Super 4th Servo

I ordered this kit with the Sonnax super hold 2nd servo and the Sonnax boost valve kit. This was installed in a Caprice wagon with about 80k miles on the transmission. I installed them all at the same time, so I don't know how much of the improvement came from each of these parts. The shift improvement was noticeable to me, but definitely not harsh. My wife did not seem to notice or at least did not complain. So if you're looking for neck snapping shifts from your 4L60, you will need to do more than just these 3 parts. In vehicle installation for this and the 2nd super servo was not easy. I had to remove the trans crossmember and lower the transmission as far as it would go. I also pulled the passenger side cat. Clearance was still very tight and this was not an easy install. Installation in a transmission removed from the vehicle would have been pretty simple.

I bought this along with the Sonnax 2nd gear super hold kit. My 03 Silverado, 2nd gear was starting to slip, but 4th seemed fine. 1st thing I did was change fluid completely(wasn't too bad) and the filter with the AC Delco Dexron IV. This didn't help much. I figured I'd spend a bit more and see if these kits would work instead of a costly rebuild. They did, and the truck has a much quicker shift too. Wasn't a quick easy job, but well worth it. Hopefully it lasts a while. Machining quality is very good. These are high quality parts for sure.

The servo is a high quality billet part. It works great, can't really tell a lot of difference in the shifting. I bought this because my overdrive suddenly stopped working, turned out to be my computer. I built my 4L60E with other sonnax upgrade parts, and am very happy with the way my trans shifts and performs.

4th gear actually engages firmly now instead of the sluggish shift Especially at WOT. Much needed if you are rebuilding a fresh 4L60E

You will definitely feel 4th gear lock in with this servo. Best bang for the on a servo. i never loved the vette servos too much. Easy to install given you know about servo pin length.

This 4th gear servo helps with firmer shifts and holding power..

Second servo used. One in old, worn trans, and other in new build. I would not build a 4L60E without one. It is IMPORTANT to set up the clearance correctly.

Awesome part for a 4l60e. Boosts band holding power. Harder shifts. Anything SONNAX iv purchased has always been great quality. Easy install.