Brake and clutch bleed interval with modern synthetic brake fluid?

[rogerh113]

Hello,

Is there a recommended interval for brake and clutch bleeding with the new synthetic fluid.  I did a bleed job after about 4 years on a different car (not the 113), and the out coming fluid looked remarkably fresh.  I gather the old stuff absorbed moisture, and was visibly degraded when I bled the brakes after 3 years.

I certainly want to keep the hydraulic components (masters and slaves) in top condition, and I know what a pain they are to replace if let go.  On the other hand, pumping out good fluids and recycling them seems a bit of a waste.

Any perspectives would be appreciated.

regards -- Roger

[dirkbalter]

@ Roger,

I was looking at dot 5 brake fluid as well a while back. It certainly has its applications but I concluded that there is no real benefit, especially if protecting your braking components is a priority. 
I would rather flush the system every few years and don't have to worry for possible internal corrosion as much.



Potential Risks of Using DOT 5 Brake Fluid
1. Incompatibility with Other Brake Fluids
DOT 5 brake fluid is incompatible with DOT 3, DOT 4, and DOT 5.1 brake fluids. Mixing these fluids can result in a dangerous chemical reaction, leading to brake failure.

2. Poor Lubrication Properties
DOT 5 brake fluid lacks the lubricating properties of glycol-based fluids (DOT 3, 4, and 5.1). This can lead to premature wear and damage to brake components, such as seals and calipers.

3. Reduced Corrosion Protection
DOT 5 brake fluid does not provide adequate corrosion protection for metal components within the brake system. This can result in rust and corrosion, compromising the integrity of the braking system.

4. Spongey Brake Pedal Feel
The lack of sufficient lubrication and poor compatibility with rubber components can result in a spongey brake pedal feel, making it difficult to control braking force.

5. Limited Availability
DOT 5 brake fluid is not as widely available as other DOT fluids, which can make it difficult to find and purchase when needed.

[rogerh113]

The brake fluid I have been using is Motul RBF600 DOT4, as polyglycol it hopefully avoids some of the noted downsides of 5.1.  Apparently not 'new' synthetic brake fluid  : ))

I would still be interested in the expected (bleed) service interval.

[rwmastel]

Is there a reason not follow original fluid service interval?  Do modern fluids always allow extended use compared to 50+ year old change intervals?

[rogerh113]

Probably like many here, I have been working on cars for over 50 years as a hobbyist.  Back in the day, the touted issue with brake fluid was its moisture absorbancy, and the resulting moisture damage to the brake and clutch components.  Perhaps modern brake fluids are no better, and perhaps worse.

I have no idea, which is why I am asking.  Is every 2 years the right answer??

[rwmastel]

I did a quick search.  Any answers in here?

https://www.sl113.org/forums/index.php?topic=35706
https://www.sl113.org/forums/index.php?topic=28106
https://www.sl113.org/forums/index.php?topic=15970
https://www.sl113.org/forums/index.php?topic=11750

[rogerh113]

Pretty much raises more issues than answers.  Apparently there is a component in DOT4 (according to a German contributor, I think), that is not kind to gaskets.  Seems most run DOT 3/4, which may have the same issue (if there is one).  Does not appear to be 113 people talking about how their brake system was damaged by DOT 3/4 fluid.  Perhaps DOT 3/4 is different than DOT 4.

I need to do some more research - right now I would consider the low moisture absorbent Prestone DOT3, which claims 50K mi service interval.  Like the LMA feature, but don't buy the service interval so much.  I don't do any competitive driving, and there seems to be no obvious superficial issues.  Have to see if there are any downsides to DOT 3. 

One guy has run DOT 5 for apparently 10 years, but them others say that water collects in parts of the system which can later rust through.

At some point, I wonder how much difference there actually is in these brake fluids.  Pretty much of a PITA for someone that just want to bleed their brakes and clutch......

In the '99 SL500 I recently did, the fluid had been in for a couple of years, and came out clear like I put it in the day before.  I am more used to the fluid coming out looking a bit dark and 'worn'. 

[Vander]

The recommended service interval by Mercedes-Benz is every 2 years regardless of miles. That is what I go by on all cars that come into my shop. Brake fluid flushes are one of the most neglected service items and one of the first items we do on any older car. Did two today actually, 74 Jaguar E-type V12 which we used Dot 3, and a modified 74 DeTomaso Pantera we used Dot 4.

Dot 3 is perfectly fine for our Pagodas. The difference between Dot 3 and Dot 4 is the boiling point, Dot 3 boils around 400F and Dot 4 is almost 450F. I save Dot 4 for high performance applications (which W113 is not), and also modern cars with certain ABS system require them due to the viscosity.

Dot 5 is silicone base, not compatible to be mixed with 3 or 4. It is really designed for motorcycles and full blown race applications.

[rogerh113]

Thanks for the clarification.  I will be going with the DOT 3.  A brake and clutch bleed does not take so long.  The correct brake fluid is more complex....

[Vander]

Another note is ALL brake fluids are synthetic. If some bottles say 'synthetic' and some don't that is just individual company marketing.

Unlike oil which can be found in the ground and drilled for, brake fluid is man made thus making it synthetic.

[rogerh113]

Not sure, but I gather natural oil products can degrade rubber gaskets, whereas synthetic does not.

If anyone can validate this, please do....  I guess other 'additives' can be put in the brake fluid which will degrade rubber parts, but one would hope that would not be the case.

[inci]

Do not use DOT 5 unless the brake system has been fully rebuilt with compatible seals.
DOT 5 is silicone-based, not glycol-based.  It deteriorates rubber seals.

Factory brake fluid was DOT 3 glycol-based. 
DOT 4 absorbs moisture faster than DOT 3 due to its borate ester additives. But it offers better heat resistance.
I prefer DOT 3 in a classic car, flushing it annually or every other year.