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Brake Fluid
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RogerB



Joined: 18 Dec 2014
Posts: 176
Location: Suffolk Coastal. U.K.

PostPosted: Fri Jan 25, 2019 6:02 pm    Post subject: Brake Fluid Reply with quote

I have to renew the brake fluid in my Standard 8 clutch and brake system as the current fluid is over 5 years old....

The question is- can I use any 4 DOT fluid as a replacement? Or, is it advisable to use a specific classic car brake fluid product?

RogerB
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Bitumen Boy



Joined: 26 Jan 2012
Posts: 1318
Location: Above the snow line in old Monmouthshire

PostPosted: Fri Jan 25, 2019 11:10 pm    Post subject: Reply with quote

Any DOT 3 or DOT 4 fluid will be fine for this job. Probably someone does market a "classic specific" fluid, but it will be no more than a fancy bottle - the contents will be the same as the stuff you'd pick up in Halfrauds or a local factors.
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RogerB



Joined: 18 Dec 2014
Posts: 176
Location: Suffolk Coastal. U.K.

PostPosted: Sat Jan 26, 2019 6:02 pm    Post subject: Brake Fluid Reply with quote

Many thanks for your advice; I just love the spelling of Halfords......!

What is the difference between 3DOT and 4DOT?

Rogerb
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Bitumen Boy



Joined: 26 Jan 2012
Posts: 1318
Location: Above the snow line in old Monmouthshire

PostPosted: Sat Jan 26, 2019 6:26 pm    Post subject: Reply with quote

Essentially DOT 4 is an improved version of DOT 3 - the main difference IIRC is it has a higher boiling point, not really an issue for clutch hydraulics anyway. The two specifications are compatible and may be mixed safely.
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RogerB



Joined: 18 Dec 2014
Posts: 176
Location: Suffolk Coastal. U.K.

PostPosted: Sat Jan 26, 2019 10:30 pm    Post subject: Reply with quote

Thank you.....
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RogerB



Joined: 18 Dec 2014
Posts: 176
Location: Suffolk Coastal. U.K.

PostPosted: Sun Jan 27, 2019 2:33 pm    Post subject: Reply with quote

As I have to renew the brake (+clutch) fluid because of the age of the existing
fluid, I have to drain the existing fluid out of the brake pipes; that is easy!

What is the best way to refill the system with the new fluid bearing in mind that the system has to be 'bled' also?

RogerB
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alanb



Joined: 10 Sep 2012
Posts: 337
Location: Berkshire.

PostPosted: Sun Jan 27, 2019 6:26 pm    Post subject: Reply with quote

Roger, you don't need to drain the system you bleed them as normal but keep topping up and keep going until you get clean new fluid coming through, I use a bleed easy kit from Halfords when doing mine, so easy. When doing the brakes I was always taught to start with the wheel furthest away from the master cylinder in your case rear nearside then rear of side, front nearside, front of side. Good luck.
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RogerB



Joined: 18 Dec 2014
Posts: 176
Location: Suffolk Coastal. U.K.

PostPosted: Sun Jan 27, 2019 9:38 pm    Post subject: Reply with quote

Thank you....

That I will try asap.

RogerB
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Clactonguy



Joined: 20 Mar 2018
Posts: 47
Location: clacton on sea

PostPosted: Thu Jul 18, 2019 11:27 pm    Post subject: brake fluid Reply with quote

as far as I am aware we cant simply use latest Dot fluid for all cars . I am given to understand my rover p6 has to use dot 3 and not dot 4. something to do with causing issues with seals /rubbers chemical reactions. can't recall exactly but do not use latest. dot 4 in my classic car of 45 years. if theres been a change be nice to know!
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Penguin45



Joined: 28 Jul 2014
Posts: 314
Location: LBA

PostPosted: Fri Jul 19, 2019 12:13 am    Post subject: Reply with quote

Dot 3, 4 and 5.1 are "improving" grades of mineral fluids.

Dot 5 is silicone based and if used inappropriately will destroy rubber seals throughout a hydraulic system.

P45.
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Keith D



Joined: 16 Oct 2008
Posts: 914
Location: Upper Swan, Western Australia

PostPosted: Fri Jul 19, 2019 2:05 am    Post subject: Reply with quote

Under no circumstances ever mix dot 5 (silicone) with anything else, including dot 5.1. Totally incompatible with glycol fluids. Silicone rejects water. Glycol based fluids will absorb up to 10% water.

Keith
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ukdave2002



Joined: 23 Nov 2007
Posts: 3369
Location: South Cheshire

PostPosted: Fri Jul 19, 2019 1:16 pm    Post subject: Reply with quote

Penguin45 wrote:
Dot 3, 4 and 5.1 are "improving" grades of mineral fluids.

Dot 5 is silicone based and if used inappropriately will destroy rubber seals throughout a hydraulic system.

P45.
I once chucked some old cylinder seals in a jar of silicon fluid; a month later they looked exactly the same, which is hardly surprising as silicon is a pretty inert substance.

I believe the reason that people report swelling of old seals after filling with silicon is because their systems still have some glycol brake fluid left in (bleed nipples tend to be higher up, its impossible to get all fluid out by just bleeding), silicon fluid is less dense than both glycol and water, (and there will be some residue of both left in the system) Silicon fluid will repel any moisture, so a high water content glycol mix will now be concentrated the bottom of the cylinders and its this that does the damage. In a glycol system the water is absorbed and distributed throughout the system so far less concentrated.

Dave
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