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Mike, I could use some advice on TH350 longevity problems. My problem is that high gear burns out after 50 to 75 passes. I have not broken the sprag or anything else inside; high gear just goes away prematurely. The trans I have is a heavy duty rebuild with a hardened sprag outer race, the normal V8 extra clutch pack, and a TCI forward pattern manual valve body. I am trying to find out if there is something wrong in the valvebody or trans, or possibly something in my driving style is killing high gear. My car weighs 3550 lbs w/driver and is powered by a small cube, short stroke BBC (414 c.i., 3.600 stroke x 4.280 bore). The rear gears are 4.56 and rear tires are 10.5 x 29.5 M/T slicks...footbrake launch. A local racer/trans builder told me that my high gear burnout is putting too much load on the high gear clutches and that if I were to do a 2nd gear only burnout, the clutches would live. Previously I would shift 1 to 2 and then 2 to 3 and hold high gear for 5 second before rolling out of the throttle and letting the line lock go at the same time. I just had the trans rebuilt as I was swapping out my old local-built 8-inch (Chrysler import core) converter for a custom-built ATI 8-inch Treemaster converter. My old converter was slipping 14 percent, so maybe the added heat from the slippage was hurting the clutches as well? I tend to get about 50-75 passes and, for one reason or another, I pull the trans and notice metal in the pan and have the trans rebuilt. My trans guy told me that aluminum shavings in the pan can only really come from the converter failing (stator). True? If so, maybe my problem all along has been that old 8-inch converter. Looking at the ET's/MPH, this engine is only making about 550-580 HP, so I would think this trans should be holding up much longer. I have emailed TCI and tried to see what info they could provide on a possible cause of the short life. They asked what the clutch pack clearance was and also what the line pressures were. My trans guy assembles the clutches by his "experienced feel" and I don't know what the line pressures are. Several racers use this local trans guy with great success. I'd like to keep a TH350 for as long as it's reliable. My feeling is that this trans should be holding up in my combination. Maybe I'm wrong? Sorry for being long winded, but I tried to give you all the info you might need. What do you recommend? Todd Geisler Todd, Clutch surface area may be your first problem. Normal 350's have four high gear clutches. In your case we definitely need to cut the piston for a five pack. What is also just as important is the main line pressure. The transmission needs somewhere between 190 and 200 psi for the drum assembly to work correctly. If the pressure is low it doesn't matter how many clutches you have in the drum, they won't hold. At these pressures it is also important that you run Teflon sealing rings. Iron rings will wear out too quickly. If the car is run at over 5,000 RPM in first gear, you will need a bleed hole. It needs to be located in the outer direct drum to bleed off excess fluid that can drag high clutches in the top of first gear. This is a very common problem on 350's and 400's. Check these things out and I think you will be in for more great
passes using your TH350.
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