Mobilgrease 28 vs SHC-100

[2.7ecoboostFordBronco]

I have an experimental Super Cub type airplane that uses grease for main wheel & tailwheel bearings, stabilizer tubes/jackscrew, and tailwheel steering swivel bearing. The maintenance manual specifies Mobilgrease 28 for all of these parts.

However, the tailwheel parts manufacturer specifies SHC-100 for the tailwheel steering swivel and wheel bearings, contrary to the airplane maintenance manual.

Which one would be best to use? The airplane sees temps from -30F to 80F and uses skis in winter so the wheels and bearings due to get exposed to snow and melted snow quite a bit (water).

 

[Nessism1]

Mobilgrease 28 is clay based. Never mix that stuff with any soap based grease, like the SHC-100.

You should try to figure out what kind of grease the tailwheel swivel and wheel bearings were built with. You may need to do a full grease flush out if switching to the Mobilgrease 28 stuff.

 

[2.7ecoboostFordBronco]

Mobilgrease 28 is clay based. Never mix that stuff with any soap based grease, like the SHC-100.

You should try to figure out what kind of grease the tailwheel swivel and wheel bearings were built with. You may need to do a full grease flush out if switching to the Mobilgrease 28 stuff.

Yeah it all has to be taken apart and cleaned annually, with parts washed in solvent and blown/wiped off so the mixing shouldn’t be an issue. Wanting to know what’s best to repack the tailwheel bearings with, specifically, given the disagreement in the manuals. The mechanics I’ve talked to seem to not think it matters and to just use what’s on hand.

 

[Nessism1]

If washing, and in the manual for the plane, I'd use the Mobilgrease 28. That's good grease.

 

[Cujet]

As I've mentioned many times here, I worked in Mobil Oil's flight department decades ago. Where we tested SHC100 v M28. Each was used on Gulfstream, Hawker 700 and 800 wheel bearings and the Citation III. Including bushings, straight roller bearings, pins and more. The components were then bagged, and hand delivered to the engineers for evaluation. (we also tested turbine engine oils for the development of High Thermal Stability 254 oil)

In your plane, it won't matter one bit. M28 is thinner (under grade 2) and (the aviation version, which is, I think, not the same as conventional Mobillith SHC100) of SHC 100 is a bit thicker at NLGI grade 2.

It is kind of funny to talk about my causal observations, but when we'd pull out (for example) a gear actuator retaining pin lubed with M28, after a winter of flying in and out of the North East's worst airports, there would almost always be minor visible corrosion spots. When the same parts were installed dry, then pumped with SHC100, often the grease was too thick to flow in and around the part and it was dry on one side. Leading to scrapping it next cycle. We learned to pre-lube it with SHC100. Which solved the corrosion problem.

EDIT to add: M28 is a superb grease. I still use it all the time on my plane, due to its thin nature, which works well on the flap actuator jack screw and associated moving monkey motion. Regular reapplication prevents any corrosion or wear problems.


TLDR: SHC100 aviation was the winner in our fairly brutal testing which involved cold wet winters, de-ice fluids, terrible weather, and Saudi trips. In fact, its become the standard grease for many modern jets. Both use a PAO oil, and provide high load carrying capability and similar temp limits. SHC100 was said to provide better water resistance, equal load carrying, and lower wear. In the end, less troublesome.

One of the fleet:

 

[2.7ecoboostFordBronco]

As I've mentioned many times here, I worked in Mobil Oil's flight department decades ago. Where we tested SHC100 v M28. Each was used on Gulfstream, Hawker 700 and 800 wheel bearings and the Citation III. Including bushings, straight roller bearings, pins and more. The components were then bagged, and hand delivered to the engineers for evaluation. (we also tested turbine engine oils for the development of High Thermal Stability 254 oil)

In your plane, it won't matter one bit. M28 is thinner (under grade 2) and (the aviation version, which is, I think, not the same as conventional Mobillith SHC100) of SHC 100 is a bit thicker at NLGI grade 2.

It is kind of funny to talk about my causal observations, but when we'd pull out (for example) a gear actuator retaining pin lubed with M28, after a winter of flying in and out of the North East's worst airports, there would almost always be minor visible corrosion spots. When the same parts were installed dry, then pumped with SHC100, often the grease was too thick to flow in and around the part and it was dry on one side. Leading to scrapping it next cycle. We learned to pre-lube it with SHC100. Which solved the corrosion problem.




TLDR: SHC100 aviation was the winner in our testing. In fact, its become the standard grease for many modern jets. Both use a PAO oil, and provide high load carrying capability and similar temp limits. SHC100 was said to provide better water resistance, equal load carrying, and lower wear. In the end, less troublesome.

Thanks, I asked hoping you’d respond! I’ve actually had that problem with my shc-100 grease gun, it won’t flow into the zerks very well, for refill between cleaning/repacking intervals. Could be a dirty zerk too, and I’ve had some success hearing the zerks with a heat gun. But if SHC-100 protects agains corrosion, wear, and water better it sounds like it’s the ticket in the bearings.

My stabilizer tube bushings would be annoying to disassemble so maybe I’ll maintain a grease gun with Mobil 28 as well as SHC-100, instead of trying to displace the factory installed M28 on those bushings with SHC-100. Presently I have M28 on the stab jackscrew and bushings but shc-100 in all the main gear and tailwheel bearings.