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Discussion Starter · #1 ·
Hey chaps, want to change the brake fluid in the aero and am considering using DOT 5.1 fluid. Can anyone recommend a suitable brand (and where to get it from ) I have Black Diamond discs (front), Brembo's (rear) and Pagid fast road pads all round (if that's relevant).

cheers
Zahid
 

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Discussion Starter · #7 ·
Thanks guys, I've bought some Ferodo 5.1 from Burtonpower who will deliver tomorrow. The reason I'm changing is because the car will be on track at the end of the month, and I suppose because it's probably due a change anyway


Zahid
 

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Faero,

Saab specify DOT 4 fluid, although some manufacturers still only specify DOT 3. The differences in dry and wet boiling points are:-

Fluid type Dry Boiling Point Wet Boiling Point
DOT 3, 401 F (205 C), 284 F (140 C)
DOT 4, 446 F (230 C), 311 F (155 C)
DOT 5.1, 518 F (270 C), 375 F (191 C


The important difference is the wet boiling point which is for fluid that has absorbed a small amount of water (typical of fluid that's been in the car a couple of years). By using DOT 5.1, you are getting and extra 36C of safety.

As the real cost of changing the brake fluid is the labour, spending an extra couple of pounds on the better spec fluid is irrelevant and buys you a significant improvement.

And you must change it at least every two years (Saab's specified interval)

You might care to read this.
 

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DOT 5.1 brake fluid is or can be a synthetic fluid. Some of it is silicone based which has a lower tendency to absorb moisture. You need to check it's suitable for the seal materials used in your car. I'm sure it's OK with Saabs, but I remember buying some DOT 5.1 fluid recently and it said on the back "do not use in XXX manufacturers braking systems". Sorry but I can't remember who's it was and I've not got the bottle any more.

Kev.
 

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Found the tech specs for brake fluids now:
DOT 5 is silicone based and does not mix with DOT 3,4 and 5.1 which are glycol based. This means you can only add it to a dry system not already exposed to the glycol based fluids. It is also very difficult to bleed as the microscopic air bubbles take hours to days to come out of solution and form larger bleedable bubbles. Because of this it is not recommended for ABS systems as the bubbles can form in the return pumps and can cause cavitation damage. It's ideal for old cars used once in a blue moon, as it doesn't absorb water. DOT 5.1 has similar boiling point properties to DOT 5 but is miscible with DOT3 & 4.
Kev.
 

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Discussion Starter · #15 ·
quote:
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Originally posted by kevb:
it said on the back "do not use in XXX manufacturers braking systems"
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Citroen? They all say that.  [/b]
Yep Bill, I've got AP DOT 5.1 fluid and thats what it says on the back
 

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Certainly old Citroens had a tie in to the hydraulic suspension system. My mate had a GSA in the 80's which failed and put the full 2000psi+ from the suspension onto the brakes at 80mph on the motorway. He ended up half-way up the embankment on the M6.
 
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