VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc TH350 Drainback cured with In-Line One Way Valve

Late Great Chevy (Part #:563169) and Classic Chevy (Part #:19-28) both offer this item to "fix" this issue on a powerglide......

Full Size Chevy In-Line One Way Valve, Powerglide Transmission, 1955-1961

Any chance this will also fix this issue on a TH350????

1,001 Googles...

Came up with this item..............

http://transmissiontechnologies.com/watch-dog-plus-monitor-drain-back-valve.aspx

Watch Dog Plus Monitor & Drain Back Valve For Most Ford, GM, Dodge

$85.65 but may work!!!!

This has been discussed before....THEY DON'T WORK

There's the rub...

After reading 101 antique and hotrod forums I've found some swear it solved the issue and some that say no...

Maybe just run a deeper pan and 1 quart low to give the drain back somewhere to go... is the answer?

I've driven many TH350's since 1970 and never had this problem... retired and on fixed income so would sure like to find a solution other than replacing the transmission...

I can do the work, but the time and expense are sure not small.

All the things I've read have been vague...

Can anyone explain exactly what happens in a drain back situation?

Is the fluid draining back from the torque convertor?

What seal is at fault?

Hello CraigB,

I think your problem is related to the front pump. Not knowing what year it is, some have a check valve that goes bad and allows trans fluid to leak back into the trans pan, others have a problem with excessive gear wear in the front pump allowing trans fluid to leak back to the trans pan.

It's been a very long time since I've worked in the trans field and I've checked my trans repair manuals but none of them describe over night leaks.

Dad is gone so I can't ask him but I do recall him mentioning the front pump in this situation.

I'll try to reach the trans guy I used to buy parts from tomorrow (10/28), he is the only guy besides my Dad that I would trust with getting the correct info.

A deeper pan will not help but running the fluid a Qt. low will. Have it on the add line when hot. Will be below the add line when cold. This will keep the fluid 1 Qt. lower when it drains down. Will e a cheap fix. It works on my Power Glides.

My thought was the deeper pans that hold an extra quart and come with an extension for the filter....

Run that a quart low and you still have the "normal" amount of fluid and at least a quart of fluid can drain back before the pan fills and finds a leak point...

The deeper pan will contain say one more Qt. of ATF but the full mark on the dip stick will still show the same level when full. When the converter un-fills you will have the same amount of reserve space.

Followed up with my trans connection and he said that my explanation is correct.

But he did add that if these cars are sitting for an extended period of time, even with a freshly rebuilt transmission, the torque converter will "leak" back into the pan.

It is not the fault of any one seal, but with the clearances of bushings and machined services.

I have rebuilt a lot of Turbo 350 / 400 transmissions of the years and the first piece I replace is the front pump. The cost of a rebuilt pump (@ $125) and it's the first piece that "fights" converter drain back.

I would guess the solution (cost effective) would be to start the engine and allow it to idle so the trans can circulate what drain back may have occurred.

The new front pump will be a big help but he was looking for a cheap and easy fix. Running a Qt. low is about as cheap as you can get and worth a try.

Yes Gene, you're right.

I guess I got carried away because I always enjoyed trans work. The following is just info.....

Depending on the size of the torque converter, a Turbo 350 can hold up to 10 1/2 quarts of trans fluid and the T400, 12-13 quarts. Close to 90% of that fluid is in the torque converter. We all know that fluid seeks it's own level. That being said.........

I know we'er all car guys but I have to advise that if a deeper pan is added, that it be a new one with the corresponding spacer to place the filter at the deepest point in the trans pan. This will guarantee that the filter is submerged in trans fluid when the engine is started and the "drain back fluid" is pulled back into the torque converter.

There are a couple of things that might be a problem once the fluid level drops to "normal"...... sloshing of the fluid as the car moves as trans pans don't have baffles, at least they didn't way back when, and the filter being uncovered if pulling a hill.

Just something to think about.

Only the top half of the converter drains down. Usually about 2 to 3 Qts.

Thanks to everyone for the comments.

I'm going to put a catch pan underneath, try running the car in gear every few days and keeping the level a little low...

See if I can live with it...

Were talking about a toy not a daily commuter...LOL
Craig

Try running the car in gear every few days.....#1 the converter will refill with the transmission in neutral....#2 will cause the muffler to fill with water and rust out .

A stock Turbo 350 trans pan holds 4 quarts. The valve body / planetary / drums may hold @ 1/2 quart total. Cooling system may hold 1/2 quart. Torque converter will hold the rest, which the math shows to be 5 quarts.

Right again Gene....

I had a lot of experiance with my converter draining Power Glides.