I'VE ALWAYS HEARD TO TRY AND GET AN 'H' SERVO FROM A C4 TRANSMISSION BECAUSE IT HOLDS MORE PRESSURE AND MAKES IT SHIFT A LIL STRONGER. WELL I HAVENT TRIED ONE MYSELF TO FIND OUT SO IM NOT ENTIRELY FOR SURE BUT I DO KNOW THAT THE 'W' SERVO IN MY GRABBER SHIFTS GREAT! IT'S QUICK, RESPONSIVE AND HAS NO FLARE-UP BETWEEN GEARS... JUST QUICK, CRISP SHIFTS (AND HAS NEVER BEEN REBUILT). SO HERE'S MY THOUGHTS.... IS ANYONE ELSE RUNNING AN 'H' SERVO AND IF SO COULD YOU TELL ME HOW IT SHIFTS OUT? IM WONDERING WHETHER TO LEAVE MINE ALONE OR MAYBE UPGRADE A LITTLE IF THE 'H' IS BETTER. AND AS ALWAYS, THOUGHTS AND OPINIONS ARE GREATLY APPRECIATED! -AND DOES ANYONE KNOW HOW MANY DIFFERENT TYPES OF SERVO'S THERE ARE FOR C4'S???
I've used a few different ones. H, R, C, A, B and I believe I used an N servo once. The best were H, C, R, and A in reguards to shift quality. The R was the absolute best (rightly so). C was next, then the H...and last, the A. A is most common it seems in JY C4's. As far as shift quality, it really doesn't mean jack schitte if you have a 200,000 mile virgin C4 because it's probably worn to the point that the best servo on the market won't make it shift 'good'. If it's remotely fresh, it'll do great and you'll notice a small difference in quality of the shift between different servos. OT: Have you ever pulled a servo out of a JY trans? There's usually a ton of 'mud' built up in the back of the case. The H servo does have a rather large apply area, but also a large release area....it holds great and that is why it gets a good reputation. The R I believe has a smaller release area and a slightly smaller apply area....they release quickly and hold quite well. I had an R in the turbo maverick...and it shifted beautifully. No flare at all and a VERY quick 2-3 shift. You could barely feel the shift it was so fast...but that was on a turbocharged 302; there was also a little tire spin on the 2-3 shift from time to time. I REALLY liked the R, but the C wasn't far behind. Have you seen the case mod? You tap the apply hole to 3/8"-16, screw in a small allen head set screw with loctite. Then grind the outside area of the servo piston down on 3 sides. This allows full apply pressure to the piston and full holding power. But be warned...I have heard/read sporadic reports of it having so much pressure that it can break the band, so try it at your own risk. I almost did it on the turbo maverick....but ended up selling the car before I got the chance.
Also the mod's mentioned for the servo plug and notch grinding, are also known to break the covers out too. The PA billet servo has a thicker aluminum cover and can be used for this mod with good results. All out pedal to the metal, such as racing, is what really does the damage as mentioned.
I use a Broader C4 in my drag car with a C code servo witch has the most surface for the most holding power! I use a A code servo in my street strip car ! The guy that out me on track to have Broader to build race tranny also says the R code is a great servo for under 400 HP after that It would be a good idea to go to the greater holding power of a C or H code! A code and R code have the same Apply area but the R code has a smaller release area making for faster shift ! If you talk to different people they will have different opinions on this but More clamping power on the bands if you have big power is just insurance to keep the tranny working!
The H code servo was used in the 1965 and 66 Gt 350 Auto and the C code was used in the 1964 Hi Po Fairlane 289 but the 1967 and 68 GT 350 had an A Code servo! The C and H code stock Servos are hard to find But P A and TCI along with others make a billet H code! and Sonnax makes a billet replacement for the C code
Here is the best info on servos I've seen..... http://mmb.maverick.to/threads/c4-diagnostics-and-data.47348/#post-493742
