Gray "sludge" in brake reservoir

[John_Mc]

Gray "sludge" in brake reservoir

I know this has been talked about before, but here it is again. I had the booster and master cylinder off for booster repairs. I'm ready to put it back together again, but when I removed the brake master cylinder I noticed a moderate amount of the blackish/gray sludge settled in it. I assume a certain amount of this is normal over time, but how much is not okay? Without rebuilding the whole system, is there anything I should do before reinstalling things? I know I've heard someone say they flushed their system with alcohol before putting new fluid in, but would that be indicated if I'm only refilling? TIA.

 

[Brosky]

Re: Gray "sludge" in brake reservoir

John, it's probably getting close to overhaul time soon. These systems won't last forever without the seals starting to deteriorate.

You could try a complete flush bleeding with new fluid, which would probably help for a while, but you may be getting that same build up in the lines, which decreases the overall efficiency of the system.

 

[SkinnedKnuckles]

Re: Gray "sludge" in brake reservoir

Yep - that dark mess of rubbery degradation can be a fact of life. I wouldn't go the alcohol flush route. It's a solvent with properties unlike either glycol ethers (DOT 3 or 4) or silicone (DOT 5), and I see nothing good with it with regards to seals. You can do a fresh flush with the fluid you're using, or blow compressed air through lines if you want to clear things out. Just my opinion.

 

[John_Mc]

Re: Gray "sludge" in brake reservoir

Thanks for the replies. I'll try the brake fluid flush then. I'm wondering what the frequency of overhauling should be, since very little of the system is OLD old. I replaced the rubber in the rear cylinders about 3 years ago, the master cylinder completely replaced about 4 years ago as well as the caliper pistons and dust boots. The PDWA has never been overhauled in the almost 8 years I've owned the car as well as the flexible brake lines. What's overdue?

 

[TR3driver]

Re: Gray "sludge" in brake reservoir

What kind of brake fluid are you using? The only time I've seen that much sludge was when the brake fluid was not compatible with the seals, and was slowly attacking them. Used to be that American brake fluid was not compatible with British brake seals, but I've not heard of that happening for many years.

Also note that DOT 3/4 fluid should be changed every few years, whether the car is driven or not. The fluid keeps OK while in a sealed can, but basically starts to deteriorate as soon as the can is opened. Which is why you are also supposed to start with a freshly opened can, and discard the leftovers afterwards.

I was told, long ago, that if you want to flush, use only methanol (aka methyl alcohol, aka wood alcohol) and dry the lines thoroughly afterwards. I did that when I converted the 3A to DOT 5, and it seemed to work out OK. But the only place I could find methanol was the local drug store, and then only after asking the pharmacist for it and explaining why I wanted it. It being both poisonous and easily mistakable for either drinking or rubbing alcohol; they don't like to sell to just anyone.