Changing Fulvia Brake Fluid

[Tim Ray]

About to change the brake fluid  on my Series 2 and have a couple of questions.
I am told Dot 4 is suitable for my application, which is normal road use, with a few mountain passes thrown in. I read somewhere it is vital to change the fluid every 2 years. Is this still the case if you use Dot 5.1.?
I understand it is better to raise the rear of the car when bleeding the brakes. How high please?
Many Thanks
Tim

[Richard Fridd]

It is important to have the rear brake bias valve in the open position, which means supporting the rear axle, rather than using the sill mounted jacking points. Richard

[lancialulu]

As Richard said raise the back by jacking and supporting the axle.

Fluid can take a long time to get through so I rig up a way of slighlty presurising the master cylinder (c2-5psi). As the master cylinder leaks air through the electrical terminals you will get a bit of a loss but do not over presurise or you will burst the master cylinder. I set the regulator of my air compressor to 5 psi. Also you need to ensure that the master cylinder always has fluid in it as you will find air will get into your refresh.

Dot 4 is vaguely hydroscopic and Dot 5 (silicone - dont use unless you are rebuilding the brake system) is not. I am not sure about Dot 5.1. Being Hydroscopic Dot 4 will take on water and this could allow the brake calipers could boil earlier. My Merc is maintained by a guy who tests the brake fluid (Dot4) and in 6 years he has not changed the fluid.

 Boiling point ranges (from Wiki)
Dry boiling point   Wet boiling point
DOT 3   205 °C (401 °F)   140 °C (284 °F)
DOT 4   230 °C (446 °F)   155 °C (311 °F)
DOT 5   260 °C (500 °F)   180 °C (356 °F)
DOT 5.1   260 °C (500 °F)   180 °C (356 °F)

I boiled my Dot 5 fluid on the descent of the Stelvio (the flowing west side) in a fully laden Fulvia Sport so I have also refreshed the fluid (6 years old at the time), and found nothing like any water present.... The brakes returned to normal after 15 minutes of cooling down - assuming the boiling vapour is reabsorbed?

Tim H

[Tim Ray]

Many thanks Tim and Richard for your response. Much appreciated.
Regards
Tim

[fay66]

I recently put "Fay" in for a checkover in preperation for the Knights Rally in September, I specifically asked that the brake fluid be checked with the view of changing it if necessary, It was reported as being ok with no problems, last time fluid was changed was before going to Turin in 2006.


Brian
8227

[nistri]

Why does old brake fluid become very dark? Andrea

[lancialulu]

Oxydation process?? I assume you are referring to Dot 3 or 4??

Silicone is a light purple that fades a bit over time to clear.

Tim

[nistri]

Yes, I refer to Dot 3 or 4. Oxidation and moisture probably. Perhaps not enough to give fluid boiling and lack of pressure but enough to produce corrosion of the cylinder bores. BTW, I was checking over my Fulvia Montecarlo yesterday prior to an alpine event and noted that my battery is now 12.5 year old. Charge with engine off is OK. Not bad performance for a small alternator. Andrea

[DavidLaver]

As it happens I just dropped a car in for a list of bits and bobs including a brake fluid change.  BMW have it down as a change every other year.

David

[fay66]

Most manufacturers have always recommend changing every two years, but I always have the fluid checked as I can't ever remembering finding it necessary to change as recommended.
I'm all for safety and checking, but IMHO it's just another one of those service items that are there to add to the profits.

Brian
8227

[lancialulu]

Most manufacturers have always recommend changing every two years, but I always have the fluid checked as I can't ever remembering finding it necessary to change as recommended.
I'm all for safety and checking, but IMHO it's just another one of those service items that are there to add to the profits.

Brian
8227

Hear hear!!!

[DavidLaver]

Brian - What check do they do?

David

[lancialulu]

My merc guy says he measure SG (hydrometer)...

[chriswgawne]

As a rule I tend to change the brake fluid in our cars roughly every 4/5 years or so - primarily because the fluid has darkened. To me, a darker fluid = contamination = shortened seal life and corroded wheel cylinders. I have never had brake fluid which has boiled.
On my race car, I change the fluid every 2 years because the front brakes do get very very hot and it is part of my regular pre-season checklist.
I have never used silicone fluid by the way as someone told me once that changing from Dot 4 to silicone would result in problems with seals although the change could be made the other way without any problems. Is this true?
Chris

[fay66]

Brian - What check do they do?

David

I know David Thomas has the equipment to check the water content but my daughter had hers checked recently and they used a refractometer, I know when I volunteered at at Vineyard we used this for determining the sugar content of the grape to check when to pick them, no doubt Simon might know a bit more about it's uses.
See
http://www.amazon.co.uk/Brake-Refractometer-DOT4---motor-vehicle/dp/B00965Y8SK/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1372788380&sr=1-1-catcorr&keywords=refractometer+for+brake+fluid

Brian
8227