Brake Adjustment??

[Wrinklemeist]

I have our '05 40fdts in a truck repair shop to check out a squealing right front brake. I was told that due to the brakes being improperly adjusted, that the fronts were doing most of the work and had overheated resulting in small surface cracks and glazing on the rotors. The fix is to resurface the rotors, replace grease seals and check front bearing oil for proper level. Does this make sense to anyone? Does an Alpine have disc or drum rear brakes? I didn't know that adjustments were possible. Any direction for some "education" on this matter would be appreciated. The rig has about 45K miles on it.

[Dave Fernandez]

The Alpine Coach has hydraulic disc brakes on all four corners. Disc brakes do not have any adjustments. They self adjust every time you step on the brakes.

If one side got hot is was probably caused by a caliper piston sticking. The sticking can be caused by a couple of things from a bad square ring or bad/old brake fluid. Your Alpine has fixed calipers, which have pistons on both sides.

[daveshan]

Oddly enough my mechanic said much the same thing only he said it correctly. The brake proportioning in our coach is putting what they felt was too much of the stopping power on the front brakes and under using the rear ones. They looked for a proportioning valve but didn't see one and couldn't find any information on the chassis (not surprising).

Most proportioning valves are not adjustable but they can fail, if Alpine used one any information anyone has on it would probably help both of us (Mike?)
Dave

[Koop]

The front brakes always do the most work. Due to weight transfer while braking, about 70% of the load is handled by the front brakes.

It sounds to me like you have a tech or advisor that doesn't know what they're talking about.

As stated by Dave Fernandez above, disc brakes do not have adjusters. There should be no residual pressure and the seal should retract the piston. If the seal cannot retract the piston, there is an issue with the caliper.

Having said all that, squealing does not mean there's a problem. Brake pads can be noisy for a number of reasons, most of which do not indicate a problem.

[TeJay]

I've worked on and taught automotive repair for 35 years. In all those years I have never had to replace a suspected defective proportioning valve. I am not familiar with your unit but if as has been told to you that you have disc brakes on all four wheels then the mechanic that said something was out of adjustment and the fronts were working to hard does not know what he's talking about. As Fernandez said they adjust themselves.
Typically on most trucks that I've worked on the proportioning valve is set for a 70-30 ratio. The fronts do 70% of the braking and the rears do 30%. That's because as you stop the weight shifts towards the front. Some vehicles were/are set to 80-20. I don't know what they are set for on a MH.
What needs to be done is let everything cool over night. Take the MH for a short drive 1/2-3/4 mile, and try not to apply the brakes to much. Using an infared thermometer (HF has them for $20) check the temperatures of all rotors. The fronts should be hotter than the rears because they work harder. They should not be smoking hot. If a right or left rotor on the front or rear is a lot different from the other side then you have a sticking caliper. If the rotors are badly scored and or below the minimum thickness then they need to be replaced.

The squeaking can be caused by several things one is the wear indicator. When the pads wear down a metal tang rubs on the rotor and caused a scraping squealing sound. The excessive heat also causes glazing which ruins the pads.

Check or have things correctly diagnosed so you can complete the repairs as they should be done.

SORRY !! I completed my post and when I submitted it I guess Koop just about said the same thing that I did. Oh well at least you have two opinions that are about identical. That should help some.

TeJay

[wa8yxm]

A fact of automotive engineering.. The fronts do most of the stopping.

[Algoma]

I agree with all the above comments. Take it to another shop!

[Wrinklemeist]

Thanks for all your input. I spoke with the shop owner and he said much the same as most of you have. I got the incorrect info from the storage facility that takes care of my coach in the winter. I was told that there was some glazing of the rotors and pads (front) also some small "heat cracks". Supposedly, turning the rotors should correct things. This damage may have happened before I bought the coach in 2010. I have always been easy on the brakes, using the two position engine brake switch. About the only time I touch the brakes is when driving in town.

[Koop]

Heat cracks (surface checking) is common. I wouldn't be concerned unless the there's excessive run-out (i.e. warping) or the cracks are more than hairline fractures.

[Old Scout]

As discs get older there will be some surface cracking and glazing. Not sure what the depth spec is but superficial cracks are not a problem. Contaminated brake fluid [moisture] can cause rubber gaskets to swell, allowing pistons to stick, and ultimately making pads drag. If you knew for sure that the brakes had been "cooked," then new/turned discs, pads, hub seals, brake fluid, and hub oil might be in order but the trick is getting an expert assessment that this has occurred.....good luck,,,,,,

[EngineerMike]

So far as I know, the following characterizes the brake system:
1) all years, all models (w/ exception of Avalanche & a few Ltd's whose original owners ordered a coach with air brakes), master cylinder is Bosch Hydro-Max power (hydraulically boosted) hydraulic brakes, 4 wheel disc. HydroMax has two chambers, one feeds front axle, the other feeds the rear.
2) from master cyl, lines go to approximately mid-coach to the ABS management assembly (each line from m.c. enters separately), then out to each of the 4 wheels.
3) calipers for early coaches are 2 piston (same side of calipers), rail or pin slide type (which rails or pins require silicon based lube regularly). Later rigs have 4 piston (2ea on either side of caliper pressing in the disc) calipers; no slides to lube.

Either type of caliper can have a dragging pad, but should give good service on average.
Small cracks in a disc surface are considered an ordinary result from more than ordinary heat, but are safe & not a cause for concern as long as the sticky caliper has released. Cracks that reach the edge of the disc endanger the structural integrity of the disc; such a heavily cracked disc needs to be replaced.
On the 04 & later rigs, make sure the "bell crank" pivot is turning free at all times. It can rust & stick & now you are dragging brakes because they are locked on & won't release. It's simple to remove & lube.
Old brake fluid carries excess water absorbed into the fluid, can cause brake fade in heavy braking, and can cause swelling of pistons that have a phenolic coating which in turn causes stuck pistons & overheating of pads & rotors. Very important to keep brake fluid fresh.

If you have an 04 or later rig, consider replacing the master cylinder next time you have brake fluid replaced (which you should replace every 1.5 to 2 years regardless of mileage). To do the fluid service correctly you have to remove all wheels to get to outer bleed screws (2 bleed screws per caliper on these 04+ rigs) and you have already done the work you'd have to do anyway when replacing the m.c. for a full brake bleed). The 1.75" m.c. is ~30% more stopping power for the same pedal push. I did it and am very happy I did.
I still can't lock up the wheels on dry pavement. Oh well. Maybe some day.

[TeJay]

EngineerMike,

That's some excellent information. Very informative. It shows that you know your stuff.

Great Job!!

TeJay

[Tom and Patty]

EM, "I still can't lock up the wheels on dry pavement. Oh well. Maybe some day."

Flat spots mean new tires!

[Algoma]

A "lock-up" would also mean your ABS isn't working.