During the 12 C4 Corvettes run, 2 different manual transmissions were available. The Doug Nash manual 4+3 offered from 1984 to 1988 and the ZF 6-speed manual transmission offered in 1989 to 1996 are two very different types of manual transmissions, with their own unique features and characteristics.
Not sure if you want a manual or automatic transmission, check out this page.
Doug Nash 4+3 (1984-1988)
The Doug Nash 4+3 is called “4+3” because it has four conventional gears and an additional three overdrive gears. The transmission was essentially a four-speed manual transmission with an additional overdrive gear that was electronically controlled. The transmission was designed to provide the performance and fuel efficiency benefits of an overdrive transmission, while still offering the fun and engagement of a manual gearbox.
The 4+3 transmission had a unique shifting pattern, with the four manual gears shifted in the traditional H-pattern, while the overdrive gear was activated using a separate switch on the shift lever or the console on early models. The overdrive gear was designed to engage automatically in fourth gear at speeds above 35 mph, but could also be manually activated using the switch.
The 4+3 transmission was not without its issues, and many owners complained of reliability problems and difficulty in finding replacement parts. In addition, the complex electronics required to control the overdrive gear were prone to failure, leading to expensive repairs.
ZF 6 Speed
The ZF 6-speed manual transmission was offered as an option in the C4 Corvette from 1989 to 1996. The transmission, known as the ZF S6-40, was introduced in 1988 and was considered an upgrade over the previous 4+3 manual transmission that was available in the Corvette.
The ZF S6-40 transmission had a maximum torque capacity of 400 lb-ft and featured a close-ratio gearing for improved performance. The transmission was designed to be compact and lightweight, with a cast aluminum case and a weight of just 135 pounds.
The ZF 6-speed manual transmission was initially only available in the Z51 performance package, but it was later offered as a standalone option. The transmission was highly regarded by Corvette enthusiasts for its smooth shifting and improved performance, and it quickly became the preferred transmission for high-performance driving.
In 1992, the ZF S6-40 transmission was updated with a stronger input shaft and a revised shifter mechanism for improved durability and shift quality. This updated transmission, known as the ZF S6-40/6, was offered until the end of production in 1996.
Comparing the Two Transmissions
The Doug Nash manual 4+3 was a unique transmission. However, the Doug Nash transmission is known for being somewhat clunky and difficult to shift, especially when the overdrive gears are engaged.
The ZF 6-speed manual transmission is a popular transmission used in many high-performance cars. It is known for its smooth shifting, durability, and ability to handle high torque loads. The ZF 6-speed is a fully synchronized gearbox with six forward gears and one reverse gear. It also has a hydraulic clutch system that provides smooth engagement and disengagement of the clutch.
In terms of performance, the ZF 6-speed is generally considered to be superior to the Doug Nash 4+3. The ZF 6-speed is smoother, more reliable, and can handle higher torque loads than the Doug Nash transmission. However, the Doug Nash 4+3 is notable for its overdrive gears, which can improve fuel efficiency on the highway. Ultimately, the choice between the two transmissions will depend on the specific needs and preferences of the driver.
In defense of the 4+3
I personally have the 4+3 Doug Nash in my 1985 Corvette and I love it. It has given me lots of happy cruising time with it and as I have said before I think a Corvette should be driven with a manual. My only issues I’ve had is having to replace my clutch master and slave cylinder.
If you are looking for a track or race type vehicle the ZF is definitely the way to go. If you’re looking for something fun to drive and don’t do the super hard acceleration, the 4+3 will work great for you.
As with any older car and a C4 Corvette the care and maintenance of the vehicle is the most important thing.
So in conclusion, the ZF is definitely the better of the transmissions. As mentioned above it is more robust and more reliable. But don’t discount the 4+3. It can give you a ton of enjoyable miles as long as its taken care of well.
See my other page about changing the transmission fluid. It’s not really very hard and it will help keep your transmission going strong for years to come.
Same for the ZF. The one you decide on is up to your personal preferences and needs for your C4 Corvette.
Question or comment, please leave them below and I’ll be sure to get back to you.