Questions and Answers

Ford Thunderbird Transmission Concern Q. Hello Vincent, I have a 1994 Ford Thunderbird LX with a 4.6 liter engine, AODE automatic transmission and 41,000 miles. I have an intermittent transmission problem similar to that described to you by Mason of Fairhope, Alabama, Ford Thunderbird Transmission Concern and perhaps I can add to his description.

My problem began when the car had about 30,000 miles on it and for the past 10,000 miles the situation has been slowly getting worse.

At intermittent intervals and usually at constant highway speeds, it can also sometimes occur at 40 to 50 mph, the transmission will down shift from OD to THIRD gear and sometimes progressively to the SECOND gear and back again for a short interval without loss of road speed. These downshifts naturally induce increased engine RPMs at each shift stage if the throttle is held constant. It might do this repeatedly for three to five times or only once or twice.

No dash warning lights are seen during each occurrence and the OD warning light remains off. When the OD is left in the locked out position a similar sporadic downshift from THIRD to the SECOND gear and back may occur again at random intervals indicating the problem is not just with the OD.

I can exactly duplicate this condition by manually downshifting the transmission with the electronic OD lockout and gear shift lever while holding the throttle constant. It does this in cold weather, in warm weather, when the cruse control is on or off, up hills, down hills or on level roads.

I can drive the car at highway speeds for 200 to 300 miles without a problem and suddenly for the next 10 miles experience several of these un-commanded downshifts. After which I can again drive for 100 to 200 miles without a problem. I've taken this car to several shops, including the Ford dealer, and no one I've talked to seems to know what the problem could be.

The test drives they perform (with scanner) naturally do not induce the problem. It is hard to find a mechanic who will test drive my car for the 200 to 300 miles needed to induce the problem. At all other times the transmission performs normally with no slippage or shifting problems. The transmission oil and filter were changed twice by these shops to no effect.

I put in a TransGo performance shift kit and found that the SECOND accumulator piston spring was broken which was replaced by the kit. The oil appeared normal and there were some metal shavings attached to the magnet in the pan. Although the kit improved the shifting performance of the transmission it did not correct this intermittent problem.

I've driven automatic transmissions for many years and feel that there is nothing mechanically wrong with this one. I get great gas mileage, 24-29 mpg and in all other respects the engine and transmission perform satisfactory. The random occurrences and relatively short duration of each lead me to suspect an glitch in the electronic control.

I've examined the throttle position sensor for dead spots with a Multimeter as you suggested to Mason and could find nothing wrong. I've come to the conclusion that I will have to progressively replace different electronic components until the defective part is encountered. However, with this strategy I will not know if I corrected the problem until I perform extensive highway testing with each replacement.

Can you provide me with a way to logically replace control components that would yield the highest chance of success for the lowest cost? Should I replace the throttle position sensor even if it appears to be normal with bench testing? Is it likely that this problem is caused by a computer module chip malfunction? Would it be worth while to replace this first?

I really like this car and it is in very good shape, spent its life in a garage and was pampered. Overall this car has given me great satisfaction in how it drives and I would hate to get rid of it because I cannot fix this problem. Can you help me? I would greatly appreciate any advice.

Sincerely,
Larry
Colonia, New Jersey

A. We can try to narrow it down to a mechanical or electrical problem by unplugging the transmission and see it the problem reoccurs. If it does, then we can look for a mechanical cause. If not, then we can check electrical possibilities.

I'm going to assume that with all these repair attempts that someone along the line checked for DTCs in the computer and found none.

New transmission temperature sensors have fixed similar problems, but in all good conscience I can't recommend replacing one part over another in an attempt to fix the problem. Throwing parts at it may also prove inconclusive since the problem could just as easily be a wiring problem.

Sometimes you have to wait for a problem to become more pronounced before you have any kind of chance of finding and repairing it.