Brake fluid leaking around bleed screw threads when screw loosened
 

I was recently using my Power Bleeder to flush the braking system on our '85 300CD-T (123.153) and got to wondering:

Is it typical and the-way-things-are-supposed-to-be that upon loosening a brake bleed screw, that fluid leaks from around the screw threads?

I am loosening the screw just a bit - enough to get a small stream that puts out 8 oz. of fluid in like, say, 2-3 minutes. Hardly loose at all.

This leaking from around the threads happens on the ATE calipers in the rear and the Bendix (ack!) calipers in the front.

Anyone have any insight on whether this leaking is right or not and if not, what to do about it?

Thanks-

It might not be "right" in theory, but it is quite common in practice.

Hmmm. I believe when I was bleeding my brakes I got some fluid coming out through the threads and did not think anything of it. It makes sense to me that some fluid would come through as there is a gap once you loosen the bleeder screw. I wiped everything off as I moved from wheel to wheel.

If you are concerned, take another look after you have bled all four wheels and see if there is any fluid after you press on the brake pedal real hard, and after you have wiped everything down with brake cleaner.

The threads don't form the seal, even when tight. The seal when you tighten the valve occurs at the conical tip of the screw against the hole in the caliper or cylinder.
I've wrapped Teflon tape around the threads of bleeder screws which helps keep them from leaking, but I've done this mainly to prevent them from seizing up from rust after a few years of sitting around. And no, it doesn't make them come loose on their own.

Thanks for the responses to my question. Sounds like some leaking is to be expected given the design of the screw and caliper. I just think that brake fluid is nasty stuff and don't much care for getting it anywhere it doesn't have to be. I appreciate the help.