Yet Another Brake Failure

DriVer · 08-26-2010, 07:02 PM

I write this piece tonight which I hope will put some closure into this brake issue by providing irrefutable evidence about the mechanisms that cause the brake caliper issue to present in as many cases as it has.

I am acquainted with a gentleman who for the purposes of this essay will remain anonymous because it serves no purpose to bring in his name.

Here is the case as it was told to me. Subject vehicle, 2004 Fleetwood Pace Arrow.

I was traveling out of Charleston on Route 17 and into Mt. Pleasant , SC when I noticed that the vehicle was pulling to the right. While traveling I began to smell what could be described as a burning brake smell however this issue didn't completely manifest itself until I stepped on the brake. Fortunately the driver was in light traffic with no vehicles directly in front of the coach. The brake pedal was applied and it immediately went to the floor. In the command center he observed a message in the window that said; "Total Brake Failure." (When asked if he pumped the brakes his response was no.)

The fact that there were no brakes compelled him to pull over to the right off the road and as he came to a stop he was out of harms way. He told me that this to be a very unusual thing to be happening because it had never happed to him before. After he stopped, he gained what was left of his composure and got out to inspect the vehicle. He knew about the brake issue however he never legitimately expected that he would experience a caliper hang up on this coach. His attention was immediately focused on the right front wheel and it was so hot that he couldn't touch it.

The Workhorse Roadside Assistance number was called and he proceeded to tell the call taker what had happened and that he had no brakes. The call center advised that the vehicle should not be driven since the pedal went to the floor The center dispatched a tow truck. The driveshaft was removed and the vehicle was towed some 80 miles.

While the tow truck operator was removing the driveshaft he told the driver that the RR ABS sensor appeared to have melted. The vehicle arrived at the service center after hours where a 30A power plug was provided so he could plug in over night.

The next day all 4 wheels were pulled, there was nothing outstanding on the RF wheel which actually exhibited heat however the RR did in fact burn out the ABS sensor and it was determined that the RR caliper needed to be replaced. At this moment the parts have been ordered and they are expected to arrive shortly.

Now given that we are talking about a 2004 W22 Chassis this sounds all too typical doesn't it, just like the rest of the cases that we have read here over the past few years.

Now here's the rest of the story ... the total number of miles on the odometer of this vehicle is 2,800 miles.

You see this vehicle was never driven however to the owner's credit before he put the motorhome on the road he did flush the brake fluid and he told me that it was a good thing that he did because if the fluid were laden with water as many 2004 vehicles exhibit the brake pedal would have faded much earlier. No amount of fresh brake fluid will keep this problem in check however having good brake fluid is better than having a slurry.

So what's this evidence you're talking about at the start of this thesis? The phenolic pistons over time absorbed a quantity of water and they become swollen in their bores. What causes this event to unfold is NOT at all related to mileage but as I have been saying it evolves over time and it's never consistent and always arbitrary. It can happen in one wheel or another it may never happen at all.

The resolution to this issue will see the introduction of a new phenolic material that will be impermeable. As we pursue our ownership we will be mindful to change or brake fluid from time to time, 2 years would be great. Aside from doing little else I don't see anything that is going to detract from the pride of ownership that we had when the vehicle was new to us and I fully expect that our confidence will be restored.

I would like to conclude this post this evening having just ticked over my 15,000th Post and "Yes" it was dedicated to bringing more insight on the Bosch Caliper Recall campaign that I expect will roll out soon.

Have the best evening you can and I hope to see you in the Workhorse Chat Room this evening (Thursday) at 9:00 Eastern.

iRV4FUN · 08-26-2010, 09:11 PM

Driver, Why is it the P 32's have not had the same moisture problems? They sit just as long as the W's.

DriVer · 08-26-2010, 09:16 PM

Quote:

Originally Posted by iRV4FUN

Driver, Why is it the P 32's have not had the same moisture problems? They sit just as long as the W's.

For the very same reasons that W24 Quadraulic brakes haven't had the problem, different manufacturer. In other words not Bosch brakes.

oemtech · 08-27-2010, 06:37 AM

My "shade tree engineering" suspicion is the piston to bore clearance is large, but within spec, maybe different dust boots/seals and lastly a different phenolic compound.

ron55 · 08-27-2010, 06:56 AM

Oemetch, would not more clearance mean less problem by swelling of the piston? I was thinking my rebuilts would have been honed and therefor more clearance, piston to cylinder wall would be better??

oemtech · 08-27-2010, 07:15 AM

My customer that built the SS caliper pistons measured his after he popped them out of the caliper with 140 psi air and found they was only 1 to 2 thousand clearance. Normal clearance should be in the .0004 range if my memory services me correctly. Now the tight clearance COULD be due to the swelling of the phenolic.

More clearance is not necessarily better. To much and they leak and not enough and the seize. The design of the dust boot and seal play an important part also. IE - its a total package!

DriVer · 08-27-2010, 08:10 AM

Quote:

Originally Posted by ron55

... would not more clearance mean less problem by swelling of the piston? I was thinking my rebuilts would have been honed and therefor more clearance, piston to cylinder wall would be better??

ron55, In past postings we spoke about the "NextGen" caliper pistons having new phenolic material, re-sizing of the bore by .010" and now add to the list more tension on the boot that pulls the pistons back into the bore.

To answer your question, you could have an 8 lane highway in relative micron sizes however Oemy will tell you that unless you resolve the root cause, simply increasing the bore size will not resolve the issue.

One thing that we are all going to want to do here and that's to keep your eye on the ball at the BrakeResourceCenter.

The dynamics that are moving this issue may change or develop into more tangible News and this will be your best and most immediate resource. Keep checking in over there for late breaking announcements as they develop.

Spoonman · 08-27-2010, 12:24 PM

I have been keeping my eyes on the brake resource site and they are getting tired, don`t believe it is my glasses.

DriVer · 08-27-2010, 03:47 PM

Quote:

Originally Posted by Spoonman

I have been keeping my eyes on the brake resource site and they are getting tired, don`t believe it is my glasses.

Spoonman, What has it been, perhaps 6 to 8 months now that we have had the BrakeResourceCenter. Unquestionably it is providing a tremendous amount of information to affected owners. The resource has not run its course and it will develop and change as the dynamics that are moving the brake recall to closure develop.

In the recent past there were many who complained that nothing was being said. Now that the information is flowing it never seems to be enough nor is it ever fast enough.

I can only restate - "Keep your eyes on the ball!"

Spoonman · 08-27-2010, 04:07 PM

Quote:

Originally Posted by DriVer

Spoonman, What has it been, perhaps 6 to 8 months now that we have had the BrakeResourceCenter. Unquestionably it is providing a tremendous amount of information to affected owners. The resource has not run its course and it will develop and change as the dynamics that are moving the brake recall to closure develop.

In the recent past there were many who complained that nothing was being said. Now that the information is flowing it never seems to be enough nor is it ever fast enough.

I can only restate - "Keep your eyes on the ball!"

Been looking, just don`t see the FLOW that you are talking about, do you mean the updates in May or am I missing something?This is almost Sept.

mfire1339 · 08-27-2010, 05:06 PM

Driver , being the nit-picker that I am. The "piston seal" and rotor runout give the pads clearance after being applied. The "dust boot" is to keep dust And moisture away from piston and bore.

Mike

DriVer · 08-27-2010, 08:07 PM

Quote:

Originally Posted by mfire1339

The "piston seal" and rotor runout give the pads clearance after being applied.

Mike, Thank you for the comeback, you are absolutely right. The property that I should have more accurately described is called "Seal Squeeze."

Piston Seal:
The piston seal, as shown in Figure 6, is a rectangular cross section seal made of a rubber compound and is compatible with DOT 3 or DOT 4 brake fluid. The piston seal is placed in a groove that is machined into the caliper housing piston bore. The piston seal’s function is to provide a hydraulic seal between the piston and the caliper housing piston bore. The piston seal also aids in retracting the piston (i.e., pulls the piston back into the housing bore) upon brake release. This retraction allows clearance for the pads to be pushed back from the rotor.

As I should, I went back and completely reviewed the materials and I did not see where lateral runout contributes toward increasing the clearance. Perhaps you have some documentation about that. I see maximum lateral runout, etc.

Thank you for the comeback and critique!