Malliard freewheel sponge- what the what?

[Wingslover]

Cleaning a newly removed 5 speed freewheel from a restoration, per normal. Saturating the tines, moving dirt, an odd layer on top. Turns out it's a dust cover sponge of some sort - a blockade for particulate from the inside of the hub.

As I picked it out, I kinda winced. Is it necessary? Maybe just a precaution? Should I replace it (and with what)?

 

[juvela]

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some models received this feature beginning about 1973-74

intended to keep lubricant in and dirt out

there are Schwinn Approved Shimano gear blocks with a similar seal of rigid black plastic

as with all such seals of this sort it is a source of friction...

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[SKPC]

When running the old freewheels in dirty, dusty, wet and gloppy conditions they became compromised and failed more quickly. I would cut custom foam discs big enough to cover the water/dirt entry points on both the inside and outside of the freewheel just to make sure there was something there to discourage water and grime from getting to the delicate pawls and springs. Labyrinth sealing systems are superior to these open-ended and vulnerable designs you see on some of the old freewheels... The Sturmey and Sachs IG hubs are good examples sporting L. Seals. The old freewheels are simply more at risk of getting crap in them, especially if they do not have some help like from say a custom foam disc cut to fit like you found on yours. The speed-scubbing effects are minimal of a foam disc compared to the other more important factors that influence wheel speed like rim, spoke and tire weights.

 

[Bendix]

Sounds like a solution in search of a problem. IMHO.

While there would be no practical concern over "speed-scrubbing" friction, I'm always wary of anything that can get gobbed up with dirt, grease, and grime or through deterioration that might prevent the freewheel from freewheeling freely.

That's when the resulting surprise gets expensive!

 

[SKPC]

I can say from years of experience, it is more of an issue if you fail to inspect it on occasion. If you simply ride your bike on a clear day on pavement for 10 miles and nothing else, then your freewheel should not have any problem. For all others who ride in inclement conditions (like myself for 40 years) or long distances in dirt, perhaps a simple, lightweight and easy to make cover of some sort to ensure even better sealing of the exposed dirt-magnet internals of an old open-bearing freewheel is simply smart thinking. For me it has been 100% effective, and as a matter of fact, saved my Dura Ace 7-spd from any maintenance because it kept the crap out. Ask @bloo as he is now in possession of this very foam-disk protected freewheel I speak of. If the seals were not on it, I would not have sold it to him. 100% effective as long as the ring is seated properly and not torn.
Again, it all really depends I believe on whether you actually ride it in conditions that have dirt and rock particles running into your bearing surfaces and freewheel mini-parts all day helped by water. I have run them with and without the foam ring, and what saved me every single time from being forced to buy another blown freewheel was the little worrisome foam disk put on both sides to help protect the inside.
Try it Bendix, you'll like it!