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Prior to the advent of electronic controls for automatic transmissions, the valve body was a large (9 inch by 12 inch) block of cast iron, containing two dozen or more precision machined and polished spool valves which routed pressurized transmission oil to various clutches or bands in the transmission through a labyrinth of worm-like passages cast into the valve body.
These spool valves and their springs effectively were the "program" which created the various shift points of the transmisison. Inputs were primarily oil pressures and flow through one-way check valves. A bad valve or spring would cuase problems by the valve "hanging up' and not diverting the oil at the proper time in the shift sequence.
With electronic controls the logic of valves and springs has been replaced with computer programs activating solenoid valves in the valve body. Spool valves are still used to shuttle oil from one port or passage to another within the valve body and then to the clutches/bands, but usually serve no logic function anymore. A sticking valve can cause the type of problem you have experienced. A burr on a machined edge, a very slightly oversized valve diameter, or a very slightly undersized bore diameter could cause a valve to be slow/reluctant to act.
Software is cheap to update so that is why it was tried first. Opening the transmission case to replace a valve body is more expensive so it was not tried until later.
posted by 198.208.22...
_______________________________________
Saabs owned:
2008 9-5 Aero Sedan, sold at 227K miles
2006 9-3SC 2.0T - Wife's daily driver
2000 Viggen Convertible - Sold May, 2022
1964 Quantum IV Formula Car - Retirement project
2000 9-5lpt Sedan, sold at 318K miles
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(#882) [Profile/Gallery]
(more from MI-Roger) on Mon, 7 Feb 2005 07:00:02
