Proper disc brake fluid time to change?

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steve raucher
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Proper disc brake fluid time to change?

#1 Post by steve raucher » Sun May 19, 2019 2:05 pm

Hi all,
It has been about 10K miles and 5 years since disc brake fluid has been changed and bled.
I think I was using a DOT 3 or 4 then. Try to keep level topped off.
Been reading about a silicone brake fluid and most people seem to give it high ratings.
My brakes are good I always pump them a time or two when I need to get on them. Although at high speeds my confidence wains when I get on them hard, always try to leave time and space for objects in front of me.
How often should brake fluid be flushed and changed and would it be a good idea to go the silicone fluid route? My brake lines are relatively new no leaks etc, original single master cylinder.
Cheers,
Steve
 

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PaulLima
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Re: Proper disc brake fluid time to change?

#2 Post by PaulLima » Sun May 19, 2019 2:22 pm

Longest time between complete flush I think should be 2 years. Dot 4 fluid. I had tried silicone (Dot 5) fluid in my '68 911L but never could get a really solid pedal like I had with Dot 4. I'd leave silicone fluid for the garage/show queens and stick with a good Dot 4 fluid

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Ron LaDow
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Re: Proper disc brake fluid time to change?

#3 Post by Ron LaDow » Sun May 19, 2019 3:22 pm

Agree with Paul and I should really take his (and my) advice.
Except: After years of that stuff being in there, the Speedster finally got a hard pedal with silicone fluid; those bubbles *will* detach and escape to the atmosphere with patience.
Ron LaDow
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Vic Skirmants
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Re: Proper disc brake fluid time to change?

#4 Post by Vic Skirmants » Sun May 19, 2019 3:35 pm

Ron LaDow wrote:
Sun May 19, 2019 3:22 pm
Agree with Paul and I should really take his (and my) advice.
Except: After years of that stuff being in there, the Speedster finally got a hard pedal with silicone fluid; those bubbles *will* detach and escape to the atmosphere with patience.
Nah; probably just a caliper piston or two stuck.:)

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Norm Miller
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Re: Proper disc brake fluid time to change?

#5 Post by Norm Miller » Sun May 19, 2019 4:53 pm

Steve,
Since humidity isn't severe in CA I'd say 2-3 years.
Here in the dry west, it seems like 5 years is acceptable.
Use only DOT 3 or 4. Avoid the soft pedal syndrome!
Norm
 

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Ron LaDow
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Re: Proper disc brake fluid time to change?

#6 Post by Ron LaDow » Sun May 19, 2019 10:04 pm

Vic Skirmants wrote:
Sun May 19, 2019 3:35 pm
Nah; probably just a caliper piston or two stuck.:)
That or, being as light as the car is, I just don't notice anymore...
Ron LaDow
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Harlan Halsey
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Re: Proper disc brake fluid time to change?

#7 Post by Harlan Halsey » Mon May 20, 2019 4:08 am

Steve,
I have silicone brake fluid in most of my cars. I hate the old stuff because it is paint stripper and its propensity to draw water from the atmosphere is what rusts your brake cylinders or pistons. I'm over 20 years without a fluid change in my Convertible D and several years since I converted the SC. Even the G4 race car is on silicone. Never had a problem with either trapped air or the fluid leaking. And if the pedal is a bit softer, I don't notice it at all.

Since you have had the old stuff in there so long, I would recommend a complete system rebuild. New cylinders where the old ones don't hone pit-less. Flush the lines and blow out with air. Renew all the flexible lines. Fill the system with NAPA silicone fluid, and then forget it.

I try to change the old stuff annually, to answer your question, but often let it run 2 years.

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Mark Roth
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Re: Proper disc brake fluid time to change?

#8 Post by Mark Roth » Mon May 20, 2019 11:07 am

I know that all the literature recommends two year intervals but I have never done it. Gone up to six years on my various cars (like on my 2010 Cayman) with no ill effects. This is while living in Houston where there is plenty of humidity. I have heard about cars that were not driven for long periods that had corroded brake components. I would like to read some real life experiences of long change intervals in cars that are driven frequently (about once a month or more). Thanks.
Mark Roth
65 C Cab (Black/black)

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PaulLima
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Re: Proper disc brake fluid time to change?

#9 Post by PaulLima » Mon May 20, 2019 1:29 pm

Mark, I think you may find (1) fluid boils at a very low temperature, making emergency stops much more "interesting" and (2) your brake maintenance costs will be much higher when the failures do occur. You may want to check your Cayman owner's manual; Porsche has recommended 2 years for complete flush for quite a long time. If you were to change to silicone, you might get away with the long maintenance schedule.

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steve raucher
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Re: Proper disc brake fluid time to change?

#10 Post by steve raucher » Mon May 20, 2019 5:16 pm

Thanks guys,
Can anyone tell me the brake fluid capacity once flushed and bled just curious in ounces?
Also since my brake lines are good, let's say last time DOT 3 fluid was used, and this time I flush system and use DOT 4. Could there be any issues of different residual fluid in the brake lines etc, being that the fluid was changed from DOT 3 to DOT4?
 

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Ron LaDow
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Re: Proper disc brake fluid time to change?

#11 Post by Ron LaDow » Mon May 20, 2019 6:56 pm

Steve,
Not sure of the exact, but a quart will certainly do it.
DOT 3 and 4 are compatible; small amounts of 3 in a 4 system will make no difference, but the 3 has a lower boiling temp, so if you mix half-and-half, you have DOT3.5.
Ron LaDow
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Wil Mittelbach
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Re: Proper disc brake fluid time to change?

#12 Post by Wil Mittelbach » Mon May 20, 2019 11:53 pm

[quote="Harlan Halsey" post:-
I have silicone brake fluid in most of my cars. I hate the old stuff because it is paint stripper and its propensity to draw water from the atmosphere is what rusts your brake cylinders or pistons. I'm over 20 years without a fluid change in my Convertible D and several years since I converted the SC. Even the G4 race car is on silicone. Never had a problem with either trapped air or the fluid leaking. And if the pedal is a bit softer, I don't notice it at all [/quote]

Also changed to silicone brake fluid years ago in my C cab after several bad experiences with the traditional fluid. Problem free, and very satisfied.

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Juha Vane
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Re: Proper disc brake fluid time to change?

#13 Post by Juha Vane » Tue May 21, 2019 2:00 am

There is also DOT 5.1 brake fluid that is compatible with DOT 3 and DOT 4. This has a higher boiling point.
Do not confuse this with DOT 5 that is silicone fluid that can not be mixed with the others.
You can to some degree see what condition your hydraulic brake system is looking at the fluid that is coming
out from wheels. If very murky and rusty, perhaps need rebuild. 2 year is very common change interval.
I have found MityVac very handy to change brake fluid. If you use the old method where one is pumping
the brake pedal and an other is opening the bleed screw and this way forcing liquid out. You move the master
cylinder piston all the way and there can be some "dirt" in the cylinder that destroy the rubber seal.
You should use fresh brake fluid, if you open a can, put a date on it and trash after a year or so. You should
not need to top up brake fluid, if you need something is wrong > leak.
KTF,

Juha Vane
Finland

'59 308
'63 356
'85 911

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Al Zim
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Re: Proper disc brake fluid time to change?

#14 Post by Al Zim » Tue May 21, 2019 9:58 am

One of the worst situations I see when Porsche cars are sold is that the owner practiced DIFFERED MAINTENANCE! In the advertisements for late model air cooled 911's the statement that the car is excellent to perfect is a misstatement. From the moment the car is new (which includes a complete restoration) it begins to deteriorate! Taking the vehicle back to the dealer or a competent shop for service allows an experienced technician to evaluate your Porsche and possibly keep you alive. If you have not serviced the brake fluid in 20 years how often have you properly inspected the brake system? Fittings, lines, master cylinder free play, wheel and master cylinders wear out. Mark Roth you state that in your Cayman you have gone "up to 6 years" without a brake fluid service. That in a normally driven vehicle is over 70,000 miles! as an accountant how did you ascertain that this was a safe thing to do? YOU have to realize that 356 vehicles were produced when cars needed a lot of service. Look at the number of grease fittings on a 1960 VW bus. Just because it is 55+years later does not mean that your car has some how adopted current technology. If you take a head on hit in your 356 depending on how hard you are hit there is a good chance the steering column will hit you in the chest. Nothing like a 30 year old seat belt to save your life in this situation. It certainly is a complement to Porsche that so many of the early cars have survived. al zim 2019/05/21
 

Mike Horton
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Re: Proper disc brake fluid time to change?

#15 Post by Mike Horton » Tue May 21, 2019 10:53 am

PaulLima wrote:
Sun May 19, 2019 2:22 pm
Longest time between complete flush I think should be 2 years. Dot 4 fluid. I had tried silicone (Dot 5) fluid in my '68 911L but never could get a really solid pedal like I had with Dot 4. I'd leave silicone fluid for the garage/show queens and stick with a good Dot 4 fluid
+1
Mike

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