Brake clunk

[Stinky]

On my '86 720....I'm not sure that I have enough data, but here goes.  When I step on the brakes, there is a clunk.  It sounds like the shoes are grabbing the drum and turning till they hit something thay stops them.

 

That said, I took both drums off and didnt find anything wrong.

 

So, maybe it is in the front.  I will continue to watch it.

 

Also, I think, that the 1st time that I put on the brakes, that the pedal is lower...not much, .5-1" and that it only seems like it does it the 1st tme that I step on the brakes after they havent been used in 10 minutes or more.

 

I do not notice anything else about the brakes....they appear to work just fine.

[datzenmike]

Fronts.

Are the lug nuts on tight?

When the brakes are applied everything on the hub and connected to the hub wants to move to the rear as the truck moves forward. I would raise the front and wiggle everything suspension related. Don't be shy, lean into it. Visually look for worn bushings and anything on one side that doesn't match it's counterpart on the opposite side.

 

Rears.

Are the lug nuts on tight?

Take the drums off and look for broken hardware like a return or anti rattle spring.

Again the entire rear axle wants to move to the rear when the brakes are applied. Are the U bolts secure and tight?

 

[banzai510(hainz)]

if you have it off again check the adjusters are too loose. mounted to the back plate.  they are designed to move but have tention on there and not loose where it moves backing up then going Fwd moving and then binding

[datzenmike]

Good point. Half way through the '81 model year self adjusters were introduced but they can seize up because "self adjusting' and no one checks them. 

[Stinky]

I haven't pulled the drum again.  But, I've noticed that it only does it after the emergency brake has been pulled, and that it only does it once. 

 

It does not seem to stop it from doing it to step on the brakes, after releasing the brakes, or by braking while backing (out of a parking spot)..But, it may reduce the noise.

 

I've done the shoes recently, in the past year, and I cleaned the adjusters when it was apart.

[datzenmike]

Try this...

 

Park the truck facing down hill in gear, engine off with e brake on.  Engine still off, place transmission in neutral and release the e brake... what happens???

 

Does the truck roll forward? with a clunk???

 

If it doesn't roll forward pump the brake. Is there a clunk and the truck now rolls forward???

[Stinky]

You may be on to something...it does not like to roll from where it is parked now (barkwards) .

 

I'll try to remember to back in tomorrow.

 

I'm gonna push it back today, when I leave work.

[datzenmike]

I expect the one of the parking brake cables is rusty and sticking. Rather than pulling everything apart to clean it and it doesn't help, try parking on a down hill grade safely out of the way. Pull the hand brake 40 or 50 times and release. If the truck does not roll try a pump on the brake pedal to release it and keep going. Rhis will put a shine on any rusty surface.

 

The best way to prevent the e brake from seizing is to constantly use it every time you park. The previous owner may not have.

[Stinky]

Yesterday, and every time leading up to yesterday, that I parked on a slope, it would roll when the brake was released..

 

When I stepped on the brake, I could hear a lot of movement in there...when I released the brakes, it sounded like the shoes were pulling back in, by the springs.

 

I went to a friends after work, and just happened to have an IR thermo in the truck.  At the friends house, this drum was 76 deg, other side 126.  At home, 52 and 76 degrees...this side aint pulling its weight.

 

I pulled the drum, it looked OK...or so I thought.  I looked at the adjusters, they turned just fine.  The drum was loose on the shoes....shoes not adjusting.

 

The cable going to the self-adjuster was off.  It was being held in place by the spring that goes to the top pivot, above the wheel cylinder.  So, I loosened everything up, and used a screwdriver to pry the cable back in to the groove.  it popped right back in.  I adjusted the adjustor all the way out....so far, so good.

[banzai510(hainz)]

the adjusters might be slipping around.            

 side to side

 

 

next time you take the shoes off see if you can push the whole adjuster side to side with your hand. If you can then I say its too loose.  when correct the adjust finds the middle spot then sits there and you then adjust the brakes and everything should be fine.  This is just a good guess on my part.

this happen to me but the main proplem the brakes were OVERHEATING to the point the rim was so HOT.  worried I was going to burn the bearings up

Edited December 7, 2020 by banzai510(hainz)

[datzenmike]

The self adjusters rely on excessive brake shoe movement which allows a ratchet mechanism to lever the adjuster star wheel one tooth. Once the adjuster moves one tooth the shoe movement is reduced and nothing happens until the shoe wears down enough for another adjustment.

[Stinky]

Yep...and because the cable was in the wrong spot, no auto-adjustment and the shoe was sloppy