What brake fluid to use?

[EJP914]

I recently purchased a '73 914 FI 1.7 with what appears to be a true 11,400 miles. The car had been sitting for approx. 20 years. It does now run again.
I have put new calipers and soft brake lines on the car.
In a log book kept by the previous owner from day one, he notes on 10/27/84 at 10,918 miles he put in silicone brake fluid.

My plan is to draw it all out of the system as best I can with the Mighty Mite pistol grip bleeder that I have. Question is how much of it will remain?

What's the downside of putting silicone (DOT5?) fluid back in the system? I've read you will get a spongy brake pedal and system is hard to bleed.

Should I be concerned at all about putting regular DOT 3 or 4 in given it had silicone put in 30 some years ago.

Don't want to make a mistake and put the wrong stuff into new calipers.

OR am I worried about nothing as to what fluid to use. Thanks for the advice.

EJP914

[Dave at Pelican Parts]

It seems to be the consensus that you really do not want to mix glycol-based fluid with silicone-based fluid. I would think that just evacuating the system with a hand-pump will still leave a fair amount in, so you would (at a minimum) want to flush it all with ... something?

Silicone fluid has a number of problems, including that it doesn't absorb water. So any water that gets in will tend to sit in one place and start corroding any steel or iron it is in contact with. You can also get stuff growing in that water, which doesn't bear thinking about. And that's in addition to generally giving a more spongey pedal feel than traditional glycol-based fluid.

I'd give Eric Shea at PMB Performance a call. He really really knows brakes, and he should be able to steer you in the correct direction about getting the silicone out.

--DD