I tried to do a search. Just got a 96 corvette with an automatic. It has the overdrive drive (D with circle around it) and regular drive. I always thought overdrive was just a overdrive gear on top but this seems different. It seems to affect response even at 30-50 MPH. I seem to like the regular Drive better than the overdrive. Can you please explain what I should be using on a daily basis. Thanks for answering such a basic question. Dan

 

Did more research on the net and I think I understand now. Dan

 

OK, One more question. Is there a top speed to drive in the non overdrive D? Can it be shifted back and forth at speed? Thank You, Dan

 

So last spring I had the fun adventure of rebuilding my own auto transmission...

I learned a ton about these things.

the only thing you should even think about the difference between OD and D is what the clutch packs do.

Pretty much they say OD should only be used for cruising mainly because one of the clutch packs that lock the forward sprag in place is not applied.

This could lead to damage if you really romp on the throttle, or so they say.

I personally beat the snot out of my 4th gear (OD), but they do recommend to do your power driving in third, and use OD for cruising.

We can go further into torque converter lockup, that one you need to be careful with, however unless you have a manual on off switch for the thing, you don't need to worry about it...

I hope this was helpful, if not to much information...

 

Thank You Gibbles. By "cruising" do you mean steady interstate driving? Thanks,Dan

 

I may bit off the mark but here's what I know. Manual transmissions have an input shaft and an output shaft.(duh) Changing gears alternately engages and disengages various gearsets within the trans to modulate the engine's power band to the speed. In low gear the input spins fast while the output turns slower. Typically the highest gear in attained when the input matches the output. The manufacturers offered different differential ratios to match the owners needs, like drag racing, track racing or towing. The top gear was a 1:1 ratio. Overgive drive was used to give better fuel economy under special conditions, like highway cruising. You would typically get the car or truck up to speed and then shift into OD. Headwinds or hills usually required downshifting to top gear, much like the C4 with a manual under 50MPH. If you forget to shift out of 6 you will think you through out an anchor. Overdrive transmissions became more popular in the 80's when fuel prices rose and economy became important. Soon everyone offered a 4 or 5 speed manual, the top gear being an overdrive. Automatics of that era were 3 speeds with a torque lockup. The 4th was added as a mathematical overdrive ratio. Pretty soon all cars, automatic or manual had at lease one overdrive ratio built into the transmission. The term technically means that the drive ratio, input to output, was lower than 1:1.

 

Thank you 73n95 for your response. I appreciate your time in doing so. I understand everything you say. From what I understand in my limited research my 4+3 transmission in drive is a regular 4 speed. In overdrive, it appears that the overdrive gear can engage in 2nd, 3rd and 4th. Thus the 4+3. PLEASE correct me but if I leave in non overdrive D everything will be fine up to any speed I will go but the engine will rev a little higher. Can I hurt anything running in non overdrive D up to say 100 mph? I know it would use more gas and more wear on the engine. Can I shift from non overdrive D to overdrive D at say 60 mph if I want to lower the rpm for just interstate driving? I do understand these questions are very basic and noobie but I appreciate the responses.Thanks all, Dan

 

Who is "they" and what kind of damage is going to occur if you "romp on the throttle"? There are hundreds of thousands of these transmissions out there in everything from pickups to mini vans. I would be willing to bet the overwhelming majority spend 99% of their time in D over.

 

If you have a 96 as stated in your first post, you do not have a 4 + 3.

 

I am really showing how little I know at this point. if you understand my basic question I would very much appreciate some help. Yes, I have a 96. How does mine work? Thank You, Dan

 

That would take too much explanation and time as it appears you have limited experience with the 4l60E. You need to google "operation of a 4l60" and then study the links. My computer shows 213,000 of them. YouTube has a wealth of knowledge. I have however, included a link to the complete GM manual that pretty much answers anything you need to know.

http://www.grail-ss.com/GRAIL%20Webs...ETechGuide.pdf

 

Thank You very much,Dan

 

My god arbee, there are way more parts in there than I ever imagined. The info answered my question completely. Thanks again for taking the time to respond! Dan

 

Many here use "D" for urban use & "OD" after 50mph.

Its a matter of poor/late throttle response while in the 40mph range waiting for the torque converter to unlock & the trans to downshift.

Other than that its an automatic trans it will select the appropriate gear depending on throttle apply.

No worries about full throttle in "OD".

 

Thank you Churchkey! One more stupid question: Can I shift back and forth while driving? Thanks, Dan

 

I do it. Have been building/rebuilding auto transmissions for years.
Am a big 3 factory trained trans specialist. (Have the tee shirt & hat)

If the trans fails due to manual shifting it was on its way out anyway it just happened sooner.

Check the trans fluid if its brown or stinks the trans needs a service.

Contrary to wives tales here your trans will not die if the fluid & filter are changed. If it does die after a service it was headed south before the trans service.

Luck with your new toy.

 

Again, Thank You sir! Dan

 

In my manual it says to not use OD to tow or going up steep grades.
also i thought he was talking about an auto transmission...

Look at the clutch apply charts, it makes a little more sense as the overrun clutch is not applied, putting mpre stress on the forward sprag roller clutch.
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The 4+3 is a manual transmission available in early C4s.

 

Guys, Thanks Much! I was way wrong when I said 4+3. It just shows how much I have to learn. I have the automatic and was trying to learn how to properly use the D with the square around it (overdrive) and the regular D. I have learned the in the regular D the transmission will not go into 4th. Took a nice 100 mile trip today. Think I have a novice understanding. Did get a PO400 service code and replaced my EGR valve and everything seems good. I felt so good doing this simple task. Thanks, Dan