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MG MGB Technical - Replacing brake fluid

Hi,

I realised the other day that the brake fluid in my B is probably a "few" years past its prime and I should really replace it. Everything works fine at the moment with no air in the system and I'd like to keep it that way! I've read the archives but I'm still not 100% clear on what the best process is for replacing the fluid - most references are just to bleeding air out of the existing fluid. The car is a Mk1 GT, so it has no servo and is single circuit. I've never bled brakes before but am reasonably competent mechanically (famous last words...).

My plan was to use a gunson's Eezibleed to do this as I can't imagine my wife will be overjoyed at the prospect of being my helper. A few questions:

1 - Will I be able to visually see when there is fresh, new fluid coming out of the bleed nipples rather than old stuff? Is it a different colour?
2 - Should I remove any of the old fluid from the resevoir before starting or just flush the whole lot through?
3 - Roughly how long should it take from start to finish? Roughly how long will I be sat waiting for fresh fluid to appear from each brake? If I see fresh fluid coming from each brake can I assume the whole system is clear and can stop?
4 - I assume it's normal mineral (non-silicone) fluid in there. I've read all the horror stories about switching to silicone so I plan to use normal fluid again. What spec should I use (normal road car)?
5 - How much new fluid will I need for a complete change?
6 - Any comments on the Eezibleed? I've seen references to it leaking fluid all over the place (eek!), anything to watch for? Is there anything better for not too much money?

Any other snippets of info obviously welcome! Many thanks in advance.

Tim
T Jenner

http://www.demon-tweeks.co.uk/products/ProductDetail.asp?cls=MCYCLE&pcode=GDRBN704SB

Thess make life so easy:)
K Harris

Shows how they work..

http://www.speedbleeder.com/
K Harris

Remove as much as you can of the old fluid first. Otherwise it will dilute the new stuff more than necessary.
Art Pearse

If you siphon out the old fluid and refill the master cylinder with fresh fluid, the bleeding process should take about half an hour with an EZ bleed unit. You should start seeing clear fluid coming out of the bleeders in less than a minute per wheel. Castrol LMA DOT4 is the fluid most often recommended for MGs. RAY
rjm RAY

Not to start brake fluid wars again, but we just had a good tech session on fluids. According to the person doing the seminar (MG shop owner that also races), The new synthetic DOT 3's do not appear to cause the damage to paint.
Bruce-C

Thanks, all. From what I can gather from the archives it's US spec DOT 3 fluid which causes (caused??) problems? In any case it seems quite hard to find DOT 3 in the UK so I'll be going for DOT 4 mineral.

The speed bleeders look great - but it does end up costing a few £££ especially as an Eezibleed could be used on several vehicles.

Any thoughts on the amount of fluid I'll need for a complete change? I'm guessing a 1 litre bottle should do (plus maybe buy some extra just in case)?

Thanks,
Tim
T Jenner

One litre should be adequate for the job. With the EZ bleed there is very little wasted fluid. RAY '67 Tourer
rjm RAY

There is no point pumping out the old fluid first, that just means you have to bleed everything! Replacing fluid is very easy using a Gunsons, you don't need the expense of Speedbleeders which are as they indicate for bleeding, and it is usually obvious when the fresh fluid is coming through. Start at the longest run, which is the left rear for a single circuit (you don't say the year) and work towards the shortest i.e. right front. A Gunsons is actually easier on a twin circuit system than pedal bleeding as you don't upset the balance switch and neither does the 'other' circuit stop the pedal going down.
Paul Hunt

Thanks for the help, all. Completed the job this afternoon surprisingly easily using the Eezibleed and less than 1 litre of fluid. Old stuff was pretty manky and the pedal is remarkably firm now!

Thanks,
Tim
T Jenner

Hi Tim - curiously enough, I did the brakes on my 'A' today. I've always found the eazibleed easy to use - the only real point to note is when they tell you "no more than 20psi in the tyre" (that you're presurising with) - they mean it! (otherwise it leaks everywhere).
Regards
Andy
A S Duff

In the first thread, Tim wrote that his brake fluid was a few years past its prime.

How long should the brake fluid last and how often should you change it?

Robert

1973 MGB
Robert Browning

Most things I've read say that mineral brake fluid should be exchanged every 2-3 years. Silicon fluid apparently lasts indefinitely.
Mike Howlett

The workshop manual says 18 months but general consensus is as Mike says - 2-3 years. Most modern cars are the same - 2 years. On that basis I figured that as I'd had the car 10 years and the fluid wasn't new when I bought it it was probably about time...! Now I know it's a straightforward job I'll be doing it every 3 years or so.

Cheers,
Tim
T Jenner

Apart from the actual braking efficiency considerations, brake fluid is hydroscopic - it absorbs water. Not only does this have an impact on your braking it also eventually ruins the seals
Regards
A
A S Duff

The ruination of the seals is actually a by-product of the rusting of the bores, which is why seal replacement is usually not worth the time and effort. But whether this is caused by water in the fluid or external dampness is debateable as the fluid is only in contact with the part of the bore the seals slide along momentarily, external dampness can be in there all the rest of the time. If the E-clips were easier to deal with it would be even easier to replace the slave as a unit.
Paul Hunt

This thread was discussed between 15/09/2009 and 22/09/2009

MG MGB Technical index

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