Hi Graham, on technical merits you are correct. I also try to make sure my MBZ cars get proper, by the book, service and parts etc..mechanics all seem to have their own opinions. (I am not a mechanic nor am I an authority on car mechanics).
However, this subject has piqued my interest.
I'd like to advance an 'academic' inquiry of sorts.
What gets hot with regards to affecting the caliper cylinder/boot and brake fluid?
The pads, I suppose and perhaps less directly the rotors.
The 'MBZ OEM' heat shields are round metal rings that have a deeper set inner ring which is pressed into the bore of the caliper cylinder.
So a part of the shield does connect with the cylinder (piston) , albeit the bore.
The outer metal ring has one half approx. attached to the inner 'mounting' base ring and the other portion is detached, kind of like a non helical spring.
The perimeter of this outer ring lip does cover the perimeter of the cylinder protective boot. This easily protects the rubber seal from debris etc.
The brake pad backing sets ontop of the metal outer ring of the shield.
Does the slight opening afforded by the detached portion of the outer ring create a small window of air venting for the cylinder bore behind the pad backing?
This elementary narrative is meant to try to understand the physics of how this heat shield does its job.
You see, as you mentioned, one can buy heat shields that basically look and can function like shims.
The PAGID metallic pads I bought had full metal (thin rubber-like paint coated) plates ontop of the pad (rubber like coated) backing. They mimic the entire pad backing form and shape.
So this extra line of 'metal' sits in exactly the same position as the heat shield, albeit if this pad were installed ontop of a round heat shield, then we are talking about two metal layers behind the pad backing. But for this academic inquiry lets just suppose regular pads are used without the 'shims'.
This link illustrates a heat shield that looks like what my Pagid pads come with although they are not titanium for Pagid pads.
https://hardbrakes.com/
My unknown is: if this design of the above referenced heat shield can supposedly work for a caliper that does not have the MBZ type ring heat shield, then why not the metal 'shim' of a Pagid pad?
Mind you there is a materials difference.
titanium is poor for thermal conductivity, about 50% less than metal or tin.
In other words a poor thermo conductivity keeps heat 'static' from transferring sort of.
These titanium shields are marketed for track racers. High speeds.
Or is this snake oil marketing?
In any event, I must also share an anecdote which has no absolute value or causal significance.
The replaced calipers of my 300D were rebuilt ATE calipers with oem round heat shields. Brake fluid replaced every 2 yrs. with ATE DOT 4. No excessive high speed driving and light use of brakes customarily. Wheels and calipers hose washed fairly regularly to wash off dust etc. Rotors are within spec, so not thin. They lasted 7 years and 20K miles.
The in-board cylinders were slow or sticking and one had an onset of minor leak. (brake pads 50% more worn on in-board) Otherwise the seals looked clean and nice and the calipers were not oxidized and a mess etc. No salt roads or snow in my City. Car does not travel to those areas. Just home City. So my anecdote minimally shows that in my particular case, calipers with proper heat shields seem to not have possibly benefited from the shields protections or at least their untimely demise was possibly not relative to heat shields or lack of. There are so many variables that I do not suggest that the heat shields are worthless or should be debunked as a general rule of thumb or otherwise. Don't get me wrong.
I still would like to understand how they work (the physics) and to what extent they really act as heat shields. They are metal and not titanium, right?
So anybody that can share insight, please do so !
Interesting !
Thanks.
