Community Forums

E Tex Engr · 03-05-2010, 06:34 PM

Has any one read the link that DriVer posted in post 94 of 3rd rate chassis thread ? If you haven't, it is a good read. lots of info and insight into phenolic and miosture reactions. has anyone looked into what phenolic is, how it is made, and its properties? Lets discuss it. Sorry about the hijack on (third rate chassis).

az bound · 03-05-2010, 07:42 PM

Its really a general name for any material made with phenol formaldehyde resin. It is combined with a base material depending on the intended use. Some trade names and base materials are. Bakelite contains wood flour. Novotext contains cotton fibre. Tufnol has woven cotton or linen fabric. Paxolin and richlite use paper as the base material. There are probably many others that I am not aware of. I know one uses fiberglass as the base but I can't remember the trade name.

E Tex Engr · 03-05-2010, 09:15 PM

Az bound: The information in your reply is similar to the info I found following a little research. I also found that the type of fiber used for strength and reinforcing, also help determine the amount of moisture that phenolic will absorb. The tests That NHTSA reported on indicated to me that 1% moisture by weight can increase a 66mm phenolic piston by over .004 in. in a fairly short time. Think how much moisture can be absorbed over years in use in your RV.

az bound · 03-05-2010, 11:08 PM

Ran into these same sorts of problems when working with filling equipment in the cosmetic industry. Rolltex and spool valves would absorb moisture at different rates depending on the base material. Another thing that will geratly alter the performance of phenolic is controlling the manufacturing process ie. temperature, pressure, humidity and mixture.
My theory would be that something failed in the mfg. process controls of the phenolic itself. That would seem to support the fact that not all pistons are failing and not all brake failures are due to piston failure. There are a lot of variables to be considered when you think of the environment brakes are subjected to, up to and including the operator.

RocketDork · 03-06-2010, 09:15 AM

Excellent information.

Keep in mind that a material will only absorb a given amount of moisture, even if fully submerged. I'm not sure what that amount is for the type of phenolic that Bosch used in the piston.

This problem seems very subtle to me. Imagine all the things that could cause this failure, then narrow it down to something growing in size by 0.004" in diameter. That's pretty hard to find. Out of all the things that can go wrong with a braking system, I would have pby overlooked this too.

The thing I grabbed from that report that was posted. ALL the phenolic pistons grew in size and weight when exposed to high humidity. Not just Bosch's pistons...that's going to make things even harder for their engineers.

DriVer · 03-06-2010, 11:19 AM

Quote:

Originally Posted by RocketDork

The thing I grabbed from that report that was posted. ALL the phenolic pistons grew in size and weight when exposed to high humidity. Not just Bosch's pistons...that's going to make things even harder for their engineers.

Now consider if you will the very same calipers in a commercial application that do not exhibit the same frequency of problems, (if at all) and the engineering complexity increases exponentially. How do you design a component that should sit around in a humid or moist environment for months at a time and assure 100% performance. As we have seen in the test samples, the metal calipers did not absorb moisture nor did they swell or expand. Problem is that those calipers are unsuited for use in our application. Where then could we graph in a curve and achieve a workable solution? We don't seem to be getting very far with plastic and metal isn't going to do it ...

so how about a silicon/ceramic based piston ???

"007" · 03-06-2010, 11:27 AM

What do they use on the W-24 braking system on pistons they do not seem to be having any problems?

DriVer · 03-06-2010, 11:30 AM

Quote:

Originally Posted by "007"

What do they use on the W-24 braking system on pistons they do not seem to be having any problems?

Roger, Believe or or not .... most likely it's a Phenolic. Now there are 4 x 70mm pistons and the manner in which the pressure is applied is quite different. You are not going to escape from finding phenolic in the majority of modern calipers.

EngineerMike · 03-06-2010, 11:54 AM

I could be wrong but I thought the Meritor pistons were all metal. If they are not, I'd say there definitely was something wrong w/the phenolic being used by Bosch, as the Meritor 73mm 4-piston design doesn't seem to have this problem.

My theory on differential between RV & commercial use of the Bosch calipers is that the commercial rig goes into use doing 40-100k per year, so it gets a rapid break in on the pistons/cylinders. RV's go into service expecting an average of 4,500 miles per year. Commercial rigs travel mostly around town (for the vehicle class using Bosch 66mm) so lots of braking in that 40-100k, RV's travel mostly on highways w/little braking per mile traveled. So initial break-in is radically different between the two, in fact no comparison in duty cycle.

DriVer · 03-06-2010, 12:18 PM

Quote:

Originally Posted by EngineerMike

... as the Meritor 73mm 4-piston design doesn't seem to have this problem.

The Quadraulic AM caliper on Workhorse W24s are 70mm

EngineerMike · 03-06-2010, 12:43 PM

My bad. 70 is correct. There are two sizes in the Meritor line of 4-piston caliper, 64 and 70. My rig uses the 70mm size as well.
Suppose the bolt patterns might be interchangeable w/the Bosch? Maybe that question has been asked & answered before.

DriVer · 03-06-2010, 01:29 PM

Quote:

Originally Posted by EngineerMike

Suppose the bolt patterns might be interchangeable w/the Bosch? Maybe that question has been asked & answered before.

EM, I'm not sure but I might think its gotta be pretty close. The rotors are slightly bigger but I don't see where the bolt pattern would be different on the spindle.

JeeperJohn · 03-06-2010, 02:42 PM

Quote:

Originally Posted by EngineerMike

My theory on differential between RV & commercial use of the Bosch calipers is that the commercial rig goes into use doing 40-100k per year, so it gets a rapid break in on the pistons/cylinders. RV's go into service expecting an average of 4,500 miles per year. Commercial rigs travel mostly around town (for the vehicle class using Bosch 66mm) so lots of braking in that 40-100k, RV's travel mostly on highways w/little braking per mile traveled. So initial break-in is radically different between the two, in fact no comparison in duty cycle.

Mike, using your theory, all we have to do is swap out our calipers for some old worn-out (at least good and broke in!) calipers off a UPS truck and waaa-laaaa

we are good to go!

Sounds like a good deal to me! Willing to try anything at this point!

E Tex Engr · 03-06-2010, 07:52 PM

edgray: This is in answer to your question about my tapered pistons I miked on my P32 chassis. The taper was not just outside the cylinder, but was all the way from the fluid end to the shoe end. You could see on the piston where there was contact with the cylinder. This area on the piston miked larger than the caliper bore. It took 125 psi air to remove the pistons in the 3 wheels that had drug and heated. these were the 3 calipers that the dust boots had never been installed. I removed the piston by hand on the caliper that had never drug. You have much more pressure when you apply the brakes and move the piston towards the pad, than you have to release the brakes. The only design force you have to return the piston and release the rotor is the seal wanting to return to its static position. Maybe a couple of pounds. Of course loose wheel bearings or warped rotors will also move the piston back. dieselclacker: In answer to your questions, Even in the southwest dew is formed when temperture drops below the dew point. At this point humidity is 100%. The original brake failures on my P32 was because of contaminated fluid. Monument Chevrolet let me see the fluid. It stunk. They said I must have put the wrong fluid in the brake system. The MH was less than 2 yrs. old, and I had never needed to top off the brakefluid. They repaired and flushed the system. In 2009 I smoked 3 wheels and when I got home found the 6 dust covers had never been installed correctly. They were just hanging on the pistons. I have never said that my P32 is having the same problems as the W series, But-----I have had piston swelling, and brake dragging, maybe caused by different conditions or reasons. All my observations come to same conclusion. My brake problems come from atmospheric moisture directly, and not thru moisture in the brake fluid. Your conclusions may be different.