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Title:Installing a Corvette Servo

Author:AcidBatH666

Installing a Corvette Servo in your 700R4/4L60/4L60E is one of the cheapest and best bang for your buck mods you can do. It is one of the most popular tranny upgrades next to a shift kit, and usually done in conjunction with a shift kit. The Corvette's "YDM" transmission is unique to all other 4L60s (700R-4) in part to its very large 2nd Apply Piston.

Take a look at the picture:

This is the piston housing. The Corvette's is on the left, and the standard 700R4/4L60E is on the right. There is actually a third size (not shown) that has an even larger piston size used for non-performance vehicles.

The other half to the servo is the piston. Once again, the YDM (Corvette) is on the left and the stock 700R4/4L60E is on the right. Notice the substantial difference in size. The larger piston allows for more holding power. Notice how theres more surface area on the Left one? The fluid has more surface area to grab, which is basically why it firms up the shift to grab even more than stock.

The actual installation and swapping of a Corvette Servo is basically pretty easy. Installation is a snap, and some good news: 1) you won't have to lower the transmission, and 2) you only loose about a quart of fluid.

First you must know where the servo is located. It is on the passenger side of the transmission. Get under your vehicle and locate this part.

If you are having trouble, just follow the transmission cooling lines as they go back from your radiator, past the motor, and into the transmission. It will be in that area. Not that hard to find at all.

First thing you need to do is raise the car up, either with jackstands or a lift, ramps, or whatever you have, just make sure it is safe. Then locate the servo cover (painted black in the picture above). There is a snap-ring to hold it into place. I cheated and used the "special GM tool" to depress the cover to remove the ring, but a simple prybar against the transmission tunnel will work, then just pry out the ring, and remove the cover. Its really not hard.

The cover has a large O-ring around it and may make it difficult to remove, just make sure you purchase new seals, because this one will probably tear. (I included my old Tech sheet from my old Corvette servo with color coded icons to show you what color O-rings go where) When you order the servo, it will come with Teflon rings, but you will need the Cover O-ring, and the Housing O-ring. Once the cover is off, the trick is to disassemble the servo in the case. First remove the housing. Then remove the E-clip, washer and spring.

Once all of this is removed, you will probably need to employ the services of a friend. You will need to pry the transmission towards the drivers side (or away from the passenger side). You may need to take the nut off of the crossmember to allow more movement. You want to pry it over far enough so that the apply piston will clear the transmission tunnel with the servo attached. If you have to lower your trans to get it out, just make sure you remove your distributor cap so you don't risk breaking it.

Once out, you will see that there is a "plate" inside the piston and is spring loaded. You will need to squeeze this together and remove the snap-ring. Once apart, the servo will separate from the pin/spring assembly. Simply install the new servo onto the pin, squeeze the assembly back together and install the snap-ring. Install the new seals and use ATF to lubricate the assembly. When you go to put the assembly back in the trans, look out for the spring still in the case. It may still be on the "nub" or it may have fallen. If you feel inside the case, you will see the hole for the pin is in a raised "nub" and the spring must rest around this nub. Then pry on the tranny again and install the assembly. Once in, push on the assembly, it should feel springy. If it does, its in right.

Below is the Piston. Make sure you get a new seal (as shown, RED). The side you see goes in towards the transmission.

This is the 4th Piston. Notice the nub on top. This goes towards the outside of the transmission.

Install the Piston, and then the 4th Piston. Once all in place, install the cover (with new seal of course). Using the same method for removal, depress the cover into the case, and install the snap-ring. Re-install everything that was undone, lower the vehicle, and check you fluid level and add as necessary.

Now here are the tech sheets i mentioned earlier. I noticed the in the forums a couple of people were confused about which colored seal(O-ring) goes under what part. If you buy a Corvette servo, It should come with the Inner Servo Piston, 2nd Apply Piston, the 2 Rings/Oil seals for the 2nd apply piston, O-Ring for the 2-4 Servo cover (Blue), and the Seal for the Servo piston housing (Red)

I have color coded them to help with any confusion.

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A few other bits of information.

In the General suspension/Drivetrain forum, There is a sticky with 4L60E information. In this I found from a transmission shop that is currently building a transmission for me that a shift kit is not always the best thing, especially for a 700R4/4L60E. You can acheive even better results from installing Servos with more surface area. There is another servo besides the Corvette servo. There is also a High Performance Billet servo. While it is drastically more expensive, it also has even more surface area than the Corvette Servo. This servo has 35% more holding power (fluid apply area) than the Corvette servo. It'll give a firmer 1-2 and 2-3 shift. The Vette servo will make the shift firmer, but the billet servo will actually make it bite even more to grab with more force. Price difference between these two is around $15-$20 for the Vette servo, and around $70-$90 For the billet servo.

There is also a high performance overdrive billet servo. This Super-Hold Servo has 40% more holding power (fluid apply area) than the stock overdrive servo and gives a firm 3-4 shift.

If you would like to purchase any of these parts, http://www.transmissioncenter.net/4L60E.htm has them. They do sell a 700R4/4L60E "Wake Up Kit" that consists of the high performance intermediate billet servo, the high performance overdrive billet servo and the oversize pressure boost valve. These three parts will wake up your 4L60E and can be installed without removing the transmission or valve body. They sell for $199, and you don't even need to worry about messing with cracking open your transmission or Valve body to install a shift kit.