Still have problems w TC lock up at around 55MPH + steady throttle highway speeds.
Have replaced EGR, EGR solenoid, EGR passages open, no vaccuum leaks found, steady manifold vaccuum, replaced TCM w known good unit. Also inspected electrical connection on side of transmission, no corrosion or visible breaks in wiring. 168,000 miles 4.0. No other issues, except cruise control also inoperable. Need to fix, great car w many repairs done. Any other ideas besides transmission? Can lock up solenoid be tested/replaced wo removing Tranny?

 

Hi Shelby676,

Sorry to hear you're having transmission issues.

How recently have you changed the transmission fluid, and did you just drain and refill, or did you do a more complete flush by draining and filling, driving, draining and filling, driving, then dropping the pan, changing the filter, reinstalling the pan with a new gasket, then refilling with fluid?

What fluid are you using in your transmission? If you used Dexron VI or another modern fluid, it may be that its lower viscosity and different friction modifiers are at the root of your TC failing to lock up. In our '93, Redline D4 ATF is the best fluid I've found to replicate the viscosity index and friction modifiers of the Dexron III that was originally specified for our gearbox.

Regarding your cruise control, a common problem is failure of the dump valve, which is mounted on the left wheel arch near the air filter housing inlet snorkel. The dump valve is normally open, but when 12V is applied it closes. You can test it to see if it blocks the flow of air when 12V is applied. If not, your cruise control system cannot hold vacuum and therefore will not function.

Cheers,

Don

 

Thanks for your input. Looking back, I realize I have done fluid and filter changes on some of our other automatics but not this one. It was on the to do list , and I found the filter and gasket purchased two years ago. I do remember adding fluid after changing head gasket and losing quite a bit after removing the radiator. I did top up with current Dexron.
I will replace and will post if that took care of the problem. On my latest fluid change (Dodge) I disconnected lines at the radiator/cooler and added clean fluid while running until I had cycled full capacity of tranny. I think that flushes out the fluid in the TC well. (This is after changing filter and topping up first.) Any thoughts on that process?