Alright - stupid question, but I bought my Vette from a dealer who knew nothing about it, and had nothing he could tell me - and its hard to find much about it online.

I bought an 87 Vette and had the tranny rebuilt - its a Doug Nash 4+3 ... now, it worked fine, but yesterday the engagement stopped working and even though it would SAY it was in overdrive when you pushed the button, you would put it in "2nd" and it was CLEARLY not in overdrive.

I took it to the transmission shop and I won't ask y'all to troubleshoot that - its obviously something that has to be looked at.

But now I'm confused as to how the thing is supposed to work in the first place.

I was told by the seller to get into fourth, and then when I needed to upshift, take it out of gear, hit the button and drop it back in second. Easy enough.

But some of the stuff I'm reading says its supposed to engage automatically - is that right? And does it do that in each gear, or only after I'm in fourth?

I'm asking because I had noticed the light come on by itself in the past and thought there was actually something wrong with it - should it EVER be necessary for me to upshift into overdrive manually? Or should it always take care of that itself?

And one last silly question - what would you say the normal highway driving RPM value ought to be?

Thanks!
-Cat

 

85 4+3 z51
First-Have overdrive serviced w/new filter and fluid every 10,000 mi.

I drive mine like you would a 5-speed- 1 thru 4 in town between lights
and use overdrive only on the hwy or long strech's. And I always use my clutch to ingage and disingage overdrive. But thats just me.

hwy w/overdrive ingaged around 1800 rpm 70mph

 

What he said, no need to use it around town just use it like a 4 speed and hit the OD switched for prolonged speeds over 50 mph

 

85' 4+3 Z51 OWNER

I drive mine the exact same way as RWH1290. The 4+3 is basically a Borg Warner T-10 4 speed transmission combined with a 3 speed electric overdrive. Hence 4+3. I drive mine like a typical 4 speed through town and some highway and when I'm looking to cruise, I put the clutch in and engage the overdrive.

Just so you are aware, the overdrive will engage itself in every gear except first. And also the over drive will not engage itself until the car has reached an operating temperature of about 150 degrees Fahrenheit. Beyond that do exactly what RWH1290 said and think of it as a 5 speed car, with the overdrive being the 5 gear.

Make sure to keep it well maintained and you ought to have a lot of fun in it!

 

If you take off fast in first gear, when you shift into second it wont go into overdrive.

Also, for me, to get it in and out of over drive manually I have to hit the button really hard... something in the switch is out of alignment, but it works for me.

 

ALWAYS use the clutch when putting it in or out of overdrive. You will notice that when you are in 4th gear and the overdrive is engaged, if you push the accelerator to the floor, the overdrive automatically disengages to give you more power to pass if needed and then will re-engage automatically once take your foot out of it. One thing that is possible with the 4+3 is that once you go through the first 4 gears and engage the overdrive is that you can actually go all the way back into 2nd gear and go through 3rd and 4th again for more top end power. Most of us with 4+3's really only use it as a "5th" gear overdrive. Follow these tips and keep up with fluid and filter maintainance and you should have no problems with it. One note: You will find a few guys on this forum who bash the 4+3 tranny. Probably 90% of them never had one and really know nothing about them. They only repeat horror stories that someones friend of a friend told them about their car that they did not no how to operate correctly and destroyed it. Find a good Corvette mechanic with 4+3 knowledge and that will keep you from spending money on parts you don't need when a small item like a relay goes bad and makes you think the whole overdrive needs replaced.

 

The 87 4+3 OD unit does operate "automatically" as long as you don't touch the button on the shifter or accelerate too hard.

This web page has information on the OD operating characteristics.

The OD unit will be "Active" every time you start the engine and don't touch the button. If you have used the button on the shifter to turn the OD off and you kill the motor (with the clutch for example) re-starting the engine will reset the OD to ON.

With my 87, I will use the OD depending on traffic conditions. On roads where the speed limit is say 40 to 45, I will use 3rd gear and OD, On roads where the speed is 35, I'll sometimes used 2nd gear and OD instead of jsut 3rd gear. It just depends on how far you travel at that speed.

If you try different configurations, you can get a good idea of what the RPM's are at different speeds. For example, the engine runs at a lower RPM in 3rd/OD than in 4th/no OD.

The OD unit is fairly strong; it was used behind the B2K twin-turbo Callaway in 87 and that motor put out some decent numbers. The 4-speed portion is a Borg-Warner Super T-10 and it should easily handle 450HP with no problems. BTW, the OD is simply a 2-speed unit; with the OD engaged, there is a .62 gear reduction, with the unit off, there is no reduction giving a 1:1 pass-thru.

I use my 87 for autocross and track days but I do not use the OD. Shifting in and out of OD under WOT conditions could shorten the unit's life. Even without the OD, the car will get up to 125-128 in 4th with no problems. Engage the OD and the car should see 150+ but in-and out at that speed without using the clutch is not conducive to long life of the OD.

Annual maintenance (or every 12K miles) is the key to long life; A filter and fluid change takes about an 1/2 hour to do. 2-3 quarts of Dexron IIL ATF and a filter is all you need.

The filter is the easy part. It's the same filter used in Ford FMX trannies that were used in early-70's Torino's, Cougars, some Mustangs, and F-150's. Figure around $7 at any parts store. Part #'s:
CarQuest 85926
AC Delco TF-184
FRAM FT1024
NAPA ATP14717
Ford D0AZ-7A098-A

Re-use the rubber grommet from the old filter. Clean the pan rails and housing flange, make sure the pan rails are even and straight, apply a 1/8" bead of a good black RTV sealant and install the pan. Tighten the bolts evenly to 4-6 ft-lbs. Fill with fluid until it rounds out the filler hole and you're done.

 

I just tell everyone I have a 7 speed and they look at me funny.

Just like what everyone else here says, use 1st-4th through town. 99% of the time I use OD when I'm going 50 MPH or more which is usually on the highway. I don't even know if I've ever used OD in 2nd. Sometimes I use OD in 3rd gear when standard 4th has too high a RPM and 4th with OD has too low a RPM during those tweener moments. Just replace the filter every 10,000 miles and lube up with Automatic Tranny Fluid.

 

I like the seven speed idea. Then they'll go, that's right 4+3 = 7.

 

Everything you need to know
Great post & thread
Long live the 4+3!

 

Thanks for posting this thread and all the replies.... will soon be owning 1 of these also!

 

Here's some info you might find useful, especially if you want to diagnose the problem.

http://members.shaw.ca/agent86/Overdrive-manual.pdf

http://members.shaw.ca/agent86/OverD...Electrical.pdf

 

Yo are so wrong this is just another stupid gimmic gm idea that was HORRIBLE! These tranny just plain suck and no you shouldnt EVER have to maintain your tranny at 600 mile intervals to keep it running right, that just shows how crappy the damn thing is

 

I find it hard to believe that anyone bought a corvette with such a stupid tranny, I feel bad for you poor guilible saps.

 

Are you trying to win the "Troll zombie thread revival" award?

 

You obviously have your quotes screwd up. I never said anything about 600 mile intervals in my reply and no one else did eigther. I did however mention that about 90% of the bashers here know nothing about 4+3 trannies. I guess I know where you fit in.

 

OK guys, what picture do you think fits this dumbazz? I think all three!

 

I think he tried to hit me up for a toll on a dental bridge once

 

Dont hate guy, the truth hurts sometimes. The weak underpowered 80's vetts were some of the crappyist cars ever built, I had mine for a week before I sold it, But I do love my '78. The tranny was a way to try and compinsate for the lack of power, It didnt work, just ended up making the car slower with all the shifting it had to do.

 

You dont need to I'm saying it, those trannys are garbage plain and simple. no need to ginger bread it with terms like "proper maintence" or "good Vette mechanic" A good vette mechanic will advise you to stay away from 80's vetts all togeather