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Hikerdogs

Wisconsin

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Posted: 09/19/19 07:01am Link  |  Quote  |  Print  |  Notify Moderator

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.


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tropical36

Southwest Florida_USA

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Posted: 09/20/19 09:02am Link  |  Quote  |  Print  |  Notify Moderator

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.

* This post was edited 09/20/19 09:08am by tropical36 *


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olfarmer

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Posted: 09/21/19 09:32am Link  |  Quote  |  Print  |  Notify Moderator

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.


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wolfe10

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Posted: 09/21/19 09:38am Link  |  Quote  |  Print  |  Notify Moderator

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


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mchero

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Posted: 09/21/19 10:48am Link  |  Quote  |  Print  |  Notify Moderator

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.


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John&Joey

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Posted: 09/21/19 04:28pm Link  |  Quote  |  Print  |  Notify Moderator

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

time2roll

Southern California

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Posted: 09/21/19 05:36pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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doxiemom11

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Posted: 09/21/19 08:42pm Link  |  Quote  |  Print  |  Notify Moderator

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.

dodge guy

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Posted: 09/21/19 09:08pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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olfarmer

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Posted: 09/24/19 08:54pm Link  |  Quote  |  Print  |  Notify Moderator

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!

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