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Posted by: EJP914 Apr 18 2021, 06:06 PM

I am trying to flush out the rest of the silicone fluid installed by previous owner from my brake system with alcohol using one of those pressure bleeder tanks. Have 3 of the lines closed off with old brake lines crimped shut while working on the one open. I am not running the old silicone fluid thru the new calipers. Pump line is attached to brake fluid reservoir. I can pump the tank up to 10 lbs or a bit more and get alcohol running thru the two front lines.
I cant get anything out of the rear lines. Not enough pressure at 10 lbs?
Is there something in the brake system that would have closed off fluid flow to the rear brakes.
Don't know where to go from here. Would appreciate any suggestions. Thanks.
Ed

Posted by: iankarr Apr 18 2021, 11:25 PM

I hate to say it, but if it were me, I'd replace all of the lines and rebuild the calipers. There's just no way to tell if 100% of that stuff is out of the system...and you don't want anythinig clogging your brake system up. Or you could just continue using silicone fluid. Why are you switching?

As to why you're not getting anything to come out of the rear, I suspect the pressure regulator is gummed up from the mix of fluids.

Posted by: GeorgeRud Apr 19 2021, 08:09 AM

Do they gel up if mixed? Though I’ve long heard about incompatibility, I never heard exactly what happens.

Posted by: iankarr Apr 19 2021, 08:14 AM

Unfortunately yep.

Posted by: rbzymek Apr 19 2021, 08:25 AM

Unfortunately there is no solvent for silicone oil.

Posted by: EJP914 Apr 19 2021, 08:40 AM

I have not added any DOT 3 or 4 into the system. The new calipers have not yet been installed. I didn't want to contaminate them with the old fluid silicone fluid.
I am trying to remove remaining silicone from the brake lines.

Ian, I have read and it seems to be a consensus that silicone fluid is tough to bleed and gives you a spongy brake pedal. That's why is was going back to DOT 4. IF you can tell me, where is the pressure regulator located that you mentioned? Thanks.

Ed

Posted by: EJP914 Apr 19 2021, 01:41 PM

Been doing some reading on this. Seems brake pressure regulator / proportioning valve may be stuck not allowing fluid to the rear. How do you unstick it or is it a remove from car and send to PMB for rebuild?

Posted by: bbrock Apr 19 2021, 01:50 PM

PMB also sells a DIY rebuild kit if that's more your style. The actual rebuild isn't very difficult but of course, if you send it in, it will come back looking like brand new.

Posted by: Stark 01 Apr 19 2021, 02:41 PM

Not sure why you are not getting fluid in back, but next time you use the pressure bleeder, pump it to 15-17.

Posted by: Johny Blackstain Apr 19 2021, 02:55 PM

I've found that silicone is best for garage queens, not so much for daily drivers and not on track cars. If the car is going to sit a lot then silicone is by far the best way to go. Nothing rusts anywhere in the system and everything stays lubed. I've heard it has a tendency to fade at high temps which is why I don't recommend it for track use.
Switching from one to the other requires lots of disassembly, cleaning and line blasting with high pressure air and it takes time, but can be done.
Eric did my brakes on the LE 13 years ago and they still work great and have had silicone in them since the rebuild... no problems.

Posted by: Racer Apr 20 2021, 10:01 AM

FWIW, when I swapped out silicone for DOT4, I also replaced the mastercylinder. If you remove the calipers you can blow them out as well. Ideally, rebuilding calipers is best too.

You can keep flushing.. drive.. flush.. drive again repeatedly to keep getting out traces of the silicone fluid left behind.

Posted by: IronHillRestorations Apr 20 2021, 08:56 PM

I wouldn't use alcohol in your brake system, it'll cause more problems than it will solve.

I've used silicone brake fluid, and it's fine for a street car, like Johnny said.

If you wanted to bleed it all out, I'd use a pressure bleeder and 2 or 3 quarts of DOT3 or 4. You should be able to push it out of the system.

Posted by: mb911 Apr 21 2021, 10:56 AM

Never even knew there was a difference..what brand is silicone brake fluid? Guess I never even looked

Posted by: Racer Apr 21 2021, 12:53 PM

DOT5 is silicone.. Don't confuse with DOT5.1, as that is NOT silicone. DOT 3 and 4 are mainstream brake fluid (not silicone).

It was the darling of those who never drove their cars since its shelf life is longer. It was designed /used for applications where moisture is an issue since it does not absorb moisture. Regular brake fluid absorbs moisture which degrades its performance over time.

Posted by: mb911 Apr 21 2021, 05:22 PM

Gotcha never used that ever in my life so all good.

Posted by: iankarr Apr 21 2021, 10:26 PM

As I understand it, you can't / shouldn't rebuild the pressure regulator on your own. They're set to exacting specs and I'd let the pros at PMB do that rebuild. As to the rest, if you don't want to run silicone (DOT 5) and your calipers are still virgin, I'd replace all the lines. Really not too difficult a job. Can be done in half a day. You also get the benefit of knowing everything in your system is fresh. PMB has the OEM green type, and stainless steel options. If you re-use the elbows, couplers and banjo bolts, make sure those are thoroghly cleaned in alcohol or some other solvent that dissolves the sillycone.

Posted by: bbrock Apr 21 2021, 11:01 PM

Eric sells the kits to rebuild and is generous with advice. The device is actually quite simple and the rebuild is easy, although I replated and repainted all my parts to refurbished to like new. The clean up is 90% of the job. When it came time to adjust, I asked Eric about sending it to him for adjustment and he told me if I didn't have a hydraulic pump and gauge, just adjust it so 10mm of the adjusting screw protrudes from the spring housing.

There's a thread about it here: http://www.914world.com/bbs2/index.php?showtopic=336046

and some before and after pics of mine: