Brake pedal fades, slowly after 4 wheel brake job - S-10 Forum
S-10 Forum is the resource on GM S-series trucks, Suspension, engine information, Body Modifications, painting tutorials.  Modifications to suit every need, budget and whim

Brake pedal fades, slowly after 4 wheel brake job

Go Back   S-10 Forum > Engine and Drivetrain Tech > Wheels, Tires & Brakes
New User? Register Forgot Password


 
LinkBack Thread Tools
Old 12-10-2007, 10:23 AM   #1
Registered User
 
Age: 49
Join Date: Dec 2007
Posts: 4
Location:
User is: OffLine
Brake pedal fades, slowly after 4 wheel brake job

04 Blazer Extreme
I did a 4 wheel brake job this weekend. New pads and had the rotors turned.
I never opened any of the bleeder valves.
After everything was bolted back together, the reservoir had overflowed from the caliper pistons being pushed back in, so I used a syringe to siphon as much of the old fluid out of the reservoir as I could get. The reservoir is split in 2 and there is a baffle between the 2 parts so I couldn't get all of the old fluid out of the front portion.
Refilled with Valvoline synthetic.
I started the truck and pumped the pedal a couple of times and it got more firm, but never gets totally hard.
I had a friend who is a Ford mechanic come over. We bled/flushed all the brake lines; rear passenger first, rear driver, front passenger then front driver. We bled them until new, clear fluid was coming out. Bled by hand/foot, no mighty vac or power bleeder.
On the front driver caliper, where the brake line attaches to the caliper there was a VERY slight leak. I tightened the bolt and the leak stopped but this didn't change the pedal pressure (we did re-bleed this line). I suspect I might have hit this bolt when I was trying to get the rotor off (they were ALL pretty much rusted in place)
During the test drive there was plenty of stopping power, though we never tried for a total lock-up or to get the ABS to engage.
But, if you sit at a dead stop and push fairly hard on the pedal, it *will* fade all the way to the floor, though what I would consider "normal" pressure on the pedal doesn't seem to be enough to make it fade.
My friend didn't have any suggestions other than to try to bleed the master cylinder, on the car.
Ideas? Suggestions?
Any help would be greatly appreciated!
I'm 99% certain the pedal used to get hard about half way down and the brakes have always been REALLY good in this vehicle. It's the first thing anyone that ever drives it, always noticed; how touchy the brakes were.
Old 12-10-2007, 11:09 PM   #2
Registered User
 
jman062006's Avatar
 
Age: 25
Join Date: Sep 2007
Posts: 192
Location: Frederick, MD
User is: OffLine
Re: Brake pedal fades, slowly after 4 wheel brake job

Quote: Originally Posted by ds8508
04 Blazer Extreme
I did a 4 wheel brake job this weekend. New pads and had the rotors turned.
I never opened any of the bleeder valves.
After everything was bolted back together, the reservoir had overflowed from the caliper pistons being pushed back in, so I used a syringe to siphon as much of the old fluid out of the reservoir as I could get. The reservoir is split in 2 and there is a baffle between the 2 parts so I couldn't get all of the old fluid out of the front portion.
Refilled with Valvoline synthetic.
I started the truck and pumped the pedal a couple of times and it got more firm, but never gets totally hard.
I had a friend who is a Ford mechanic come over. We bled/flushed all the brake lines; rear passenger first, rear driver, front passenger then front driver. We bled them until new, clear fluid was coming out. Bled by hand/foot, no mighty vac or power bleeder.
On the front driver caliper, where the brake line attaches to the caliper there was a VERY slight leak. I tightened the bolt and the leak stopped but this didn't change the pedal pressure (we did re-bleed this line). I suspect I might have hit this bolt when I was trying to get the rotor off (they were ALL pretty much rusted in place)
During the test drive there was plenty of stopping power, though we never tried for a total lock-up or to get the ABS to engage.
But, if you sit at a dead stop and push fairly hard on the pedal, it *will* fade all the way to the floor, though what I would consider "normal" pressure on the pedal doesn't seem to be enough to make it fade.
My friend didn't have any suggestions other than to try to bleed the master cylinder, on the car.
Ideas? Suggestions?
Any help would be greatly appreciated!
I'm 99% certain the pedal used to get hard about half way down and the brakes have always been REALLY good in this vehicle. It's the first thing anyone that ever drives it, always noticed; how touchy the brakes were.
Sounds like to me you may have a weak master cylinder. I would do a line clamp test which consist of clamping all four brake hoses off and hold the brake pedal firmly down. If the pedal sinks down then that means that fluid is bypassing the master cylinder, which means that it is getting weak. If the pedal does not fade out I would have the brake system flushed by a shop that can hook a machine and do a vaccum flush. This always works alot better than hand bleeding.
Old 12-11-2007, 12:37 AM   #3
Registered User
 
Age: 49
Join Date: Dec 2007
Posts: 4
Location:
User is: OffLine
Re: Brake pedal fades, slowly after 4 wheel brake job

I can certainly try that test, but what jumps out at me would be, why would changing pads and machining the rotors cause the master cylinder to be weak. The brakes were working fine before this, the rotors were just wearing somewhat oddly. I have no reason to suspect the master cylinder as having an issue, other than perhaps air in it.
Any other ideas?
Old 12-11-2007, 01:07 AM   #4
rc guy
 
Age: 27
Join Date: Jun 2007
Posts: 597
Location: MI
User is: OffLine
Re: Brake pedal fades, slowly after 4 wheel brake job

Im having a similar issue with my 83 jimmy. My instructor said that when you push the pistons back in the calipers that it pushes all of the sediment past the seals with the fluid, which makes sense, and that the sediment wears down the seals inside the MC. My pedal was more firm with worn front brakes only (blew a piston out of a rear wheel cylinder) than it is now with all new rotors, pads, shoes, drums, and a line. I was going to try and bleed the fronts out a bit more, until I got clear fluid out, but the passenger caliper bleeder twisted off before I could even bleed that side.
Old 12-11-2007, 02:40 AM   #5
is a fungineer
 
ka_jd7and1's Avatar

 
Age: 28
Join Date: Jun 2005
Posts: 6,105
Location: Bakersfield, CA
User is: OffLine
Re: Brake pedal fades, slowly after 4 wheel brake job

I got money on the synthetic fluid. I've heard that it has a problem eating the rubber seals/ O-rings in the master cylinder, proportioning valve, and rubber brake hoses.
Old 12-11-2007, 08:22 AM   #6
Registered User
 
Age: 49
Join Date: Dec 2007
Posts: 4
Location:
User is: OffLine
Re: Brake pedal fades, slowly after 4 wheel brake job

Well...that would be the first I've heard of synthetic fluid causing an issue.
BUT...I just did the work this past Saturday, so that would mean the synthetic fluid would have to be about as caustic as a mild ACID to eat the seals THAT fast.

::edit::
I actually just googled for issues with synthetic brake fluid and found nothing. I think you might have meant *silicone* brake fluid causes some issues, not synthetic. There were several articles mentioning that early types of silicone (which is NOT what I used) fluid caused problems with seals, etc.

I could not find any mention of synthetic fluid causing problems nor any issue with mixing them, though we did flush the system. Although I'm sure it's not 100% synthetic in there. Probably closer to 90%. It would be impossible to be 100% with just a flush. I'd need to completely drain the system, clean it and then refill with sythetic.
::edit::

So far, the answer about it pushing sediment back into the system when you compress the pistons sounds the most plausible.

Anyone else?

Last edited by ds8508; 12-11-2007 at 08:39 AM.
Old 12-12-2007, 02:02 PM   #7
Forvm Lurker
 
anALLSHOx's Avatar
 
Age: 29
Join Date: Dec 2002
Posts: 795
Location: Vegas.
User is: OffLine
Re: Brake pedal fades, slowly after 4 wheel brake job

sounds like you blew your master cylinder... if you could never push your pedal all the way to the floor it's most DEF the master cyl.. you probably just busted a small piece which sucks cuz chevy will only sell you the whole master..
Sponsored Links
Advertisement
 

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the S-10 Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 02:05 AM.

Powered by vBulletin® Copyright ©2000 - 2011, Jelsoft Enterprises Ltd. SEO by vBSEO 3.2.0
SEO by vBSEO
vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.