Brake Fluid Replacement

[alanrichey]

Apologies if this has been covered before but I couldn't find anything in the last couple of years.

 

Have decided that after 8 years on the road it is time to replace the brake fluid in my Superspec. I assume that I can simply 'bleed' the brakes as normal, starting at the nearside rear (furthest from the reservoir) and continue until all the old fluid has been flushed out of each pipe and replaced by the new fluid.

 

So the question is: Roughly how much fluid should I expel from each wheel to ensure all the old fluid has been flushed ?

[nicko]

Can't answer your question, but my local garage tests the brake fluid every year to see if it needs changing.

Nick

[theduck]

I'd imagine the colour will be noticeably different.

[Big Jim]

Actually Alan you should start with the nearest wheel first, ie F/O/S, then F/N/S before going to the rears. With the rears, sometimes it's just one line and it goes "through" one side to get to the other, yours may be 2 separate lines, so either "shared" side first, or O/S first for twin lines. (Don't forget to have H/Brake on)

You need to empty the reservoir of old fluid before putting new stuff in, So start by bleeding enough out of both a front & rear wheel to just empty the reservoir (Most reservoirs have separate halves for front & rear) This is to stop old fluid mixing with the new stuff. Now fill up the reservoir with new fluid and bleed them in the order as above until the fluid coming out of each caliper etc. Is nice and clean, so obviously new stuff. job done.

[Guest mower man]

When it runs clean and clear at each nipple you are done mick

[emptyat]

I have an plastic syringe which I use to remove all the old fluid from the master cylinder before I bleed anything. I refill the master cylinder with fresh fluid and then bleed the brakes. Probably do get a little bit of mixing but this way I never let any air into the system so the bleeding is just getting the fresh fluid into the brake pipes.

 

Malcolm

[alanrichey]

I have an plastic syringe which I use to remove all the old fluid from the master cylinder before I bleed anything

 

I like that idea, thanks

[Guest peter2b2002]

I have always started on the furthest wheel then the next and so on do all till the fluid comes through clear on each wheel, keep your eye on the resivoir when the fluid is at the bottom start to fill with new fluid, after so many years you should see the fluid change colour after be careful when you use the brakes as they will be more effective as brake fluid adsorbes water, my garage advise to change every 2 years

peter-2b

[alanrichey]

So Peter says start with the furthest wheel (which I had originally thought) but Big Jim says start with the nearest wheel.

 

Who is right ? Anyone else with an opinion ?

[kevin the chicken]

I've always done it furthest wheel first. Doesn't mean it's right though, just what I was told. Never had any trouble getting a good pedal though.

[Guest Gargoil]

You're probably going to need at least a litre of fluid for the job, so anything larger than a litre bottle should be enough.

[alanrichey]

Done some more research and the 'generic' answer is definitely to start from the back. However, Jim is right in that the Sierra manual is different and states you should start at the front. Go figure

[Big Jim]

Think of the system as a large canal fed from a small lake with two distinct arteries and a couple of branches along each one. If you start at the last branch and drain that until clean water shows, it can still drag in dirty water from the branches further up, but if you start with the nearest branch to the lake, drain that until clean water shows, it can't drag anything from other branches because they are further away. So as you clear each one in turn, you're sure of getting fresh fluid to each branch.

This is the "better" way of doing the job, but whichever way you do it, you're certain of getting most of it out.

 

Clearing the master cylinder reservoir with a clean syphon tube is a great way to start, but make sure that you clear it from both front & rear feed areas. If you don't have a syphon tube, then you need to bleed fluid from both the front & rear of the vehicle until both sides of the reservoir have emptied before you put clean fluid into the reservoir.

[megadodo]

This is an interesting discussion, I like this sort of debate. My thoughts, I would agree with Big Jim that as much of the old fluid as possible is extracted from the reservoir ensuring both chambers are emptied. This will be quicker than bleeding out the whole mass of old fluid and probably reduce the risk of mixing old with new although the amount of mixing will be negligible if bled though to clear fluid anyway.

However, given there are 2 separate chambers, Big Jim, I would say it makes no difference at all whether the front was bled first or second!

As to which side you do first I have always done the longest path first but I don't know why. Thinking about now in this context, I'm not sure it matters. Again the chance of mixing more than the tiniest amount of old fluid with the the new at a junction is so insignificant to be ignored. If the system was completely empty then I would think that due to the compress-ability of air in the system then bleeding the longest path first would give a slight advantage, but only just. Just to further complicate the issue, as I vacuum bleed would increase the risk of mixing and if so would that be significant enough to worry about?