Bleeding brakes - just another reason to do it

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I'll share my recent brake fiasco.

My 04 GMC Sierra had a mushy pedal since I bought it this past winter. It has 45K now, and I decided to throw a set of pads in the front and inspect the brakes. The pads on the front and rear appear to be brand new. So, in effort to track do that mush pedal feel I bled the brakes. The front calipers had what looked like water bubbles (dirty discolored bubbles) in the fluid. There is no fluid leaks and the brakes respond perfectly now.

I'm a believer of bleeding the system now. Seems like no matter how well sealed the brake system is, moisture can still get in.
 
More likely poor workmanship on whoever replaced the pads the last time. A good example of screwing things up messing with what could have been left alone.
 
BMW recommends brake fluid changes every year on their bikes. Did some track time once with other BMW bikes and one guy came in white as a sheet. His front brake handlebar lever pulled all the way in like it was disconnected - his brake fluid was contaminated with water and it had boiled!
Best to change your fluid at least every 2 to 3 years. I like to use a Mityvac.
 
I see rather than answering my question on the fluid protecting the boots, somebody brought up another subject. I have some questions there too that I have asked before and weren't answered. With so many people not changing their fluid, why isn't boiling more common? Is it because most people are running organic or semi metallic pads that give out long before the fluid boils? Could it be the rare cases of boiling follow somebody topping up with coolant? I know power steering fluid happens all to often. The consequences are quick and undeniable. Coolant wouldn't show until it has a chance to work down to the calipers and hard braking. So blame it on the old fluid and ignore the real problem.
 
Before BITOG, I never did it. EVER, on any car I've driven.
Just had my Honda in for major preventative service and had the fluid flushed. 5 years on it. I'm interested to see/feel the difference.
 
labman, I did not see anything about the 'boots' in your post where you said:

>> You used to be able to run the factory fill on most cars until the rubber parts started to go after 10 years. Still that way with GM.
I interpreted the 'rubber parts' to mean the seals inside the brake cylinders.

You are correct in your belief that brake fluid has no effect on boot longevity, but it may have significant effect on the life of the seals.
 
Well, maybe if you changed the boots.

Actually it is common for calipers to go 10 years without changing anything. Good PM to through in new seals and boots along wiht a good coat of silicone grease on the part of piston having little or no contact with the fluid.
 
I think I'll stick with a diet rich in fiber instead, mechtech2.
pat.gif
 
Quote:

Perform a 'turkey baster' flush at regular intervals.
Clean and easy for you, and it will keep your system fresh and clean.

Click to expand...


That fluid does not circulate like power steering. You must remove the fluid from calipers.
 
Looks like I'll be doing this soon. I have never bleed the brakes. The dealership(s) insist that it's a "lifetime" fill and they only have to top it off at every service. They said they same thing about my coolant and gear oil.
 
That is interesting. The owners' manual for my Chevy says never top off the brake fluid. It drops as the pads wear, but comes back up with new pads. Otherwise, you should fix the leak rather than top up.

I wonder if occasional accidental topping up with coolant accounts for the rare instances of problems due to excess moisture? I do know of swift problems from topping up with power steering fluid. More ways to get in trouble doing unnecessary messing around. Haven't had the cap off my 02 in 85 K.
 
labman, caliper seals cant block out 100% of the moisture. the piston is "wetted" with brake fluid internally, as it goes outward some of this fluid stays on the surface of the piston which collects moisture. when the piston goes back inside, some of that moisture which is on the piston wall goes back into the caliper.
 
Quote:

labman, caliper seals cant block out 100% of the moisture. the piston is "wetted" with brake fluid internally, as it goes outward some of this fluid stays on the surface of the piston which collects moisture. when the piston goes back inside, some of that moisture which is on the piston wall goes back into the caliper.

Click to expand...


So true. And to make matters worse, brake fluid absorb's moisture. The main reason I flush my brake system every year isn't that the fluid itself is bad. It's to remove the moisture that is traped in the fluid that causes rust.

Another thing to remember. Whatever you do, never ever put silicone (Dot 5) brake fluid in a system that takes DOT 4 fluid. You haven't seen a leaking system until you see one that had done.
 
The pistons don't move that much, and what little movement is mostly out. The outer part of the piston doesn't touch the current fluid from one pad change to the next. Yes, the boots do allow some moisture in, and the older they get, the more. Changing the fluid may line your stealer's pocket, but it does nothing for the outer part of the piston where trouble starts. You need to take at look at the real world.
 
alright lets talk about real world.
real world is me using a grease gun to blow out pistons which have stuck into the bores because their previous owners felt it was not nessassary to bleed brakes once every 2 years or so. once those pistons are out, the ammount of black gunk and surface rust BEHIND the ring is incredible. ive got calipers that i cant even rebuild because the pistons and bores are too rusted out behind the ring seal. in front of the ring seal its even worse. ive seen flakes of rust in those areas.

as i said, no piston seal is 100% waterproof. even when you look at hydraulic cylinders, the shafts are awalys lightly coated in fluid even when they are extended out of the cylinder. when they go back in they take with them some of the contaminants.
think of how many thousands of times a brake piston goes in and out over the course of a few years.
i rebuild special oversize porsche calipers and sell them on ebay with some lines and pads as an oversize brake kit. ive done enough of them to know!
 
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