Brake update

[Cedar41]

We finally found a place that will work on the Peak Chassis. Holt Cat. in Fort Worth has a division to work on Diesel pushers. They also just got the computer program to diagnose ABS systems.

It seems at this point our brake problem was caused by the Hydromax pump failing. That pump is what makes your brakes pedal come back up after pressing the brakes. Seems as we were taking the coach back to storage it was like driving it will the brakes on. We hope the only thing wrong with the ABS is the sensor "melted"�.

We did find a Mobil mechanic that came to the house to help diagnose all this. Thanks for the suggestion for that. He assured us we could drive the Coach and manually pull the brake pedal back up and safely transport with out a tow. Can you believe I only had to brake 7 times in 125 miles?

Bosch/Bendix makes the Hydromax pump and they do not have a repair facility in Texas. They told us they rely on the MH manufacture to direct you. I told Mike at WRV this and its was only an hour later that Dave called us and told us they were going to provide the new pump out of their inventory and had it sent to Holt Cat.


Yes, we have had more than our share of problems with this coach. Even out of Warranty, they continue to give us personal attention and we really appreciate it.

Will keep all posted as how the service is at Holt Cat. They are only 5 miles North of I-20 on 820 west of Fort Worth, which may be good to know in an emergency while traveling.

John

[Cedar41]

We finally found a place that will work on the Peak Chassis. Holt Cat. in Fort Worth has a division to work on Diesel pushers. They also just got the computer program to diagnose ABS systems.

It seems at this point our brake problem was caused by the Hydromax pump failing. That pump is what makes your brakes pedal come back up after pressing the brakes. Seems as we were taking the coach back to storage it was like driving it will the brakes on. We hope the only thing wrong with the ABS is the sensor "melted"�.

We did find a Mobil mechanic that came to the house to help diagnose all this. Thanks for the suggestion for that. He assured us we could drive the Coach and manually pull the brake pedal back up and safely transport with out a tow. Can you believe I only had to brake 7 times in 125 miles?

Bosch/Bendix makes the Hydromax pump and they do not have a repair facility in Texas. They told us they rely on the MH manufacture to direct you. I told Mike at WRV this and its was only an hour later that Dave called us and told us they were going to provide the new pump out of their inventory and had it sent to Holt Cat.


Yes, we have had more than our share of problems with this coach. Even out of Warranty, they continue to give us personal attention and we really appreciate it.

Will keep all posted as how the service is at Holt Cat. They are only 5 miles North of I-20 on 820 west of Fort Worth, which may be good to know in an emergency while traveling.

John

[EngineerMike]

Reminds me of the time Red Adair was dickering with the owner of an oil well that caught fire. Suddenly, over the hill came Pancho's Bomberos (firemen) in a large flatbed truck. They raced straight down the hill & right into the fire. Hopping aroung, swatting furiously at the fire with their sarape's, they managed to extinguish the blaze in only a minute or two.

Red walked down the hill and congratulated Pancho on "the most brave stunt in fire fighting I've ever witnessed."
Pancho said, "Not really, no brakes."

[Jim&MaryJo]

John,

Thanks for the update.

For future reference, can you describe what it felt like when the brake pedal didn't return.

Was it subtle or very noticeable? ANything else we should look for? (beyond smoke)

Thanks again.

[Cedar41]

We always check our MPG at every fill up. No reason, just do. Ours had dropped to 7.5 on this trip, (no hills either) normal is 8.5 or better. Also, the acceleration was some different.

The smell is the real clue. It came and went at first. We thought we had diagnosed it right as a fluid drip on the hot generator. WRONG!

[Ted III]

I was truly becoming concerned that Engineer Mike had not made a comment on the brake issue. Alas, he has and as usual not let us down. Can we imagine this forum without him. In all sincerity we would lack a phenomanal amount of highly important info without his input even though the rest of us are highly intelligent.

Ted & Carol
2005 Alpine 34'FDDS
2006 PT Cruiser GT

[EngineerMike]

Here is the Bosch Brake Diagnostic Manual

and here is the HydroMax Brake Booster Manual

that John referenced above. Exciting reading (for Pancho anyway )

[EngineerMike]

John- After perusing the HydroMax manual fur a bit, I'm thinking:
1) the master cylinder is made up of 3 major components, R to L viewed from front of coach = actuator rod & Power Piston, Hydraulic Control Unit to which the Backup Pump is mounted, and Master Cylinder/Reservoir.
2) The HCU is the hydraulic assist for the brakes. It recieves hydraulic pressure from the same system that powers the radiator fan, via a blue-braided (on my coach) hydraulic line from the rear of the coach, and it has a return line; the lines run along the DS frame rail. This middle section has hydraulic fluid in it, not brake fluid.
3) if the hydraulics are not operating (e.g. engine off), or fail, there is a relay that powers the BP to provide some power assist even when the ignition key is off. Relay is above HCU & has 4 wires to it; the fat white one goes to power the BP.
4) There are 3 return springs- one in the hysraulic oil bath of HCU to return the PP, and one each in the two MC chambers (middle chamber is for front wheels, Lt end chamber is for rear wheels) to return the cylinder cups to their unloaded position. The MC return springs are in the brake fluid bath of the cylinder. These 3 should act in series to return the foot pedal to its fully upright & (not) locked position, but they are not doing their job- I think something inside the assembly is sticking.
5) you also have (I think) the electrically positionable foot pedal assembly, which introduces another mechanical variable. If not you have some pedal assembly. If that has not been fully checked for some sort of restriction, it should be eliminated B4 anything else is monkeyed with; I assume that has been dispensed with, along with checking the pivot arm in front of the bulkhead & gen slide cap for return-restrictions (I think your mobile mechanic would have done these checks?).

Assuming 5) is OK, and that the elimination of caliper issues was authoritative (hard for me to envision a failure mode where the caliper(s) would contribute to pedal not returning), I would guess that the problem is within the HCU, MC or PP, and therefore a serious issue (meaning if I had to drive it to get service I'd leave about 10x my normal stopping distance) & I'd seriously consider a tow. Because of the different possible causes, I don't think R&R'g parts is advisable, since the cause could be elsewhere, so as to repeat this process again later. E.g., there is a hydraulic filter in the HCU; if the coach's hydraulic system is sufficiently contaminated and that was the problem, the filter within a new HCU could be reclogged fairly soon & if the old filter came apart due to pressure build-up, so too might the new filter thereby jambing the PP return spring. So I'd encourage pinpointing the trouble, and IIWM that'd be by removing & disassembling the apparatus until the issue was positively ID'd.

You can use a bungee cord hooked to the brake pedal arm & wrapped around the steering wheel to provide a return spring assist if you have to drive it.
For service, I'd try calling Bosch @ 248-553-9000 (MI) to see if they have tech support &/or service facility recommendations. And as always, adherence to any advice you get over the internet is only advisable if all your life, health and vehicle insurances are fully paid up with low deductables, and your last will & testament have been recently updated.

[Dale777]

EMike,

Thanks for the links to the Bosch brake manuals. However, it appears that the 1st link provided is broken. I think the correct link should be:
http://rb-kwin.bosch.com/en-NA/start...ulic_Brake.pdf

Is this right?

Dale

[EngineerMike]

Thanks Dale. Guess I shouldn't try fixing brakes if I can't fix an URL.