Rear End Clamshell Gasket

[Scott Rosenthal]

Disclaimer: I'm not for one minute naïve to assume I can fully stop rear end leaks with a pressed steel clamshell rear end.

That said, I put this rear end together with only Permatex Black silicone (no clamshell gasket), and must say it does a reasonably good job...every 2 weeks or so, I get a very small oil drip at the bottom of the seam between the (2) housing halves (90 plus degrees heat here in Cincinnati does not help). Is there the possibility that adding a standard paper gasket between the housings will perform better, or do you figure inherent flexing of the assembly will ultimately cause this seal to fail? A known problem with silicone is that extreme squeeze of clamped parts will ultimately cause two metal surfaces to fully evacuate the silicone at the squeeze area, therefore creating a metal to metal conduit for the oil. I'm running standard 85/70 gearbox oil, which is lesser viscosity than the recommended Model T rear end grease, so I expect this is further aggravating the potential for leakage (long story for another day, why I selected this lube).

Is there anyone out there making this a clamshell paper gasket, and do folks here believe that adding this gasket could improve the problem, or do you think I may create other problems by adding this?

Regards,
Scott

[Allan]

Scott, there may be another way. Loktite make a red flange sealant which does not cure hard like silicone type sealants. I use it to good effect in the later diffs with the cast centre pieces riveted to the axle housings. These may be more rigid than the pressed steel items, but it certainly seals up well.

Allan from down under.

[Bill Robinson]

A couple of years ago I found this Permatex product highly recommended on the forum. 3 of my axles halves have been sealed with it and, so far- no leaks. The specs state "Specially formulated to withstand the harsh gear oil environment found in differentials and transfer cases".
https://www.permatex.com/products/gaske ... ket-maker/

[Mark Gregush]

Also, adding a gasket will move the housing apart acting like a shim. Of hand you would be moving them apart in .005 range depending on the thickness of the gasket compressed.

[Scott Rosenthal]

Thanks Allan, Bill and Mark:
I'm sure mine is not a new dilemma, and I suspect the inclusion of a gasket here may not be a solution for multiple reasons. Of most concern is the constant flex issue, where I expect any movement at this center area would likely be aggravated by a pliable gasket.

I also suspect that the potential for Clamshell leakage is greater at the boss positions of the (7) mounting screws. Because there is a noticeably reduced seal surface at these locations, any variation in these exposed bosses creates that much more likelihood of a leak developing there.

Could be that porosity of the housings is allowing oil to pass, and if so, interior coating that will be applied may reduce this. I have yet to see one of these rear ends that does not have some leakage at this location, so could be that physics is simply not going to let this go away, but I will make the effort to shut down as many potential contributors as is possible. One of the assembly procedures that I use is to pour a small amount of sealant into the assembled lower half of the housings, and then pour this back out before installing the driveshaft.
This may help or may do nothing...we'll see. Many thanks again Gentlemen.

Regards, Scott

[Mark Gregush]

While it would require a repaint, why not hot tank the housings and coat the inside with the same stuff suggested for sealing the inside of engine blocks? Any sealer you would pour in would require a clean oil free surface to bind to.

[Scott Rosenthal]

Hello Mark:
Good point...Apologies, I did not lay out my entire rebuild process here, but interior coating of the housing center sections is part and parcel to this. The parts were rushed together to get the car on the road, especially the qualification of this rear end. I use a standard gas tank sealer product which I believe is a urethane base. Assumption has always been that the car would be fully assembled and all corrections made before tearing back down for surface finishing. Because of the extensive fabrication work involved in building this rear end, additional welding could well have resulted....looks like we may have dodged that bullet. I also want to point out that this rear end was assembled with no leak problems being evident until just recently, so this leads me to question whether flex of the assembly over time may be the source or possibly a contributor.
Regards,
Scott