Rear wheel lock up during hard braking

[Steve P.]

Rear brake "camming" is a design flaw, for lack of better words. It is caused by racking of the shoes during braking.  The better the condition of your system and the better adjusted, the more control you have over full on camming or lock up.  I came across a quick video that will better explain. Most people don't really understand how a drum brake system works on cars and light trucks. Follow the link to get a better understanding.

http://auto.howstuffworks.com/drum-brake1.htm



Now that you have sen it in action you can understand why having your shoes adjusted up right is so important. Also why having drums with plenty of meat is so important.  The farther the shoes must travel to make contact the harder the camming action will be.

Another common problem I came across when finding brake problems on customer cars was improperly installed shoes.   Yes, for those of you that don't know it, there are (2) sets of shoes that come in every box of replacement shoes. ( Set 1) is the PRIMARY shoes. These shoes ALLLLLLWAYS go toward the FRONT of the car.  (Set 2) is the secondary which go to the rear. This is very important as putting them on wrong can make for some terrible braking control.

I have seen 2 primaries on the same side. Primaries put on toward the rear and mixed. Meaning a primary on the front on one side and on the rear of the other... All of these will cause your rear brakes to act crazy.

Like I said before, your brakes are the most important part of your car. Check and double check that you are installing them the right way and with top of the line parts. The payback is your life and others. 

[Steve P.]

Come to think about it.. I had a leak from the axle seal at that side..

Soo i guess problem solved 

NOPE...  Problem not solved until you have no leaks and your braking surfaces are excellent.

Now get to work.. 

[NYCMille]

Rear wheel lock up can be reduced by putting in knew rear wheel cylinders that have a small diameter this will reduce the braking force to the rear wheels.

[BrianShaughnessy]

Rear wheel lock up can be reduced by putting in knew rear wheel cylinders that have a small diameter this will reduce the braking force to the rear wheels.

My 7/8" bore wheel cylinders work much better than the 15/16" I had.   This is from ye olde Disc-o-tech article.

There are other ways to alter front/rear balance. One way, which reduces rear lockup, is to use a 7/8-inch rear wheel cylinder in place of the standard 15/16-inch unit. Try Raybestos part number WC37236 for this. (Original application: late '70-early '80s light-duty Dodge trucks w/10-in. rear drums).