I have a Th400 behind a LSX and 3rd gear keeps going out. I have had it rebuilt 3 times by 2 different people and still the same problem. The Car weighs 3200 pd and runs 10.00's on motor. and we have sprayed it with 150 shot on progressive with 9.44. This last time it made 20-25 passes before acting up. 1-2 is smooth but when you shift 2-3 it acts like it is in Neutral. If you take your foot off the gas for a second it will go ahead and make the 2-3 shift. This is a footbrake car with no transbrake installed. It does have a Tran-Go Man. Valve body installed and the last time a new pump was installed also. The shifter cable is set right (that was the first thing we checked). I have heard that Th400 have a problem with 3rd gear, what is the cause and the solution. Thanks Ryan

 

Block the 3rd gear accumulator.

 

there are many things it could be. You might want to give me a call.first thing first CHECK LINE PRESSURE!!!!

Greg

 

Builder error, I'm sure. As FTI said, there are many things it could be, and probably a combination of everything. Basically, you need to dual feed, block the accumulator, and use 6 b/w high energy frictions at .010 per friction clearance. It also wouldn't hurt to put a heavier p.r. spring in it as well.

 

Take a good look at the boost valve. I have seen some of these very worn in TH400's. Also recently I used a sonnax pr valve that uses a Teflon seal on the end of the valve to help tighten up this circuit. The seal is a PITA to get it in the pump with the pr valve. I found if you use a zip tie and a small piece of plastic like from a sand blast cabinet lens as a sizer, it works pretty well. If that makes any sense. As mentioned there are many things that can cause issues. Just figured I would throw this out there. Vince