TC Lockup was working now wont lock

[tombombadom]

Hey All,

Just picked up a 90 Ranger last night, 4.0 EC, good ole A4LD, from a recipt I found has 70K or so on rebuild, was driving it today up a slight hill and the TC unlocked, and now it won't lock back up. I checked fluid and it was a little low, topped it off and drove it, and it was the same thing. I'm kinda new to thease A4LDs I know they can have issues, but can be good too. Just want to know whats going on so I can fix it!

No codes were found when I scanned it. Trans otherwise shifts fine, you can feel it go into OD but no lockup.

Let it sit for a while and took it out again, still no lock-up. I shifted from OD to 3 and it did downshift.

Thanks.

 

[PopRichie77]

Did the OD light flash? It takes about 3 failed lockup a temps to set a code. A standard OBD2 reader will not read transmission codes.

 

[MrShorty]

TC lockup is electronically controlled, as you seem to know. The first step I would take would be to test the TClockup circuit and see if the computer is commanding the shift or not. It is a simple ground side switched circuit, so it is pretty easy to hook up a voltmeter to the circuit (either measuring voltage drop across the solenoid or measuring voltage drop across the PCM). Then you can use the output state test (see my notes on pulling EEC-IV codes thread) to see if the computer can switch the solenoid. On a test drive, you should be able to see if/when the computer commands lockup and observe whether or not the transmission seems to respond.

The basic idea is, if there is an electrical problem -- find and fix it. If the computer can and chooses to command lockup and the transmission does not respond, then there is a mechanical/hydraulic problem inside the transmission.

 

[tombombadom]

Thanks for everything! Great information. unhooked tps, brake light switch and wiggled the VSS wiring in the back and rehooked everything then took it for a drive. Now everything is working as it should. Must be an electrical gremlin somewhere.

 

[tombombadom]

Another Update:

After still having some problems, I have determined that the problem is temprature related. It seems that once it gets up to a certain temprature that is when I'm losing the lock-up.

Its been cold here but there have been a couple of days when its gotten up into the 40's and it would work for a while then not work after it got up to temp. Let it sit a few hours and then it would work. I know. Weird.

I've decided that the TCC solenoid is the likley culprit, I know changing it (them, if I do it I'm going to do the 3-4 and TCC) involves dropping the valve body, what do you all think? How difficult of a job is it? I'm not sure if I feel comfortable doing it, I've never had one apart before. I've been trying to do some reading, but this is the best I can come up with. Definatly an intermittent problem.

 

[PopRichie77]

You don't have to drop the valve body to change the solenoids. Warm fluid will leak faster than cold fluid so it could be seal related.

 

[tombombadom]

hmmm. Yeah I spose anything is possible. Its been really difficult to get an accurate diagnosis since its intermittent. I've replaced the VSS, checked the BOBO switch, and TPS, all seem to be fine. It won't produce a code either.

I know its kinda a hybrid trnasmission with half being hydro and the other half electronic control. The truck has been great and to me is worth keeping, still in pretty good shape body wise, not sure what I should do next. I would hate to do solenoids and that still not be the problem.