Postby xtech » August 10th, 2008, 9:12 am
I will break down a few things that I feel are very large misconceptions about our automatic tranny in general. And hope to answer the questions people have about Valve body upgrades, Shift kits, Tranny coolers, and how to pick the right stall converter.
So why did car makers tuned our tranny so soft and what can I do to make it better?
Factory programming achieves comfort.
The automatic transmissions coming off the assembly lines are truly masterpieces of engineering. But engineers have been asked to program the shifting for smoothness and comfort. Also, consumer attitude surveys show that drivers believe a soft, smooth shift is easier on the transmission. Actually, just the reverse is true.
To add comfort, designers have had to subtract a considerable amount of efficiency and durability. They have achieved comfort by extending the time duration of every shift. Not only does power slip away during this extended shift, but all friction surfaces receive excessive wear because they are asked to work overtime.
The stock automatic takes longer to complete each shift so only mild acceleration. During this period only a partial power condition exists because the friction elements are slipping.
This extended slipping time prevents the inertial energy from being efficiently utilized. It is lost in the form of heat on the clutches and bands, instead of being utilized for forward motion. Continually operating a stock automatic at full throttle will cause early friction element failure.
To get high performance and improved durability in an automatic, we must improve the way it executes every shift.
So how do you make the shift faster without losing precision?
An automatic with a
Re-programming kit
Shift kit,
Valve body upgrade kit
will shift fast enough to take advantage of inertial energy from rotating mass, including the inertial energy from the transmission itself. In driving this conversion at full throttle a sudden forward lurch can be felt when it shifts, very similar to a power-shifted manual.
So as the elapsed time of shifting is decreased, the life of the transmission friction materials is increased.
Installing a re-programming kit, Shift kit, or Valve body upgrade kit will at least double the life of the friction materials in the transmission. In many heavy-duty applications, a kit has made the difference between a few months service without repair and several years.
The shorter shift time allows the friction elements and gears far less time to wear themselves out. The useful life of the friction elements in a transmission is directly related to the amount of slipping that is allowed to occur during shifts.
Slipping converts useful energy to heat on the surface of the clutches and bands. This heat transforms the friction material to ash, which polishes its mating element, causing further slipping, heat and deterioration of the friction elements.
The gears receive less wear, too. A slow shift causes them to be partially engaged for a longer period during the gear changing process, resulting in unnecessary heat, wear and power loss.
Now when dealing with Higher HP cars the amount of force that is applied may and has caused hard parts to fail as there stress levels have been reached. One that jumps out at most is the Sprag gear.
A Sprag gear is a one way roller bearing with a z spring that holds the rollers in place. These are made from stamped material and are not as solid a solid unit would be. The unit will free roll in one direction but will lock when tried to role in the opposite direction.
Think of a tranny cooler like and Intercooler for your tranny. The factory cooler is actually part of the stock radiator and is not a true cooler like the radiator for the motor. By adding an inline cooler with the factory cooler you help extend the life of even a stock car. And car that is having any type of performance mods done should have one installed as soon as possible. Always remember heat kills and auto tranny faster then anything else.
Shift Kit
A shift kit is the most basic upgrade to a transmission. It usually involves the replacing of a few springs, adding a few spacers, which can range from small puck, small shafts, and washers. Drilling or enlarging a few holes in a separator plate. Adding changing or removing check balls.
* Separator Plate is the pcs that separates the main body and valves of the Valve body from the transmission case this is usually covered on both sides with a gasket with holes for proper fluid flow.
* Check balls are small ball bearings that are use to restrict flow threw a passage in the valve body so that exicive overlap does not occur or that a certain gear is not applied while in the middle of a gear.
Valvebody upgrade
A Valvebody upgrade is one step up from a shift kit it requires more skill and time to preform. It involves all of the basic items from in shift kit but will also include the following. Full replacement of necessary valves with new valves made to spec these usually replace the valves that were spaced. Involves increasing passage way’s and restricting flow threw certain passages of the Valve body and case. New redesigned gaskets for the separator plate and case.
Not all of these items are necessary for a valve body up grade but notice the differences between the shift kit and Valve body upgrade
Re-Programming kit ( electronic shift kit)
A Re-Programming kit deals with the electrical side of the transmission. There are no mechanical adjustments made to the transmission with this type of kit. The kit can be programmed to tell the solenoids when to come on and off or how much line pressure should be in the system at any given time.
In my opinion a re-programming kit that is used with out a Valvebody upgrade will force the tranny into a higher overlap time with greater pressure and will cause the transmission fail sooner. If properly tuned with a valve body upgrade this is the ideal unit as pressure can be regulated and shift timing can be determined.
