gmc truck

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  #1  
Old 10-22-09, 08:13 PM
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gmc truck

i have to put new rear brake rotors on my 2003 gmc 4x4 truck, was wondering if i had to bleed the brake line to do this, or can i push back the cylinder with a c-clamp........
 
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  #2  
Old 10-22-09, 09:13 PM
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Location: santa fe /texas
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'i' think you can 'easily' push the caliper -piston-back,into the caliper,? unless,the park-brake ,is used wth the rear brake-pads.
 
  #3  
Old 10-23-09, 05:16 AM
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The parking brake works on the inside of the rotor with a seperate set of shoes, so you should be able to push the pistons in. These are 2 piston calipers so you will need to put an old brake pad or something across the pistons so you can push both at ths same time. Do not forget to remove the top from the master cylinder, and put a pan under it to catch the overflow if there is any.
 
  #4  
Old 10-23-09, 03:12 PM
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Location: Pennsylvania
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Not all Chevy trucks had dual piston calipers on the rear.

As a matter of fact, most had a large single piston caliper.

The calipers are not interchangeable nor is the mount or how the caliper mount attaches it's self to the axle.

Do not push the old fluid back into the caliper. Gm has a real problem with their calipers and anti lock brake systems and master cylinders.

The trick is to open the bleeders and then push back the piston in the caliper one side at a time.

Then take a one man bleeder and remove all old fluid from the master cylinder and then replace with new fluid and then bleed until the fluid that comes out of each caliper bleed screw is as clear as what you poured into the master cylinder.

Be careful how you bleed the brakes, if you run the master cylinder dry you will need a Tech II tool to pulsate the ABS to get the air out of the system. - Which usually requires a trip to the GM garage - because most shade tree mechanic's do not have a Tech II tool.

If the caliper mounts to a slider - it looks like a pin with a head on the outside and a boot on the end - pressed into the caliper mount or snapped over a lip over the pin. You must make sure that the pin slides freely. If it doesn't - you need to clean out the bore and inspect the pin for corrosion. You might need to replace the pin, they sell a kit to rebuild the caliper mounts. You must also add a dielectric grease inside of the bore to keep corrosion out of the mount.

If the pins do not slide freely, then you might need to take it to a machine shop or mechanic to get the old pins out and restore the bore - before you put the new pins in.

You also need to make sure that the surface under the stainless steel slider plates is clean and smooth. Anything sticking up will make the pads hang up on the mount and will cause pre mature wear.

I usually take a flat file to mine and then prime and paint them and then add some dielectric grease before final assembly.
 
  #5  
Old 10-23-09, 08:22 PM
Join Date: Jan 2007
Location: North Central Indiana
Posts: 912
bleed brakes

Excellent post by claw hammer. I go one step farther by clamping off the brake hose so fluid cannot go back to ABS. (there are clamps made for this but are hard to find) I made mine by welding 1/4 rod to the jaws of a small pair of vice grips.
 
  #6  
Old 10-25-09, 07:34 PM
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My bad, you are right hammer, just the HD versions have the 4 piston calipers.
 
  #7  
Old 10-25-09, 09:56 PM
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Retired and Claw,
why all the concern about pushing the fluid back into the BPMV? 99% of the failures we see are electrical and have found no corelation between brake servcie and BPMV failure. I agree with most everything else you had to say with the exception of the dielectric greese on the claiper slides, the only lube recomendations there is something called "aero shell #5" a rather nasty substance that one can of will last the average wrech 5-10 years.
I do suggest to the poster that he inspect the "drum in hat" style rotors and ensure that they are clean and true, warping in the back is not much of an issue but I have seen it more than once.
 
  #8  
Old 10-26-09, 08:43 AM
Join Date: Jan 2007
Location: North Central Indiana
Posts: 912
bleed brakes

Dirt; Being that I dont work on stuff on a daily basis anymore I keep in touch with local guys that do and when I tackel something I confir with them. Two different brake shops warned me about this so I took their advice and had no trouble. A friend did his and didnt heed the warning and immediately started having trouble with his ABS. Not being a gambler I will err on the side of caution.
 
  #9  
Old 10-26-09, 11:11 AM
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Originally Posted by retired wrench View Post
Dirt; Being that I dont work on stuff on a daily basis anymore I keep in touch with local guys that do and when I tackel something I confir with them. Two different brake shops warned me about this so I took their advice and had no trouble. A friend did his and didnt heed the warning and immediately started having trouble with his ABS. Not being a gambler I will err on the side of caution.
good to not dive in blind, we do perform the abs bleed function anytime the system is open, however we do not usually do it when we do a brake flush, figure that one out
from 89 to 2006 I could answer about any question someone had about a gm truck, after the 07 change forget about it. The most simple things have become so complex that its a research situation before almost any repair. I had a 07 denali in here this am, 300 bucks to get the low beams working due to a failed relay.
Im done wrenchin for the most part after disc replacement to my neck, now im running the show from a desk, and I thought it was rough in the shop, lol
 
  #10  
Old 10-26-09, 12:58 PM
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Join Date: Oct 2009
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The reason for the long explanation is due to the fact that GM did so many updates and technical bulletins that they had problem after problem and most of the solutions came from me on the Chevy Avalanche Fan club Forum.

I have dealt with GM directly and have spoke to the plant managers at the Pontiac Mich and Oshawa Ontario plants on several occasions on problems and cures.

First off, when you walk into the parts store, they are either going to need the last 10 digits of the Vin number or they are going to have to know what the rear gear ratio is before they can even sell you a set of pads or rotors.

The 3.73's had one size and the 4.11's had ones that were 2 or 3 mm bigger. The same holds true with the later models that had the 3.42 gear ratio.

Truthfully 3 mm doesn't make all that much difference as long as you use the right pad. But the stock pads for the non HD models in the book - looks to be the same pad used on the Chevy Trailblazer and not for a Avalanche or Silverado. It won't even fit inside of the caliper it is so small.

Then if you live in a rust belt state, you will usually have a backing plate issue where it is rusted out with most any truck more than 5 years old. Dorman now makes a replacement backing plate, but back in the day, the only way to get one was through A GM dealer.

The bonded band inside of the drum is usually wore when you have a customer that uses the emergency brake frequently.
Which I advise everyone not to use, due to the fact that it is not big enough to hold the vehicle - even on the flat and level and usually in time the brake cables corrodes and sticks and then it wears the band out. You have a bear of a time just trying to get the rotor off because usually there is a rust ridge inside of the drum and the pad adjusters are usually seized and will not turn and you are stuck sledgehammering them off.

There is no reason to resurface a used rotor in a rust belt state because the rotor was too thin from the factory and usually is covered in cracks from the heat build up from the emergency brake cable sticking or from the pads not sliding on the mounts.

The pins inside of the mounts usually gets corrosion inside of the bores and makes the pins stick - if you are lucky, or makes them seize - which causes premature wear on the brake pads and makes the rotors rust, glaze and crack.

So basically every 2 years or almost every time the brakes needs new pads, it will also need new rotors.

The reason for Dielectric grease is due to the fact that if you use chassis grease inside of the caliper mount, it will attack the rubber that is used for a seal that goes over the pins and in time the rubber will fail and the pins will stick anyways.

The front pins with the Torx headed studs, you just throw away and buy new ones at NAPA auto parts, because in time they will seize in the mount and you will not be able to get them back out.

The front rubber bushings - are pressed in and looks somewhat like a valve stem seal. They go bad all the time.

Usually when you have a caliper issue, the back side of the rotor will turn black and you will not have any brakes when you step on the pedal.

When you push the dirty fluid back into the system it attacks the seals in the master cylinder and in time you will be replacing it. Most times it will leak to the Vac assist side and will drip out across the front of the booster.

Some people goes to the extent of disconnecting the battery terminals when they bleed the brakes because if you cannot get the ABS to cycle - you cannot get the calipers / system to pump up after you bleed the brakes. If the ABS senses a loss of pressure in the system, it will sometimes not let the system pressurize.

The pedal will get so spongy that you can step it to the floor and the vehicle will not want to stop.

I could write volumes on this subject.
 
  #11  
Old 10-27-09, 09:12 AM
Join Date: Jan 2007
Location: North Central Indiana
Posts: 912
bleed brakes

[
Im done wrenchin for the most part after disc replacement to my neck, now im running the show from a desk, and I thought it was rough in the shop, lol[/QUOTE]

I have turned down service managers jobs many times. If you are at a dealership you have the company,the owner, the techs, and the customer to make happy. I just ran my own place that way I only had a few hundred bosses. I thought I had put my wrenches away but after paying $188 to have the oil and filter and filter in trans changed I drug them out again.
 
  #12  
Old 10-28-09, 02:08 PM
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Location: tulsa, ok
Posts: 48
WOW claw lots of info there, down here our brakers last over 100k miles and dont have many issues out of them. I would say 99% of the gm light duty units around here go 100k plus with out any issues. I also cant say we have ever run into such a combination of events as you descibre when performing a simple brake service. Lots of park brake issues on the older units but mostly either inop or a new guy trying to get them apart. I had a 99 3/4 ton that would hold a 26' regal boat on the boat ramp in Nutural, that about 7k lbs. The Aeroshell greese I spoke about was a recomended greese for caliper slides by GM on all medium duty trucks.
Have fun man,
 
  #13  
Old 10-29-09, 08:21 AM
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Location: tulsa, ok
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Inspect the fluid level in the brake master cylinder reservoir.
If the fluid level is midway between the maximum - full point, and the minimum allowable level, no fluid needs to be removed from the reservoir before proceeding.
If the fluid level is higher than midway between the maximum - full point, and the minimum allowable level, remove fluid to the midway point before proceeding.
Remove the tire and wheel assembly. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
Compress the brake caliper pistons.
5.1. Install 2 large C-clamps over the top of the caliper housing and against the back of the outboard pad.

5.2. Slowly tighten the C-clamp until the pistons are pushed completely into the caliper bores.

5.3. Remove the C-clamp from the caliper.





Remove the brake caliper bolts.
Remove the caliper from the caliper bracket .
Support the caliper with heavy mechanic's wire or equivalent. DO NOT disconnect the hydraulic brake hose from the caliper.





Remove the brake pads from the caliper bracket.
Remove and discard the anti-rattle clips.
Inspect the caliper and caliper bracket. Refer to Brake Caliper Inspection .
Installation Procedure




Install the anti-rattle clips to the caliper bracket.
Install the brake pads.



Install the caliper to the caliper bracket .
Notice: Refer to Fastener Notice in the Preface section.

Install the brake caliper bolts.
Tighten
Tighten the bolts to 108 Nm (80 lb ft).

Install the tire and wheel assembly. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
Remove the safety stands.
Lower the vehicle.
With the engine OFF, gradually apply the brake pedal to approximately 2/3 of its travel distance.
Slowly release the brake pedal.
Wait 15 seconds, then repeat steps 7-8 until a firm pedal is obtained. This will properly seat the caliper pistons and pads.
Fill the master cylinder reservoir to the proper level with clean brake fluid, if necessary. Refer to Master Cylinder Reservoir Filling in Hydraulic Brakes.
Burnish the pads and rotors. Refer to Brake Pad and Rotor Burnishing .


With all that had been said on this subject I was wondering if there was something I was missing so I did some research with gm's service info that we use for everything. For those of you who do not know this is a private website that is updated everyday with the latest and greatest direct from gm. I was unable to find anything realated to brake pad replacement and abs problems or failed units after pad replacement. there was 1 very short one about air traped in the system, the cause was a due to incorrect bleeding of the system when the system was open for componant replacement.

The above is the procedure straight from gm

the below one is straight from alldata online, a service provided and respected by all maintenace shops


Inspect the fluid level in the brake master cylinder reservoir.
If the fluid level is midway between the maximum - full point, and the minimum allowable level, no fluid needs to be removed from the reservoir before proceeding.
If the fluid level is higher than midway between the maximum - full point, and the minimum allowable level, remove fluid to the midway point before proceeding.
Remove the tire and wheel assembly.
Compress the brake caliper pistons.
Install a large C-clamp over the body of the top of the caliper housing and against the back of the outboard pad.
Slowly tighten the C-clamp until the pistons are pushed completely into the caliper bores.
Remove the C-clamp from the caliper.








Remove the brake caliper bracket bolts. Caution: Do not depress the brake pedal with the brake rotors/calipers and/or the brake drums removed. Damage to the brake system may result. If brake system damage occurs and is not repaired, vehicle damage and/or personal injury or death may result.
Notice: Refer to Brake Caliper Notice in Service Precautions. Remove the caliper and caliper bracket as an assembly.
Remove the brake caliper bolts.
Remove the caliper from the caliper bracket.








Remove the brake pads from the caliper bracket.
Remove the anti-rattle clips.








Remove the slide pins (5) from the caliper bracket (3).
Remove the slide pin boots (4) from the caliper bracket.
Inspect the disc brake hardware.
Installation Procedure









Lubricate the caliper bracket bushings and the slide pins with high temperature silicone brake lubricant.
Install the slide pin boots (4) to the caliper bracket.
Install the slide pins (5) to the caliper bracket (3).








Install the anti-rattle clips to the caliper bracket.
Install the brake pads.
Install the caliper to the caliper bracket.
Perform the following procedure before installing the caliper bracket bolts and the brake caliper bolts:
Remove all traces of the original adhesive patch.
Clean the threads of the bolt with brake parts cleaner or the equivalent and allow to dry.
Apply Threadlocker GM P/N 12345493 (Canadian P/N 10953488) to the threads of the bolt.
Install the brake caliper bolts. DO NOT tighten.








Install the brake caliper bracket and caliper as an assembly.
Notice: Refer to Fastener Notice in Service Precautions. Install the brake caliper bracket bolts. Tighten the bolts to 300 Nm (221 ft. lbs.) .
Tighten the brake caliper bolts. Tighten the bolts to 108 Nm (80 ft. lbs.) .
Install the tire and wheel assembly.
With the engine OFF, gradually apply the brake pedal approximately 2/3 of its travel distance.
Slowly release the brake pedal.
Wait 15 seconds, then repeat steps 7-8 until a firm brake pedal is obtained. This will properly seat the brake caliper pistons and brake pads.
Fill the master cylinder reservoir to the proper level with clean brake fluid, if necessary.
 
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