Brake problem

[olfarmer]

Just drove our old 2001 Winnebago Brave that has 32,xxx miles on it from N.C. Iowa to Kalispell, Mt. about 1400 miles. Every thing worked great until I pulled into the campground we had reservations at. Brakes worked good all of the way and even when I stopped at the office to register. As I drove slowly to our sight the brake pedal went almost to the floor, the brakes did slow me down and stop me but I don't think I could have locked them up. I got it backed in the site and let everything cool off and it feels like the pedal has come back up. I looked underneath and at the wheels and no signs of a fluid leak and the master cylinder is full. So, is it a failing master cylinder, boiling moisture in the fluid or something else? I did hit the brakes real hard about 70 miles back when a dog ran out in front of me and the wife said the tires were squealing the brakes were working good then so any ideas what might be wrong? I feel lucky that they didn't cause any problems until we were about stopped! We just drove through a lot of mountain grades but I didn't ride them, I shifted down for long down grades.

[olfarmer]

The large GM dealership that I trust from previous service tested the system including the master cylinder and said it was OK. I drove it 1400 miles home including Mountain driving with no problems. I think the MC is fine!

[dodge_guy]

ScottG wrote:

olfarmer wrote:
Wouldn't a failing master cylinder have leakage and fluid loss? Or, could the fluid pass by the piston and not leak out?
Ed

Exactly, it probably wont leak externally but the fluid has bypassed the piston seal. The problem may seem to correct itself later but don't be fooled.
It's time to replace the MC.

Yes, these are the signs of a master cylinder failing. And the brake fluid should be flushed (the entire system) every 2-3 years.

[doxiemom11]

That happened after a hard/fast stop on the x-way to me, in a car, there was a brake fluid leak that was only leaking when the pedal was depressed. Have someone sit inside and pump the brakes while you look for a leak.

[time2roll]

olfarmer wrote:
Just a follow up. We drove the MH the 1400 miles home and had no more brake problems. So I am satisfied that it was the moisture in the old fluid that caused the problem.

Put the brake flush on your maintenance schedule. Every 2 to 5 years or whenever you replace pads.

[John_Joey]

Glad to hear you made her home safe and sound. Thanks for the follow up.

[mchero]

Had a 93 Pace Arrow DP on an Oshkosh chassis for 12 years. Front disc brake calipers had a bad habbit of dragging after sitting awhile. Had to do a couple slow forward/reverse braking to loosen them up.
Also found that their was NO master cylinder rebuild kits for the master cylinder ( hydraulic with hydra boost).
Called up Freightliner who bought out Oshkosh chassis a number of years back. Ordered one of the last remaining master cylinders in stock.

[wolfe10]

OR that the tire bead broke loose from the rim??

[olfarmer]

Just a follow up. We drove the MH the 1400 miles home and had no more brake problems. So I am satisfied that it was the moisture in the old fluid that caused the problem.

[tropical36]

Hikerdogs wrote:
It doaesn't take much heat to boil DOT 3 brake fluid when it becomes satureated with water. Dot# 3 is the original brake fluid installed on your 2001 chassis. The dry boiling point is 401*F or 205*C. When it becomes saturated (4% water) the boiling point is lowered to 284*F or 140*C. Remember when you step on the brakes you're changing the energy of inertia to heat.

Most motorhomes today come with either DOT 4 or Dot 5.1 brake fluid. The DOT 4 has a dry boiling point of 230*C or 446*F and a wet boiling point of 155C or 311*F. In most cases vehicles that were originally equpiied with DOT 3 fluid can be changed to DOT 4. It's not advisable to mix them, but when the system is flushed DOT 4 can be used to replace the DOT 3.

The most recent fluid used is DOT 5.1. This fluid has a dry boiling point of 270*C or 518*F, and a wet boiling point of 190*C or 374*F. Unfortunately in most cases it cannot be used to replace either DOT 3 or DOT4. It is not compatible with the rubber parts in the system.

To further confuse things there is also DOT 5.0 fluid in the market. It is a silicone based fluid primarily used in racing and aircraft applications. It does not absorbe water like the other styles therefore has limited long term use. Since it does not absorb water any water in the system will gravitate to the lowest point. In cold weather it can freeze and block the flow to the calipers. If left too long in the system it can cause the lines to rust through.

This fluid is also not compatible with the rubber parts in most production vehicles. In systems where it is used it needs to be changed on a regular basis to avoid the fore mentioned problems.

Everything I've ever read, says that they are compatible, as in this statement....
"Yes, DOT 3 brake fluid is compatible with DOT 4 brake fluid. However, DOT 4 offers a higher boiling point. DOT 5.1 is used in high-performance and heavy-duty applications due to its high boiling point. It's compatible with DOT 3 and DOT 4 fluid""
Not so for silicon based 5.0 however and that is a no no.
Don't know why the numerical similarity, unless it was done to confuse the general public. Not too much confusion however, since most have never even heard of 5.1.

[Hikerdogs]

It doaesn't take much heat to boil DOT 3 brake fluid when it becomes satureated with water. Dot# 3 is the original brake fluid installed on your 2001 chassis. The dry boiling point is 401*F or 205*C. When it becomes saturated (4% water) the boiling point is lowered to 284*F or 140*C. Remember when you step on the brakes you're changing the energy of inertia to heat.

Most motorhomes today come with either DOT 4 or Dot 5.1 brake fluid. The DOT 4 has a dry boiling point of 230*C or 446*F and a wet boiling point of 155C or 311*F. In most cases vehicles that were originally equpiied with DOT 3 fluid can be changed to DOT 4. It's not advisable to mix them, but when the system is flushed DOT 4 can be used to replace the DOT 3.

The most recent fluid used is DOT 5.1. This fluid has a dry boiling point of 270*C or 518*F, and a wet boiling point of 190*C or 374*F. Unfortunately in most cases it cannot be used to replace either DOT 3 or DOT4. It is not compatible with the rubber parts in the system.

To further confuse things there is also DOT 5.0 fluid in the market. It is a silicone based fluid primarily used in racing and aircraft applications. It does not absorbe water like the other styles therefore has limited long term use. Since it does not absorb water any water in the system will gravitate to the lowest point. In cold weather it can freeze and block the flow to the calipers. If left too long in the system it can cause the lines to rust through.

This fluid is also not compatible with the rubber parts in most production vehicles. In systems where it is used it needs to be changed on a regular basis to avoid the fore mentioned problems.

[atsrmf]

Check the brake booster rod adjustment in the master cylinder. If the rod is too long, even my a millimeter or two, it can cause the brakes to drag. If it is too short, you can get a spongy pedal. Something in the booster or pedal linkage may have cause this clearance to change over time. Verification is easy, and takes a special tool that cost $25. It may be the best money you ever spent!

[olfarmer]

John&Joey wrote:
Sounds like you found yourself an excellent shop while on the road. Nothing is worst then going cross country and not knowing if your brakes will stop you.

A thermal gun at Harbor Freight is very cheap and is a handy tool. When you pull over for fuel shoot your rotors and start to get a feel for them. You just may find out that one which ran hot still does. Clearance changes when things start warming up.

Safe travels back.

Thank you

[John_Joey]

Sounds like you found yourself an excellent shop while on the road. Nothing is worst then going cross country and not knowing if your brakes will stop you.

A thermal gun at Harbor Freight is very cheap and is a handy tool. When you pull over for fuel shoot your rotors and start to get a feel for them. You just may find out that one which ran hot still does. Clearance changes when things start warming up.

Safe travels back.

[rgatijnet1]

olfarmer wrote:
OK, I took the MH in to the large local dealer here. They tested the brake fluid for moisture and there was 4% water in it so they flushed the brake fluid, checked the calipers, tested the pressure, and test drove it. They said one rotor showed signs if being hot at some time but that the caliper was free and moved easily. They checked all calipers for being free to move as they should. They said the master cylinder was OK. I am very happy with their service, it was not cheap but very thorough and were very good at keeping me informed on their progress. Thanks for all of the comments!

If you still have your invoice, check to see how many quarts of brake fluid they used. I have seen others charged for brake flush when really all they got was a brake bleed. They should have used 3 quarts of brake fluid for a flush and only 1 quart for a brake bleed. Glad things worked out with a minimum of expense.
A fluid flush should be done every 2 years. Your fluid showed 4% moisture content but that moisture tends to accumulate at the lowest point in the system, which is the calipers, which also get the hottest and causes the fluid to boil.