The A-904 required ATF+3 when it added the lockup torque converter in '86. Will ATF+4 satisfy all ATF+3 requirements, or is it incompatible? I know that running Dexron in post-'85 A-904 is inviting a clutch failure, as it will with the later four speed,
the lock up came out in 78 Lockup Converter had one more or one less tooth so they could not be installed on a reg 904 trans
So I've been told! The '86 is a real pip...it must lock up from straight governor pressure, as it locks up whenever 1.) the vehicle goes past 36 MPH, and 2.) is in third gear. Later 904s in M-bodies had an electric solenoid to provide part throttle unlock in third, but the '86 doesn't...no electrical control of the TCC at all. Driving around town or on the flat is not a problem and, although it sure slows things down, I get excellent mileage when everything's as it should be. However, up in the mountains on a grade, it's a real pain in the butt, as there's simply no way to knock off that TCC unless you either get below 35 MPH or downshift to second.
My Torqueflyte guru told me that swapping with an '87 or later (along with the contactor, vacuum switch and an '87 EFC unit) makes life a lot better. Since this 904 works perfectly and has no leaks, I think I'll just pass for now...and drive slow in the mountains.
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