Transmission Shift Kits


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How To Install A Shift Kit in an Automatic Transmission

Before we discuss how to install a shift kit, we should probably look at what a shift kit is and the purpose it serves in an automatic transmission.  First of all, a shift kit is a collection of parts that are installed in the valve body of an automatic transmission in order to reprogram the valve body to change the shift characteristics of the transmission.  In a modern automatic transmission, the valve body is a electro-mechanical-hydraulic controller that manages the way that the transmission shifts.  In effect, the valve body is the "brain" of the transmission controlling when and how it shifts.  These days, since modern vehicles are largely computer controlled, the transmission is also controlled through programming in the vehicle's computer system.  In the past, prior to all the modern computer controls, a transmission valve body didn't have all the electronic controls and it was simply a mechanical and hydraulic based controller with a vacuum diaphragm that received a vacuum signal from the engine.  The vacuum signal would help to tell the transmission when to shift up or down.  If engine vacuum was high, then that meant that the throttle plate was only open a little bit which means that the car was being driven more leisurely.  Under these conditions of light loads, the transmission would shift up to a higher gear sooner to help conserve fuel.  Smash the throttle and engine vacuum drops when the throttle plate is wide open.  In this situation, the lower vacuum signal would be used to tell the transmission to downshift to a lower gear for greater power and acceleration such as when passing or climbing a steep hill.  In the old days, these were the type of signals that were used to help the valve body determine how to shift.  Simple but effective given the technology available back then.  These days, the control of an automatic transmission is much more complex.  The picture below shows what the inside of a typical valve body looks like these days.  The maze-like passages are where automatic transmission fluid (ATF) flows.  The valve body has an orifice plate (upper left hand corner of picture) which controls the amount of fluid passing in and out of certain areas of the valve body.  If you think that it looks rather complex, then you would be right.  The modern automatic transmission is an engineering marvel that most people take for granted when the get in their cars and drive.    

Valve Body

Most automatic transmissions are programmed from the factory to shift as smoothly as possible.  In terms of occupant comfort, this can be good.  In terms of transmission longevity, it is not always so good.  In order to achieve these smooth and unobtrusive shifts, there needs to be a lot of slippage, and this means more heat build up and wear.  While a silky smooth shift might be easier on you and your passengers, the clutch packs can take a beating with all the slippage.  A shift kit will usually give firmer shifts.  With the firmer shifts, you usually have less slippage, less wear of clutches and bands, and less harmful heat build up in the transmission.  Of course, this only goes so far.  You don't want to have an extremely harsh shifting transmission, or else it can stress out the driveline unnecessarily. 

When installing a shift kit, you should also plan to just do a fluid change.  Even if the fluid looks clean and could normally be left in the transmission longer, it just makes sense to use new fluid since you will have to drain the old fluid to access the valve body anyway.  While you are at it, you also should change the internal transmission filter.  Since many automatic transmission pans don't have drain plugs, you should also plan to get a new pan gasket.  To summarize, in addition to the shift kit itself, you should also get the following items:

  • New automatic transmission fluid (ATF)
  • New transmission filter
  • New pan gasket

You can find these items at your local auto parts store.  They also might be able to tell you how many quarts of transmission fluid you will need to buy for your particular vehicle.  Whenever I've changed automatic transmission fluid, I've usually gone with a fully synthetic ATF.  It is more expensive, but the way that I see it is that it's cheap insurance.  An automatic transmission rebuild or replacement is extremely expensive on modern vehicles, so it's a good investment to use a high quality synthetic fluid.  Mobil 1 Full Synthetic ATF is my personal favorite.  I've never had an automatic transmission fail while using Mobil 1 ATF.  Even if you just choose to use regular transmission fluid, you are still going to be better off because your transmission will have fresh, clean fluid that will help contribute to longer life.  Some people swear by Amsoil products.  If you're interested in the Mobil 1 ATF, then below is a picture showing the bottle in case you want to look for it at your local auto parts store.  You can also find it online, which is often the way that I order it.  

Mobil 1 ATF

I remember when I installed a shift kit in an E40D transmission found in my Superduty 1 ton Ford E350 van.  I installed a Bully Dog shift enhancer kit because I planned to do some heavy duty towing.  I removed the bolts on the transmission pan and drained the old ATF.  If there is no drain plug on your transmission pan, then you need to partially loosen the bolts all around the pan, and then further loosen the bolts around one corner so that it hangs down lower.  In this way, the lower corner will funnel the fluid and act as a drainage point.  If you aren't careful about this, then it can become a big mess with fluid leaking all over the floor.  After draining the fluid, then you can remove the pan altogether.  You can then remove the internal transmission filter.  The valve body should be accessible at this point.  Remove the bolts holding the valve body to the bottom of the transmission.  Be very careful when you split open up the valve body.  Try to keep the lower half flat and slowly tilt it over to drain out fluid from the passages.  Take careful note of any balls or other small parts that might fall out.  You will need to install these in exactly the same place.  I wasn't so careful when I installed the shift kit on my E350.  After I was done, I took it out for a test drive, and that's when I discovered something was very wrong.  The transmission didn't want to shift up at all.  It was like the transmission was stuck in low gear.  At first, I was very puzzled by what happened.  I drove home scratching my head about what I had done wrong.  Then, while emptying out the old fluid from the drain pan, I noticed some small metal balls at the bottom of the pan!  YIKES!  I didn't even know that these balls had fallen out of the valve body.  Their absence was the reason my transmission wasn't working right.  Obviously, they put them there for a reason, and they are critical to the way the transmission works.  Problem was that at that point I didn't have a clue where they were supposed to go!  I called Bully Dog but they were unable to help me.  I took a chance and called Transgo and explained my predicament.  Even though they knew that I didn't have a Transgo shift kit, they were very helpful.  The faxed me a diagram showing where the balls needed to go back into the valve body.  I was very thankful to Transgo for their great service.

Shift Kit 

All this to say... make sure that you take your time when opening up the valve body while installing the shift kit.  If possible, take pictures or jot down some notes to ensure that you put everything back exactly the way that it was originally installed.  The Bully Dog shift kit for the E40D transmission was relatively simple with only a few parts to install.  If you have a more comprehensive and complex shift kit such as some of those made by Transgo, then you will want to be extra careful during disassembly and reassembly of the valve body.  If you are not experienced or interested in opening up your transmission, then you might also consider hiring a professional to install the shift kit.  On a related note, if you really do not want your transmission opened by you or anyone else, then there might be a way to reprogram your shift pattern with the use of a computer tuner/chip.  As I mentioned earlier, most modern automatic transmissions are computer controlled.  That means that you can sometimes also reprogram your transmission shift pattern using a tuner chip.  On my E350, I had a Bully Dog tuner (and now have a DP Tuner system) that electronically modifies the shift pattern.  When I am running in tow mode, the firmer shifts occur at higher engine RPM, which is better for towing heavy loads.  When I run in economy mode, the transmission shifts earlier to keep engine RPM lower in the effort to conserve fuel.  Since modern automatic transmissions have electric solenoid valves, parameters such as line pressure going to the clutch packs can also be increased some electronically.  This helps reduce slippage and firms up the shifts as well.  There are limitations to what can be done electronically, and so major changes will likely require a shift kit to be installed.  In my case, I have both the shift kit and the tuner that change the way my transmission behaves.  Even with both, my shifts are not too harsh at all.  So, whether you want to try to electronically modify your shift pattern with a tuner, or if you want to go with the traditional shift kit (or both), you have options for fine tuning your transmission for better performance and longer life.