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Seeking advice regarding 4-spd front seal leak

611 Views 12 Replies 7 Participants Last post by  bolbers
Hi all,

I decided to address a nagging trans leak today. I’m pretty sure it’s leaking through or around the front shaft seal because I have fluid seeping out of the bellhousing from behind the shift fork boot etc.

I was hoping to find clear evidence of a failed or torn seal but it looks brand-new to me. So I was hoping by posting some photos I could get some experts to weigh in on a few things.

Here’s the seal after cleanup. No wear that I can see on the lip, but there is a bit of a high spot on the mating flange. My guess is that the thing is really only supposed to seal on the shaft itself and that the flange area is in the “wet” part of the system which is contained by the paper seal around the perimeter. If so, that high spot shouldn’t matter?

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The shaft is a bit cruddy and so I think I’ll try cleaning it up with some Scotchbrite or similar. There’s a bit of pitting too but not as bad as the shifter shaft which some of you may recall I successfully addressed with some JB Weld in a non-structural “filler” application. I could try that here as well but I don’t think it looks that bad. I’m hoping cleaning the shaft will make a meaningful difference but since the seal lip looks pristine I’m not convinced.

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Is there anything I should do about the “cup” that receives the seal in the bellhousing ? It seems to me that there is an obvious leak path around its outer surface to the bellhousing interior. Does it need some sort of RTV there? Does the mating surface roughness matter here? Am I missing something?

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(Not Rally) Bob
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The paper gasket is the real seal between the transmission and bell housing. It’s normal for the gear lube to be fin that area between the bell housing and transmission. Clean both mating surfaces and replace that gasket. You may as well get a new front seal while you’re at it, that’s just what I would do. There’s two critical paper seals, the second one is a round thin paper gasket in between the bell housing and throw out bearing sleeve in front of where your screwdriver is on the last two pictures I put mine together one time and left it out, then gear lube got into the clutch area and gradually soaked the clutch pad.

That throw out bearing sleeve sits pretty firmly in there so if you haven’t disturbed it then just leave it it will probably be fine as is. When the throw out, or sometimes called release bearing gets replaced that sleeve gets popped out from the rear of the bell housing and the gasket gets replaced with the release bearing.
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Thanks Cub. Is there a source for that throw out sleeve gasket? I can’t seem to find one at OGTS or Splendid’s websites. Is it more or less an annular ring that sits under the flange of the sleeve?

That sleeve is a little loose in my trans. I can wiggle it a little back and forth and rotate it a few degrees. But it doesn’t want to come out more than that much. Should I take that all apart, clean and seal it up when I reassemble? I guess I could bed it in some sealant but I want to make sure that wouldn’t cause other issues.
The paper gasket under the throw out bearing sleeve is not a liquid-tight seal. It’s just there to prevent galvanic corrosion between the steel and aluminum.
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That little pocket (where my pry tool is in one of my photos) is exposed to gear oil, correct? I’m not understanding what keeps the oil from seeping around/through that gap between the bell housing and the sleeve. Is it just supposed to be a tight-enough metal-on-metal seal? Or is there another liquid-tight interface that I’m not considering? Do you think my problem is mainly the surface of the trans input shaft being rough and dirty?

Thanks much for the help :)
Well Bob knows these cars far better than I do. I had the conversation with Gil at OGTS asking him why I had gear lube all over my clutch disc & he told me that paper gasket needs to be in there, that was my problem. Its primary function may be to act as an insulator, perhaps it acts as a spacer and keeps the front seal & TO bearing sleeve in in place as well. I completely left that little gasket out when I re assembled everything. I’m not really sure other than what Bob’s saying that it does, all I know is that my problem is solved now, and I attribute it to it being in place now. It’s a very thin gasket. If it’s there in place on your bell housing even though you may have jiggled the sleeve for the TO bearing, especially if you haven’t removed the bell housing I’d leave it alone, just make sure it’s in there.

I had other problems with the throw out bearing adjustment too so hopefully seeing this post # 5 then read on will be of some more help. You can see in one picture the bottom of the TO bearing sleeve was tilted that’s how it was when I took my transmission off the back.
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FWIW, I have omitted that paper gasket without any leakage issues, but I have applied a thin smear of RTV. But I DO ensure that the mating surfaces of the seal against the release tube and bellhousing recess are clean, and I always apply a thin layer of RTV sealant to the related front seal surfaces (the inner and outer rubber faces). And absolutley NO leaks when done.

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That oil seal should be con caved. You need to check and see why it’s been bent flat.
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That oil seal should be con caved. You need to check and see why it’s been bent flat.
Yes, concave. that seal looks bent. like something didn't go together right at some point in the past.
and extra dimples, like some body tried to fix it.
My only other thought is a bad or missing pilot bearing which would let the trans shaft move around...
just a thought.
Might want to check or replace pilot bearing if no one has mentioned? If they are worn it can cause play in the main and make it leak. Did on mine long ago; have fun.;)
Hello again, got the new seal and I’ve been working on cleaning and prepping things. The trans shaft cleaned up reasonably well (I’ll probably do a little more on it though):

Thanks Keith W for your input. I’m hoping to clarify exactly where you recommend adding smears of RTV. If I understand the way the seal works, it seems that there are three sealing surfaces to consider. First is the outer surface/flange of release bearing sleeve to bellhousing cavity (as indicated here by pick):

Since the cavity in the bell housing is wet, it seems that I need a liquid-tight seal here (paper and/or rtv). So I think bedding the sleeve in RTV is reasonable.

Next of course is the rubber seal lip that rides on the outer surface of the trans shaft which should not require anything extra.

And finally, there is the interface between the front face of that rubber seal and the recess in the release sleeve. This also needs to be liquid-tight since the seal has vent holes that allow gear oil to flow into that area. I think those surfaces are compressed against each other when everything is assembled and as long as the they are clean and smooth it should seal ok. However my sleeve has some surface pitting which seems could cause some leakage there, so I’m thinking I should add a little RTV to fill in the voids. Or I could do an application of JB Weld as a filler and work the surface smooth but that sounds like a PITA.

Am I on the right track?

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However you decide to re assemble, be sure to tap on the bearing sleeve to get it firmly seated, I’m wondering if I didn’t do that correctly the first time when I didn’t use a gasket or RTV. This last time i didn’t want to take any chances so I used both gasket & RTV just between the bell housing and the sleeve, then firmly seated the sleeve for the release bearing.
Got it all back together today and it looks like I fixed it! New shaft seal, sealer around release bearing sleeve, sealer between shaft seal and release sleeve cup.

That’s great ‘cause now I can start another thread about the fact that the bottom of my engine oil sender is wet :confused:

Thanks again for the advice. Hopefully this thread will be valuable for the next guy…
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