I must admit that automatic transmissions represent a great big hole in my automotive knowledge. They are the only thing I don't work on. Just got back from a drive this morning in my '26 T coupe, the trans would not go into lock up in 4th gear. The shift into 4th was kind of delayed, then would not lock up. Shifts up from a stop just fine, but 4th is just a little delayed from what it was. The car has been running for about 25K miles now since rebuilding the trans with no trouble. Can't figure why the trans was just fine when I parked it the day before, and the next day it's not. Fluid level is right on the money. I have the throttle lever corrector on the Holley carb. The TV cable is adjusted correctly and hasn't been changed. I called my buddy Dan's trans shop. I got an answering machine that said they were not working due to "pandemic related" problems. Well crap! Dan is the guy who rebuilt my trans. I always get the buddy price, and I hate to take it to someone else. My Model T is my daily driver, really. I'm afraid to drive it for fear of messing it up even worse. So I need to get this figured out. I suppose I am into removing the trans. Is there any chance of diagnosis from my description of the problem? Thanks guys.
I checked for 12 volts at the lockup switch. I do have power there. So not electrical. It is wired with no switch. When it shifts into 4th, lock up is immediate, then downshifts to 3rd, no lock up, upon slow down...when it was working. Yes, I'd say you are correct. But I wouldn't have the foggiest idea what I was looking for. Anyway it is 3/4 of the way out already. I'm gonna drop it at Dan the Trans Man's shop and he can get to it when he gets to it. HA! I lucked up. Dan just called and said bring it in, he would get on it.
For the trans to get lockup the way you describe, it would need to have a two terminal, normally open 4th clutch pressure switch to ground. It was common for those switches to go bad and leak pressure, like an engine oil pressure sending unit would leak. That could cause lockup to not work and possibly make 4th later due to the pressure leak. Bill
There is a temperature switch inside the trans pan that prevents lockup until trans is warm. The power to the lockup solenoid is often fed through the brake light switch, this unlocks when you are on the brakes. Not sure if any applies to your car, just tossing out two ideas. There is a small o-ring on the input shaft that can get damaged also.
A few points here. They make senders with 1/8 pipe , 1 wire, that will ground through the case with 4th gear pressure. The temp device could be gone by now on an aftermarket build. O/ P said the switch had power but then said no switch. In either case , he didn't mention a brake light switch. Now that it's on the bench, throw the solenoid away, even if it clicks. Put a new one in. They're cheap, and not known for longevity.
I guess I could have stated that better. There is no switch to turn the lockup on or off. The wire leading to the plug in the trans has 12 volts. The 1 wire switch you describe must be what is in mine. I'd bet you have hit the problem.
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