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Discussion Starter · #1 ·
I have a 2006 Trailblazer LS & the brakes sounded like they were shot!
They originally had that typical squeal-tab sound which went away & then they started to sound like metal-on-metal.

I took the main wheel making the noise off & I was surprised to see the pads are still pretty thick, Probably about 3/8" of pad left!
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The pads do look like their glazed & the inner half of the rotor appears to have some small grooves in it.
Probably from a quick "Pads Only" change by the previous owner?

Can glazed pads & marked/grooved rotors make a actual grinding metal-to-metal sound?

Doug
 

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In all my experiences, grooves on rotors mean zero - nothing. GM put huge, deeply cut grooves in their rotors for years to force the pads into alignment with no untoward noises at all.

Glazed pads can indicate silicon has been drawn to the surface of the rotors and contaminated the friction material.

Silicon is used in cast ferrous metals to help it flow evenly during casting and minimizes striations in the dispersion of the alloys in the iron/steel amorphous mix with whatever other allowing products they add ... but cast iron, naturally brittle, becomes more ductile and vastly more machine-able with silica and nickel, etc.

Cheap pads can be problematic as they have inferior materials that can glaze easily too. With the asbestos ban, I've seen flax, peanut husks, bronze flakes, graphite, U-235 and Kevlar added instead of it. Some worked ... some were miserable failures.

Then there's the hardware ... were the shims replaced? Did the full compliment of clips, flat springs and spacers get installed?

In some vehicles, a healthy application of Permatex Aviation 303 works wonders as does another of my favorites: EMP.

I never allow the friction material to become thinner than the steel platform.
 

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Discussion Starter · #3 ·
Then there's the hardware ... were the shims replaced? Did the full compliment of clips, flat springs and spacers get installed?
Yeah that was my thinking also since I've only had this Trailblazer for about a year, So I really don't know for sure what the hardware etc. is suppose to look like?
The previous owner mentioned that he just replaced the brakes shortly before I bought the TB.
It does look like the inner part of one of the pad clips may have been rubbing the rotor?
So it's possible he may have just used the old hardware & bent or distorted something in the process?

Glazed pads can indicate silicon has been drawn to the surface of the rotors and contaminated the friction material.
I think for now I'm going to just clean up the rotors with some Scotch-Brite, Install new pads & hardware (front & rear)!
Hopefully that will get me through the Winter & providing the TB is still running good I'll do a full complete bake job in the Spring.

Doug
 

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Discussion Starter · #5 ·
Well it's strange how sound travels through different objects!

I was pretty sure that the grinding sound was coming front the front brakes?

After finishing up the back brakes I realized that most of my squealing/grinding sounds were probably coming from the rear breaks! I had checked the back brakes before & they were worn down, But not to the squeal tabs yet.

Once I got the back brakes removed I seen my problem the inner pad on the drivers-side was almost down to bare metal.
Also the pads that were on there had two squeal tabs per pad which created even more noise.o_O

Got everything back together & there's no more squealing or grinding noises.:cool:

Doug
 

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Discussion Starter · #7 ·
Got everything back together & there's no more squealing or grinding noises.
Well I thought I could get by with just a quick pad change, But murphy's law kicked in & I now have two calipers (1 front one rear) that periodically hanging up. :(

This TB has 145K miles on it so I have decided to bite the bullet & replace all the brakes including rotors, calipers, & hoses.

Being I'm also replacing the hoses, I figure it would also be a good time to flush & replace the brake fluid.
I've flushed & refilled brake lines before but not on vehicles with anti-lock brakes. I plan to use a vacuum pump to pull the new brake fluid through the system. Are there any special requirements with the anti-lock brake system?

Doug
 

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Well I thought I could get by with just a quick pad change, But murphy's law kicked in & I now have two calipers (1 front one rear) that periodically hanging up. :(

This TB has 145K miles on it so I have decided to bite the bullet & replace all the brakes including rotors, calipers, & hoses.

Being I'm also replacing the hoses, I figure it would also be a good time to flush & replace the brake fluid.
I've flushed & refilled brake lines before but not on vehicles with anti-lock brakes. I plan to use a vacuum pump to pull the new brake fluid through the system. Are there any special requirements with the anti-lock brake system?

Doug
Yes. Don't use a vacuum to pull fluid through the ABS from the Master Cylinder.

You might get away with it ... prolly not.
 

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Discussion Starter · #9 ·
Don't use a vacuum to pull fluid through the ABS from the Master Cylinder.
Just to be clear I wont be actually connecting the vacuum to the master cylinder!
I was figuring on starting with the old right rear caliper & draw the vacuum from there & get the majority of the old fluid out. Then as I replace the new hoses/calipers I'll use the vacuum to bleed each brake.

Doug
 

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Just to be clear I wont be actually connecting the vacuum to the master cylinder!
I was figuring on starting with the old right rear caliper & draw the vacuum from there & get the majority of the old fluid out. Then as I replace the new hoses/calipers I'll use the vacuum to bleed each brake.

Doug
No. Don't do that.

Never pull old brake fluid from the master cylinder through the ABS and then to the calipers.

Just place a full can of new brake fluid upside down in the top of the master cylinder reservoir and let it gurgle like a water cooler bottle.

Then remove the calipers individually, and let the fluid drain by gravity until it's clean. Do this one caliper at a time.

Make sure that the master cylinder does not go dry! It will slowly lose fluid as you work on the other end of the car. That's good.

Do NOT press the brake pedal or start the engine during this gravity bleeding time.

If you do this right and take your time, you will not have to force-bleed the system at all.

Let me know when you want to start this and I'll give you some other tips.
 

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Discussion Starter · #11 ·
Never pull old brake fluid from the master cylinder through the ABS and then to the calipers.
I'll be removing all the old brake fluid from the master cylinder reservoir first, Then refilling the reservoir with new fluid.
Here's the type of pneumatic vacuum pump/bleeder kit I planned on using.
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Let me know when you want to start this and I'll give you some other tips.
I'm probably going to start on it today once it warms up outside a little bit.

Doug
 

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1. You cannot clean the master cylinder.
2. You cannot clean the master cylinder.
3. You cannot clean the master cylinder.
4. You cannot clean the master cylinder.

You might only disturb the general mulm in the bore and once it's angry, it will try to destroy everything it touches.
If you want to clean the master cylinder, disassemble it and wipe the old rubber particles and moisture contamination flakes that are at the back of the bore.​

Unfortunately ... buying a master cylinder overhaul kit is nigh on impossible any more. You'll need a rebuild kit to reassemble it correctly.

Remember, you cannot clean the master cylinder unless it is disassembled first.

Don't go there ...........
Just do the gravity bleed I mentioned and you might not have to buy a new master cylinder or a new ABS unit when the gunk gets into it and you cannot successfully clean it either.​

You MIGHT get away with your intentions ... but numerically, you're in the small numbers for success.
 

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Discussion Starter · #14 ·
you cannot clean the master cylinder unless it is disassembled first.
Ok I follow your logic!

Don't go there ...........
Just do the gravity bleed I mentioned and you might not have to buy a new master cylinder or a new ABS unit when the gunk gets into it and you cannot successfully clean it either.
So by doing the gravity bleed wouldn't the gunk & old fluid still run past the ABS unit also?

Doug
 

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Discussion Starter · #16 ·
Well I had a two day rain delay, But I finally got back to working on the brakes!

You might only disturb the general mulm in the bore and once it's angry, it will try to destroy everything it touches.
You're probably right, but I still figured that getting as much as possible out first would only help!
Remember, you cannot clean the master cylinder unless it is disassembled first.
Yeah you're probably correct on that also, But I really didn't want to get into disassembling the master cylinder.

I cleaned the outside good with some brake cleaner before opening it & then I used the vacuum pump/bleeder to suck out as much as I could. This is what I got out of the master cylinder & the old passengers side rear caliper.

Pretty nasty looking brake fluid!
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Here's a few pics of the new brakes & new rubber hoses!
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Doug
 
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