I've a '71 Plymouth 383/727; the trans was rebuilt about 5000 miles/14 years ago by a very competent fellow. The car only comes out for shows and cruises and is babied.

It suddenly now seems to *sometimes* be not filling the converter in D; the level appears way high until I step through the gears, even though it's just been driven.

After being on the highway 20 miles it suddenly bucked so badly I had to stop; it felt like it was being shifted from D to N, but after 5-10 minutes sitting there idling, ran just fine when I started up again. Later that day after sitting at a light I couldn't move, even though the engine revved. I shifted through the gears twice, and then I could drive normally again. Checking the fluid immediately afterward, it appeared way high, but going through the gears again it dropped to normal.

Everything looks normal except that the fluid appears way (>>2qt) high until I cycle through the gears and check it in N.
There's no sign of a leak I can find and the fluid appears normal.

I suspect that the torque converter is just not being sent enough fluid sometimes; has anyone seen this problem or know of a fix? The '71 FSM doesn't seem to cover this one.

I am not sure but I bet Slant Six Dan would

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Nothing beats a slant six
1987 D150

That's an interesting one…I'm going to defer to Charrlie_S on it.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I've not heard any good ideas yet on what to try. Since the trans has so little mileage on it for its age, would it be reasonable to try the following? Could it do any harm?

1) add Trans-X (or similar) trans flush to free up any stuck valves
2) drive it a few miles (if possible; idle in N if not)
3) drain trans and converter
4) change filter; reset bands and kickdown
5) refill and hope for the best?

sounds like your losing pump prime AKA a leak in the pickup, plugged filter or loose pump tolerances , drop the pan and check the valve body bolts,filter, and for anything abnormal.If nothing, problem is likely the pump. When the pump flows little or no fluid it will cause high fluid level and neuteraling.If you haven't changed the fluid and filter since rebuild then thats proble'y the culprit

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Nick
86 d150 turbo /6.

Thanks. I did change the fluid & filter <100 mi after the rebuild when I changed the gear selector lever (to run my start/reverse switch). I had to drop the valve body, so I retorqued the bolts, and adjusted the bands and kickdown at the same time (about 5000 mi /14 years ago). Everything looked perfect then and I've had no problems with it since then until now.

Sitting for months, the level leaks down very slowly (about 1 pint/2-4 months). I check the trans level before every drive and again after 1-2 miles after its warm, so I know the problem appeared suddenly. I didn't see many bubbles, so maybe it isn't an air leak. I suspect something is sticking or broken in the pump or related paths rather than a gradual wear problem. The car sees only very gentle use driving to shows & events (a combination of city & hwy driving) and usually runs long enough to get completely warmed up.

Can using Trans-X (or similar) to try to free any sticking valves do any harm before I change the fluid? I expect I'll find nothing obvious when I drop the pan and I'm wondering if there's anything else I can easily check with the pan off.

transx is good stuff can't hurt. but I still believe the problem still lies in the pump the bushings can spin on the converter and cause problems

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Nick
86 d150 turbo /6.