Torque Converter Question.

I am running a SBC 350 engine with a TH400 transmission pushing a Ford 9 inch rear end and I am looking for a new torque converter.

When shifted into reverse or drive from park, there is a sizable impact/jolt, from a complete stop, the transmission hesitates quite a bit at the start and then there is a jolt upon moving, and while driving if the accelerator is floored, again there is a sizable hesitation and then jolt. A friend has suggested Hughes 2500 stall series. This would probably be the GM25-400bp model.

I have also looked at the TCI Saturday Nite Special, the B&M Tork Master 2400 and the Summit and JEGS knock-offs.

Is one brand better than another? Other than price what are the differences?

I have a TCI sns in my powerglide...have had no problems.

I have always used Coan http://www.coanracing.com/ and have never had a problem. They have great customer service and will build you a converter to your cars needs just my two cents. It is truly up to the person of what brand they use.

diagnosis

That behavior does not sound like a defective torque converter. Has the transmission been rebuilt? Is it full of fluid? I've had transmissions do that when they were either low on fluid or had a partially clogged filter. Also, there have been aftermarket filters for Turbo 400 transmissions that do not allow adequate fluid flow, especially cold; they usually have a green colored cloth filter material visible where the pickup tube goes. Speaking of the pickup tube, it has an O-Ring that seals it to the case - if that O-Ring is missing or hardened, the pump will suck air there. Finally, does the transmission have a deep pan or shallow pan? Did you change to a deep pan? The deep pan requires a longer pickup tube and longer filter bolt with a spacer that goes between the filter and valve body (68-up; early 400's had a totally different filter). The filter must "float" on its bolt, not be bolted fast. Another odd problem you probably don't have is if an early pan was swapped to a late transmission, or vice versa.

Second issue, that is related to the initial jolt on engagement, but not the hesitation problem. What is the engine idle speed? Do you have an aftermarket "big" rumpity-rump cam in it? If you do, a stock, tight converter will bang on initial engagement, but then would stay engaged, usually resulting in the car wanting to lunge forward against the brakes, not "hesitate."

Another probable cause, IF the transmission has NOT been rebuilt, is hardened clutch piston seals. As the engine revs, and builds pump pressure, the leaky seals are finally overcome and the piston moves to apply the Forward (or direct/reverse) clutch with a bang. At idle, the pump pressure drops off, allowing the seals to leak and the clutch to release. Couple the hardened rubber seals with a typically worn pump that no longer delivers adequate pressure at low engine speeds, and you have the problems you describe - IF the transmission has NOT been rebuilt. (Or a bad pump was reinstalled).


Start with the simple stuff; It would be a shame to go through the money and effort to change the torque converter only to find the problem lies elsewhere.

440shorty

Diagnose twice, replace parts once.