Manually Controlled Automatic Transmissions: Myth or Fact?

Posted by on Monday, November 19th, 2012

Does this question even make sense?  “Automatic transmission” sounds like the transmission is automatic, as in it shifts gears automatically with no manual control required by the driver. The truth is that manually controlled automatic transmissions do in fact exist.

Manually Controlled Automatic Transmissions


The next question is why in the world would anyone want to manually shift a transmission that was originally designed to shift on its own? There are a couple of reasons.

The most popular reason for converting a fully automatic transmission to manual use is for use in high powered drag racing cars. Automatic transmissions can be made to be more consistent (more repeatable performance) than manual transmissions.  Regular automatic transmissions are designed to shift at pre-set rpms as well as shifting softly in between gears as to not jolt the car when they shift. Drag racers want to hold the transmission in first and second gear longer than the factory designed them to. They also want the time delay between shifting from one gear to the next to be as small as possible.  Manually controlled transmissions give you both options.

The second popular use (although much less popular) is for industrial applications. Anything from heavy duty mining trucks to machinery.

Valve Body for a manually controlled automatic transmission


How is  a fully automatic transmission converted to manual use? Basically the conversion is done with replacement of the valve body. The reverse valve body will have different hydraulic passages. They also use different separator plates, springs and check balls.

c4 reverse manual transbrake valve body


Most manual valve bodies are also reverse pattern oriented. What that means is that instead of the pattern “Park, N, R, 3, 2, 1” The pattern is changed to “Park, N, R, 1, 2, 3”. The reason for doing this was originally to prevent the user from missing a gear and hitting neutral (where the motor is at risk of being over revved) or hitting reverse, which could result in loss of control of the vehicle or the breaking of the drive shaft.  Modern racing shifters are designed with reverse lockouts so reverse valve bodies aren’t necessary. Some manual valve bodies also include a trans brake.  A trans brake works by applying both the forward and reverse clutch packs at the same time. These types of valve bodies are used exclusively on drag racing cars.

remanufactured transmisssion


Manual valve bodies are not recommended for street use. They are mainly for off road use and industrial applications.

 I highly recommend you replace your customer’s transmission with a re-manufactured transmission. A remanufactured unit will include major alterations and upgrades designed to make them both stronger and more durable. A re-manufactured transmission will also include a much better warranty: three years compared to an average 90 days for a rebuilt transmission. In the rare event that a re-manufactured transmission fails within the warranty period, they will cover your R&R cost to replace your customer’s transmission. And remember, the companies that re-manufacture transmissions are very easy to contact. They are just a quick phone call or email away.

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