Most common cause for drum lockup?

[pvfjr]

My rear left drum keeps locking up with light brake application. Feels like the whole back end is getting kicked around violently. What gives? Mud? needs adjustment? Or is the brake lining gone, with rivets grabbing into the drum? What should I expect to find/look for...

 

[unclematty]

axle seal went away gear oil all over brake linings and instant grab every time you touch the pedal!

 

[readymix]

Either that or grooved drums

 

[pvfjr]

axle seal went away gear oil all over brake linings and instant grab every time you touch the pedal!

Ughh, don't like that one. Hope not! Haven't seen any oil coming out in the wheel area, hopefully that's not it. I wouldn't really mind replacing the drums though. Or maybe it's just time to do the home made disc conversion...

So where is this seal though on a 12-bolt? In the diff, or at the wheel? Is it that one that has to be pounded in with a certain size pipe or something? How much to buy, how long to replace? Thanks.

 

[k20]

Mine will do that very rarely, usually after its rained for a few days and I havent driven the truck, I guess the drums rusted up bad or somethin. First stop at the end of the street, itll lock down. Tis rather entertaining when the kids standing at the bus stop go running for cover when they see a truck boiling smoke off the rear tires from a 20mph stop......

 

[dyeager535]

My experience with a leaking axle seal and drum brakes is that COLD the "grabbing" problem was not evident. Two or three applies and after that, on dry pavement the one wheel would lock and slide even at 10MPH.

Could be junk in there, glued pads coming off the backing piece, broken hardware, etc. Not hard to remove the drum from a 12 bolt, so shouldn't take long to open it up and see.

 

[pvfjr]

Mine tend to do it cold, I think. There have been trips where it never did get better though. Would grab when I stopped, and still be holding when I went to take off again.

 

[BigBurban350]

Proportioning valve?

 

[dyeager535]

Not for one side in the rear. Both rears run off the same line post-proportioning valve.

My 10 bolt brake(s) were locking up when cold (attributed that to rust since the truck sits a lot) and sometimes/more commonly when traction was lowest, (mud, snow) it would also do it. Didn't really inspect them when I pulled the axle, but it wasn't the drums that were bad, and it wasn't the wheel cylinders.