Re: CAUTION ON THE USE OF SILICONE BKAKE FLUID IN ESAMATIC BRAKE SYSTEMS

Posted by BH On 2007/9/19 18:56:12

Peter -

When converting to DOT5, I've used alcohol (as well as aerosol brake cleaner) to flush out steel lines (that were otherwise in good condition), but never attempted to clean the rubber parts with alcohol.

My understanding is that DOT3 (or DOT4) will become impregnated in the rubber parts and those that are exposed to air will continue to draw water (due to the hygroscopic nature of glycol-based fluids) - even with the system otherwise full of silicone-based DOT5 (wich is essentially inert). As such, I simply replaced all the decades-old rubber parts.

However, in a much newer car, I did notice an incredible amount of swelling of the rubber diaphragm in the master cylnder cover of conventional dual-chambered master cylinder when I flushed it with aerosol brake cleaner from a DOT3 system. After removing it, the diaphragm returned to its normal hape after giving it sufficient time to ai dry. (Good thing I didn't introduce any of that cleaner into the reservoir.)

I'm no engineer, but my gut feeling is that you have experienced some sort of reaction between the DOT5 and whatever chemicals might have remained in the old rubber parts.