Brake lockup

hello,

Having problem with my 66 coupe front drum brakes. Shoes are locking up during normal braking. Not in the typical way as I can feel the shoes suddenly shift causing the affected side to drag and the wheel to pull. If I stop and back up the shoe will break loose with a clunk and work normally. I have replaced the shoes and all hardware as well as bled the system. Everything such as the pins and backing plates appear ok and different degrees of adjustment still doesnt help. I have had many cars with front drum brakes but never encountered this problem.  

i would like to ask...   you did notice.. that there are 2 different lengths of brake friction linings on the shoes..

there are short lining and long linings...

the short linings go toward the front of the car....

the long linings go toward the rear of the car...


i would really like you to take the drums back off...    i would almost bet.. that the brake backing plates are loose from the spindle...

here is a picture of the right side brake backing plate with the shoes installed

http://www.mustangmonthly.com/projectbuild/mump_0103_front_drum_brake_rebuild/photo_21.html

you can see in this picture #21... that the shoe lining on the right.(the front) is shorter than the lining on the left...

so one long and one short on each side...


there is a whole article on just this job... here is the link

http://www.mustangmonthly.com/projectbuild/mump_0103_front_drum_brake_rebuild/index.html  

I have seen very worn backing plate pads, weak springs, and incorrectly arced shoes do this. If the pads are good and flat, and the shoes are on correctly (primary and secondary and reasonably true in arc), change all of the springs. (hold-down, including pins, and return.)  

Yes primary and secondary shoes are correctly placed and all hardware is new. I purchased quality shoes and hardware not the Autozone specials. I am guessing that it has something to do with the backing plates. They appear to be straight but It is difficult to determine while on the car. They seemed to be tight but I must admit I did not check the fastners. I have no problem purchasing new ones but who sells a quality replacement? I have had this thing apart 3 times and still no success.  

just because the shoes are quality.. does not mean they are properly arced...  look at the wear pattern on the face of the shoe... does it touch

all the way along evenly..

only in the center...

only at the top and the bottom...


i am expecting you to check both sides...

look for wear patterns on the backing plate... on the back side. where it bolts to the spindle..

you can also check the gap between the backing plate and the drum...   to see if its flat...

i have removed a lot of backing plates... taken them for sand blasting.. at the engine rebuilder after cleaning them.. then off to the welding shop to weld up the wear spots where the shoes contact .. then grind the welds down flat..

just curious.. how is the adjustment????  

before you take it apart.. turn the wheel so you can see through the adjuster slot...  look through with a flash light..  with the tip of the screwdriver.. push the star wheel forward.. then back.. if it moves more than 1/16 of an inch.. the brakes are probably out of adjustment..

rusty drums will also cause the brakes to lock up for the first few trys after its been parked for a while...  

I will testify to the difference having your new shoes arced instead of just slapping the new shoes in unarced. Unbelieveable. Smooth, even L to R side, front to back balance ( after finding to sweet spot on my adj proportioning valve). It felt like almost ABS. Not one tire broke traction and this was with stock fr disk brake and large station wagon drums rear.