Brake Fluid Question
 

I am in the process of redoing the hydraulic brake system on the antique in my fleet ('56 Imperial) and am deliberating between using DOT3 vs. DOT5 fluid. One consideration that I have is keeping all of my cars on the same fluid to make future maintenance easier and lessen the chance of mixing fluids. Hence my questions:
Can I run DOT5 in an '87 560SEL?
I know DOT5 is available in different colors to make system flushing easier; is DOT3 also available in different colors?

Thanks,
jlc

I know DOT 5 is synthetic. I would go with the number that the manufacturer calls. I had a friend who had to replace a master cylinder on an older Porsche which the tech claimed that it was the fluid used. Who knows if thats really the case.

I didn't know that ANY brake fluid came in different colors, but it is unnecessary. Simply start flushing (bleeding) and watch for the fluid to start coming out clear before moving to the next wheel. For a really good flush, go back to each wheel again after you have gotten clear fluid from all of them in give it another good squirt or two.

I would do that car with DOT3 which is much better than what they had in those days anyway.

BTW When I was in elementary school in the fifties a neighbor friend of mine had a '56 Imperial. What a car for its day!

Good luck,

ATE blue fluid is still available it has dry boiling point of 536 degrees F. same BP as the Type 200. You can alternate brake flushes between the two to see when you don't need to flush any further.

DOT 5 is silicone based. DOT 3 and 4 are glycol based. Do not attempt to "flush" a system that had DOT3/4 with DOT 5. The two are not miscible and have significantly different specific gravity,and there is no way that the glycol fluid can be compelete purged by flushing. The only way to change over to DOT 5 is to take the system completely apart and start with everything new, clean, and dry, then assemble all the hydraulic components with DOT 5. The lines should be thoroughly flushed with denatured alcohol and dried and the hoses replaced.

The advantage of DOT 5 is that it does not absorb water, so it need not be flushed as often, but DOT 5 is also NOT RECOMMENDED for ABS systems.

Duke

MB specs DOT 4 that is what should be used. I wouldn't put DOT 5 in a 20 year old brake system, you are just asking for problems.

I've seen info on the ATE fluid before. They don't seem to indicate what spec it is but I'm assuming from the boiling points that it is DOT5. Is this correct?

jlc

No it's just DOT 4. It's just good high quality brake fluid. The container says it can be mixed with DOT 5.1

I don't use DOT 5.1 as it not recommended for any of my cars.

Isn't DOT 5 racing brake fluid?

ALL brake fluids are "synthetic"! The polygycol base of DOT 3, 4 , and 5.1 are created by a petrochemical process. So is antifreeze. Polyglycols don't exist in nature. They are "syntesized" chemicals. Same applies to DOT 5 silicone based fluid.

"Synthetic" refers to virtually any chemical that is not derived from distilling crude oil - same as "petrochemical" which is anything that is synthesized from petroleum based feed stocks, which includes most of the polymers used in modern society.

Duke

I'm confused here...

I thought you wanted the brake fluid to absorb moisture so it doesn't rust the system! DOT 5 is for racing where you need a higher BP.

DOT 3 goes way back, DOT 4 has much better moisture absorbsion, so you don't have to change it every 6-9 months.
DOT 4 plus has a slightly higher BP.

DOT 5 is not recommended for ABS cars.

Michael

No, it would be best if brake fluid did not absorb moisture because it's the absorbed moisture that corrodes the hydraulic system internals.

Polyglycol brake fluid is a legacy. Back when the first hydraulic brake systems were developed in the early twenties, seals were natural rubber based and they didn't hold up to petroleum based products. Think of the big construction projects of the depression era. The shovels, draglines, and bulldozers were all cables and pulleys. Hydraulics was still off in the future.

A hydraulic brake fluid that had a high boiling point, low freezing point, and would not attack natural rubber seals was required, and polyglycol was the answer, but its Achilles heel is water absorption.

The shortage of natural rubber due to Japanese imperialism in the thirteis and the need for hydraulic boost controls in aircraft drove the development of petroleum based elastomers, which could resist petroleum based hydraulic fluids.

Automotive brakes are still stuck with their legacy polyglycol fluid, and it is not likely to change.

Duke