Torque Converter Drainback

[66/440]

I would like to find out how many of you have issues with TC drain back. I have a newly rebuilt 727 by a reputable company (A&A) that has this issue. I also have 2 other cars with 727's that leak and have owned many over the years. It seems like about a third of the cars had transmission leaks that can be attributed to converter drain back. I have seen multiple post here of members bemoaning these leaks but I have never seen a thread that addresses how to solve the issue.
If you know how to solve this issue or are experiencing this issue and have tried various fixes that did not work I would like to hear about it. I am tired of the leaks everywhere I go, it's not a Harley it's a Chrysler and it should not leak!

 

[oliver]

A few of the Mopars I've had over the years had this issue. Not a big deal, just let the car idle in neutral for 10-15 seconds before driving

 

[66/440]

A few of the Mopars I've had over the years had this issue. Not a big deal, just let the car idle in neutral for 10-15 seconds before driving

My drain back is causing a leak at the front seal. Seal has been replaced and the converter does not have any bur's that could cut the seal. I would not be so annoyed except for the leak.

 

[66/440]

Just to be clear the LEAK is the issue I am trying to solve. It seems like that when the converter drains back I have some leakage around the front seal.

 

[saforwardlook]

I have converter drain back in some of my cars after sitting for some time before driving them again, and they do not leak at the front seal. I am questioning something else affecting the seal, such as wrong seal, poor installation or perhaps a front pump bushing that is worn, not allowing the torque converter hub to line up properly with the seal, thereby affecting the seal's ability to prevent a leak. Perhaps more likely is that the hub on the torque converter has been cut down too much to eliminate a grove or other wear characteristic that doesn't allow the seal to really do its job. What torque converters that leak down can usually affect is leakage around the throttle selector shaft seal if that seal is worn, but that isn't the case with yours from what you are saying. Maybe some others have some suggestions.

 

[65sporty]

Does it leak always for the front pump or just at times. I have seen the hub on the converter crack.

 

[WorkerBee]

Torque converter drain back is a normal thing on our old 727's.......you're just going to have to seal up the trans.
If your leaking fluid around the torque converter hub and the seal is new, it's either that the converter hub is under size from wear or the front pump bushing in worn causing premature wear of the seal. Chances are it's your converter hub. On my last trans rebuild, I found a trans shop to rebuild my converter and weld on a new hub. Another way and a lot cheaper is to install a repair sleeve over the hub like this.....More Information for SKF 99156

1969 CHRYSLER 300 7.2L 440cid V8 Repair Sleeve | RockAuto

 

[saforwardlook]

Torque converter drain back is a normal thing on our old 727's.......you're just going to have to seal up the trans.
If your leaking fluid around the torque converter hub and the seal is new, it's either that the converter hub is under size from wear or the front pump bushing in worn causing premature wear of the seal. Chances are it's your converter hub. On my last trans rebuild, I found a trans shop to rebuild my converter and weld on a new hub. Another way and a lot cheaper is to install a repair sleeve over the hub like this.....More Information for SKF 99156

1969 CHRYSLER 300 7.2L 440cid V8 Repair Sleeve | RockAuto

And I have seen a front pump housing crack as well.........................

 

[66/440]

The transmission has a new, not recon pump. I am using a Hughes 24XTM converter. My understanding is that these use a HD front hub. I have replaced the front seal twice thinking that was the issue. The leak usually appears approx 3 hours after last driven. Leak is from front housing around TC. I have a Mancini deep pan with extended pickup and a factory 14 x 18 trans cooler that bypasses the radiator cooler. I am wondering if the additional fluid in the system coupled with converter drain back is over powering the seals. That is why I am trying to understand what part wears or malfunctions and causes the drain back issue. If I could solve that I might be able to control the leak.

 

[66/440]

Does it leak always for the front pump or just at times. I have seen the hub on the converter crack.

Leaks after it sets 3 + hours.

 

[66/440]

I have converter drain back in some of my cars after sitting for some time before driving them again, and they do not leak at the front seal. I am questioning something else affecting the seal, such as wrong seal, poor installation or perhaps a front pump bushing that is worn, not allowing the torque converter hub to line up properly with the seal, thereby affecting the seal's ability to prevent a leak. Perhaps more likely is that the hub on the torque converter has been cut down too much to eliminate a grove or other wear characteristic that doesn't allow the seal to really do its job. What torque converters that leak down can usually affect is leakage around the throttle selector shaft seal if that seal is worn, but that isn't the case with yours from what you are saying. Maybe some others have some suggestions.

Leak is from front housing around TC

 

[saforwardlook]

I assume the metal seal rings on the input shaft (and assuming the new pump had new metal seals supplied with it?) were changed when the transmission was rebuilt. When these are worn, then some drainback will occur, or perhaps the parts they seal with are worn and should be replaced.

Now I am also wondering whether you might just have an overfilled transmission and when the converter drains back, it fills the transmission such that fluid drains out the vent in the top of the front pump housing? The elastomer seals should be capable of sealing the transmission even if the oil level is above them if they are in good condition and sized correctly.

There is also an elastomer seal around the front pump housing (large diameter, square cross section) that must be installed correctly with even pressure applied to the front pump housing as it is knocked in place into the case while riding on some studs placed in the transmission housing where some of the bolts go to guide it in evenly, so the seal doesn't get cocked and possibly cut if not done correctly. Are you sure you trust your rebuilder to do a quality job? It seems the vent, the seal that rides on the torque converter hub and the large front pump housing seal are the only possible sources of a leak from the front of the bell housing area unless there is a crack in either the converter hub or front pump housing itself. The front pump housing bolts should also have some rubber seals on the underside of the heads of the bolts to ensure no leakage from them either.

 

[66/440]

I assume the metal seal rings on the input shaft (and assuming the new pump had new metal seals supplied with it?) were changed when the transmission was rebuilt. When these are worn, then some drainback will occur, or perhaps the parts they seal with are worn and should be replaced.

Now I am also wondering whether you might just have an overfilled transmission and when the converter drains back, it fills the transmission such that fluid drains out the vent in the top of the front pump housing? The elastomer seals should be capable of sealing the transmission even if the oil level is above them if they are in good condition and sized correctly. I am using the factory dip stick with the deep pan. fill it to factory recommended level/per dip stick when checked in neutral.

There is also an elastomer seal around the front pump housing (large diameter, square cross section) that must be installed correctly with even pressure applied to the front pump housing as it is knocked in place into the case while riding on some studs placed in the transmission housing where some of the bolts go to guide it in evenly, so the seal doesn't get cocked and possibly cut if not done correctly. Are you sure you trust your rebuilder to do a quality job? It seems the vent, the seal that rides on the torque converter hub and the large front pump housing seal are the only possible sources of a leak from the front of the bell housing area unless there is a crack in either the converter hub or front pump housing itself. The front pump housing bolts should also have some rubber seals on the underside of the heads of the bolts to ensure no leakage from them either.

This is the first transmission I have purchased from Rick Allison at A&A. They have a good reputation but you never know. I have considered installing a spring loaded check valve in the cooler return line to see if that helps.
Looks like I will pull the transmission again and recheck seals and measure the converter shaft.

 

[saforwardlook]

This is the first transmission I have purchased from Rick Allison at A&A. They have a good reputation but you never know. I have considered installing a spring loaded check valve in the cooler return line to see if that helps.
Looks like I will pull the transmission again and recheck seals and measure the converter shaft.

So what does Rick Allison say about the leakage? Doesn't he take responsibility for delivering to you a proper transmission that doesn't leak? Pulling a torqueflite multiple times is no fun at all and messy. It would be worth crating up the trans and sending yours from Texas to Indiana where his company is located and ask him to fix it, at least that is what I would do if I were you (with prior approval from them if they are legitimate). This is one of the reasons I rebuild my own, as then I know I am replacing everything and not skimping on the work and taking the time to inspect everything. There are many ways of saving time and money on rebuilding a Torqueflite, but hardly worth it if you want it to be trouble free and last. It is a shame to have to go through your ordeal.

 

[66/440]

I agree pulling the transmission multiple times is a PITA.
But....... I purchased the transmission 3 years ago and just got my project driving last summer. Then it shucked a cam and I did not have the time to get it repaired until earlier this year. I wanted to be sure I had covered all of the bases before I started bitching. The transmission was married to the engine 2 years ago and I originally thought that the front seal may have stuck to the converter snout, even though I lubed seal and converter on installation. So being the responsible individual I am I thought it may have been my fault. However when I removed the transmission the first time I could not visually see any snags or cuts. Since it was out I replaced the front seal, why not, just to be sure. Converter shaft looked good and I could not see any step or chamfer that might indicate the converter shaft had been turned and, this converter was supposed to have a new HD shaft.
Reinstalled and problem still existed. Ok, maybe I cocked the seal on install, don't think I did, or maybe the quality of the seal was poor, so one more time. Same results.
A round trip ride to Indiana is $225, plus the drama.
I have never done a compleat rebuild on a 727 but I don't think it is out of my capabilities, besides it does not need a full rebuild.
I will call Rick and and see if he has some ideas but I will probably end up repairing it myself. I honestly believe it is a a wear issue that causes the converter to allow to drain back ( and in my case causes a leak)I just don't know where the wear is occurring. That is why I started this thread, once the issue can be identified them we will all know what to pay attention to to solve the problem.

 

[ws23jrt]

My drain back is causing a leak at the front seal. Seal has been replaced and the converter does not have any bur's that could cut the seal. I would not be so annoyed except for the leak.

You say that "your" drain back is causing a leak at the front seal.

I think that is wrong. Drain back is what happens when the TC is full and the oil is seeking level by draining back through the hollow reaction shaft. (where the oil came from by way of a port/passage from the valve body.

If the trans. input shaft bushings and seal rings were --perfect-- (as well as the valve clearances in the valve body) "drain back"would not happen in the first place. --These places I mention where leakage could occur are what affect "TC drain back" and are all internal.

You have a leak that comes from a seal that is an -external seal- (independent of whether the TC holds it's oil or not) such as those already mentioned like the front pump seals.

The front pump input seal is my bet for where the leak is coming from. Just because you have a new one does not eliminate it as the source of the leak. That seal has a tough job to do if the trans. to crank alignment is not so good. It also can be easily damaged at installation of the TC.

BTW their should be a drain plug on the TC. It is another place a drip might come from.---That's my two cents worth.

 

[saforwardlook]

While I haven't traced just which seal rings are responsible for the drain back, I understand from previous information that it is mainly due to wear of the metal seal rings or the housing they reside in that allows the fluid to flow back into the transmission. Given the history of your transmission, I don't see how anything you have done could affect their proper operation. I still maintain that the front pump seal and all the other seals are capable of preventing an oil leak with the torque converter drained and the transmission has the proper amount of total fluid in it. I have witnessed over the years that some problems like yours have been solved when the proper total fluid level is achieved, as when they are overfilled and the converter drains back, then excess fluid will drain out the vent at the top of the front pump housing (covered by a small metal plate). At a minimum, I would contact Rick and get his opinion and see if he can suggest something else. I doubt you have done anything wrong despite the length of time you have had it that could cause the leakage unless it is over filled.
Good luck in any case.

 

[saforwardlook]

Also, you might want to contact Don Verity who has been a rebuilder of Torqueflites for the Chrysler 300 Clubs for many years. He might have some good insights or might be able to offer some help. His contact information is 401 231-7816 or [email protected]. He is in Rhode Island. Rebuilding a Torqueflite is not that hard and the service manual is pretty complete and accurate about all the steps that must be taken. The one handicap is that you would need some special tools to take apart the clutch packs and perhaps for other operations depending on how clever you are at getting around the difficulties with home made solutions.

 

[66/440]

I think that is wrong. Drain back is what happens when the TC is full and the oil is seeking level by draining back through the hollow reaction shaft. (where the oil came from by way of a port/passage from the valve body.

If the trans. input shaft bushings and seal rings were --perfect-- (as well as the valve clearances in the valve body) "drain back"would not happen in the first place. --These places I mention where leakage could occur are what affect "TC drain back" and are all internal.

This is exactly the information I was looking for with regard to the cause of converter drain back, Thanks!

My leak may or may not be caused by drain back but in order to understand which path I need to take I need to understand what the root cause of drain back is.

One thing I have not mentioned is that my transmission cooler is mounted 12+ inches higher than the center line of the input shaft of the transmission. I also remeasured my cooler and it is 22" x 18". I just want to make sure that the weight of fluid in the cooler and the supporting lines coupled with the possibility of drain back are not creating an over fill situation that is over powering the front seal.
You also mentioned a drain plug on the converter. My understanding is that the drain plug was not present from the factory. I thought that drain plugs were added by reman or rebuild folks to fully drain and flush converters. I always thought that this caused an out of balance condition for the converter however minor. Please correct me if I am wrong.
You may be correct that the front seal is at issue but I am now on my 3rd seal ( each a different brand). Any recommendations on a quality brand of seal?

 

[66/440]

While I haven't traced just which seal rings are responsible for the drain back, I understand from previous information that it is mainly due to wear of the metal seal rings or the housing they reside in that allows the fluid to flow back into the transmission. Given the history of your transmission, I don't see how anything you have done could affect their proper operation. I still maintain that the front pump seal and all the other seals are capable of preventing an oil leak with the torque converter drained and the transmission has the proper amount of total fluid in it. I have witnessed over the years that some problems like yours have been solved when the proper total fluid level is achieved, as when they are overfilled and the converter drains back, then excess fluid will drain out the vent at the top of the front pump housing (covered by a small metal plate). At a minimum, I would contact Rick and get his opinion and see if he can suggest something else. I doubt you have done anything wrong despite the length of time you have had it that could cause the leakage unless it is over filled.
Good luck in any case.

I am going to remeasure the fluid level in my transmission today to see exactly where I stand. Over night I had an epiphany and may have the answer to my issue.
My original transmission was a 904 and I converted to a 727. I am wondering if I have the dipsticks switched and I am indeed over filling the transmission. Does anyone know if the dipsticks are different lengths between a 727 and a 904?