When I bought my 78 and drove it home a couple of years ago, the gearbox seemed to work fine. It then sat for 6 months in my garage while I started work on it's restoration. At this point it was still driveable and I needed to get it out of the garage for a few weeks. It started up okay, but when I moved it I found 2 things. First I had to rev it quite hard to get it to move. Second it had been leaking auto trans fluid on the floor. I put these 2 things together and decided the problem was a lack of oil in the transmission. Another 18 months later I've got the entire car stripped down and I'm looking at what needs to be done to the engine and gearbox before putting them back onto the chassis. I noticed that a previous owner had put RTV all around the transmission dipstick tube, so I removed this and pulled out the tube to see if it actually still had an o-ring on it. A couple of pints of trans fluid came out of the hole. Having found the o-ring was in place I put the tube back and pulled out the dipstick (for the first time ever) and found the level to still be 1 inch above the hot fill line. It doesn't seem to me now that my only problem is a lack of fluid in the transmission!
Is it likely that I've got a torque converter seal leaking? Or any other ideas?
John

 

Yeah...I'm there! I've got a 78 L48 M38 and a few years back replaced all gaskets on the engine, oil pan, valve covers but since then the leak has persisted. I've traced to the tranny torque converter...as you've acknowledged. I run it...it leaks. I've concluded the only fix is to pull the tranny and replace the seal.

 

Not likely that you have a bad torque converter. If you have to put it in gear and rev it to get it to move, it's more likely that the seals on your clutch pack drums have gone bad, and your clutches are slipping. Smell your tranny fluid - I'll bet it's brownish in color, and it probably has that burned smell to it... time for a tranny rebuild/refresh.

Lars

 

Just to be sure....are you checking the dipstick level with the car hot and RUNNING, and on level ground ? it will show much higher on dipstick if engine is off.

 

Thanks for the suggestions. Here's a bit more background.
The engine and gearbox are currently sitting on my garage floor, so no chance of running it yet, I need to get the chassis rebuilt first. They are sitting level though.
The trans fluid is bright red and clean and smells fine. However I suspect the previous owner had changed all the fluids. He had bought the car after it had been sitting for 15 years, got it up and running and then sold it to me. It's probably only done a few hundred miles since being put back on the road.

 

Since the fluid was leaking out before you changed the seal, it's likely the fluid level is quite low. As FISHSLAYER said above, the engine needs to be running and trans in neutral to check.....once the trans is operating in neutral the fluid level will drop considerably from where it was with the engine off.
To me it sounds like a low fluid level problem....having to rev it up to get it to move is a classic low fluid level symptom, if it was an internal trans or a torque converter problem the fluid would turn dark in a real hurry.
Just remember it worked OK when you brought it home, don't try to create a problem that isn't there.....

 

2 years into the restoration and at least another year to go, I'm certainly not trying to create work! On the other hand, I'll be pretty fed up if I have to take the transmission back out after re-assembling the whole car, to fix something I could do quite easily now. I'm hoping it's just a case of the trans fluid draining out of the torque converter into the transmission whilst its been sitting idle for so long. Is this likely or even possible? Presumably there's a seal that supposed to stop this happening (I'm no expert on auto boxes, we don't have many in the UK!) if so, is it an easy job to replace it?
John

 

It's likely OK. Put new seals in the front and rear. Make sure the converter snout isn't grooved. Seal that dipstick properly.

Sitting long periods the converter drains into the pan so the level is high and then it leaks. The leaking then causes it to be low when started and then the pump sucks air, makes no pressure and the gears won't engage.

 

Thanks Lionel, that is what I was hoping to hear Sounds like I should replace the seals whilst I've still got easy access to the transmission.