Hot Rods 40 Ford Tranny Leak

I've had my 40 deluxe coupe on the road for about 4 years. Works good but it has one aggravating problem. It's a 300 horse 327 backed up by a 350 turbo. As long as you drive it at least once a week it stays dry underneath. After about a week of sitting a small puddle of tranny fluid appears and slowly grows. I've had reputable shop replace every seal in the trans including the often over looked shifter shaft seal. When it's on a lift you can't see any leaks. The tranny shop is stumped only to say that it must be the converter draining back? It's a major job to pull the tranny but this is getting annoying. Over the last several years the fluid I've added has been minimal because you all know a small amount of fluid looks like a monumental leak. Everyone has an opinion but no one to date has come with a solution. I've had a lot of 32's with 350 turbos and no leaks. Stumped!

 

I’ve had them leak out the breather if they are overfilled. Could be the season sky humidity and etc causing it to expand a bit and dribble?

 

Get under there with some baby powder. Coat the case with a fine mist on both sides at least half way up. The trail should be apparent after sitting as per the complaint.

 

Ok, does it favor the front or back of the trans? Does the trans 'nose down' or up as installed (and I'll assume up in the front)? The turbo hydros can develop a sneaky little leak around the dipstick tube. As we all know trans fluid has an insidious way of tracking away from the leak source. I've seen a wee bit of leak creep fwd, roll around the pan/gasket edge, then follow where gravity takes over. Sometimes a new o-ring isn't the final solution and you need one just a little fatter. As the car sits more fluid ends up in the tube creating enough liquid wt to dribble around and out. Brain food, somewhere else to look. New rubber materials don't swell in chemicals like the ol tried n true stuff did and without constant use can compromise their sealing characteristics just enough to tug your hairs. Good luck...

 

I have used UV dye additive and Black light to help pin point the source of the leak. That way you could all some go for a spin then a few days later see the highest point the UV light picks up for your leak source

 

Good question and timely. I fired up my Olds last weekend to drive it onto the lift and it leaked tranny fluid all over the place! It wasn't leaking when I parked it and I haven't touched the fluid level. Seems to be leaking at the fill tube or the pan gasket. Maybe just age and sitting for the last several months? Bars Stop Leak? TCI turbo 400 with 30k on it.

 

I had one that leaked around the kick-down cable after sitting for a while; guessing the convertor drained back enough to let the level get high enough.

Like the other guys said; ATF is sneaky and hard to locate the exact spot of the leak.

 

Time for a true story , had the same problem with my 350 trans, the shifter shaft leaked ,replaced it 3 times ! it still leaked ? The shaft had no grooves or scratches, looked perfect, I asked an old retired gm trans mechanic how to stop it . He said to replace the shaft and seal at the same time ??? Why ??? He didn’t know , but if it didn’t work he would pay for my parts !!! It hasn’t leaked since.

 

Had a powerglide that leaked at the shifter shaft seal if I let the car sit too long.In the end I put a manual trans in it. Use the car more often is the real fix.

 

I'm going to do the same thing with my '41 p/u in the future. Aluminum Powerglide converter drain back on a sloped driveway. Some seals aren't made to under liquid, just keep dirt out and oil splash in.

First you need to dry/clean it off completely, then find the starting point of the leak. Like others said above, it likes to run all over. Another place to look would be the speedo bullet, o ring outside and seal around plastic gear (which you can get a new gear).

There's repair stuff like this (depending where the problem lies):
https://www.sonnax.com/parts/4493-shift-shaft-seal-kit

If it is drain back and it's leaking from dust type seal, the only option besides removing the trans might be starting it up once a week.

 

Moriarity has the right solution, other cure is to drive them every week at least once. Seems to work for mine. 80K on the clock and no spots on the floor.

 

I've had it in a very reliable shop several times that has done all the fixes suggested at least twice. Same shop built the 350 on my 32 delivery, not a drop on the floor, I've done a lot of 32's with 350's and no leak problems. My deuce pickup doesn't leak a drop even after sitting over a month last winter. It's frustrating.

 

I don’t know much about a 350TH but many transmissions torque converters leak back and “overfill” fill the main transmission body. On the trans I have I attached a line to the overflow vent up beside the fill tube and no more leak from it.
The overfill on mine also filled the area in the tailshaft where the governor was and its inspection cover was a leak. Mine sits normally for aWeek and I let it run a minute before moving.

 

A very common thing to leak on a 350 when it sits is the o ring on the pump. It always looks like the pan leaking but it is not. You might add some high mileage additive to swell the o ring up. But probably not ! might as well pull it out and fix it.

 

My newly rebuilt 400, new converter, with about 200 miles on it, sat in my shop for 4 months with out a drop. Last week there was a puddle under it, wtf?

 

Like master cylinder rebuild kit materials, the composition has changed and the shit doesn't stay swelled up for surface tension like it used to. Regular use helps but no guarantee.

 

fluid leaks... standard on all TH 350's

 

Funny that complaints about gasoline, oil and parts all seem to be common, but ATF gets a pass even though it's changed over the years too.

 

My 350 turbo leaks from a porous casting on the tail housing extension. 3 new seals later I noticed the oil seeping out of the aluminium casting. It still leaks and my floor pan isn't rusty.

 

Another very common place to leak I haven’t seen mentioned and probably the most common is the speedo bullet seals. Aluminum bullet is always worn out and will never hold a seal.

 

Not so, have over 35000 miles on the 1 in my 34 roadster (see avatar) dry as a bone

 

My experience with my TH400 is that if I fill the fluid to "full" on the dipstick it's actually over full, and will spew out the vent until it finds it's happy level.