4 + 3 transmission

[rwpeders]

I've never driven a vette with a 4 + 3 transmission. Those of you who have one, I'm curious to know what you think of it and how you use that overdrive setup most?

 

[1stiff84]

Hi RW

I liked it. I typically only used it at freeway speeds in 4th, or 3rd under 60 mph for extended periods of time.

1

 

[rrubel]

I find the overdrive is the only thing keeping fuel economy above 15... I tend to use it for anything above ~35-40 mph.
[RICHR]

 

[c4cruiser]

I tend to keep the OD off until I hit the freeway. But if I travel on roads with a 40-45MPH limit for any distance, I will use 3rd gear with the OD engaged. That combination gives an engine RPM between 3rd and 4th gears and still allows the auto kickdown with the throttle.

The system on my 87 provides for auto OD engagement when coolant temp hits 112 degrees or so and that is the only rub I have with the system. In addition, the 87 allows for OD engagement in 1st gear, effectively giving me 8 forward gears :eek !!

I never use the OD during open track days as I'm not too sure what those types of driving conditions would do to the clutches.

With the proper maintenance, this is a very stout tranny setup and performed very well behind the Callaway twin turbo cars. Just expensive to fix!!

 

[rrubel]

C4Cruiser, I think someone must have clipped some wires on yours. The stock 4+3, regardless of year, wouldn't let you manually select 1-O (although there are some instances when you can downshift from 2-O and wind up in 1-0). This is a common "upgrade", though.

If you remember to hit the OD button when you start the car, it should stay out of OD even after the temps reach the auto threshold...

Oh, and I'm not sure about your year, but on the 86 OD will automatically come on (regardless of the switch setting) when you hit 120 MPH. So depending on the track, you may wind up in OD anyway (I did, just once - the last 20 mph or so above 100 take a LONG time to arrive).

[RICHR]

 

[c4cruiser]

Ooops, should re-prhase that to say OD will engage in 1st when downshifting if the OD is already engaged. And the water temp must be at 122 degrees not 112 (typo). I have an 87.

As far as automatically going into OD while in 4th at high speed, mine doesn't seem to want to do that. I've done a number of track days where I have hit 125+ and the OD will not engage. I do make a point of hitting the switch at startup at autocross events or track days and have not had any problems with the OD coming on.

Found this page: http://www.5speeds.com/43table.htm that shows a comparison of 84-88 OD operations by year.

 

[rrubel]

Hm. Not sure that chart is *quite* right; I cannot force OD in 1st by hitting the button on my 86, and have to be going well over 103 in 4th to get the auto OD. Then again, things are probably just getting old on my car...
[RICHR]

 

[Corvettephil]

rrubel: something funky on yours, I think. I also have an '86 4+3 and can engage 1+OD manually and can get 4th+OD at any speed.... mine follows the chart to the letter. Good luck!

 

[rrubel]

Not saying I can't get 4th OD at any speed... but at 120 or so is when my OD *forces* itself on.

I'll have to try the 1 OD again when the car is back on the road. Pretty sure I tried it and it just kept kicking back out.
[RICHR]

 

[Harley1@coiinc.com]

Where is the button to engage or dis-engage on my 85 4X3 ?

 

[rrubel]

Should be on the dash, in or below the driver information console (where all the tell-tales are).
[RICHR]

 

[SSTibet]

4+3 Question

Folks,

Is 4+3 an automatic transmission??? Dumb question I know, but just curious...

 

[rrubel]

4+3 is a 4-speed manual transmission (the 4 part) attached to a 2-speed automatic, which allows for overdrive in gears 2, 3, and 4 (the +3 part). Weird setup, mainly because GM wanted a good transmission for power, but also needed something for fuel economy, and didn't have time or money to develop a decent 5 or 6 speed.
[RICHR]

 

[SSTibet]

4+3 is a 4-speed manual transmission (the 4 part) attached to a 2-speed automatic, which allows for overdrive in gears 2, 3, and 4 (the +3 part). Weird setup, mainly because GM wanted a good transmission for power, but also needed something for fuel economy, and didn't have time or money to develop a decent 5 or 6 speed.
[RICHR]

Okay... What does 'overdrive' mean in this context??? Do you for example manually shift between 1 and 4 and then hit a button for OD??? And what happens when you do the OD stuff, does it get faster / slower?

 

[rrubel]

"Overdrive" means that the gearing is less than 1:1 (ie, for every revolution of the engine, the rear wheels travel more than once around). Basically the engine goes slower for a given speed.

Once we shift to second, the computer will automatically turn on overdrive (essentially switching gears on the 2-speed automatic transmission attached to the back of the gearbox). Or we can hit the contro button and it'll NOT switch to overdrive unless we say to. Or if it IS in overdrive, hitting the button takes it out. Also, if the RPMs are below a certain level, pushing the accelerator more than 2/3 will also drop it out of overdrive.

Confused yet?

I'd personally prefer a 6-speed, but was happy to at least get a manual transmission in my price range.
[RICHR]

 

[SSTibet]

Rrubel,

Thanks for the explanation, I am feelıng somewhat more educated now about the 4+3 transmission although I am still confused. Must be because I have not driven one of those before.

I have a 95 with 6-speed manual and I guess it is much easier to use. But I did not have the faintest idea what I was getting when I bought my car... I am also reading that the 4+3 was produced between 1984 & 1988; I am wondering what they did before 1984 for the manual transmissions? Just 4-speed manuals??? Or, did they produce only the automatics??

 

[rrubel]

4-speed manuals. 3-speed before that . Less gears meant that there had to be compromises - lower top end or lower acceleration or better fuel economy or not quite being able to keep the engine in its sweet spot when you shift gears, and so forth.

In your 6-speed, 5 and 6 are overdrives while 4 is 1:1.
[RICHR]

 

[SSTibet]

Thanks Rrubel,

This was very informative. Thanks really for your forthcoming with all this information. Hey, have you been in Turkey before? Or Europe???

 

[rrubel]

Turkey, no, though I'd love to go sometime. Europe, yes - England and France. Also Israel, many years ago.
Glad to be of help... This forum is great because we all absorb what we can and spout off when we're able.
[RICHR]