Brake help!!! Danger!!

[ScottyTightdog]

So I rebuilt my drum brakes this weekend. Everything new drums, cylinders, all new small parts/springs/etc. I go out for a test drive and initially they weren’t great but I assumed it would take a couple stops for them to grab. As I thought they started working pretty good after a couple slow stops. Took it on the highway and hit them pretty hard a few times with good stops. So I headed back to the house and as I was coming to a stop sign I hit them and had no stopping power!!!! Just had to roll on through, pedal was pretty firm, tried pumping them but had no stopping power. Went down the road a little and they worked fine again. Worked several more times until I got back to my street and same thing happened had to roll right on by my driveway and fortunately I was going slow enough to make the u turn in my cul de sac. So any ideas on why they would work fine and then not at all?

[Blazerowner]

You might want to take them apart and see if they are sticking. There are some grease points where they move on the backing plate. Check out the site below. I used it to do mine. It’s pretty easy to put comething in wrong.

https://www.pbase.com/nufsed/drumbrake

[Mike C]

Did you manually adjust the shoes out to where they were touching the drums pretty much when you put them back on? If you did not, it’s possible for the pistons to overextend from the wheel cylinder causing a leak. It’s possible for the springs to pull the piston back in the bore then setup a repeat of that. That’s the only thing I can think of that would cause complete brake loss, or near, and then have it come back?

[ScottyTightdog]

Originally Posted by Mike C

Did you manually adjust the shoes out to where they were touching the drums pretty much when you put them back on? If you did not, it’s possible for the pistons to overextend from the wheel cylinder causing a leak. It’s possible for the springs to pull the piston back in the bore then setup a repeat of that. That’s the only thing I can think of that would cause complete brake loss, or near, and then have it come back?

I thought I had them adjusted pretty good and they seemed to be working right while I bled them but I’ll double check. Thanks.

[SeventyOne]

Front brakes dont work either??

Fluid level in the resevior good?

[litebulblsc]

Did you remember to replace them with disc brakes?

[WorkinLonghorn]

Power brakes or manual? If Vacuum assist, check the vac line to the reservoir/assist unit. Check the reservoir for ability to hold a vacuum.
If manual brakes, they are the dual system (starting in '69 i believe) so if both front and rear were KNOWN to be working and then suddenly not working with a firm peddle then you have something wrong between the peddle and the distribution block. Did you bleed the MC? Do you have the warning light operational that shows pressure differential between front and rear systems? You need to look into this area.

[Ewr101]

I would check the set up you did to a known good pic for comparison. You can find one either on this site or online. If that checks out put the drum back on and adjust the star wheel till you just begin to feel the shoes engage. Then do a few stops in reverse. Make at least one a semi abrupt stop. That's what will cause the star wheels to adjust the shoes properly. I redid my rear drums, EVERYTHING new, just like you and the drums didn't have the slot to adjust the star wheel. I did the instructions above and it stops amazingly well for a big heavy Blazer. Good pedal feel as well.