Robert G. Smits Posted July 30, 2012 Share Posted July 30, 2012 Just broke a front brake hose on my 68. Although it has a dual master cylinder I had no rear brakes. In addition to new hoses all around do I need a new master cylinder? Thanks, Bob Smits Link to comment Share on other sites More sharing options...
Guest Commodore Posted July 30, 2012 Share Posted July 30, 2012 This guy claims that dual master cylinders give false sense of security. See link.Dual Master Cylinders - False Sense of SecuritySee this link for how a dual master cylinder works.Figure 7-5.Dual master cylinder. Link to comment Share on other sites More sharing options...
NTX5467 Posted July 30, 2012 Share Posted July 30, 2012 To me, it sounds like you should have noticed a decrease in brake performance with just the front brakes apparently being all that worked. IF you have front disc brakes, the proportioning valve would be what ultimately puts fluid to the rear brakes. IF you have front drum brakes, what looks like a proportioning valve is just a fluid "divider block" which also houses the fluid-bias switch which turns on the warning light if one brake section looses fluid.BE SURE to check the rear brake flex line for internal "issues"! In many cases, they have been known to internally separate and effectively make an internal one-way fluid "valve" which restricts or inhibits brake fluid flow.BEFORE you start spending money and possibly "chunking parts" at the car, troubleshoot the situation. To do this, you can get some short pieces of brake line tubing and cut and shape them to return fluid to the master cylinder reservoirs . . . also can be used to bleed the master cylinder before hooking the vehicle's brake lines back up to the cylinder. Check that both sections of the existing cylinder move fluid in response to brake pedal input. Once this is established, then replace BOTH front brake lines on the vehicle, then bleed the front brakes. With the front brakes taken care of, then replace the rear flex line at the rear axle. Bleed the rear brakes. Recheck for proper brake performance and action.Also, given the age of the vehicle, using the bleeding method which also flushes clean fluid through the system might be the best way to do it. This can possibly be accomplished with one of the hand pump vacuum bleeders, attaching the vacuum side line to the bleed screw on the rear wheel cylinder. The "classic" method is by pumping the brake pedal while openning and closing that same bleeder screw. Just don't let the master cylinder become empty or "dry" in these bleeding processes!Just some thoughts,NTX5467 Link to comment Share on other sites More sharing options...
Robert G. Smits Posted July 30, 2012 Author Share Posted July 30, 2012 Thank you for the replies. The car has front drums and has only been driven a couple hundred miles since purchase. My wife has complained about the poor brakes since day one and I was actually on a test run after flushing and bleeding the system when the line broke. Since it appears that the rear brakes were not working properly I suspect my wife was correct. Bob Smits Link to comment Share on other sites More sharing options...
NTX5467 Posted July 31, 2012 Share Posted July 31, 2012 Thanks for the update. Might just be the need for correct adjustment? Several years ago, I bought an inside-outside caliper for adjusting drum brake linings with the drums off. Works pretty slick! Beats the old "spoon and screwdriver" action!Take care,NTX5467 Link to comment Share on other sites More sharing options...
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