727 Rebuild Woes: Oil Pump stator / drum air leak

[MacMan45]

Rebuilding my 727 and first off, trans condition was unknown other than slips bad when warm. Checked end play before teardown, bad, 0.088".

Fried rear clutches, no other metal. Figuring a straight up rebuild.

Get to air checking, and it hisses quite badly. Both on front and rear clutches. Tried adding ATF to holes, still leaks bad.

Remove and bench test just the stator on the front drum, still hisses. Clutch basket does move, using 35psi of air, but leaks and hisses badly. Drum is not excessively worn, just two shiny spots where the rings were. Tried with original sealing rings, and with the new rings from the kit. Still hisses. Using plenty of assembly goo...

Any ideas? I assume if I re-install it will leak and let the clutches slip and burn up again quickly...

THanks

 

[MacMan45]

Forgot to mention, added a 25" end play shim between the two clutches, and when fully assembled my end play is 0.40" so figuring that is good.

Possible the horrible end play allowed the drum to walk on the stater and I know can't ever get a good seal?

Do oversized sealing rings exist?

 

[thrustbucket]

Rebuilding my 727 and first off, trans condition was unknown other than slips bad when warm. Checked end play before teardown, bad, 0.088".

Fried rear clutches, no other metal. Figuring a straight up rebuild.

Get to air checking, and it hisses quite badly. Both on front and rear clutches. Tried adding ATF to holes, still leaks bad.

Remove and bench test just the stator on the front drum, still hisses. Clutch basket does move, using 35psi of air, but leaks and hisses badly. Drum is not excessively worn, just two shiny spots where the rings were. Tried with original sealing rings, and with the new rings from the kit. Still hisses. Using plenty of assembly goo...

Any ideas? I assume if I re-install it will leak and let the clutches slip and burn up again quickly...

THanks

I am having a little difficulty reminding myself of the 44re rebuild I did six months ago, and I know they are more of a 904 than a 727..

But, isn't there a piston in the drum with a large diameter rubber seal behind the clutch pack? Did you replace that large seal? It sounds like you are talking mostly about the sealing rings on the input shaft?

Did you remove the shaft completely from the drum assembly? There may be a seal hidden in there between snap rings.. (doubtful. but, a guess)

Maybe disassemble the drum and be sure that you put the correct piston seal in/it wasn't damaged/displaced during install? Do you have any seals left from your kit?

Some kits have multiple seals for multiple models in the same kit and sometimes the only difference is the width and not even the diameter.. Mine had a bunch. I had to measure the old vs new with dial calipers.

Also, a previous rebuild can have the wrong seal installed, so replacing with what came out is sometimes a mistake...

Hopefully that helps..

 

[CudaFactHackJob]

Is the drum scored where the rings ride?

 

[thrustbucket]

I took a look at an exploded view of the 727. First, check all the scarf cut rings and be sure they are floating freely in the grooves, and the ends aren't jammed together. If you replaced scarfs with the steel 'clasp' type (not sure the true name) rings, make sure they are locked/snapped together at the ends. (stator)

I would rebuild the pump as well while its out. Just to be sure that the two halves, or the stator/pump are not 'clocked' incorrectly. Causing Obstructed passages or venting them to atmosphere. (leaks) Or just clogged with trash from a failure.

There are two large lip seals in the direct drum on the 727, an inner, and an outer. The forward drum has both these seals as well. Check that you did not mix the seals up between the direct and forward drum sets. Additionally, the lip seals are often an "L" shape. I believe that they need to be installed in the correct direction. The large diameter outer seals need to have the 'lip' or 'skirt' of the seal protruding towards the 'thin' side of the piston in relationship to the groove, for both the direct and forward drum. The inner seals 'lip' direction should mirror the outer seals, so all seals face the same direction after install. Not getting this right will cause a drum leak for sure during clutch engagement.

I believe there is a seal on the direct hub as well, that engages with the direct drum. I think it is accessible without removing the shaft from the hub. its out of the equation with a bench test. But, I would just check that too while you are at it.

If I remember correctly I had to install my pump into the direct drum (on the bench) and rotate it around a few times to help seat the rings and then air check on the bench.

 

[CudaFactHackJob]

"added a 25" end play shim between the two clutches"....If you mean between the drums, never insert more than one washer between the drums; an extra one won't stay in place. (over 2 feet is a LOT!) And never air check unloaded drums. (damages the seals). I see a lot of terms that I'm not familiar with..I guess we're supposed to know what you're talking about. Clutch basket, assembly goo, straight up rebuild ; I think maybe if the repair you're doing is as imprecise as your use of terminology, this thing isn't going to work very well for very long. Helpful hint: made up terminology will discourage others from chiming in.

 

[thrustbucket]

"added a 25" end play shim between the two clutches"....If you mean between the drums, never insert more than one washer between the drums; an extra one won't stay in place. (over 2 feet is a LOT!) And never air check unloaded drums. (damages the seals). I see a lot of terms that I'm not familiar with..I guess we're supposed to know what you're talking about. Clutch basket, assembly goo, straight up rebuild ; I think maybe if the repair you're doing is as imprecise as your use of terminology, this thing isn't going to work very well for very long. Helpful hint: made up terminology will discourage others from chiming in.

There is truth to this for sure. But, you gotta start somewhere.

Question: By 'loaded', do you mean fully assembled with clutches/steels/plates springs etc..? That's how I checked mine..I'm not sure how else you would do it without shooting the piston across the room.. haha!

 

[CudaFactHackJob]

Simple, install the pistons, return springs, retainer, and snap ring; no clutches....air pressure will push the piston up out of the bottom of the drum, seals pop out, piston goes back down and snags seals...you sure you ever worked on a tranny?

 

[thrustbucket]

Simple, install the pistons, return springs, retainer, and snap ring; no clutches....air pressure will push the piston up out of the bottom of the drum, seals pop out, piston goes back down and snags seals...you sure you ever worked on a tranny?

Yes. I have rebuilt one 42RE automatic transmission. Seems to be successful so far.. I guess time will tell.. I am not claiming to be a profession transmission tech, or an expert by any means. I am just trying to assist someone who appears to be trying to learn how to do this operation himself, maybe for the first time, like I was.

I had forgotten that there there is a snap ring that captures the piston/spring assembly and limits the piston travel. I was thinking in my mind that the selective snap-ring and second pressure plate was retaining the whole piston/clutch assembly. I was clearly wrong there. I will own that one absolutely.

I just know my drums didn't leak, and appeared to engage and disengage correctly. So, I was offering what I thought was legitimate information. Please correct me if I am wrong on any account. I don't wan't to make this guys project any harder than it needs to be...

I had installed the loaded direct clutch drum on the pump/stator assembly and applied air. Then, I installed the loaded forward drum on the assembly. Then, I secured the forward drum and applied air to that. (I figured this is what he was doing as well..with fully loaded units..) I retested both for actuation via the case ports after the assemblies were reinstalled into the case.

The fact that he has leaks on the direct, and forward clutch respectively makes me think it could be swapped/improperly installed lip seals... Assuming there is not major seal surface damage, I'm not sure what other area would affect both clutch packs during an air bench test besides stator/pump misalignment or stator/forward drum sealing rings.. Which, appears to be his focus. But, he has tried multiple approaches (swapping seals) there with the same result. Maybe it's possibly the sealing rings on the input shaft/direct hub assembly? But, the later seems like it would likely affect only the forward drum, and not the direct drum as it actuates on the bench without the input shaft in place.. That leads me back to piston lip seals as a very possible cause.

I think a good approach is to help him by suggesting what he should do, as far as checks and assessment. Rather than what to 'never' do. Especially, if it is not obvious he was even attempting the 'no-no' unloaded method.

 

[CudaFactHackJob]

What are the thicknesses of the thrust washers between the front (direct) drum and the pump? What is the thickness of the thrust washer between the rear drum (forward) and the front drum (direct)?

 

[Duane]

Rebuilding my 727 and first off, trans condition was unknown other than slips bad when warm. Checked end play before teardown, bad, 0.088".

Fried rear clutches, no other metal. Figuring a straight up rebuild.

Get to air checking, and it hisses quite badly. Both on front and rear clutches. Tried adding ATF to holes, still leaks bad.

Remove and bench test just the stator on the front drum, still hisses. Clutch basket does move, using 35psi of air, but leaks and hisses badly. Drum is not excessively worn, just two shiny spots where the rings were. Tried with original sealing rings, and with the new rings from the kit. Still hisses. Using plenty of assembly goo...

Any ideas? I assume if I re-install it will leak and let the clutches slip and burn up again quickly...

THanks

Air check does not work very well on Teflon sealing rings, but under hydraulic pressure work superb.

 

[MacMan45]

"added a 25" end play shim between the two clutches"....If you mean between the drums, never insert more than one washer between the drums; an extra one won't stay in place. (over 2 feet is a LOT!) And never air check unloaded drums. (damages the seals). I see a lot of terms that I'm not familiar with..I guess we're supposed to know what you're talking about. Clutch basket, assembly goo, straight up rebuild ; I think maybe if the repair you're doing is as imprecise as your use of terminology, this thing isn't going to work very well for very long. Helpful hint: made up terminology will discourage others from chiming in.

Hmm. Let’s work backwards: I didn’t make up any terms. Assembly goo is a brand of transmission assembly lubricant made by Lubegard. I can post a link.
Perhaps due to my background in motorcycles, a “clutch basket” is referred to differently with automatics. The “basket” holds the steels and clutches. Anyways, that’s obvious.

Lastly, a straight-up rebuild implies installing every piece in a Master rebuild kit, seals, bushings, steels, clutches etc.

Lastly, clearly the “ was a typo, I meant thousands. IE 25 thousands or 25/1000 inches of spacing.

moving on: trans is assembled and works fine. I guess I had a higher bar for the smoothness of the air check.

Thanks others for the helpful insight.

I do have a small leak at the dipstick tube, need to adjust the bracket on the bell housing and seat it better.