It is a good idea to spray both front & back brake calipers if you have been sitting for more than a week, especially if the weather has been humid.



We recently left a campground after 2 weeks of damp weather and after 12 miles we smelled something burning. Our rear brakes were at 870 degrees and the brake fluid had boiled over. We sprayed the caliper slides (pictured above for the front brakes although not so obvious on the rear brakes) with a rust penetrating silicone spray. After an hour the temp dropped to about 120, the brake fluid cooled and the calipers released after pumping them several times.

Before leaving the campground we noticed that the rear brake lights were on and thouht that it was just because we had on the parking air brake but after the calipers released the brake lights went out. During the next 120 miles we had no more issues.

Since they got that hot you might want to have them checked out for damage and maybe/probably replace them. I would definitely replace the fluid.

quote:

Originally posted by Shadow man:
Since they got that hot you might want to have them checked out for damage and maybe/probably replace them. I would definitely replace the fluid.

Very good point. I'm embarrased I didn't think of it.

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Originally posted by Carl Feren:
Before leaving the campground we noticed that the rear brake lights were on and thouht that it was just because we had on the parking air brake but after the calipers released the brake lights went out.

This is normally an indication of a sticking brake pedal or a bad air brake valve... Seeing that your system is Air Over Hydraulic - I would strongly suggest you also lubricate your brake pedal pivot point.

I am pretty sure that your brake lights work off of an air psi switch, if this is the case, what you saw was your air psi releasing the brake application - Maybe Ed (Mwrench) can comment on how his brake pedal/lights work.

How old was your brake fluid? Does it get much road spray? How much humidity? Brake fluid will boil as it absorbs moisture.

My standard practice is to change brake fluid yearly. Flatlanders might be OK with every two years if they are in a dry area and have little road splash. This keeps the boiling point high. A good brake fluid has a higher wet boiling point than an ordinary one. There was a thread here a while back with a lot of good input. My own choice is ATE blue on even years and gold on odd years.

For sliding surfaces of disk and drum brakes I also use Molykote G-407. It has two virtues:

1. It uses molybdenum disulphide as a solid particle lubricant. This is totally impervious to heat and will remain embedded in the pores of the metal even if the carrier is burned or washed away.

2. It uses a synthetic carrier which also acts as a lubricant. It takes heat really well, and does not collect much dirt and grit. It also gives protection from water and salt.

MolyKote just sent me notice of a new product in the same line, G-3407, which has a higher (by 50 deg C) operating temp range, but I have been unable to locate it on the retail market.

Carl, I am almost positive that your problem is with the foot peddle/air brake valve. The key to this is the "rear brake lights were on". Brake lights are activated by 2 air operated switches on the air brake valve. Air pressure to either the front or rear brakes will turn on the rear brake lights. Further you state that the brakes would release after pumping probably got the air actuator working again.

Certainly with the brake getting that hot, the calipers and other brake associated things will need to be watched. The biggest thing to watch for now is oil leaks from damaged wheel bearing seals and/or rear wheel bearings going out.

At your next opportunity check for rotor damage/cracking.


I have not had a problem with the air brake valve yet, although I may be on the verge of having one. Previously the air pressure would very gradually decrease or a week or 2, now the pressure will decrease to near "0" in less then a day. Both tank go down at nearly the same rate. I have checked all the connections with soapy water and found nothing, the only common link between the two air sources is the air brake valve.

Thanks for all the advice, everyone. We finished the last leg of our trip from St. Augustine to Malabar,FL without incident and have been sitting still for the past 10 days. Today is the first opportunity that I have had to thoroughly check things out, however, my inspection in St. Augustine before we got back on the road showed no sign of any damage to the rotors but I am going to check out all the things that you mentioned ...sticking brake pedal, bad air brake valve, brake pedal pivot point & bearings.

I am also going to get some of the Molykote G-407 recommended by bill h.

I use a prestone syntetic brake fluid which was changed about 20 months ago. Almost all of our driving has been in the dry southwest and since we don't like driving in the rain there is little chance of damage from road splash. I am curious though why you would switch between fluids i.e. (choice is ATE blue on even years and gold on odd years).

A couple of questions: (1) how do I check for leaky bearing grease and can I lubricate the bearings without removing the wheels? (2) where is the air brake valve?

Thanks for all your help.

Carl Feren

The main reason that I and Bill use amber and blue brake fluid is you can tell when you have flushed all of the old stuff out. If you started with amber, as soon as it changes to blue (I usually continue until it is solid blue)at the caliper, then you know that all of the amber (old fluid) is out, next year the reverse.

Leaky wheel bearings will show a lot of oil on the brake rotors and inside of the rear wheels. The rear bearings are lubricated by the differential oil and are not serviceable or need to be serviced. Fronts, depending on what type you have, if greased pack, hub has to come off, if oil lub, then you can add or drain old oil with out removing the wheels, gets messy though.

Air brake valve is located right below the brake peddle and that is and assembly. Check the brake peddle attachment, there is a pin that retains the peddle to the air brake valve and I have had that pin come out could get exciting if the peddle come off.

Hi Ed,

Glad to see that you made it back safely from Mexico.

I found the brake actuator and it appears OK ... no obvious leaks or anything but it may very well be the problem as we had a similar thing happen with the front brakes after we came down a twisty, winding road in TN. Lee Smith RV said that it appeared as though our front caliper slide on the drivers side had accumulated rust and would not retract. After he disassembled it , cleaned it & greased it we have had no problems with that rotor again. The passenger side rotor and the back brakes were unaffected. They never mentioned anything about the brake actuator being a possible problem.

If it is the actuator, how do I check it? I am going to send a picture of the actuator and the brakes as well as the rear brakes which seem to be getting some grooves in the rotors. The front rotors are nice & smooth. All rotors have a good 1/4"+ of meat on them so I think they are OK and Lee Smith RV said that our pads had plenty of life in them.

There is no grease or oil of any kind in or around the brakes or inside the wheel rims which is where I would expect to see it.

Good point about 2 different colors of brake fluid.

The pedal linkage is fine. All the pins are in place and secure.

... back to you shortly.

Carl

quote:

Originally posted by Carl Feren:


I use a prestone syntetic brake fluid which was changed about 20 months ago.

Not a very high wet boiling point.

quote:

Almost all of our driving has been in the dry southwest and since we don't like driving in the rain there is little chance of damage from road splash.

This is one of those things where the question is "How lucky do ya feel?" Long time ago, I lost my brakes on level freeway stop and go traffic. I had an idle problem, and was keeping a little pressure on the gas pedal and riding the brakes to keep the speed down. Stupid Me!
It was a non-event, as I turned on my brain and used low gear and the trailer brakes for braking, and got off the freeway. By then, the brakes had come back. I had an ordinary fluid (Prestone, I think) and it was between one and two years old.

Is ATE Blue the same as ATE Super Blue? The reason I ask is this:

NOTE TO FLORIDA RESIDENTS ONLY: ATE Super Blue Racing Brake Fluid, due to its blue color, cannot be registered in and is not DOT-approved for street cars in Florida.

Not DOT approved cuz it's blue? I don't get it.

http://www.tirerack.com/brakes...soryDetail.jsp?ID=21

I have no idea. I have used both colors since it hit the market and so have a number of folks whose opinion I respect. They all say both are the same.

My next door neighbor is a track day guy at Willow Springs, and is really plugged in. Says the same thing.

It must be something Florida hasn't dealt with yet, so it can't be any good.

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It must be something Florida hasn't dealt with yet, so it can't be any good.

Amber brake fluid gets darker as it degrades so it's very easy to tell if the fluid is old or infused with moisture.
Florida only allows pre-qualified brake fluid types as the high humidity has caused brake failures in the past.

Here's the approved list:
http://www.freshfromflorida.co.../petro/bfbrands.html

quote:

Originally posted by Moonbeam-Express:

Amber brake fluid gets darker as it degrades so it's very easy to tell if the fluid is old or infused with moisture.

That makes sense except for a coupla things:

1. The color change is very hard to discern unless an eyedropper is used to pull a sample. A test strip or an electronic tester would be much better.

2. ATE Super Blue also turns darker with moisture contamination. It is easily seen with an eyedropper or clear bleed tube. I recently observed this with a motorcycle that I brought out of storage.

quote:

the high humidity has caused brake failures in the past.

That is interesting. Most brake failure stories I hear of occur downhill in steep terrain.

I do seem to recall a lot of brake lights illuminated while cars go straight down the road. Maybe lots of folks there ride their brakes. Perhaps the same folks that drive straight with a turn signal on.

quote:

That is interesting. Most brake failure stories I hear of occur downhill in steep terrain.

The highest point in Florida is 345 feet, so there aren't many steep hills to test the theory. Perhaps they didn't want the color of the brake fluid to compete with the color of hair of the little old ladies.

Blue brake fluid is claimed to be much harder to see a change in, whether true or not that is the theory that prevails.

Western states apparently don't have blue hairs, so they must be far more sensible about this subject.