Automec DOT 5
Hi, after some critical issues using silicone brake fluid on my Gulia spider I have detected that one brand don’t suite my setup. This is my observation and I don’t claim you will have the same issue that I do.
During my restoration project 2009/2010 I bought a re-sleeved BMC (bore 3/4”) as alphil describe and bought all new seals for the brake master cylinder, rear wheel brake cylinders and front calipers. All seals new of high quality brand via AlfaStop UK, assume original Girling.
During the restoration project I was reading about brake fluid on several InterWEB forums including AlfaBB and found several topics regards to silicone brake fluid, some
negative some
positive and I made a decision to go for a test as the car will be driven only a few month during the year and the rest parked in a garage. I was excited to go for Atomec DOT 5 and everything was evolving positive. Bleeding the BMC and brakes was no different than for any other fluid.
In absence of reference to characteristics regards to brake pedal pressure etc. I assume everything was fairly ok and that some “sponginess” was to be expected. Even better the Automec DOT 5 fluid was purple, who can say no to that color!
After a test run I couldn’t feel any problem with the setup and behavior during braking and was happy about my chose to go for DOT 5 (Automec). The Pedal felt firm and solid during pressure and brakes was awesome.
Last summer I was on a road trip on a hot summer day and suddenly lost pedal pressure! The braking pedal vent all the way to the floor. First thought was that the BMC heating shield, protecting BMC from exhaust pipes, had dropped off. After a quick visual inspection checked out OK and intact why I parked the car for 1H to cool down as I expected that I had some overheating issues regards to BMC anyway. Didn’t get any better and “linked home” carefully.
The next day I checked the brakes again a got back some of the firmness in the brake pedal but removed the BMC anyway to check. I found out that both BMC seals was expanded and didn’t understand why as I was using silicone fluid, it shouldn’t happen! Silicone should be the best a car can get.
Did a bench bleeding test on the BMC and got nothing out from it. Ordered a new seal kit for the BMC this time from OKP to hopefully get another brand, just for test. Installed both new seals and the BMC went back to life again.
The BMC has not been in use (exposed for fluid) for that long time as this was back in June this year. This weekend I decided to check the rest of the wheel cylinders and calipers and found that all of them are expanded too. They worked barely and if they stay as-is I will most likely get problems.
So what to learn about this then.:detective: My conclusion is that some seals, at least the ones I bought, don’t cooperate with Automec DOT 5 brake fluid and will expand during a year or two and loss of brakes as result. From a personal perspective I strongly recommend to use DOT 4 and from a well-known brand i.e. ATE or Castrol. I personally will go for the ATE racing blue DOT 4 and next time exchanging fluid use Motul RBF 600. The main reason is to see when new fluid gets out of the benders. Both of them has fairly high wet boiling point which is good and for Giulietta and Giulia spiders the BMC is somewhat exposed for heat from the exhaust down pipe.
Finally, this is my personal observation based on the selection of products I have made, nothing else.