Brake line resitricion

[geunther]

Short: Should the rear flexible drop down line with T block offer any restriction?

Long: I know any designed in restriction should be handled by the proportioning valve. I flushed out my rear lines starting at the proportioning valve (pv). When I had the butt connection inside the frame rail (near the rear axle) disconnected, air would blow freely from the pv to the junction. When I had the butt connection connected, there was some back pressure when blowing in at the pv. Wheel lines were disconnected so any change in restriction would have been from the drop down line, or the line between the drop down line and the butt connection.

I wold still get flow at the T block (wheel lines disconnected). The flow seemed to be restricted either within the flexible line or due to the size of the T block orifices. Im just not sure if this is normal or air should flow freely from the pv all the way to the wheel cylinders.

[Keith Seymore]

Originally Posted by geunther

Short: Should the rear flexible drop down line with T block offer any restriction?

No. Air (and fluid) should flow freely.

It is common for brake hoses to deteriorate and the inside lining detach, causing a restriction, even if they look ok from the outside.

That may be what has happened here, or maybe one of the hard points is restricted by debris.

K

[geunther]

Thank you. Are factory (or similar) replacements available?

[67 chevelle]

Got mine at rockauto

[100%Chevy]

Also,if one is bad,the other 2 aren't far behind!
Cheap insurance to replace them all at once.
Mike.

[RichardJ]

>> any designed in restriction should be handled by the proportioning valve.<<

A brake system is designed to transfer Pressure from the MC to the wheel cylinders. The proportioning valve reduces pressure, not flow. Pressure is measured in PSI. Flow is measured in GPM. Very little fluid is transferred when the brakes are applied.

Check the flex line by itself.

Blowing air through the line only and then adding the flex, "T" and axle lines has a cumulative flow restriction.

Depends on the type of compressor used or the air is very well filter, make sure your flush isn't getting any oil added to it. Flushing the old brake fluid with new fluid is all that is needed.

[geunther]

Originally Posted by 100%Chevy

Also,if one is bad,the other 2 aren't far behind!
Mike.

I assume you mean the front two?

A little history. Truck is bone stock. Since I've owned it the brakes have been iffy. So I thought I would bleed the brakes as a start. The rear chamber of MC was bone dry. That was just an indication of the problem.

Fluid was coming out of the MC into the booster. MC beyond repair because it had dried out and rust had set into the piston area. Wheel cylinders were fairly dry too, and rust had set in. They were rebuildable but went with new.

Replaced MC. Cleaned out booster. Flushed lines. Air was fairly dry but I am sure I introduced some moisture. Hoping to flush all that out.

I found a new flex line locally. Will install that tonight and see how it goes.

[geunther]

Just for close out and thanks. The flexible line was mostly clogged. It allowed some passage but not much. As soon as I replaced it, fluid gravity fed all the way to the wheel cylinders. Haven't driven yet, but after a bleed the pedal feels great.

Thanks.