Hi everyone . I have a problem with my Silverado 350 c1500. the TH700R4 transmission only started slipping in 4th gear all of a sudden. the others gears work fine as always. I've read that if the other gears don't slip it means it's not a problem with worn friction discs. Has this happened to any of you? THANKS
You can check for an excessively worn 4th apply servo piston scarf cut sealing ring with compressed air with the pan off. First, check servo travel - should not exceed 1/8 of an inch inboard. If it checks out, drop the pan and look for the small hole on the pan rail of the case, just below the servo cover and put air into it. Watch for firm band apply. If the apply is weak, you hear air hissing from the servo, remove the servo cover and piston and replace the seal.
As mentioned above, slipping in 4th is usually 3/4 pack failing, the above servo and apply trouble shooting assumes you dont have any black clutch material or other debris/metal and fluid smells good (ie not burnt) and is still normal looking red.
Otherwise, if you see black clutch material or any other debris, put the pan back on with a few bolts, yank it out and overhaul it.