With the TH350 transmission in particular, they came in many "flavors". Most transmission "builders" don't know enough about them to prepare one for serious high performance use. They changed internals frequently thru the years of production, at times adding potential failure points to the unit. This is the single biggest reason they get a bad rap and folks quickly jump to the TH400.
Mike, you would have to define "several" transmissions. If that is two, then the failure rate is 50 percent? If he built 4 units for you, then the failure rate is 25 percent? Way too high if it were a full time transmission business!
We have had one particular TH350 in service for 5 seasons in a customers car running well into the 10's. We pulled it down while the engine was out for repairs recently and only needed to replace the direct drum frictions and steels. They were just starting to show some blue spots on the steel plates. This is prettty much "normal" for a transmission that is being hit with near 700hp every time it's used! Let the frictions take the abuse, NOT the hard parts, that's what they are supposed to do. It's my opinion that the hydraulics of the unit are more important than the parts used to set it up. The high line pressure and window shattering shifts provided by many shift "kits" can be extremely hard on the unit, and decrease it's life expectancy accordingly. We've been leaving the accumulators operational and being more conservative for separator plate hole sizes in recent years. Ya, you don't get the loud "chirp" between gears for "normal" driving, but the trans will love you more for it!....Cliff
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