The "Doug Nash 4+3"...

[vigman]

Smell... that smell... smell's like $$$$

Ok when it rev's up do you smell anything? A burnt clutch has a VERY distinctive odor like hot dusty brakes ridden to hard. Where does your pedal engage at near the floor or at the top of travel? can you make it slip without O/D engaged?

It's gonna be about $2-2500 I think the Mid america unit is 1300 and since you will have the tranny out DO THE CLUTCH!
and you will always find OH by the ways.. while things are out

Sorry
Mike

 

[lunar]

auto OD in 4+3

Seems my tranny's always got something going on -

is there anyway to disable the the "automatic" part of the automatic overdrive in an 87 doug nash? i'm tired of my car constantly kicking it on off whenever she sees fit. and while i'm at it, the button on my stick needs to be replaced. actually, i think it's a little more than that (i bought the car used, and right from the beginning i found you really have to kind of "hit" the OD button to engage it; no doubt she's taken abuse somewhere...) The plastic button is gone now, and all that's left is the pin. the pin is really starting to wear down my finger, especially given how hard i need to hit it to engage the OD. and it seems to just be getting less responsive over time. I think just replacing the whole stick will solve this (the leather's worn after 14 years anyway), but i'm not sure. how should i go about doing this, if i should? and where can i get a stick, preferably stock? thanx,

kev

 

[Ken]

More Doug Nash 4+3 info...

Excerpt from Cars & Parts Corvette Magazine:

The real trick though is to get rid of all these complicated electronics, and turn this transmission into an eight-speed.

A Major Modification
I discovered this one by accident. Well, not quite by accident. Actually Chris Petris, who used to build transmissions for the Corvette Challenge, helped me with this. There's a switch on the side of the transmission that tells the computer which gear is engaged. This second gear switch is one of the first things to go bad on the 4+3. The switch is engaged every single time you shift the transmission, whether the overdrive is engaged or not. It's no wonder this is usually the first item to wear out.

When my second gear switch went bad the car simply wouldn't engage overdrive properly. I could hit the switch on the console to turn on the OD and it might not actually engage until I drove some 20 miles down the road. You can imagine how aggravating this was. When Chris and I couldn't locate a replacement switch right away, we simply grounded the switch by running a very short shunt from one terminal to the other. This effectively made the OD a completely mechanical unit, operated only by the interior switch, which in my case is on the console.

Eliminating this switch made an the difference in the world. This was like giving me a new Corvette. This same modification was made to the World Challenge Corvettes. While Chevrolet designed all the electronics to pass the EPA fuel mileage cycle, we simply want a useful transmission. The 4+3 actually works better if you take some of the sophistication out of the system.

What we did was fool the computer into thinking that I'm always in second gear or higher. This switch is on the left side of the transmission, and can be seen easily if you have the car on a lift. This switch moved around a little during the years, but it was always the switch toward the rear. Remove the wiring harness from the switch and hook it out of the way with a tie-wrap. You won't be using this harness. Now make a little jumper wire that fits into the two terminals. You can actually remove the switch from the transmission and make the jumper wire on your workbench. It shouldn't take more than 15 minutes.

This explains the difference in the codes also:

I keep finding more stuff that previously, for me at least, wasn't to be found. :gap

 

[Paul G]

My switch was leaking fluid, I got a new one from the local Chevy dealer. I did have it bypassed for a while on my 88. I did not like that. With it bypassed the OD would engage in first gear just like an auto shifting to second. I feel this put to much wear and tear on the OD unit. I like to let it come in while the clutch is engaged. It just feels like it is easier on the OD unit that way.

 

[Ken]

With it bypassed the OD would engage in first gear just like an auto shifting to second.

Do you mean Paul, that you were unable to lock it out? :confused

 

[Paul G]

I could kept it off by pushing the button. Then it will stay off till the button is pushed again. I normally I let it come in by itself as I shift to second. For normal in town driving I let first wind out a little long then go to second with overdrive. the next shift could be third if traffic is light. Most times in town second with overdrive is the right gear for me.
Otherwise with the overdrive off I could be in fourth gear by 30 MPH. I tend to putz around a lot. Dont really drive it hard that much.

 

[Ken]

I understand now. I just never use my OD in town.

Ken

 

[afbrat]

1987 Z51

I have just signed on in hopes of receiving some much needed info about my 1987 Z51 Dk Red Conv. It has a rebuilt engine, new transmission with new 6-speed, new compressor and alternator, new leather and carpet and top, refurbished wood trim, etc you get the idea. The mileage is high over 187K.
It runs great, no problems other than a new switch for the passenger window to replace. What is its market value? Thanks to any that can help!

 

[Ken]

Welcome To The Corvette Action Center afbrat!

Air Force Brat, eh? Welcome!

I would say the C4s are just about bottomed out as far as depreciation is concerned.

In order to get an accurate idea of the value of yours, checking the auction reports is your best bet. There are plenty of magazines and tabloids out there that carry the weekly or monthly auction reports from around the country; both Corvette Fever and Vette magazines have sections set aside for those reports, and Old Cars Weekly has a ton of aucton information.

Join a club. Many people in your local clubs have a good idea of current marketplace values.

Check out eBay. You can look to see what's selling and for how much.

The resources are limitless, and everybody has different likes and dislikes. Good luck.

 

[Ken]

More 4+3 info...

I see that Darrell Shepherd (4-Speeds by Darrell) is now working with the Doug Nash 4+3.

If ya don't wanna go there, and are unfamiliar with what it looks like:

_Ken

 

[Ken]

Welcome To The Corvette Action Center nyernga!

If you already have the button off, you should see the little metal wedge the keeps the knob aligned correctly. Pull that wedge out and unscrew the knob from the shaft.

Oops! Forgot something:

Unscrew the T-bar rod that you'll see towards the front of the knob. Be sure to count the approximate number of turns it takes to unscrew and remove the rod, it will aid in keeping the button surface level with the knob top when you reinstall the button.

It's been a while since I replaced mine, but I think it was easier to remove the complete switch assembly from the shifter when replacing the overdrive switch. You'll have to judge for yourself if you can reach the switch (I couldn't).

I don't know if you saw my update on the digital dash repair I just went through (C4 Wiring...), but I think my overdrive is functioning properly since I cleaned the contacts in the dash. Mine does appear to be an electrical problem.

Good luck and I hope this helps you.

_Ken

 

[afbrat]

Re: Welcome To The Corvette Action Center afbrat!

Air Force Brat, eh? Welcome!

I would say the C4s are just about bottomed out as far as depreciation is concerned.

In order to get an accurate idea of the value of yours, checking the auction reports is your best bet. There are plenty of magazines and tabloids out there that carry the weekly or monthly auction reports from around the country; both Corvette Fever and Vette magazines have sections set aside for those reports, and Old Cars Weekly has a ton of aucton information.



thank you! yes, raised by a pilot and then married one too!

thanks for the direction, we'll see how I do in the next few months
(hope I have submitted the reply properly)

 

[Ken]

Re: Replies...

(hope I have submitted the reply properly)

You'll get the hang of it.

_Ken

 

[Ken]

I've got a bunch of information for the DN 4+3, the transmission that was used in the Corvette from 1984 thru 1988, gathered from various sources, and put together on one page at my web site: Doug Nash Info if anybody wants to check it out.

I will be adding more information as I find it, and will keep you all informed.

 

[Ken]

So many things are inter-connected with this set-up it makes it a pain to diagnose, but from the sound of it, it seems as though the signal is getting through when you punch the button, but not when the throttle goes past, what is it - 60% or 75% depressed in fourth?

That would point towards the throttle position sensor (TPS), or even possibly the electronic control module (ECM).

Are you sure the fluid level is up to where it should be? But a low level there would keep it from staying in overdrive; it would kick back into direct ratio drive in that case.

Keep lookin' and if I think of anything I'll be sure to post it here.

_ken

 

[Ken]

Len, have you taken a look in My Garage?

There, can be found, a lot of info on the DN 4+3, including a table showing what SHOULD occur in each gear.

No downshifts over 4100 RPM in fourth gear.

_ken

 

[ROCKO]

Great info

Best info i've seen on this trans. I bought my first 4+3 on my 88 conv and so far it's been running fine. Always like getting more tech info. Keep up the good work.

Rocko:cool

 

[Ken]

Thank you Rocko.

_ken

 

[Edmond]

Guys,

Please excuse me for asking but what exactly is the 4+3?

Also, what exactly is the automatic overdrive?

 

[racecar]

I never could tolerate that automatic down shifting. I had an aftermarket computer chip that made the OD totally manual. No guessing about what it was going to do next.