCC-relock delays -- to many # to write
TCC-LoGr TPS% to stay unlocked -- to many # to write
TCC-LoGr to unlock -- to many # to write
TCC-HiGr TPS% to stay unlocked -- to many # to write
TCC-HiGr TPS% to unlock -- to many # to write

By driving at a frequently variating speed between 37-41 without load, right trough the 3-4 gear shift point, or any variating speed and load trough any shift point it would probably be better to select the lower closest gear. These are special situations and do not necessarely hapen during city traffic.

Yea, because our stock motors start running out of power at maybe 3500 Revs.. Holding it in gear any longer only slows you down, burns more fuel and makes noise.. not even good noise..

i ordered a t.b.i spacer so im not worrying bout it

LOL blkfirebird, what gain in numbers are you expecting?

UglyBronco, i'll agree with you, that's about right - and yeah, not even good noise

thomas, thanks a lot for supplying us with these numbers and clearing my up my question

well if you have a good exhaust it will be fine so say what you want man doesnt bother me and for gain out of a t.b.i spacer im not expecting anything so like i said say what you want

In my old 83 z28 it has a heaven sent joy with its almighty 14mpg hwy and like 8-10 city. But after replacing the 700r4 three times and swapping in a th350 I was able to drag race with the juice again and didn't have to worry so much about blowing gears out.