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Old 03-20-2009, 03:13 AM
jakeshoe jakeshoe is offline
The Trans Guy
 
Join Date: Aug 2007
Location: Texas
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Default Re: 200-4R Rebuild ... step by step!

The stock 200-4R has a weak 2nd apply due to a small servo apply area. The Buick Grand Nationals in 1986 and 1987 had the largest stock apply area and these servos are good to 400 HP but above that an aftermarket servo is necessary.
Shown here is a stock generic 200-4R servo, a GN servo, and a CKPerformance servo. The CKPerformance servo has the largest apply area of any servo on the market.
The Sonnax Super Servo is the 2nd largest, and the Superior/Fairbanks servo is 3rd.
Any of these will work well.


You must assemble the servo without the large cushion spring and seals and install into the case with the snap ring.



Be sure you have the band pin in the case to hold the band. You should be able to depress the servo cover .060" once this is done. This is how you set band clearance. If it is too tight and you cannot install the servo snap ring, you must grind the servo pin end down to get clearance. When you depress the servo cover, you should see the band tighten on the drum inside the trans. You can see this beside the VB area. If the clearance is too loose, you must get a longer servo pin or install a pin extender.

Once the servo has seals installed and is installed you can air check the servo here:


Be sure the band tightens around the drum.

Servo clearance is important. Too tight and you burn the band. Too loose and you can have a sloppy shift from 2nd to 3rd. The trans applies oil to 3rd gear, and this oil has to push the servo back into the cover away from the band. The longer the travel, the more oil is consumed by this cavity, and it slows the feed to the 3rd gear clutches
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