50 Merc overdrive question

DAG74

DAG74

Junior Member
So I was driving around the other day with the overdrive engaged. I had been driving for 25 minutes or so on a road with no stop signs. Just cruising at 50 to 55 mph.

It does not have the button under the accelerator, it has a toggle switch on the dash to engage the solenoid. I stopped at an intersection in overdrive, took off from the stop sign, got up to speed and everything was fine until I started slowing down to approx. 40 mph. I was still in 3rd gear.

All of a sudden the car lurched, rear tires chirped and I heard a slight grinding noise from the transmission. It felt like I downshifted to second at too high of a speed. I immediately pushed in the clutch, turned off the overdrive toggle and pulled over. I shut the car off and pulled out the overdrive handle. I did a quick check of everything, fired it up, made sure it was out of overdrive went through the gears and started home. No weird noises and it shifted fine.

Has anyone ever had something like this happen?
 
I had it happen to me. The OD portion of the transmission had gotten low on lubricant and froze up. If the transmission wouldn't freewheel with the handle pushed in and the transmission acted like a standard shift I suspect you need to rebuild the OD section.
 
Last edited:
Thank you 40cpe. That makes sense. Prior to the issue everything was working fine. It was freewheeling like it is supposed to. I haven't tried to engage the overdrive since. Ill be checking the fluid levels this weekend in addition to reading the overhaul section in the overhaul manual.
 
Complete overdrive electrical harnesses are available and most of the electrical components are out there. I'd advise to connect things up as they should be. This gives a safety factor to the operation of the system. Even taking all precautions and performing regular service doesn't guarantee that things won't break down.

Kick down is a handy feature to have. Hopefully you are at least using a governor. A person shouldn't have to worry about starting out from a stop with the OD solenoid still engaged. They don't like working the planetary that way. The governor will automatically shut the solenoid off below 25 mph or so.
 
Thank you for taking the time to reply rotowrench. I'm not sure if the governor is working properly. I need to get under there and check. I definitely would like to get it set up properly with kick down.
 
Last edited:
I had a problem with the o/d in my 51 merc a couple of years ago. same symptoms, apparently when the wheels "chirped" they locked momentarly, and bent the output shaft in the o/d unit. It took out the rear tailshaft bushing and the driveshaft yoke. I did not know these were bad, because the car still moved under its own power when not in overdrive. I found the problem when I tried to remove the drive shaft. it was very hard to pull out of the trans, I also found that the output shaft was twisted when I tried to insert a new yoke into the trans to use as a plug while removing the trans. I ended up rebuilding the whole trans, turned out there was more damage discovered when the trans was completely dismantled. hope you are luckier than I was.
 
Oh man Alaska Jim, I hope there isnt that much damage to mine. That is a real drag for sure. The car drives and shifts great, but I haven't had the guts to engage the overdrive yet...
Thanks for taking the time and replying.
 
DAG74, yes, I hope you do not have that much damage. I was surprised at all the damage I did find. my car also drove and shifted ok, but I knew there was something wrong internally. It had even chipped teeth on the cluster gear. good luck to you, and hope you find very little damage
 
I've had problems with various things on my old hand me down family cruiser but I've also had two friends that had major malfunctions. One completely locked up the drive system and came screeching to a halt. The other had a blown planetary. Both of these guys did a little street racing till the malfunctions happened.
 
I will say that although I have never abused my car, the person I bought it from did. when I bought it, the eng. was out of the car with a chunk blown out the side of the block, and 1 rod and piston missing. there were reports of the guy being seen trying to burn rubber and racing the car, or trying to. I installed a new eng, and never had any problems with the drive train, until the trans suddenly gave up. I put 20k on it. I suspect the planetary blew up and locked up the trans and did all the other damage. it only locked momentarily and then the trans seemed to work except for the overdrive, but i did not take it any further than around the block after I drove it home.
 
Dag74, Almost all the warner CAR overdrive guts will interchange so parts are out there. It sounds like your planetary pack blew out . I have rebuilt so many of these OD's over the years I've lost count. I do have a complete planetary pack if you can't find one. I always like to have a spare on the the shelf. Tim
 
Tail shaft lengths varied between makes. Ford units were a bit different than Mercury but some parts are the same. This is where a person needs a parts book and an O/H manual. T-85 &T-86 transmissions are different than the 259 pattern units. There are still units and some NOS parts out there.
 
Hey guys. Thanks for the info. I may have dodged a bullet. The overdrive engaged and disengaged with no issue. I didn't drive far at all with the overdrive. I still need to check it further just in case.
 
Just my opinion Dag74 but if something went "bang" or locked up or whatever in the driveline I would drain the trans, OD unit and the differential. You are looking for metal in the oil, grey putty like material may or may not mean anything, chunks or slivers are another thing. Do not run it until you figure the source of the problem, more junk going the trans, OD or diff is only going to make repairs more expensive. I hope you got lucky!
 
DonT-That is definitely what I will do. Driving season is pretty much over in Arizona anyway! I hope I got lucky as well. Thank you.
 
You must log in or register to reply here.
Back
Top