Yes, we seem to be in almost total agreement except for two points, one minor and one MAJOR.

I haven't overhauled very many disc brake caliper/piston assemblies but I seem to remember that the piston dust boot had a not insignificant "springness" to want to always return to the flat state, not be accordianed "out". I am not proposing that the rotor "high spots, points", are not the MAJOR piston retracting force, but what about overnight, would the dust boots have enough force to retract the piston overnight even with no wheel rotation?

Would I be incorrect, do you know, if I said that I have seen. used, dust boots that had an integral "return" spring.

"...Fluids at not compressible to any real extent..."

I'm glad you left yourself a bit of an "out" here because fluids ARE compressible.

I think you would agree that most fluids will increase in volume as they are heated,... right...??

And now if you take a non-compressible fluid and put it in a hermetically sealed container with enough wall thickness/strength that the container will not "give" when the entire assembly is heated what would you say happens to the fluid inside...??

What I have just described above, basically, is the way a viscous clutch or coupling works.

The way you increase the viscosity of the fluid in the VC is via the heating brought about by the two clutch plate sets counter-rotating, Stearing the fluid. The VC fluid CANNOT expand so it's viscosity, DENSITY, does.

 

In a braking system, compression of the brake fluid is negligible. Any sponginess is the result of air in the system or flexion of rubber hoses. That's why stainless steel covered teflon lines are a desired upgrade as they will virtually remove the flex of rubber lines.

When you think about the force required to move the pads away, I doubt that those dust seals have anything to do with it. When you do a brake job the pistons require considerable force to drive them back into the calipers. Usually a C-clamp is used for this. Way beyond the force exerted by the soft dust boots. Their function is only to keep dirt out of the close tolerances of the piston and caliper bore.

 

"What I have just described above, basically, is the way a viscous clutch or coupling works.
The way you increase the viscosity of the fluid in the VC is via the heating brought about by the two clutch plate sets counter-rotating, Stearing the fluid. The VC fluid CANNOT expand so it's viscosity, DENSITY, does."
Sorry, wwest, but a little research shows that isn't quite true. Viscous couplings contain DILATANT fluids, which behave very differently than water, or most fluids. The viscosity of dilatant fluids increases quickly with the application of shear forces. If you have a dilatant fluid in an open container, and you stir it with something quickly, it displays more viscosity than if you stir it slowly. Pressure isn't part of the equation, nor does the density change if the volume remains the same. Just being picky.

For whatever it's worth, www.autoshop101.com/forms/brake04.pdf and other documents indicate that deformation of the seal/dustboot by the sliding piston DOES cause an elastic return force. Tiny, yes, but enough to pull the piston back a fraction of an inch.

-J

 

While I am FASCINATED by all the discussions about disc and drum brakes, did I somehow miss the answer to my original question?

Why is it that Ford had to go to drum brakes on the rear in order to get the RSC to work for the 2009 FEH? Why wouldn't RSC work with rear disc brakes?

Are we in agreement that there is no technical reason? Do other Ford SUV vehicles use rear discs?

 

 

'Where did you get this apparently eroneous information..??


Why wouldn't RSC work with rear disc brakes?

It doesn't...??"

It is not erroneous. All the reviews indicate there will be rear drum brakes.

 

....

 

While it has been reported by several sources that 2009 FEH's will have rear drum brakes, the photographs of the "2009" California lifeguard FEH's show disk brakes all around, adding to the confusion.

In a time when Ford is reducing options, the most likely explanation is simply that Ford decided to standardize on the rear drum brakes for financial reasons. I doubt that the drums are required for mechanichal reasons to allow RSC, etc. to work. Rather, drum brakes may be required to financially allow RSC to be a part of the FEH. Just speculation.

-J

 

"The first full rotation of a wet rotor that has been clamped by the sqeezing of the brake caliper is enough to wipe the water from the disk..."

NOT....!!


DANGEROUSLY UNTRUE....!!

I have had instances, as I'm sure have MANY others, wherein my brakes being wet resulted in a braking/stopping overshoot, HARD, even DESPARATE braking, of 20 to 50 feet.

NOT driving through puddles, just driving in the rain.

 

Those "2009 FEH" pictures were published before production began on the 2009 FEH! I think we decided that those were actually 2008 FEH dressed up as 2009.

However, it would be nice if the FEH retained the 4 wheel disc.