TR4/4A A type OD working in 3rd but not in 4th

[TRclassic3]

This seems like a bit of an odd problem. A little history: After OD and transmission rebuilt an installed, a test drive gave sporadic results. Initially seemed fine but began dropping out of OD or not engaging at all. After a bit of analysis it was determined that the new switch was the culprit as it would not consistently work when testing. A new switch work every time. Feeling confident the problem was solved the interior was reinstalled. Test drove today. Again initially seemed fine, but then started acting up in 4th. Oddly, no problem was experienced in 3rd, but rather only in 4th. If in OD and going from 3rd to 4th it would drop out of OD. If not in OD and in 4th OD would not engage. Upon return I tested to see if I could hear the solenoid in both 3rd and 4th (car had sat for maybe 10 minutes). I could hear it actuate every time regardless of gear. Any thoughts? could it be a wiring issue with the isolator switch that only raises its ugly head with car in motion?

Thanks

 

[Sarastro]

It really sounds like a lockout switch to me, probably right on the edge of working. There are shims under the lockout switches, which adjust the protrusion of the switch actuator into the shifter assembly. If they are not right, the OD may not work or may just work sporadically.

 

[TR3driver]

FWIW, I had exactly the same symptoms from a failing lockout switch. Initially, it would just sometimes fail to go into OD and I could usually get it to work by shifting to neutral and back to 4th. Sometimes, just wiggling the shift lever fore and aft a little would get it to make contact.

Connecting a test light to the relay (so it could be seen while driving) confirmed that the lockout switch (or the wiring to it) was the problem. This switch had been working correctly for a very long time, so I'm inclined to believe it was just wear that made it fail. Anyway, replacing the switch (and adjusting the shim pack for the new switch) solved the problem.

But it's also possible for the relay or OD solenoid to go intermittent. A bad solenoid will often work OK when the car isn't moving, because it doesn't have to work against as much hydraulic pressure. Relays seem to be more temperature sensitive (ie they get hot in operation and quit making good contact).

FWIW, adding a kickback diode to the relay seemed to really improve the life of replacements. I went through 3 different replacements in just a couple of years (including a fairly expensive reproduction of the original) before adding the diode. With the diode, my "Made in China" brand relay has held up fine for some 20 years.

I wanted to do the same thing to the new solenoid, but realized later that I didn't wire it correctly. It seems to be working OK without the diode, though

PS, I don't mean to suggest those are the only possibilities, just the ones that have given me the most grief.

 

[JerryVV]

I had a similar issue which was finally traced to a loose ground wire that attached to the transmission top cover. It was frustrating in that it didn't always drop out of OD.

 

[HAWAIICJ]

Just as a curiosity has any one measured the height dimension of the machined OD switch mounting (through the threaded hole) to the neutral surface of the shift forks? I understand this can be adjusted with the fiber washers, I am looking for a measurement for the installed height with out washers so that I may modify my shifter housing in preparation for installing my A-type.

 

[TR3driver]

Sorry, my mistake. He just matched the height of the hole for the reverse switch.