Slow stop squeal - Rear drums?

[Mossyoakglock]

So I'm getting a slow stop squeal lately and I can't figure out where it's coming from. The front brakes are new and I regreased them on Sunday and made sure everything was operating correctly and moving freely.

 

I read on another forum (performancetrucks I think) and some people were saying that the GMT-900 are known for having a slow stop squeal and that it comes from the rear drums. Is there any truth to this and has anybody else heard of this?

[KMGZ400]

i have a 13' and ive been hearing what sounds like a moaning/squeal coming from the rear drums on slow stops occasionally .. not sure exactly where from yet

[music]

Clean the brake dust from the drums.

[Mossyoakglock]

That was my plan. I'm actually going to be replacing the shoes this weekend hopefully.

 

Last time I had an alignment/balance they said I had about 10,000 miles left on the rear shoes anyways and that was about 5,000 ago.

[amc31b]

A slight squeal when slowing down is usually from the front brakes and usually the caliper pin bolts either being dry or not properly lubricated. Cheap pads, bad brake fluid and bad calipers can also cause it but is usually the caliper pin bolts. The slide bolts being stuck and not letting the caliper press the pads evenly into the rotor are what make the noise.

 

Did you use a rubber compatible, none petroleum based grease for the caliper pin bolts and bushings? That being said, did you overly pack the caliper pin bolts or not use enough lube? Did you use some sort of lubricant such as anti-seize or high temp synthetic brake grease on the pad ears and caliper mounting bracket? Did you use anything on the face of the piston or caliper fingers to prevent brake noise? So many variables on the topic of brake noise.

 

Rear brake noise is almost always a groan or "rrrrrunnnchhhh" noise when stopped and pumping the brakes or just before you come to a stop while slowing down. Another good test for rear DRUM brakes is to test the Parking Brake. Put the parking brake on, shift to drive and slowly left off the brake pedal. If you get a groan or "rrrrrruuunnnchhhhh" noise from the rear as you let off the pedal, you can bet your drums are all caked up with brake dust and need to be lubed too.

 

If this is your problem, remove the drums, blast out the entire inside of the drum and brake system with brake clean, pry the shoes out a little and use a q-tip to remove the old lubricant where the shoes and backing plate meet. Obviously, if your brake shoes are thin, this is the time to replace them. If the shoes have plenty of meat, continue on. Take 100 grit sand paper to your braking surface inside the drums and apply a swirl finish to remove the baked in glaze. Clean the drums again with brake clean and set them aside. Now pry out your brake shoes with a screw driver and apply new anti-seize or high temp brake grease with a q-tip to your backing plate where the shoes make contact with the plate. Be sure to not get any lubricant on the shoes, for obvious reasons. Now, apply anti-seize to the wheel stem where the drum fits, all round the hole in the drum, and on the outside of the drum, in between the lugs where the rim mates. Adjust your star wheel so the drums are just barely not rubbing when you put the drums back on and rotate them. Put everything back together, making sure you have pressed the drums back onto the wheel stems and torque your lugs nuts down. Seat the pads again, much the way you seat pads after a front brake job. Also do 10 or so firm stops while backing up to let the drum adjusters do their thing. You should now have a good firm brake pedal and no more noise coming from the rear. Test the parking brake again and it should be a little more positive with no noise now.

 

I just had to do the above job to 3 vehicles that I worked on and all the rear brake noise is gone. You will have to do this job every 2-3 years or 20-35K miles or so. it isn't a very easy job, especially the first time you have to pull the rear drums but it is worth it. I hope this helps.

 

Mossy- No offense but I highly doubt whoever did your alignment job took the time to remove your rear drums and look at the shoe material. That job is a biatch and a half and usually takes 5-10 minutes alone to get the drums off, even with a drum puller tool. Most shops are on a time crunch to make as much money as possible in as short a time as possible and will not take the time to remove your drums just to take a look.

[Mossyoakglock]

The noise happens just before I come to a stop during a slow stop, like if I'm inching up at a stop light. Maybe going 2-3 mph. It doesn't do this every time though. Sometimes every 2/3 or maybe every 5, just depends.

 

I lubed all brake contact points, backs of pads and guide bolts with Syl-Glide. I also have the CRC synthetic brake grease that is dark gray/black with the brush but didn't use that.

 

I used what I thought was a resonable amount. I didn't pack it tight but put a medium light coating on the guide pins before putting them back in the caliper bracket. I've had the fronts apart twice since putting the pads on to regrease so I think they are greased well and don't feel like pulling them apart again.

 

I've got to replace the rear shoes anyways so when I take everything apart I'm going to clean everything real well and put it all back together.

[amc31b]

It sounds like you are on the right track then. I recommend whatever shoes you get, get the riveted friction material. The bonded ones come off way too easy and cause problems. So long as you use quality parts and do a good job, rear brake shoes can last 100K miles. I replaced the brake shoes on my pontiac at 105K and they still had about 50% thickness to them. The shoes were cracked and making noise so I replaced them anyways.

 

Let us know how you make out!

[Mossyoakglock]

I picked up some AC Delco Durastops.

 

How much braking force do the rear shoes apply? Do they engage the drums under light braking pressure or only under hard braking?

[amc31b]

Well the general rule of the thumb is the front brakes apply 80% of the braking power and the rears apply the other 20%. The drums should always be at least barely engaging with light pedal pressure but they really kick in during medium and hard pressure, especially so when backing up. This is why you need to do 10 or more firm stops while backing up after you do anything with the rear drums. It will force the star wheel adjuster to expand the shoes and make the rear braking more positive. This will give better stopping power, a better pedal feel, and make your E-Brake more positive.

 

When people tell me they have a mushy, weak brake pedal, the rear brakes not being right is one of the major causes. Air in the brake lines or bad fluid, bad front calipers, rear brakes out of adjustment and a bad master cylinder all cause the mushy spongy pedal. Flushing the brake fluid and cleaning/adjusting the drums are usually the fastest, easiest, most common fix. If that doesn't work then it is time to look at the calipers and MC.

[Mossyoakglock]

So that might explain a squeal/noise when coming to a slow stop using light pedal pressure. Since most of the clamping force will be going to the front brakes, under light pedal pressure the rears would be just contacting the drums possibly causing the noise.

 

I'm hoping I can get them replaced this weekend but with temps in the 70's that might get pushed back due to some much important fishing.

[amc31b]

If that that is your suspicion, you could very well be right. Depending on how many miles your rear drums have and how hard you are with the truck, you could very well have worn your shoes down to the rivets. The hardened rivets could be gouging the drums and making a high pitched noise every time you step on the brakes. I really hope this is not the case because you will have to buy new drums and they aren't cheap.

 

If you are going to be doing this work yourself, let us know how you make out and take some pics if it is anything interesting. Good Luck!

[Mossyoakglock]

I've got about 68K no the rears. They have not worn down to the rivets and still have a little pad left. I pulled them a few weeks ago just to see how much was left and nothing was gouging into the drums. Everything else looked good other than the shoes getting a little worn.

[amc31b]

Well whatcha' waitin' for??? Either just clean and relube them or change the shoes out and do the whole job.

[Mossyoakglock]

Finally got around to installing the rear shoes. The only issue I had was when putting the drums back over the shoes. I had the adjusters all the way in and the drums were still hard to over the shoes. Whe i tried to spin the wheels they wouldnt make any revolutions. I finally got them installed and went for a drive. I did a few stops in reverse but never heard any clicking that told me they were self-adjusting. I also never heard any noises or sounds like they were dragging. I drove about 5 miles and everything seemed to working well. I sat on a hill in neutral and applied the parking brake and it never moved. I also kept it in gear on a flat section in our neighborhood and applied the parking brake and in never moved, also did the same in reverse.

 

When I got home I felt the wheels and they were not hot at all the drums were warm but not hot. I wanted to see if they were really hot like they were dragging.

 

Does it sound like everything is ok? I guess the real test will be tomorrow morning on the interstate to work.

[amc31b]

Yup, sounds like a job well done too me! You will not hear the star adjuster clicking or moving so don't worry about that part. If anything, you will feel the brake pedal firm up after a few stops while reversing. If you are really interested in it, you can mark the position of the adjuster threads with a black marker and see if it has moved but that is overkill IMO. What you are describing sounds perfect; no more noise, firm stopping, the E-Brake holds firmly and the drums are warm but not hot.

 

The reason the drums were a little tough to get on were either one or two things. 1- You left the e-brake on during the job which caused the shoes to drag on the drums. 2.- The parking brake cable was adjusted too tight and you did not loosen it to make room for the new shoes. When you pressed the drums back on, the shoes happened to fit ok so now they will spin freely again. Torquing the lugs nuts pushes the drums back into their all the way on the hub position and fixes the tension issues you had when installing the drums back on the first time. To double check this, I would lift the rear of the truck, take of the wheels and spin the drums again. They should spin smoothly, with maybe just a tiny bit of drag. It sounds like you are on the right track though. You will know when the shoes are majorly dragging because the drums will be too hot to touch after even a short trip. I have made that mistake myself and had 1st degree burns from touching the drums after a short trip.

 

My only other concern for you now, did the noise you were originally complaining about go away completely?