727 Front Seal Leak

[69'Net]

So I have had two different transmissions leak from the front seal on the same 440. One transmission I pulled back out and replaced the seal and it still leaks. It leaks slow at first then gets worse over time. Near as I can tell from looking at the rubber on the seal, it looks like the seal is tight on the top side like its sitting too far up. Could this be a block alignment issue or a torque converter issue? Or am I just lucky?

 

[Cranky]

Is this trans a match with the engine? If not, it could be an alignment issue. Did you install the seal using some grease on the lip and converter snout? Also, did you test fit the seal on the converter snout?

 

[Greg Ducato]

Does it leak when it is running or when it sits after being shut off? The converter hub seal only has pressure on it when the vehicle is running , the pump o-ring is exposed to fluid when the vehicle is shut off and the fluid rises to that sealing area. The transmission's vent is located on the top side of the pump and if the trans is overfilled will push out of this vent when running. Be sure and check fluid level with the vehicle running and the trans in neutral, fill to between add and full mark to allow for expansion.

 

[Fran Blacker]

Worn front pump bushing? If the convertor was left on engine when engine or transmission were removed bushing could be damaged.

 

[66Satellite47]

I had a 727 that leaked a lot out the front seal. replaced the seal & bushing a few times, used offset dowels on block. Finally at end of race season had trans out & used the dial indicator to discover the bore in the case for the front pump was egg shaped. tossed that case, put the guts in another case no leak for many hundred runs. If you can see the wear pattern on the bushing maybe offset dowels would work.

 

[vance.dykes]

Does it leak when it is running or when it sits after being shut off? The converter hub seal only has pressure on it when the vehicle is running , the pump o-ring is exposed to fluid when the vehicle is shut off and the fluid rises to that sealing area. The transmission's vent is located on the top side of the pump and if the trans is overfilled will push out of this vent when running. Be sure and check fluid level with the vehicle running and the trans in neutral, fill to between add and full mark to allow for expansion.

i agree i would add if the builder did not change the Teflon washers for the pump bolt then add that to the list.

 

[ksurfer2]

I am also battling a leak that appears to be coming from the front shaft seal of my torqueflite. When I had the engine out of the car last year, I replaced the torque converter and the front seal. Oddly, the leak I am facing now is EXACTLY like the leak I had prior. I would think that after replacing the seal and converter, there would be some change.

 

[Dipstick]

Could be the way you installed the seal. Hammering the seal into place sometimes dislodges the garter spring, I always pack the spring with heavy grease before installing.

 

[R413]

Maybe it’s leaking someplace else if no change? There is a pipe plug for the 2nd gear band lever hole. Is the drain plug in the converter tightened?


You can’t assume anything, and everything is a potential leak point.

 

[69'Net]

Is this trans a match with the engine? If not, it could be an alignment issue. Did you install the seal using some grease on the lip and converter snout? Also, did you test fit the seal on the converter snout?

Neither trans was original to the engine. Both leaked in the same spot. I put grease on the lip all 3 times. How do you test fit it?

 

[69'Net]

Does it leak when it is running or when it sits after being shut off? The converter hub seal only has pressure on it when the vehicle is running , the pump o-ring is exposed to fluid when the vehicle is shut off and the fluid rises to that sealing area. The transmission's vent is located on the top side of the pump and if the trans is overfilled will push out of this vent when running. Be sure and check fluid level with the vehicle running and the trans in neutral, fill to between add and full mark to allow for expansion.

It leaks out when shut off, the fluid is coming out of the bell. I always assumed it was the converter seal. It did it in two separate transmissions

 

[69'Net]

I had a 727 that leaked a lot out the front seal. replaced the seal & bushing a few times, used offset dowels on block. Finally at end of race season had trans out & used the dial indicator to discover the bore in the case for the front pump was egg shaped. tossed that case, put the guts in another case no leak for many hundred runs. If you can see the wear pattern on the bushing maybe offset dowels would work.

How do you measure run out on an automatic? I cant find any info on that, except for manuals

 

[Fran Blacker]

Think you have to remove pump housing. Then a dial indicator like you do a clutch housing. Don't forget to tighten front band or the trans guts will come out. SM will help!

 

[Fran Blacker]

Think you have to remove pump housing. Then a dial indicator like you do a clutch housing. Don't forget to tighten front band or the trans guts will come out. SM will help!

Might be impossible to do it by just removing pump housing and using a mirror to read dial indicator. May need to gut trans. It's not hard but READ service manual first!
@dvw would know if it is possible to do it without gutting trans.

 

[493 Mike]

You need the case totally empty so you can work through the bottom to read a dial indicator fastened to a adapter bolted to the crank flange. Rotate the crank and read the indicator at every 90* interval. Then you can determine if the engine and transmission center lines are matched up. I used dowel pins from McRobb to correct my alignment. I'll try to remember to get a photo of the adapter tomorrow.
Mike

 

[Fran Blacker]

Mike493 I'd find where its farthest off center and closest to center. I'll post how bellhousings are done just the hole is bigger.

 

[Greg Ducato]

If it is only leaking when shut off it is a pump o-ring or pump bolt washer leak. It could also seep from the pipe plug that covers the front band lever pin but that doesn't seem likely.

 

[493 Mike]

You need the case totally empty so you can work through the bottom to read a dial indicator fastened to a adapter bolted to the crank flange. Rotate the crank and read the indicator at every 90* interval. Then you can determine if the engine and transmission center lines are matched up. I used dowel pins from McRobb to correct my alignment. I'll try to remember to get a photo of the adapter tomorrow.
Mike

Here are a couple of photos of the adapter I made to mount my dial indicator to the crank flange.
Mike

 

[69'Net]

Mike493 I'd find where its farthest off center and closest to center. I'll post how bellhousings are done just the hole is bigger.View attachment 806036 View attachment 806037

Awesome! Thank you!

 

[71airgrabberRR]

I would also check the flex plate to see if there are any possible problems with it while you're at it...... I had a problem with one many years ago. It caused me to wipe out the front pump housing bushings in two separate transmissions before I found the problem.

Mine was bent..............