4R70W Front Seal Leak After Rebuild.....
10-01-2018, 07:39 PM
#1
4R70W Front Seal Leak After Rebuild.....
Not sure if this has happened to anyone else, but I rebuilt my 4R70W transmission from my '97 F150 4x4, 4,6L, bone stock. I replaced most all of the hard parts with either new or rebuilt, and rebuilt the valve body and added a shift kit as well, and the torque converter is a rebuilt unit, so everything is stock all around.
I've installed, pulled and re-installed this thing 3 times now...and every time, the front seal leaks. And not just a "drip"...it leaks. I put about 10 quarts in to start it up, it doesn't leak, sounds fine etc....not a drop. But as soon as I start cycling it through the gears to circulate fluid, it starts leaking....about 1 quart in 2 minutes. The pump is rebuilt, the front seal is new, the pump gasket is new and there are no cracks in the case. I am perplexed. My scientific wild *** guess says that pressure is being placed on the seal that doesn't belong there...but that's obvious. I'm not a transmission expert, but every time I call one I get the same answers.....front seal, spring in the front seal, bad gasket, cracked case.... etc, etc... So, if this happened to anyone else, please share...if not, let's figure this thing out and let everyone know about it.
I've installed, pulled and re-installed this thing 3 times now...and every time, the front seal leaks. And not just a "drip"...it leaks. I put about 10 quarts in to start it up, it doesn't leak, sounds fine etc....not a drop. But as soon as I start cycling it through the gears to circulate fluid, it starts leaking....about 1 quart in 2 minutes. The pump is rebuilt, the front seal is new, the pump gasket is new and there are no cracks in the case. I am perplexed. My scientific wild *** guess says that pressure is being placed on the seal that doesn't belong there...but that's obvious. I'm not a transmission expert, but every time I call one I get the same answers.....front seal, spring in the front seal, bad gasket, cracked case.... etc, etc... So, if this happened to anyone else, please share...if not, let's figure this thing out and let everyone know about it.
10-02-2018, 06:45 AM
#2
Driving the wheels offer
aftermarket front seal ?
10-02-2018, 07:30 AM
#3
Thanks for your response, but no....this series 4r70w front seal is basically a "press-in", as-in press in with your fingers. It has a rubber-coated exterior with a 'bead' that fits into a groove in the seal boss in the pump housing.
It now seems my flexplate is busted. I'll get it apart sometime today to confirm it, but I'm pretty sure that's what it is. I'll make sure and post pics. The thing is, I DID inspect it...but apparently not well enough. I didn't wipe it down well and check it closely enough for hairline cracks. Guessing... I would say that it was cracked and spinning out of round... causing my mysterious leak, and finally just gave way. When it did, it created so much 'wobble' in the TC that the seal naturally couldn't contain it, and the gushing began.
I've ordered a new flexplate and front seal (which I'm half certain is trashed after this incident), and they'll be here today.
Pretty sure this lesson is going to be: if it's a high-mileage truck, and you're pulling the tranny anyway...replace the flexplate.
It now seems my flexplate is busted. I'll get it apart sometime today to confirm it, but I'm pretty sure that's what it is. I'll make sure and post pics. The thing is, I DID inspect it...but apparently not well enough. I didn't wipe it down well and check it closely enough for hairline cracks. Guessing... I would say that it was cracked and spinning out of round... causing my mysterious leak, and finally just gave way. When it did, it created so much 'wobble' in the TC that the seal naturally couldn't contain it, and the gushing began.
I've ordered a new flexplate and front seal (which I'm half certain is trashed after this incident), and they'll be here today.
Pretty sure this lesson is going to be: if it's a high-mileage truck, and you're pulling the tranny anyway...replace the flexplate.
10-02-2018, 08:22 AM
#4
Senior Member
Are you talking about the big o-ring for the pump?
10-02-2018, 08:58 AM
#5
Senior Member
I know your torque convertor is a rebuild so this probably doesn't apply to you, but when this kind of thing happened to me it turned out to be a cracked torque convertor.
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retiredinoregon (10-03-2018)
10-02-2018, 10:24 AM
#6
Senior Member
I've seen "rebuilt" converters leak. The Recon Transtar converters are junk. If you find that is your issue, I suggest trying to find a local rebuilder. It's a lot easier that way... usually can be done in a couple hours if they don't have one to exchange with you.
Last edited by white89gt; 10-02-2018 at 10:27 AM.
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retiredinoregon (10-03-2018)
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10-03-2018, 06:32 AM
#8
Senior Member
Some people refer to the pump seal as the front seal. Just making sure we are talking about the correct part.
My Buddy that owns a trans shop taught me a trick that worked really well on my CD4E that is in my Escape. He packs the lip of the seal with grease. What this does it hold the spring in place. Sometimes when you are assembling, that spring will get nudged and get just enough off kilter to leak. The grease holds the spring in place, making a better initial seal.
My Buddy that owns a trans shop taught me a trick that worked really well on my CD4E that is in my Escape. He packs the lip of the seal with grease. What this does it hold the spring in place. Sometimes when you are assembling, that spring will get nudged and get just enough off kilter to leak. The grease holds the spring in place, making a better initial seal.
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retiredinoregon (10-03-2018)
10-03-2018, 01:45 PM
#9
Senior Member
Nice trick of the trade. 
11-04-2018, 03:19 PM
#10
Just checking back in with this project....I've had the transmission out, and back in numerous times now. Checked everything. New sealing rings on the pump, new bushing, new torque converter, new front seal, new flex plate AND a completely rebuilt unit. When I start it up, it gushes fluid from the inspection hole in the bell housing. I have not a clue. I'm at the point now where I've got $800 in the rebuild, and I can't drive it so I'm going to have to strap some kind of container to the bottom of the bell housing to catch the fluid (@ $5/qt), and just move it out of the driveway and out of everyone's way. It saddens me greatly, but it seems no matter who I call, no one... and I mean no one.... can seem to tell me WHAT will make a transmission gush fluid right past a new front seal...in Park, Reverse, Drive, Neutral...doesn't matter. As an Engineer myself, I'm truly shocked that I get the same answers over and over again: Front seal, pump gasket, front bushing. That's it. There is SOMETHING that can cause a tranny to put pressure against that seal that it was never intended to hold, and whatever that 'thing' is, it's happening here. When I find out...IF I find out.... I will post the result in detail. In 35 years of wrenching on cars and trucks, I've never seen a front leak this bad that didn't reveal a bad seal upon removal. Ever. I'm no professional mechanic, but I know for certain this seal isn't supposed to have this kind of pressure against it. Stay tuned, lol.