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740 Brakes dragging when hot

Vyrus616

Member
Joined
Sep 13, 2013
Location
Vancouver, WA
About a year ago my rear brakes dragged so hard they caused my engine to overheat and warped the head.

I've since fixed the head up and replaced the brake lines with stainless steel ones and replaced the fluid.

Recently in HOT temps got stuck in stop and go traffic. Rear brakes seized again and nearly redlined my coolant temp.

What is it about stop and go traffic in the summer heat that would cause my rear brakes to bind up? Do I need to rebuild the master? All lines and fluid are new on the brake system.

Any idea Volvo Wizards?
 
Kjets On a Plane covered it above thoroughly but I would add another possibility is the internally deteriorating brake hose issue where that can create a loose inner flap that ends up working as a one-way check valve so the brake fluid stays trapped under high pressure at the caliper.

More common is a seized caliper however. How often do you flush the brake fluid? :roll:
 
Sorry for the lack of context. It's a 88 740 Turbo Wagon. It has ABS. I've just recently replaced the brake lines with braided stainless lines and put fresh DOT4 in all lines.

Most components of the cooling system have been replaced. New Nissen radiator, water pump is a few years old, new upper and lower radiator hoses, installed a coolant bypass valve from an astro van for the heater core, fresh coolant.

The rear brakes were acting like I had the pedal pressed and there was zero play in the pedal when I touched it. At one point when I was driving I felt the rear brakes finally let go (after normal driving, not stop and go anymore) and it seemed normal. Maybe once they cooled?

I recently replaced the rear pads and slide pins with bosch parts. The pistons seemed to compress normally when I was installing the new pads.

As 2manyturbos stated I've been asking lots about this car. Seems like everytime I get something buttoned up, something else breaks. Thanks to everybody for their help as always.
 
Does the pad slide easily within the caliper? I've had an issue where some new pads I had installed were a bit too tight in their groove, and would get stuck gripping the rotor. Add heat to make everything a little bigger and it would get wedged in pretty good. Little filing fixed it.
 
If the pistons are working well so the calipers seem ok. Plus you know the lines are ok. I have had master cylinders that the check valve stops working after a few minutes of driving which causes the brakes to stay on. You may also want to give the pressure regulators a light whack with a small hammer. Maybe there is a bit of corrosion in them making them slow to respond?

I've had brakes that stay on happen in Volvo single circuit brakes and the dual circuit brakes. A new master cylinder solved the problem. But I had to eliminate the other possible problems before I blamed the master cylinder.
 
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