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Changing Brake Fluid


geoffbeaumont
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There seem to be two schools of thought on changing brake fluid:

  • drain the system down then refill and bleed it
    • advantage: much less risk of getting water in the new fluid
    • disadvantage: more risk of leaving air in the system

    [*]flush the old fluid out with new fluid

    • advantage: less risk of getting air in the system
    • disadvantage: some cross contamination from the old fluid

Opinions? What do you do?

In this case I'm changing the brake fluid on a classic Range Rover with ABS, and the old fluid is well past it (shamefully I have to admit that it probably hasn't been changed since I've had the truck - certainly since I've been servicing it - and I've no idea how old it is :blush: ).

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I bleed a corner until the reservoir is quite low, then top up and bleed it through until it runs clean, topping up the fluid as required. This lowers the amount of cross contaminated fluid. I err on the side of caution and bleed through quite a lot, then a bit more. I don't really see it as a waste.

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If you drain down, there's a chance you could get problems with trapped air. I use an old syringe to empty the master, or remove the reservoir and flush it out (this is where the majority of black gunk collects), then flush through with new fluid until all 4 corners are done. A litre of DOT 4 is only a fiver, so not a great deal of money. If you have an eezi-bleed kit, then doing this is very easy and quick.

Les.

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yep, just flush it through with new fluid, start at the furthest caliper from the master cylinder and work back....

I wouldn't drain it down...

but then I always just remove the caliper when i change wheel bearings, so my fluid is never that old...

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The recommendation is about every 2 years - but I suspect most people change it less often.

Doing this to my RR recently unleashed a lot more stoppingness - made me wonder if I'd just drained factory (1990) brake fluid. :o

Edited to add this tip: Use a pound shop turkey baster to drain the master cylinder, but mind the drips!

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At work we have a device that tests the boiling point of brake fluid....made by Sykes Pickavant. We use it on all annual services and change any brake fluid that boils under 200C. DOT 4 minimum boiling point is 180C.

Anyone of these would do. Ours is similar to the bottom one.

Also worth noteing that it is wise to have the ignition switched on with an ABS system so that the ABS pump is running if you are changing fluid with a pressure bleeding system of any kind.

HTH

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Also worth noteing that it is wise to have the ignition switched on with an ABS system so that the ABS pump is running if you are changing fluid with a pressure bleeding system of any kind.

The procedure in the Haynes manual does the calipers first without the pump, then the pump (from this point on you're using the pump), the accumulator, the valve block, then the front caliper hydrostatic circuit again with the pump. Seems to have done the trick, but it's definitely a two man job - there's some bits were you have to have the pedal already down before you open the bleed valve, and so on. I'd also not like to do this job without a pressure bleeder, if only because you'd need a third person continuously topping the resevoir! Some steps would have emptied it in one go without any trouble :blink:

I now have nice sharp brakes again :)

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Les has the best way, or at least that is what I do at the workshop a couple of times a week. Most vehicles (especially those serviced by LR agents) have never had their brake fluid changed. The reservoir becomes full of black gunk. So, syringe out the old brake fluid and keep it (see below). Then remove the reservoir. Put sand and small stones in the reservoir along with a bit of detergent and water. Then pretend you are a maracca player for a few minutes. Then clean all the sand and stuff out of the reservoir. It should now be perfectly clean. Blow out with air, or put in the sun to dry (this is South Africa, so the sun does shine). Put rubber oil or grease on the connnections and push the reservoir home. Fill up with new fluid and bleed the brakes.

The old brake fluid makes magnificent paint brush cleaner or even removes paint from wheels, panels etc. You just have to be patient :)

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At work we have a device that tests the boiling point of brake fluid....made by Sykes Pickavant. We use it on all annual services and change any brake fluid that boils under 200C. DOT 4 minimum boiling point is 180C.

I have to admit to a mistake here. We change fliud under 180C. DOT 4 minimum is 155C.....180 is for DOT 5.

As for pressure bleeders, an Ezibleed is a great tool.

I only warned about ABS pumps becuase they are easy to destroy on some cars with incorrect bleeding.......VW Golfs are a prime candidate.

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