Brake goes straight to the floor

[1972_442]

Ive bleed these brakes for over 4 hours and every time the brake pedal still goes straight to the floor when the engine is running, the wheel cylinders, rubber brake lines, and master cylinder were all replaced and i bench bled the master cylinder but still have no breaks. could it be the booster? is it common to need to replace the metal lines? this is a very aggravating problem. i was going to do a disc brake conversion should i just go ahead and do that?

[kevinkpk]

Originally Posted by 1972_442

Ive bleed these brakes for over 4 hours and every time the brake pedal still goes straight to the floor when the engine is running, the wheel cylinders, rubber brake lines, and master cylinder were all replaced and i bench bled the master cylinder but still have no breaks. could it be the booster? is it common to need to replace the metal lines? this is a very aggravating problem. i was going to do a disc brake conversion should i just go ahead and do that?

If you have no external leaks, then you have an internal leak, check the vacuum booster.

[Dapapadon]

Or a bad master cyclinder.

[kevinkpk]

Originally Posted by Dapapadon

Or a bad master cyclinder.

yep, an internal leak, master cyl. could be bleeding through the front and rear.

[Modern Motoring]

if it's taking you 4 hrs to bleed brakes, I would recommend that you NOT go ahead and do a disc brake conversion. You think you're aggravated now? Holy Crikey! Call Booster Dewey in Portland Or. Tell him what is happening, dime to a donut it's the booster.

[1972_442]

yea i went ahead and got a new booster, i know i dont think its the master cylinder because its the second one ive put on the car. the white plastic sleeve on the back of the booster was cracked in some places would that affect the brakes. id have to order it from year one but i really dont want to wait a week just to put the new booster back on.

[ozoneblue]

When you bench bleed the master CYL. Do not push in over 1" that will cut the new seals to bleed system start with RR & let it gravity bleed -Drip for a while then LR RF &LF Keep a eye on your fluid level.

[crackie]

I had the mastercylinder and booster rebuilt and I bench bled it and put on car but couldn't get it to bled , I was told that when I pushed the plunger all the way down when I bench bled that it cut the seals is this true. Crackie

[Oldsguy]

yes, as ozoneblue posted just above....it is true.

[Kaline]

1972 442:

Did your new booster take care of the issue? I'm having a strange issue on my '64 Dynamic 88. The brake pedal was not returning and the fluid in my master cylinder was rusty, so I went ahead and installed a new master. However, when the engine is running the brake pedal drops to 1/2 its normal height and the engine nearly stalls when I hit the brakes (I have the car on jackstands). When I shut the car off, the brake pedal returns to its normal height after 10 seconds or so. I figure it is probably the booster. Any ideas?

[Kaline]

Update to my question (above): I installed the wrong master cylinder on my car. I have a Bendix brake booster and I installed a rebuilt Moraine master cylinder (which is what was on the car). That is why I was having issues, and why the previous owner had brake problems! Off the auto parts store I go, to order the proper master cylinder!

UPDATE 7/12/08: I installed the Bendix master cylinder, but I still have the same issue. Actually, the booster pulls the brake pedal down when the engine is running whether there is a master cylinder attached to the booster or not. Also, the brake pedal has a "catch" at about 1/2 travel, which does not feel super-safe. Is it safe to assume my brake booster needs rebuilt? Who do forum members recommend tp rebuild the booster?