Mondial 3.2 Differential - Help

I redid the diff seals on my 1988 Mondial 3.2 last winter, and despite meticlous attention to details and following the lead of various Fchat threads, Birdman, etc. the seals leaked anyways, actually worse than the original seals I replaced. The right one notably more leaky, not extreme but still weeping and flinging gear oil onto the header leaving a burnt oil smell in my garage after a ride.

So I am at it again.

Can a pro confirm if the right side seal is supposed to be a depth different than in the picture? I also note the diff hub surface looks very nice, I had sanded it lightly as noted in the threads. No wear grove from the original seal. I used the Hill seal installer, so the seal should have gone in nice and straight.

Also, can someone re confirm the same silicone sealing around the diff hub bolt and splines is necessary on the left side? I did that last time, but just emulated the approach in eg. Birdman for the right side diff seal hub, made sense from what I could see. I have not found any thread dealing with the right side seal installation.

What am I missing? I am not even sure I want to remove the seal I had put in, there is no sign of any damage. It should be sealing. Maybe just resand the hub seal surface more thoroughly, maybe I did not sand non directionally enough? Or did I just get some bad seals?

I don't want to do this over again!
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I did not measure these things, but I did test fit the seal over the hub originally and it seemed snug enough.

From the factory, did these seals weep a bit until the break in, ie. I only put on less than 1,000 km since I did the seal job, maybe takes longer to seat the seal?

 

Good question, will investigate this, thank you.

 

I did indeed coat the outside of the seal, based on the Birdman tutorial, but I get that the rubber exterior of the seal should seal fine on its own.

I am going to put in a new seal, and dress/polish the sealing surface on the flange. I will also check for unusual run out of the spline. Should the flange have some grease on it when assembling, or should his be dry? I get conflicting info. online, some say the seal surface needs to wear in dry to break in, others like Birdman grease the flange sealing surface, which I would expect was common practice, but the new seal compounds may be better off installed dry?

As far as I can tell the seals are not directional, there is one Ferrari part number for both sides, 125078.

 

Got it, thank you.

 

Great insights, will check the new seals closely.

I am thinking the problem may simply be that I did not sand the sealing surface carefully enough, have resanded with 800 grit and then 2000 grit in a circular omnidirectional way. Not quite polished, but not really any meaningful sanding strakes either. Combined with a new seal, will see how that goes.

 

These are the new seals. Also, a close up of the output flange sealing surface as finish sanded with 2000 grit.
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The little "key" mark is in the same direction on both.

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I have the old seal out, and I measured the inset to the inner shoulder at 14mm deep. The seal is about 10mm, so if the seal was pushed in right to the inner lip, that would inset the seal in the casing quite a bit at 4mm. I don't recall the original (I presume) seal being in that deep last I did this, more like flush with the face of the casing ie. not inset much at all.

I can't find anything in old threads that is clear on this left hand side, nobody has a picture of what is normal.

Are you sure I should install the new seal in that deep? Would also make it harder to remove if god forbid I have do do this again in this lifetime.

I appreciate any further perspective on this.

 

Here is the only pic I could find from an old Fchat thread on this right side seal...no idea if this is correct.




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Here is a picture of mine with the seal out....
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Thank you very much for the greater certainty on this.

And, yes I removed the seal using the drill and screw approach as you suggested. A bit unnerving to drill in there, I wish there was a useful seal puller, I bought one that looked good but it could not grip the lip properly, and that spline gets in the way of many types of pullers. So the old drywall screw method and prying out seems the way to go.