Front brake drag

[LCarter69]

69 disc swapped, front driver side is holding pressure after brakes are applied causing engine bog and steering pull to the left. After a few seconds it lets go. Everything is new on the entire system. Hoses, calipers, M/C, prop valve, new lines. If you apply the brake, get out, and crack the bleeder it releases, if you press the plunger rod in on the prop valve (CPP PV2) it releases as well. Any ideas? Ive also checked for any pre-load on the M/C, wouldn't make much sense anyway due to only one wheel having issues.

[colnago]

First, did you do a bench bleed of the MC before installing it?

Second, when you bled the system, did you use one of those tools that prevent the shuttle inside the proportioning valve from moving? Here's one on the 'bay:

http://www.ebay.com/itm/Combination-and ... 9g&vxp=mtr

If not, does your dash warning light work? Did you notice it turning on and off during the brake bleeding (if you had the key on; not sure it would light with the key off)? It's possible you still have air in the system, and it's only affecting the left front because the right front is further away, has more air in the line, and is able to release.

I'm going through similar issues on my '67, so these are the things that come to mind.

Joseph

[LCarter69]

Yeah M/C was bench bled, I didn't use a tool like that for the warning switch. Brakes were great for awile, just recently I started noticing the drag, which leads me to believe something has failed. I'll re-bleed and give it another go. Thanks

[Nitekruizer]

Possibly a particle of dirt somewhere in the system or you could try temporarily removing the Residual Pressure Valves to allow all fluid back to the MC. It's a long shot, but ...

[LCarter69]

New proportion valve and M/C fixed the problem. I'm guessing it was the valve. I wanted a different M/C so I figured now was the time to do it. Brakes release nice now.

[JIMO2]

LCarter69 Just curious....the first master you had in there with the problem, was that a 4 drum brake master? The drum brake systems use a residual pressure valve located within the master cyl. It will hold a few psi all the time. When switching to disc, this is a problem on boat trailers from first hand experience. I have been wondering if it comes into play here as well. Thanks.