Brake Fluid Flush GMT800

[WFO]

The brake pedal on my 03 goes down just a little bit more than normal. Brakes work fine though, and master cylinder is still full, with the original fluid in it. Has 72k miles on it.

I'm about to flush it the old fashioned way with a helper, and I was wondering if I need to do anything different due to the ABS?

 

[Edelbrock]

I would try this:

Have someone start the engine and stomp hard on the brakes repeatedly while you check each rubber brake hose for bulging and replace any that are. Should be 3 hoses to check. Then I would bleed the brakes starting with the shortest brake line and ending with the longest brake line - so probably LF RF LR RR. Once this is done, the brake peddle should be back to normal.

If there is a bulging hose, then replacing the fluid wont help anything.

If there is no air in the system, then replacing all of the fluid might introduce air, compounding the problem - making it harder to isolate.


Brake fluid wont compress, regardless of its age.

 

[fast 99]

If the excessive travel developed with a full master here are a few possibilities. Am sure there are others. Rear shoes out of adjustment if drum brakes, as suggested swelling brake hose, bad master, loose front wheel bearings causing pad retraction, tight wheel cylinder or caliper. I would do a complete inspection and if nothing found flush fluid being very careful not to run it out.

As an alternate get a turkey baster suck the fluid out of master and refill. Won't be as good as a flush but better than doing nothing.

 

[Grit dog]

^What he said.
I’ve become a big fan of the lazy man’s fluid flush on brakes and power steering. And sometimes differentials if no drain plug and no real reason to open up the differential cover.
If you run the numbers and don’t mind “wasting” fluid at the expense of ease and time, you’ll find that usually 3-5 lazy man flushes gets mostly all new fluid in the system.
I lucked out on both squares as they both had extensive work done to them and very fresh brake fluid. On those I do a single suck and refill bout once a year.
The 77 had a leaky steering return hose so it got self flushed over the first few months. Went thru a couple quarts refilling occasionally. It was the one original component on the new engine the PO had installed in it.
But for the OP, if they’re a little spongy, likely have to figure out the cause which could be bleeding them so may as well do a real flush.
But think about it, the lazy man’s flush is about as good. Most brake calipers have the line coming in the top and the bleeder on top. So not really draining the fluid behind the cylinder completely just during a couple bleed ing sequences.
lazy man’s way allows the old and new fluid to mix for a while (I usually drive for a few weeks or longer between brake refills)

 

[TotalyHucked]

I need to do this as well, the brakes on my '05 work just fine but the pedal goes a little further than I feel it should and just feels mushy. Front and rear brakes are all completely new as of 2mo after buying last summer, parking brake/rear drums are adjusted correctly. Figure it's either old fluid or the booster giving up

 

[fast 99]

Booster failing would cause hard high pedal, suspect master.

 

[Sad Sack]

Some GM ABS systems need the GM Tech2 dealer scanning device to engage the ABS modules solenoids for proper bleeding, whether that pertains to your situation I do not know. I had a 07 Vette that I gravity bled the system and then slow bled after reassembly, but brakes just didn't feel right so I took it in and had dealer use their Tech2 scanning tool for like $69 dollars to bleed the system and it felt much better after I got the car back. So moral of the story is...when in doubt just do the job right the first time.

 

[WFO]

If the excessive travel developed with a full master here are a few possibilities. Am sure there are others. Rear shoes out of adjustment if drum brakes, as suggested swelling brake hose, bad master, loose front wheel bearings causing pad retraction, tight wheel cylinder or caliper. I would do a complete inspection and if nothing found flush fluid being very careful not to run it out.

As an alternate get a turkey baster suck the fluid out of master and refill. Won't be as good as a flush but better than doing nothing.

That's what I was planning on doing, but was wondering if anyone here had any problem with ABS while doing an old school brake bleed.

And it's disc all the way around.

 

[TotalyHucked]

That's what I was planning on doing, but was wondering if anyone here had any problem with ABS while doing an old school brake bleed.

And it's disc all the way around.

I have done an old school bleed on these a couple times and it worked fine, just make sure it's the old school slow pump method, not the rapid pump method.

 

[WFO]

I would try this:

Have someone start the engine and stomp hard on the brakes repeatedly while you check each rubber brake hose for bulging and replace any that are. Should be 3 hoses to check. Then I would bleed the brakes starting with the shortest brake line and ending with the longest brake line - so probably LF RF LR RR. Once this is done, the brake peddle should be back to normal.

If there is a bulging hose, then replacing the fluid wont help anything.

If there is no air in the system, then replacing all of the fluid might introduce air, compounding the problem - making it harder to isolate.


Brake fluid wont compress, regardless of its age.

Just wondering what the reason is to bleed the brakes starting with the shortest line first?
I've always started with the longest first.

 

[WFO]

Some GM ABS systems need the GM Tech2 dealer scanning device to engage the ABS modules solenoids for proper bleeding, whether that pertains to your situation I do not know.

That's why I was asking if anyone had done this on their GMT800.

 

[edgephoto]

suck the master and refill that with clean fluid then just bleed old school. You should do this at minimum every two years. Brake fluid is hygroscopic. Beside the obvious damage water does it significantly lowers the boiling point of the brake fluid. So when you need your brakes the most the fluid boils and you get fading brakes.

Google the boil point charts for brake fluid and you will see that changing the fluid often makes sense.

If those hoses are original you should replace them.

 

[WFO]

I have done an old school bleed on these a couple times and it worked fine, just make sure it's the old school slow pump method, not the rapid pump method.

Much obliged
That's what I was lookin for. You still bled with a dead motor didn't you?
This is the only vehicle I've owned with ABS.

 

[Ricko1966]

I need to do this as well, the brakes on my '05 work just fine but the pedal goes a little further than I feel it should and just feels mushy. Front and rear brakes are all completely new as of 2mo after buying last summer, parking brake/rear drums are adjusted correctly. Figure it's either old fluid or the booster giving up

It's neither. A booster causes a hard pedal not a soft pedal or low. Old brake fluid is still hydraulic,so still noncompressable, so still not a soft pedal or a low pedal. Air in the lines,something out of adjustment,warped rotors,bad wheel bearings,cause low pedal. Some say old brake hoses can expand and cause a low pedal. I've never seen that,they usually swell shut and cause dragging brakes and brake pull.

 

[Ricko1966]

Just wondering what the reason is to bleed the brakes starting with the shortest line first?
I've always started with the longest first.

You do start with the longest line,it removes the most fluid and air minimizing the risk of air bubbles being reintroduced to the system.