Brake fluid

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philhoward
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Brake fluid

Post by philhoward » Wed Feb 06, 2019 2:03 pm

halfpenny wrote:
Wed Feb 06, 2019 1:47 pm
If switching, or unsure, you will need to change all of the seals, including the servo cylinder (which does have fluid in it), and wash everything very thoroughly in brake cleaner or meths. The servo vacuum can should be ok.
If you've got fluid anywhere in the servo of a 6a, you've got problems. In a 5/5a, then yes you would need to change the seals in the cylinder part.


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Brake fluid

Post by Roger Pennington » Wed Feb 06, 2019 2:26 pm

halfpenny wrote:
Wed Feb 06, 2019 1:47 pm
including the servo cylinder (which does have fluid in it),
This is a 6a that we're talking about, there isn't a servo cylinder, the servo is integral with the master, not a remote like on the 5 series :)


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Brake fluid

Post by Laters » Wed Feb 06, 2019 3:08 pm

My experience of silicone brake fluid is generally positive but as has been said silicone fluid doesn't play well with other brake fluid.

Many moons ago I bought a damaged kit car that had not only a small plate pop riveted to the bulkhead but also the stickers/labels all over the master cylinder that stated "Silicone Brake Fluid Only".

The brakes of the car did work & I didnt really need to do any brake work to the car so all was left connected up to save bleeding the brakes etc.
It was only when I decided to upgrade the front brakes, after a few years use that for road use were ok but a little lacking on the track, that something didnt look right and it became apparent that despite all the labels/warnings that someone at some point had topped the master cylinder up with normal brake fluid.

Caused a bit more work than expected as I had already bought more silicone brake fluid so a nice easy job became a few day job washing things out.
Performance wise it never gave any trouble and despite being laid up for a extended period never gave any trouble.

When the brakes of the se6 get to the point of needing rebuilding I wont think twice about using the silicone brake fluid thats on the shelf.


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Brake fluid

Post by TrevorG » Wed Feb 06, 2019 4:07 pm

Thanks halfpenny.....😊will get some brake cleaner for the masters, then change their seals, rest is new.....that's the reason for my questions. Plenty of time while the engine and box are out and chassis etc. completed.



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Brake fluid

Post by TrevorG » Wed Feb 06, 2019 4:10 pm

Thanks laters, mine may have been just the same.....while I've put new cylinders and callers and lines in I'll recovery back to glycol but use dot5.1



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Brake fluid

Post by AllingtonGT » Wed Feb 06, 2019 5:34 pm

My Toyota Altezza V8 uses a Saab concentric slave for the clutch connected to the original clutch master cylinder. We used Dot 5.1 in clutch and brakes as it's a track car and tends to get a trifle hot.... The slave cylinder seals kept dissolving in the Dot 5.1 and we removed the gearbox about 4 times to replace the slave cylinder when it failed. We assumed it was just not able to take the beating, but having decided to change to an AP slave, only to find there were none available for six months, the AP sales person suggested we stick a new Saab one in but use DOT 4.

There's never been a problem since and the fluid stays beautifully clean. It appears the type of rubber used in older slave and master cylinders can be affected differently by Dot 5.1.
Last edited by AllingtonGT on Wed Feb 06, 2019 9:23 pm, edited 1 time in total.



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Brake fluid

Post by TrevorG » Wed Feb 06, 2019 7:20 pm

Thanks for that.....I'm old, the car is old, we aren't likely to go racing about...so dot4 it'll be!



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Brake fluid

Post by Dennis Nicholas » Thu Feb 07, 2019 12:35 pm

Some of the original problems reported by people changing to silicone DOT 5 was the system all seizing up. It was later found that such people were NOT changing all the rubbers. Silicone migrates into the rubber faster than Dot 4 migrates out....hence swollen seals and all stops working.
Remember the origin of DOT 5 silicone was the American army and its thousands of vehicles stored in the desert awaiting possible back up use; they got fed up having to change the fluid on them all at regular intervals and had the new stuff designed to get round this.....silicone based.

As others above I changed to DOT 5 many years ago in both brakes and clutch and have enjoyed the "fill and forget" experience.
There may be implications in the racing fraternity?
It is a pity they labeled the new glycol DOT 5.1......surely should have been 6......it just created confusion with those not in the know thinking the 5.1 was a better version of the silicone!!
Reiterating again another advantage is that the silicone is reusable....bleed - save fluid and let it settle and any dirt falls to bottom.....decant good clear stuff......misers anonymous.
I am sure I have read somewhere in the spec for brake systems that by definition the seals of a certain spec have to be of suitable material to be used with any fluid?
Dennis


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