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Brake and clutch fluid change


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Hello all

With modern brake and clutch fluid (not silicon ) is it still advisable to change the fluid in both the brakes and clutch system. If so is just a matter of opening the bleed nipples one at a time and getting another person to pump the pedal, and does it matter which brake a bleed first

Thanks in advance


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Normal procedure for the brakes is to bleed the furthest away from the master cylinder first, then the second furthest, third furthest, then the brake next to the cylinder. With our cars, and a right hand drive, it is nearside rear, offside rear, nearside front and offside front.


Good luck,



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Glycol based Brake fluid should be changed every two years as it absorbs water, which reduces its boiling point.

Water saturated brake fluid can cause sudden brake failure when braking hard and often.

Silicone based brake fluid has other issues, but that is another story.

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Starting a discussion about the pros and cons of silicone based fluid is like opening a hornets nest.


For me, the biggest problem is that it doesn't absorb water. Any water that gets into the reservoir, such as condensation inside the lid, will fall to the bottom of the reservoir as liquid water - silicone fluid floats on water. With the passage of time, it will get pumped down the pipes an will always pool at a low point, just as air pools at a high point. Once it gets to the brake calipers and rear cylinders it will boil at 100C to make steam, and cause massive brake failure under heavy sustained braking, just as wet glycol based fluid does, but at a much lower temperature. And as it pools at the bottom of the calipers you can't bleed it out unless you remove the calipers and turn them upside down so that the bleed nipple is at the bottom.


Consider the hornets nest open

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to add why you need to change dot 4 etc  we had to check moisture content on our trucks whilst in storage, some are parked for ages , 

the results were appalling , a reservior with two year old fluid could be as high as 45% water 


all down to atmosheric  and  temperature  changes allows moisture in through the cap vent hole as it breathes the differences .


doesnt have to be rain , just airbourne moisture



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To save time and effort in dispersing the hornet's nest, see: http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm


. . . which, in summary, says:


Summary:  So what have I learned:

  • Silicone based DOT5 fluid has a higher dry boiling temperature that DOT3 & DOT 4 fluids.
  • All glycol-based fluids (DOT3 DOT4 & DOT5.1) can quickly absorb moisture that lowers the boiling point to the wet minimum DOT specification or in many cases even lower. 
  • In one study virtually all glycol-based systems examined after 24 or more months use had the 3.5% or greater moisture content used for the wet boiling point specifications.  In some cases, this much absorption occurred in as little as a few months as the vehicles sat on new car lots.  
  • Silicone based DOT5 fluid has a much higher real wet boiling point than any of the glycol-based fluids discussed here because it absorbs very little water and the wet boiling point is essentially the same as the  dry boiling point.
  • Silicone based DOT 5 fluid prevents entry of moisture and salt into the brake system through the hoses. 
  • Silicone based DOT 5 fluid was reported to be compatible with all types of brake seals way back in the the early 70's.
  • Silicone based fluid doesn't mix with glycol-based fluid.
  • Extensive testing of brake systems with 50/50 mixes of silicone and glycol-based fluids have shown that the mixtures performed properly with no failures recorded.
  • Silicone based DOT5 fluid is slightly compressible but the compressibility is manageable at temperatures below which the standard Glycol fluids vapor lock (wet boiling point).
  • Silicone based fluid retains small suspended air bubbles.  This requires extra care when filling the reservoir and may require a subsequent bleeding a few days after first filling the system to extract any air bubbles that remained in suspension during the initial bleeding.
  • Glycol-based fluids attack paint whereas the silicone fluids do not. 

I know which 'side' I'm on but you must make up your own mind.


Now, I'm 'out'



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Wow sorry I asked why can't life be as easy as when my Herald was made is it me or is every decision in life so hard. Still no wiser as which to use

I think I will buy a push bike!!



If you think that's complicated, have a look and see how heated things get on another Triumph forum - http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl?m-1456552876/



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Going back to the original questions

Yes change Dot 4 every 2 years or so -and the clutch fluid

Yes , change fluid by following usual bleeding sequence which is very straight forward as long as the bleed nipples aren't seized and you keep watching the fluid resevoir is well topped up during the proceedure  or you'll  get air into the system and end up going round again at least once to bleed it.


As for the silicone\dot 4    religious debate Both are fine - it really depends on what you want from the brake fluid:



=If you want a brake fluid that  is perfectly satisfactory(and much better than that available when these cars were designed  then Dot 4 is fine) but change it every 2 years or so.


=If you store the car for years between doing jobs on it or using it  and want everything to be uncorroded and unsieized ( ie regard it as having a  preservative function) so that  things  working next time and/or are worried about fluid stripping the bulkhead paint then go for the silicone fluid.


I went for silicone over 10 years ago and I find it fine for my requirements 

As  long as you don't furiously pump the brake pedal when your bleeding  it won't  produce little bubbles.



: as stated Dot 4 is a good paint stripper. It stings like ***** if you get it in a cut( or in your eyes -don't ask)

it is flammable.


-Silicone is pretty inert stuff and  doesn't strip paint -even polishes quite  well.

Main hazard I found was that  if you spill it on floor it is very slippery.....

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If silicon is dot 5 and the earlier glycols dot 3 and 4, why is the latest glycol-based fluid called dot 5.1? What were they thinking? :lol:


Is it a marketing ploy? "There's a very cheat dot 5, I'll have that!" You get it home and discover your mistake but too embarrassed to tell anyone. Don't ask! :wub:  

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