'86 Bronco - rear drum lock-up

I'm having a strange problem with my 1986 Bronco XLT, where the right (passenger) rear drum has started locking up after heavy use. This only happens if I've been driving in heavy traffic (stop/go, you know the
drill) for about half an hour. Basically:
- Initially driving: no problem...no lock-up, no vibration, acts fine
- Drive in stop/go traffic for roughly thirty minutes: the right rear wheel will lock at any speed, not much pressure is required on the brake. There's also a vibration after this starts happening (i.e. if there isn't a lock-up, I get a vibration when braking).
I've never had this problem before...actually, my drum brakes always got worse when heated up so this is REALLY a new one on me. So far I've replaced the master cylinder, brake shoes, and rear drums (driver and passenger). No change. Just to be clear: this only happens with the right rear wheel.
Anyone ever experience a similar problem, or have thoughts on a solution? At this point I can only see replacing the guts of that right rear brake.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Eric Faust wrote:

this is what happened to me and it might be related to what you have??? 93 taurus, drive in city traiff for about 20 minutes, stop and go traffic and try the brakes.. it hits the floor... pedal goes to the floor...no brakes.... getting ready to pull the master cylinder thinking thats it.. well i pull the right rear wheel and drum off and find out that the springs on this wheel would not pull the shoes back away from the drum so the metal parts that come out the cylinder were not being held in place and were shoved out way past where they weere to go so the pedal hit the floor as the cyl. had no resistance against it to send the rest of the fluid to the other brake lines..... something simple like a new set of springs from autozone for $5.00 for the both rear wheels solved the problem...... that was about 5 yrs. ago and still going... back to your problem... the hose for the rt. rear wheel cylinder might have collapsed and will not let the fluid flow back when you take your foot off the brakes.. its been know to happen.. the inside of the hose closes and stops the fluid....
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wheel cylinder is going bad.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.