lost 4th/ overdrive- need help in troubleshooting

[Evans Ward]

Car lost overdrive today. Trans has about 27,000 miles on recent fluid change and has been shifting fine. Haven't adjusted or reset the TV cable either. Car will not shift into OD even at speeds exceeding 55 mph. That's lock up when it does that final shift with revs dropping, right? Had been shifting into OD at about 45 mph. Car has not been raced and I do not have a manual lock up switch either. Could the TCC Solenoid be bad and in need of replacement? What about the 4th gear pressure switch? Do these or one or the other go bad? I suppose I need help with a systematic troubleshooting tree before I drain tranny and look inside pan. I sure hope my transmission isn't going out or the torque convertor crapping out? If I haven't supplied enough information, please let me know and I can give further details. I am parking it until I can fix this as I do not want to risk further or more damage at this point. Any and all help greatly appreciated!

 

[chris718]

puty the car on a lift and in d4 at 55 mph see if you have any oil at the fourth pressure tap.if not blow air into it and see if it shifts into 4th .if it does its the valve body if not its damage at the 4th clutch

 

[Evans Ward]

puty the car on a lift and in d4 at 55 mph see if you have any oil at the fourth pressure tap.if not blow air into it and see if it shifts into 4th .if it does its the valve body if not its damage at the 4th clutch

Chris,

I am a trans novice. Where is the fourth pressure tap located and how do I blow air into it? Here's also some updated info on the problem/ situation:


I checked fuse that TCC is on and is was good. Wires look intact at connector trans DS. I checked brake switch under steering wheel by pedal and that looked adjusted although I did readjust to give slightly more clearance. I decided to change the chip from a Thrasher to a Jay Carter burn I had to see if that would affect anything. From a test ride, it is shifting into 4th now and locking up although it does seem sluggish and hesitant to do so. When I tap the brake with the car in lock up, it does disengage as it should. Does any of that help further? Thanks for any help.

 

[chris718]

no fourth cannot be electrical.the 4th tap is on the rear of the trans by the tailshaft on the passengers side .compressed air via an air compressor and blow gun will charge the circuit,or a portable air tank and blower.

 

[Evans Ward]

Chris,

Thanks! The car is now shifting great and back to where it should have been but I did nothing to it? Maybe some debris or trash cuased a glitch? My plan is to drain and cahnge trans fluid with a filter change in the next few days. What does that 4th gear pressure switch actually do that has the single electrical connector attached to it?

 

[bison]

Chris,

Thanks! The car is now shifting great and back to where it should have been but I did nothing to it? Maybe some debris or trash cuased a glitch? My plan is to drain and cahnge trans fluid with a filter change in the next few days. What does that 4th gear pressure switch actually do that has the single electrical connector attached to it?

It signals the ecm when in 4h gear so the ecm can follow parameters in the e-prom such as boost in 4th, and lockup in 4th. But note that the 4th switch isnt the only info used by the ecm for commands.

 

[Evans Ward]

Thanks Bison. I'm going to change out the 4th gear PS when I change the trans fluid and filter. Can't hurt and part is $11.00