touchey brakes locking up

[blazer84]

Hi

my new to me 84 Blazer has very touchy brakes. Several times now, I've had to stop quick, and seems like the rears lock up, and I can't modulate them to roll. Does not pull, at least

Shop has been all though it, say it checks out (including the proportioner valve) - but agree it is essentially unsafe. I was browsing the Chilton manual and it says "Brakes Oversensitive" = 1.binding linkage
2. Defective Hydro-Boost
-the shop didn't check these two things - said they never heard of Hydro-boost causing brakes to grab like this . . . anyone have this experience?
-Eric

[DieselEnvy]

I posted a similar question (about my '85) a while back on this forum and got some good ideas, but I still haven't figured anything out. My current 14 bolt semi-floater tends to lock up easily in damp and/or cold conditions. My original 10 bolt did the same thing.......just not as severe. No fluid leaks, no grease contamination, yadda, yadda, yadda. I just ride the brake a little when I first get underway, just to drive off any moisture. Good luck!

[DogDiesel]

Several have complained of these same symptoms before, especially RVers over on the RV forum who park on the coast.

Their symptoms checked out as oxidation, most noticeable on the rears. Why, because the proportional valve modulates the rear, significantly reducing braking when empty and the rust dramatizes initial braking until rust removed with a few applications.

I always apply the brakes for a short distance on mine when parked for longer than a week.

Wayne

[blazer84]

thanks for the tips - have had the brakes checked for rust etc, and it's been warm to hot inland N. Cal. . . So far, the failure-to-yield almost t-boned M-B, and the swearving sidewalk/driveway riding biker would have been the losers the couple of close calls I've had. If I have to stab the brakes in a corner though, I can forsee the potential for hooking right off the road into a ditch

I thought about a racecar adjustable proportional valve if I have to, to get less braking power to the rear (maybe then can do burnouts with stock 6.2 ! )

[G. Gearloose]

1) Adjustment
Too much free play in the adjuster makes them lock up. The purpose of the front shoe (the smaller one) is to use its power to mash the rear shoe (larger one) into the drum. Too much slop and the whole mechanism rotates and binds uncontrollably upon application. When the brakes are well adjusted, the action is more proportional to pedal pressure.

Make sure the self adjuters are not frozen, and sounds like they need some hand adjustment first.

Self adjuster actuate upon applying braje firmly while backing up.

Over time, the teeth on the self adjusters can loose their edge, as well as the arm that rotated it. Fresh parts may be in order.


2) Lock-up in the morning.

This can be exaperated by too much free play, but after a ride in wet conditions, light rust can form overnight making first application scary.

take a file to the shoes, and file the leading edge of each shoe a very shallow bevel. verify adjustment. This works great.

[DieselEnvy]

Thanks G. Gearloose for the ideas.............I'll try them as soon as I can.

I'd love to have a 14-bolt full-floater with discs, but it wouldn't be worth it for this rust-belt truck.

[blazer84]

Originally posted by G. Gearloose:
1) Adjustment
Too much free play in the adjuster makes them lock up. The purpose of the front shoe (the smaller one) is to use its power to mash the rear shoe (larger one) into the drum. Too much slop and the whole mechanism rotates and binds uncontrollably upon application. When the brakes are well adjusted, the action is more proportional to pedal pressure.

Make sure the self adjuters are not frozen, and sounds like they need some hand adjustment first.

Self adjuster actuate upon applying braje firmly while backing up.

I tried 'self-adjusting' (jammed the brakes while backing up a couple of times) and now they seem to respond much better! Haven't had a chance to find a open wide spot for a test panic stop yet - but that does seem to have done it! Thanks!
Followup - tested brakes The auto adjusting did the trick! In 'Panic stops' I could hear the rears howl as they lost traction during weight transfer, and then modulate the pedal to keep them from locking up. Thanks for both tips on the auto-adjusting!
-Eric

[ 09-13-2003, 07:12 PM: Message edited by: blazer84 ]

[78Chev]

My self adjusters were not working at all due to wear and tear and rust after 25 years. As a result my shoes were way loose (weren't adjusting themselves). So I put in an adjuster rebuild kit ($22 each side from NAPA) which inludes the adjuster arm and star adjuster assembly, plus springs. Made a world of difference. You can tell if your brakes were too loose by looking at the top edge of the front pad. It will have a bevel worn into it from contacting the drum at that point instead of along the entire length of the shoe (since the adjuster spreads the bottom of the shoes while the brake cylinder spreads the top). This makes it grab tight sometimes, and will also cause the drum to shudder at times. To adjust, the instructions said to turn the adjuster until there was heavy drag on the drum while rotating. This makes sure the entire shoe is making contact with the drum. Then you back off 20-30 teeth. (My Haynes manual said to back off until there is just a slight dragging noise which I did as counting teeth is difficult through the little inspection hole!). From there the adjusters take up the remaining slack as necessary each time you back up and apply the brakes.

This made a world of differnce in my braking and in eliminating front brake drag. Seems the proportioning valve overcompensates for too-loose rear brakes by directing additional pressure to the front brakes. Anyway, you might want to consider changing out the adjuster set up. Good luck. There is nothing like a truck with good brakes!
Randy

[blazer84]

Just wanted to say thanks again to Gearloose and 78Chev for the great info. Luckily for me the auto-adjusters still worked -just needed to do the backup proceedure, but if not, I would have had a clear plan on how to fix it myself.
-Eric