Leaky Fluid Drive Options, 2022

[Bryan G]

What!? Another fluid drive leak thread I've read most the old threads, plus some on the HAMB and AACA forums. What I know: seals/seal kits are readily available. Bernbaum, for one, has a full kit for the later style (or to upgrade an older unit to the newer style) for $480. The question is, installing it. Even if I had all the tools, which I don't, I'm not sure I'd trust myself to do it right. Maybe I could convince my mechanic friend to tackle it...but it goes back to the tools again. As it stands, these are the options I see:

• I talked to Chris at Bernbaum; I can ship the coupler to him and he will have it resealed for $1400. Resurfacing is an extra $275, and of course shipping will be involved. 2 weeks turn around and he says they guarantee it.
• I talked to Gary at Robert's; he doesn't offer the seals nor does he have anyone that refurbishes the units. He suggested I check Hemmings as he thinks there is someone advertising in there that they do it. I must have thrown away my last copy. Previous threads suggest the advertiser might be Northwest Transmission Parts; discussions also mention failed attempts at bearing replacement by them. I haven't called them yet...maybe they will do just the seals? I didn't see anything about FD on their website. 
• Moparmall.com states on their site that they will replace seals and bearings (really?) for $1517.
• I see in old discussions that some folks on here have the tools and maybe could do the work themselves. Is there a guru in our midst who does resealing and has a decent amount of confidence in turning one around?
• Is there someone who rents/lends out the tools to replace the seals? 
• Or, does anyone have a known-good fluid drive unit for a straight 8?

Where I sit right now is that my FD works fine, but drops a quart on the ground in about 200-300 miles. I even tried tossing in a pint of engine oil stop leak (which seemed to slow it down for a week!) If I had in my backyard my dream garage, complete with 4 post lift and transmission jack, I'd take a different stance on this. As it is, I feel like I'm asking a favor of my mechanic to deal with pulling the unit, then having this '49 Pushmobile taking up space for 3-4 weeks.

[Dan Hiebert]

I had the same issue with the FD in our D24.  It began leaking quite a bit after we had the car for a while.  Replacing the seals is something I would take on myself, but I didn't have, nor could I find the tools to do the job.  I also couldn't find anyone that would do the work, not even AB at the time.  A couple places said they'd "try", but no guarantees.  Other than the leaks, the unit worked well.  To shorten the story, I replaced the FD oil with Type F automatic transmission fluid, the stuff with the additives that swell seals.  After maybe 20-30 miles of driving the car around, the leaks stopped, completely.  This was at least 15 years ago, maybe even closer to 20, and it hasn't leaked since.  I read a few years afterwards, and you've probably read some of those threads herein, recommendations not to use automatic transmission fluid, especially with the "seal conditioning" additive(s).  I believe the rub is that the additives that condition the seals will eventually cause their failure, so it's not a true fix.  That may be, but as I wrote, I've had no issues with our FD unit for quite some time - even though I'm prepared for the failure of those seals due to the info from this Forum.  

[Bryan G]

Dan, that's an idea I hadn't heard of...and something I'm seriously going to consider. Of course, I suppose it matters just where the leak is coming from and if it's not the rubber seal I wouldn't think it would help much. Anyway, a real option.

[Dodgeb4ya]

There are no rubber seals in the FD coupling..

There is a hard graphite seal ring and a flexible copper and steel bellows seal assembly.

The bellows seal assembly steel wear ring pushes down against the graphite seal forcing it against the inner FD sealing ring surface.

These parts last almost forever.

But leakage can occur from...

***Cracked or pitted bellows seal

***Cracked broken or pitted graphite seal ring

***Pitted or damaged inner FD sealing ring surface...

***Worn out/loose FD front ball bearing

***Worn/ loose inner and outer input shaft bushings.

   Typically a worn or pitted graphite seal ring and new bellows will fix any leakage as long as the front bearing and both pilot bushings are not worn.

   IMO replacing the front bearing cannot be done and keep the FD coupling in balance and not cause vibration in the car.

The original service tooling to remove said front bearing out the front of the coupling is long gone and now they cut the FD open to replace the bearing...then weld it up out of balance.?

Also the FD inner seal ring surface can be pitted and then needs to be micro finish ground as was originally done...

Not going to happen with out cutting the coupling open.

Once the bellows and grahite ring are out you can examine that surface to see if it's damaged.

As said usually a graphite ring and bellows will stop the leakage if the other mentioned items are good.

Some pics of said FD pieces...

 

 

 

[greg g]

I believe the seals are some sort of carbon impregnated material.  Don't know if they are soft and flexible or stiff and resilient.  But I don't think the additives in atf will have any effect.  I remember my Dad had a 49 Wayfarer that started to leak.  I heard him talking to the neighbor about draining and spiking it.  I guess there was a back yard fix were you put a bolt in the drain hole to connect the impellers.  This of course defeated the fluid drive but you could still drive normally using the clutch and three speed trans.  They also talked about swapping in a junk yard unit.

 

Neither happened cuz about 3 weeks later, a 54 Meadowbrook was in the driveway in place of the 49.  It was a fluid drive three speed also.

[MarcDeSoto]

Interesting discussion.  I'm working on a 48 DeSoto and it ran fine before I tore it down 40 years ago.  I've drained the FD and put new Mobil Light Circulatiing oil in it.  No leaks so far.  I do have the FD tool kit and I have a junk 48 FD unit out of a 48 Dodge.  It is rusted through, so it can't be fixed, but I might try to tear it down to see what rebuilding one would be like.  But I'm not going to buy an expensive seal to do it.  Just try to tear it down and put it together again.  

[Dodgeb4ya]

The black carbon seal is hard and brittle...

The bellows portion is copper and the folds can crack...

[Dan Hiebert]

Now I'm slightly confused.  Making the seal "swell" was not a good word choice, I know/knew the seal is rigid.  I recall the discussion about using ATF with seal conditioner(s) mentioned it (possibly) degrading the seal by virtue of how it actually conditions it, because it is not a soft seal and it is graphite.  Another argument was simply that it wouldn't work to fix leaks... because it is not a soft seal and it is graphite.  Either way, the FD unit in our D24 quit leaking after I changed the fluid to Type F ATF.  At the time I did that, the appropriate oil for the FD units was either not readily available, or we hadn't nailed it down quite yet, I don't remember which, and ATF was identified as a good replacement, it has the appropriate weight, and contained anti-foaming additives, but the caution was for the seal conditioning additives, which not all ATFs have.  I could only guess as to why/how it is working for our FD unit.  I'll quit babbling - Ultimately, the best fix is to replace the seal(s).  If using ATF works, count on it as a temporary fix.  Of course, now I'm probably jinxed and will have to fix a leaking FD in the near future.   

Edited December 15, 2022 by Dan Hiebert

[Bryan G]

Some more excellent information that I didn't have before. I had previously envisioned the bellows as being rubber. 

 

Greg, I had thought about the "spiked" option...sure seems like it would be fairly easy to do. Not sure what kind of load that would be on the bolt and how it would hold up, or how a Tip-Toe shift would react to direct drive. Not sure it would care? But I'm going to be more optimistic-I'm not going to have to try that route!

 

I wonder if, back in the day, many transmission shops offered resealing? My mechanic is checking with someone he knows to see if they have the Miller tools or any experience with these. I know of another really good, old-time auto transmission rebuilder but it seems a stretch that he'd have spent time with these. 

[Doug&Deb]

The Mopar semi auto trans is the only old trans that doesn’t have specialized repair available. At least none that I’m aware of. Perhaps they are more robust than most.

[MarcDeSoto]

In my restoration of my 48 DeSoto, I did nothing to the M-5 trans or the FD, except change the fluids and replace the ring gear on the FD.  Why, because they worked perfectly before, but that was in 1980!  Hopefully they still will. The car has been garaged since then.