Brake Bleed Screws

[93centsp]

Hello,

I recently vacuum bled (Lisle vacuum bleed system) my non-ABS brake system of old fluid. During bleeding operation, air bubbles were present in the expelled fluid. Apparently, air is entering the old fluid by way of the bleed screw threads (the hydraulic system doesn't contain air). Does anyone know of a thread sealer that can be used on the screws? Or should I buy new thread seal coated bleed screws?

Thanks

[Prospeeder]

Well, some vehicles really dont like vacuum bleeing for that reason, manually bleed them and you will probably be fine. they say the air is drawn in from the wheel cylinder cups according to my shop manual.

[93centsp]

Interesting point about drum brake rubber seal cups.

My problem has been with the front disc brakes (which have the square type o-ring seals). When I use a check valve type bleeder with the brake pedal, fluid dribbles out through the bleeder screw threads.

So, in my case, the bleeder screw threads (which are clean with no corrosion) don't provide a tight seal.

The leaking occurs with the screw cracked open about an eighth of a turn.

[Prospeeder]

Maybe just try replacing the bleeders? I dont think any type of sealer tape will work, brake fluid is nasty stuff

[High Mileage]

Interesting point about drum brake rubber seal cups.

My problem has been with the front disc brakes (which have the square type o-ring seals). When I use a check valve type bleeder with the brake pedal, fluid dribbles out through the bleeder screw threads.

So, in my case, the bleeder screw threads (which are clean with no corrosion) don't provide a tight seal.

The leaking occurs with the screw cracked open about an eighth of a turn.


I believe the bleeders seal when tightened down on their tapered seat. The threads don't really do the sealing.

I'll be going by the garages I rent in a few hours. I'll take a look at one of my spare bleeders to confirm. But my guess is that is how they seal. The thread is not pipe thread.

[Prospeeder]

^ i think hes correct on that The picture of the caliper cutaway in my text books look like the bleeder seats down to seal.

[Pontiac6ksteawd]

High Milage is right. The threads have nothing to do with sealing of the caliper. The tip of the bleeder screw bottoms out, and prevents fluid from coming out. If that taper was bad, the bleeder would have fluid coming out alot more, and you would constantly be putting brake fluid in. Any open area in a brake system causes that, where you are always putting in more fluid.

So I have to ask, what makes you think there is something wrong with the system? Brake pedal soft? Loosing brake fluid? or???

[High Mileage]

High Milage is right. The threads have nothing to do with sealing of the caliper. The tip of the bleeder screw bottoms out, and prevents fluid from coming out. If that taper was bad, the bleeder would have fluid coming out alot more, and you would constantly be putting brake fluid in. Any open area in a brake system causes that, where you are always putting in more fluid.

So I have to ask, what makes you think there is something wrong with the system? Brake pedal soft? Loosing brake fluid? or???


Did I get something right,there Schteevie? ! Omg.... Arrrrrarrrgh.

Where's George from up in Wisconsin? Hey George!

[93centsp]

Thanks for the replys.....but

The problem is not when the bleed screw tightened against the caliper seat. The problem is during the bleeding operation with the screw slightly unseated...as stated in the first post.

I'll post a solution when I find one :)

[High Mileage]

When the bleeder's threads are not used as the clamping force to keep the bleeders tapered seat bottomed out tightly against the feed-hole on the wheel cyl or caliper,the bleeder will be loose. When the bleeder is loose, fluid is gonna leak from the threads.

I'd highly recommend either pressure bleeding or gravity bleeding.