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Old 11-07-2013, 06:41 AM   #15
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I have seen cheap rebuilt calipers where the inside bore was sand blasted and was rough as a cob. It should be smooth and if the bore is not smooth it will cause the pistons to stick. Hydraulic brake systems are well sealed and water won't come in if there is nothing to attract it. However, if there is conventional brake fluid in the system it will absorb any and all moisture. If you don't believe me take a piece of bare steel and put a drop of DOT5 and a drop of DOT 3 or 4 on the steel and tell me which one rusts first. Do the same thing on a piece of painted steel. The conventional fluid will eat the paint off and start rusting. The silicone won't do any harm. Silicone is used for its chemically inert properties and high temperature properties. If you are using conventional brake fluid and the vehicle sits for a long time, the small amount of brake fluid that leaks past the O-rings on the pistons will start to absorb water and corrode the bore. If you drive the vehicle every day, then the rust does not have time to form and the heat from braking helps dry things out. Driving an RV often is a good thing if you can do it. Any system that sits will degrade faster than one that is driven. The Silicone does not attack rubber like conventional fluid does.


Perry
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Old 11-07-2013, 07:54 AM   #16
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Some things to consider if you do choose to go DOT5:

Silicone fluids are not miscible with water. It’s the classic oil and vinegar scenario. DOT 5
Silicone, being less dense, tends to float on water. Therefore, if water ever entered the system
it would collect at the lowest point, meaning the bottom of the caliper. Water in the bottom of
the caliper could be hard to get out without removing the caliper and rotating the caliper to
place the bleed nipple at the lowest point. Any trapped water will have the lowest boiling point of any brake fluid ever used. Since trapped water will form at the lowest point in the brake system it will also be at the highest temp area as well, the caliper. You wont boil the silicone, but you will boil the water.

While it’s permissible to mix DOT 3, DOT 4 and DOT 5.1 brake fluids, DOT 5 Silicone fluid
cannot be mixed with any other type. If the system is not completely purged before
conversion, the mixture may gel and result in very poor braking. Therefore conversion
usually requires disassembly and a thorough cleaning, or at least numerous bleeding sessions
over several days. Obviously then, the best time to consider conversion to DOT 5 is before
rebuilding the master cylinder, hydraulic power assist unit and caliper.

DOT 5 is not compatible with most anti locking brake system.
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Old 11-07-2013, 08:31 AM   #17
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That's a good reply.

DOT 5 should indeed not be used with ABS systems. I have been unable to find original documentation of this, but brake and auto manufacturers certainly believe it so there must be firm documentary evidence.

DOT 5 is also unnecessary in a vehicle that is driven regularly.

DOT 5 is appropriate for vehicles with non-ABS systems and that spend most of their lives (months on end) standing.

To avoid all potential problems associated with DOT 5 fluid replacing a glycol-based fluid (3 or 4), it is best to use it following a complete rebuild of your braking system.

But, for a vehicle without ABS that does spend most of its life unused, DOT 3 or DOT 4 filled systems will corrode, thus rendering seals ineffective and leading to leaking and potentially failed brakes.

It's your choice.

PS. I am dealing with the consequences of DOT 4 caused seal failure on two classics I own right now.
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Old 11-07-2013, 09:42 AM   #18
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Great!! Now on to the original issue here. If the brakes were locked, then lets determine if it's a caliper failure or a colapsed soft line. Not likely a master cylinder issues since it only affected one wheel. Go into the MH and step onto the brakes hard with the engine running and then stop the engine. Raise the suspect wheel and see if you can turn it by hand. If not then open the bleeder on the caliper and see if you get a squirt of fluid and then the wheel will turn. If so, then it's a soft brake line issue and you should go and replace all of the soft lines. Probably should anyway. If you have disc brakes on all four corners, then you have 5 lines. Two in the front, two at each rear wheel and one that connects at the center of the differential. If you have rear drums then you only have 3 lines.

Let us know how it goes and above all.... Post some pictures of you new to you AS.
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Old 11-13-2013, 09:58 AM   #19
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Previous suggestions re the lines and replacing pads, calipers and disks are valid. Also flush every 2 years and lubricate the slides. And forget about using DOT 5.
Here are the facts re: DOTS 3,4 and 5. Rather long but worth the read

Stolen from the Airheads BMW Club newsletter - July 1995
Battle of the DOTs

DOT 3-4 Verses DOT 5. Which brake fluid should I use?
From Oak Okleshen #35 "With regards to the DOT 3-4 verses DOT 5 brake fluid controversy, here is an article sent to me by Mr. Steve Wall. It is one of the most professional treatments I have seen on the subject".

[I had to condense this article from 6 pages to 1 due to space limitations -ed]

Brake Fluid Facts
by Steve Wall

As a former materials engineering supervisor at a major automotive brake system supplier, I feel both qualified and obligated to inject some material science facts into the murky debate about DOT 5 verses DOT 3-4 brake fluids. The important technical issues governing the use of a particular specification brake fluid are as follows:

Fluid compatibility with the brake system rubber, plastic and metal components.
Water absorption and corrosion.
Fluid boiling point and other physical characteristics.
Brake system contamination and sludging.
Additionally, some technical comments will be made about the new brake fluid formulations appearing on the scene.

First of all, it's important to understand the chemical nature of brake fluid. DOT 3 brake fluids are mixtures of glycols and glycol ethers. DOT 4 contains borate esters in addition to what is contained in DOT 3. These brake fluids are somewhat similar to automotive anti-freeze (ethylene glycol) and are not, as Dr. Curve implies, a petroleum fluid. DOT 5 is silicone chemistry.

Fluid Compatibility
Brake system materials must be compatible with the system fluid. Compatibility is determined by chemistry, and no amount of advertising, wishful thinking or rationalizing can change the science of chemical compatibility. Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components such as caliper piston boots, which are attacked by silicon fluids and greases.

Water absorption and corrosion
The big bugaboo with DOT 3-4 fluids always cited by silicone fluid advocates is water absorption. DOT 3-4 glycol based fluids, just like ethylene glycol antifreezes, are readily miscible with water. Long term brake system water content tends to reach a maximum of about 3%, which is readily handled by the corrosion inhibitors in the brake fluid formulation. Since the inhibitors are gradually depleted as they do their job, glycol brake fluid, just like anti-freeze, needs to be changed periodically. Follow BMW's recommendations. DOT 5 fluids, not being water miscible, must rely on the silicone (with some corrosion inhibitors) as a barrier film to control corrosion. Water is not absorbed by silicone as in the case of DOT 3-4 fluids, and will remain as a separate globule sinking to the lowest point in the brake system, since it is more dense.

Fluid boiling point
DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases. DOT 5 in its pure state offers a higher boiling point (500F) however if water got into the system, and a big globule found its way into a caliper, the water would start to boil at 212F causing a vapor lock condition [possible brake failure -ed.]. By contrast, DOT 3 fluid with 3% water content would still exhibit a boiling point of 300F. Silicone fluids also exhibit a 3 times greater propensity to dissolve air and other gasses which can lead to a "spongy pedal" and reduced braking at high altitudes.

DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. In an emergency, it'll do. Silicone fluid will not mix, but will float on top. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures, which is why the US Army likes silicone fluids. Since few of us ride at temperatures very much below freezing, let alone at 40 below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances.

With the advent of ABS systems, the limitations of existing brake fluids have been recognized and the brake fluid manufacturers have been working on formulations with enhanced properties. However, the chosen direction has not been silicone. The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas.

Brake system contamination
The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

New developments
Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).

Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590F. It is miscible with DOT 3-4 fluids but has yet to see commercial usage.
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Old 11-13-2013, 10:03 AM   #20
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As an afterthought you also may want to check the ABS sensor if it is melted after the fire.

Steve
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Old 11-13-2013, 05:19 PM   #21
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I don't think there is ABS on a 1990. There isn't one on my 1992 36' LY
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