Rear brake drag...new system

[Michael G.]

Good day all.

Did the inital road test on my '66 this weekend. New brake system installed with new lip seal calipers, refurbed original master cylinder (both redone by Lone Star Caliper) and new brake booster from CSSB. System was installed around 9 months ago and bleed down to a solid pedal. Now....back to the road test. Drove about 8 miles and upon return noticed the smell of brake pads with rear calipers very hot. Front calipers show to have no issue, just warm to the touch.

Any thoughts as to why the rear calipers appear to be mildly engaging w/o the brake pedal applied.

[Richard M.]

Re: Rear brake drag...new system

Park brake?

[Michael G.]

Re: Rear brake drag...new system

Park brake?

Park not engaged....check that. Thanks.

[Richard M.]

Re: Rear brake drag...new system

Hmmmmm......Strange problem.....

You didn't mention changing the brake hoses......The rubber hoses in the rear may have a blockage, allowing fluid under pressure to be applied properly, but not allowing fluid to return.

I'm not familiar with the '66 master cylinder......Is there a check valve of some sort in it?

Rich

[Chuck S.]

Re: Rear brake drag...new system

Check for actual tension in the brake cable and adjust per the CSM if needed. I would probably adjust to put obvious slack in the cable, with park brake mechanisms at the wheels are moving freely, until this problem is actually diagnosed.

Otherwise, since only the two rear wheels are affected, it sounds like something is preventing hydraulic pressure from being released freely back into the system after pedal application...an obstruction in the line, tubing crimp, etc.

The other possibility that comes to mind is both rear calipers have some sort of rebuild defect/error, but that is less likely to happen on both rear calipers. On a later car, I might suspect a problem with the distribution valve, but it seems to me your car is too early for separate front/rear brake systems?

[Wayne W.]

Re: Rear brake drag...new system

Otherwise, since only the two rear wheels are affected, it sounds like something is preventing hydraulic pressure from being released freely back into the system after pedal application...an obstruction in the line, tubing crimp, etc.

The other possibility that comes to mind is both rear calipers have some sort of rebuild defect/error, but that is less likely to happen on both rear calipers. On a later car, I might suspect a problem with the distribution valve, but it seems to me your car is too early for separate front/rear brake systems?

66 with PB would have had a dual MC. With the list of changed items, I would check the adjustment of the plunger between the MC and the booster. It may not be uncovering the rear vent hole.

[Stephen L.]

Re: Rear brake drag...new system

Make sure there is no check valve in the rear brake line at the M/C outlet. This will cause the brakes to slowly apply on a disc brake system as the brakes heat up due to drag and eventually lock. It took me a long time to find this problem many years ago when I had my first experience with disc brakes.... a lesson I'll never forget.

[Brian K.]

Re: Rear brake drag...new system

I had a non power master that would cause drag on the pads. Replacing the master fixed it.

Also make sure there is a little clearance before the pushrod engages the master with the pedal released.