pmedic9

I have a 2001 Silverado z71 5.3 with 4L60e transmission that was just replaced from a 01 junk yard trans with 100,000 miles on it. The installer stated the trans looked like new inside they installed new cooler lines and cooler all factory and replaced all the fluid with the new synthetic transfluid from GM. The transmission runs great but I tow occasionally about 1800 pounds in a trailer approx. 200 miles each way a few times a year and haul pellets for my wood stove. I would like to modify the transmission slightly without having to remove it. I have seen many things written about modifying these transmissions but I don't want to modify 1 item and have it weaken another area of the transmission. There seems to be a large amount of people here with a lot of knowledge so your input would be appreciated. I don't mind pulling the valve body or modifying it as long as I don't have to remove the transmission. I am not trying to have a drag tranny but don't mind if it shifts crisp but won't break anything inside. Thanks

mrvedit

For improvements for towing, I would first start with a Sonnax 4l60E-LB1 boost valve ($25) and a performance 4th gear servo piston ($70). Next, add a 2nd gear servo piston ($90). Both Sonnax and Superior make good servo pistons. So far you only have to drop the pan and remove/rebuild the servo.

If you want to go a bit further, Fairbanks makes a "Towing" kit with a boost valve, both servo pistons and a complete shift kit for $270:

http://hptransparts.com/general-moto...t-1996-05.html

Installing all of it will require dropping the valve body and rebuilding part of it, but you could start with just the boost valve and servo parts.

carlsonauto

for what you are doing I would personally go with...

Sonnax super servo 2nd (77911-03K)
superior super servo 4th (K034)
.500 boost valve of some nature.. the sonnax valve (4L60E-LB1) is a good choice

Or if you want Ted is spot on, the fairbanks kit (PT4L60E) comes with the perfect setup if you are willing to spend the little extra $$ and take the time.. It will be correct when its done with that kit and well worth it.. It comes with both servos that are the correct ratio for what you are doing and a bunch of other goodies that will make your trans a lot happier...

pricesgarage

i just did a modified corvette servo and a superior 4th gear piston in my 03 zr2 s10 shifts are a lot quicker 1-2 is a lot better at light throttle it not harsh at any throttle position a .500 boost valve is a easy mod but does require pan removal

mrvedit

pricesgarage's suggestion of using the Corvette servo is good cheaper alternative to a billet 2nd gear servo piston.

The issue is that when towing in OD, the band is known to slip in 4th gear. The 2nd and 4th gear pistons in the servo work together in 4th gear to hold the band tight. The pistons mentioned above have more surface area and therefore hold it tighter. The bigger boost valve increases line pressure, which further tightens the band.