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The "Doug Nash 4+3"...



Hello all, I am a newbie and about to purchase my 1st vette,. I have a question regarding the 4+3 transmission. What is it, how does it work? I have seen several ads with people listing the 4+3 as an option, so any explanation will be helpful..... Also are they problematic?
First Things First

CLABORN1960~~Welcome to the CorvetteActionCenter~~

Back in the dark ages, The Second NEW Corvette I owned was a 1984 with the 4-speed 3-over. It was one of the first 300 made and had the overdrive button (switch) in the console. The car was very quick and worked great until I started autocross racing. By the end of the summer of '84 the trans had been rebuilt once and needed another by winter. From my experience it did not hold up too well being pushed.

The car got great milage on the highway in OverDrive. The OverDrive worked in 2nd, 3rd and 4th, thus the 4-speed 3-over. I haven't heard much good about them if you're a heavy footed gear jamming type driver, but most cars won't hold up to a lot of abuse either :D

I'm sure you'll receive several opinions on this subject ;)

Have you driven one? That might help answer some of your questions or concerns. Be sure to get a maintenance history of they car you think of buying, IMHO and be sure to ask Lots of Questions.

Good Luck
I autocrossed my '84 with 4+3 this season. No problems yet. When I got the car, I was told that I should change the overdrive fluid on a regular bases. I use the kit from Mid America and change the fluid and filter about every six month. So far the trans works as advertised.

CLABORN1960 - 4+3 is a manual 4 speed with an automatic trans mated to it for overdrive. It's not the best transmission. If I was looking for a vette with manual trans, I'd look for an 1989 or newer with a six speed. Much less problems with ZF.
The 4+3, or as it was known by Corvette engineers back then, the "Doug Nash" was a four-speed manual transmission with an electro-hydraulic overdrive grafted onto the back. Generally the OD worked in the upper three gears, hence the name "4+3.".

When the Borg-Warner got out of the four-speed manual trans business in the late 1970s, it sold the design and tooling for the "Super T10" (used in the Corvette from about 1975 to 1980) to the DNE Corp, which was started by hotrodder Doug Nash.

Nash, sold GM and Dave McLellan on a slightly-strengthened version of the Super T-10 with an electro-hydraulic overdrive unit Nash marketed for RV applications.

Well, the end result was the 4+3 and unfortunately, it was a poor example of quality, reliability and durability. The gearbox section was a pretty good piece, but the overdrive unit was a disaster. The 84-86 OD's are notorious for problems. The 87 and 88s are better, but still a problem child, especially if the car is raced a lot.
Hib Halverson said:
...The 87 and 88s are better, but still a problem child, especially if the car is raced a lot.

Hib, after talking at some length lately with Dick Guldstrand, I've decided to stay with my 4+3 after all. I was thinking about the Richmond six-speed or the ZF now that it's readily available, but seeing as how I don't have racing in mind for the near future I don't think that I'll do that switch yet.
As for racing, the 4+3 will hold up alright for some road racing and auto-x'ing, correct? At least that's the impression I get from Dick.

1985 4+3

Hi, I've got one of those "Doug Nash" Tranny's w/overdrive. I have not had a problem, but I only have 41k miles and I don't beat it up. The overdrive is great for the highway and that is the only time I use it. Otherwise just a normal 4 speed. Hope this helps.
You can find lots more info at www.5speeds.com:

01.06.04: I haven't a clue as to where those attachments came from. I certainly didn't have attachments when I posted this years ago! Curious... Very curious. :L
Hope this will answer some of the questions regarding the Doug Nash 4+3 Overdrive Transmission in '84 thru '88 Vettes.


01.06.04: I haven't a clue as to where those attachments came from. I certainly didn't have attachments when I posted this years ago! Curious... Very curious. :L

OK, now I'm beginning to run out of both time and patience. And I don't need to hear any bad-mouthing the DN 4+3 anymore! ;)

The following is from some e-mails I've shared with "Paul" from the "Gearzone.com"

At 01:56 PM 3/29/01 -0800, I wrote:
Complete remanufactured Overdrive assembly with 1 year warranty - $1150
Does the rebuilt overdrive unit for the DN 4+3 unit contain the following?
* New design carrier, complete?
* Updated carrier bearing, not available from GM?
* Updated direct clutch thrust washer?
* Updated pump assemblies?

At 03:42 PM 3/29/01 -0800, he responded:
Yes they do, I think that is stated on our website. The bad new is that I am not building them due to the success of out JT5 transmission line.
Paul Cangialosi
www.5speeds.com "Live ! - ShopCam"
Creators of the JT5 5 Speed and New Rally Clutchless Model RC!

At 08:41 PM 3/29/01 -0800, I wrote:
Paul, sorry to bother you again, but if you are "...not building them due to the success of out JT5 transmission line.", what do you recommend I do?

At 09:46 PM 3/29/01 -0800, he responded:
Call 631-957-9427 ask for Brian. He does a great job

Well, it turns out that "631-957-9427" is S-K Speed.com, anybody familiar with 'em?
Perhaps you have an alternative? My overdrive is evidently beginning to slip, which is the reason for it not staying engaged. (If it won't stay in overdrive, and it kicks back to direct drive, and the indicator light and button are both ok, that is an indication that the overdrive unit is slipping.)

JUNE IS RAPIDLY APPROACHING, and it is a bit uncomfortable cruising at 3600 rpm, not to mention the reduced gas mileage.

Guldstrand's shop still doesn't have a tranny specialist, and I don't know if I just want to go blindly into the fray and choose my own, although why not?

4+3 Nash

They are problematic. First things first Nash builds the Overdrive unit not the Tranny. They are found on 84-88 vettes. Most problems are found in the early years 84-86. Many are caused by not putting trans fluid in the OD unit which is similar to an auto transmission stuck onto the rear of the tranny. 87-88 are better but still have their quirk. If u have problems getting it in to reverse have it checked. :w :eek:

I finally broke down and ordered a remanufactured unit from Mid America. It costs $1299.99, plus a $1200.00 core charge, and of course, $35.99 freight charges, and that's not counting the labor for installation at Guldstrand's. (I dunno, in the Solid Axle Lounge last night, Dave said something about taking 1000 hrs. to install! :p )

Actually,after it's all done, it isn't much more costly than most transmission rebuilds. (Hopefully, my 4-speed internals are alright. It feels alright! ;) )

BTW, "Earlene" at Mid America was very helpful in filling the order, and on top of that had an extremely courteous and friendly manner throughout. She actually called back today because she wanted to visit my web site but lost the address! :D

I'll keep y'all updated.

I really haven't been following this post closely though I should as I also have a 4+3. Thanks goodness no problems...yet! Let me know how you make out, Ken!
Well, let's add some more cost to the bill. :D

I figured as long as the transmission will be out of the car, I should replace the clutch while we're at it. It only makes sense to me! :L And besides, I've been thinking about it for awhile anyhow.

I've decided to go with McLeod after some "channeling with the spirits, throwing the bones and conversing with the gods."

Now, I've spent hours today shopping around to compare prices and can't find much at all. I couldn't find McLeod at Jeg's, Summit, or numerous other known aftermarket distributors.

I did find a McLeod application for my Corvette at RaceSearch.com, but it was lacking in any description whatsoever other than
Size (O.D. & Spline): 10.75 x 1-1/8 x 26
Application: Street
Pressure Plate: Diaphragm
(The price quoted was Retail -$316.00, Our Price - $278.08)

I also found a referrence to one at Internet Racers Supply:
McLeod Dual Performance Clutch Disc & Pressure Plate Assy 1985-88 L-98
for $229.95, but once again that was all the information to be found.
They also had clutch assemblies for the 1989-1990 L98 and 1992-1996 LT1 at $424.95, and 1990-1995 ZR-1 for $445.95.

There were also several referrences to the Dual Disc Clutch kit, including flywheel, but those were for the LT1 and up Z28 Camaros. Amongst them was this from L.G. Motorsports for $1150.00:
1993-97 LT1
Street Twin Clutch Assembly
1 1/8 X 26 Spline
Aluminum Flywheel
(with a steel flywheel it was $825.00)

I know that McLeod makes the Soft Lok & Soft Lok I for the street (their web site has that info), but I can't tell from any of these sites just what it is they are offering.

Is McLeod's distributorship that limited? :confused:

All of the comparison shopping services like AltaVista or My Simon, etc. only cater to automobile sales or nothing automotive at all. How can I find a fair price with a clear description of the item?

I've gotta come up with a good price; Dave said he'd try to match it. ;)

4+3 Tranny

I have a 1987 vette that's got about 100K on her. a couple months ago, i started to notice that shifting into reverse was pretty tough for her. sometimes it would even grind in. now, i can't shift reverse at all without grinding; i need to kill the engine and start in reverse. all my other gears work fine. any ideas?



Welcome to the CACC site. You've come to the right place. This is where to get your questions answered and enjoy the company of other Corvette people. Look around this site, Rob has done a wonderful job in setting it up and making it easy to get around.

The Doug Nash 4+3 transmission is a unique combination of a 4-speed manual coupled with an automatic overdrive in 2nd, 3rd and 4th gears. The difficulity and grinding of shifting into reverse is an indicator that your clutch needs replacement. Reverse gear grinding is an early indicator of clutch problems. There is no adjustment on your hydraulic clutch as it finds it's own center. I recommend that you get the entire clutch pac kit which includes the pressure plate, clutch disk, release bearing and alignment tool. Check the surface of the flywheel, it probably needs to be resurfaced. If you resurface the flywheel be sure to shim it upon reinstallation. Also replace the pilot bearing in the flywheel.

Just to complete the process, replace the filter and fluid in the overdrive unit, that service is recommended every 10,000 miles.

Once complete, everything should be as good as new.
Wow I just posted clutch probs to (gonna replace her) I grind to bud but 2nd gears my trannys choice LOL
Good Luck~!
4th gear switch

I seem to have a bad 4th gear switch on my '84. I think it's the 4th gear switch anyway, 4 wire connector on the transmission(only three wires are used). It's either that or the TCC solenoid.

When it's plugged in there is a direct short from the "GAUGES" fuse to ground. Which of course means that pretty much every active sensor on the engine will not work, including MAP and ESC.

What does this switch do besides turn on the "OVERDRIVE" indicator lamp? Has anyone ever replaced one?


1988 4+3 Transmission

After it has warmed up and the OD has kicked in the engine revs
real fast and high almost like something is slipping. Any ideas?

Time for an overdrive unit.:(
I know you can get a rebuilt one from Mid America and I'm sure other places too.
Sounds like the Clutch isnt grabbing hard enough Id look there first personally( Exact same problem on my 85 I dropped a new clutch in and everythings fine)

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