midiwall

So... I had The Local Guy power flush my brake lines a couple of weeks ago.

When I drove off, the pedal went farther to the floor than it had, but it was well within my personal safety level. I'm thinking that there's air in the line and "I'll get to it".

So two days ago I'm out driving around, head for the brakes and push, push harder, push harder... @*&$^!!! The pedal's about 2" off the floor at the point the truck stops. This is outside of my "personal safety level". So much for the "air in the line" theory.

I stopped in on The Local Guy this morning, and he told me that what can happen is that the power flush will knock crap off of the O-rings in the piston and there's not enough left of the rings themselves to give a good seal. As a test, pumping the brake pedal (engine off) does _not_ get harder. That seems to match his theory.

Am I right in thinking that he's right? fwiw, this is the original master cylinder in the truck, 126k miles.

Good Times

It sounds like your master cylinder could be bad or needs replacing.

AgRunner06

I also think you should check and make sure you aren't leaking any fluid anywhere.

rimpainter.com

Bleed it first, then get the MC replaced if it still does it.

midiwall

Nope, no leaks...

And yeah Christien, I'll cross my fingers and try to bleed it. The thing though is that even with an air bubble, I'd expect the pedal pressure to come up in a couple of pumps. Maybe not.

Our buddy Todd here ("TOR") just gave me a great quote on a new master, so I may just go ahead and do it.

HondaTec521

Naw,if you have air in the system,your pedal wont pump up.I would try manual bleeding(dont push the pedal to the floor-inside the mastercyl. bore corosion builds up where your piston seal never travels.about halfway is recommened)If it still is mushy after bleeding your looking at a new master.

midiwall

Well, I have a new master cylinder on the way (thanks TOR!) and I think I'll just replace it. If I take the time to bleed the brakes and all, then find that I need a new master anyway, it becomes wasted time and fluid. I figure that at 126k miles, I'll be happier knowing that there's a new master under the hood.


Thanks for your help folks!

FunRunner01

Did this fix your problem? I think I have the same issue brewing, but do not know what to do.... My post is at https://www.yotatech.com/forums/show...608#post364608

midiwall

Hi there;

The short answer is "no, it wasn't the master cylinder, and I never had to install it".

I posted into your thread, and I don't want to confuse the issue by posting the same thing over here. So let's let this thread continue in yours.

FunRunner01

But since I did my brakes, and did not open the valves, how did I get air in the system, should I be concerned it will happen again?

Figit090

Well i can't help you on the brake cylinder problem, but i will say that if you use this truck as a daily driver... try using your e-brake once or twice to get the feel for it and check it to make sure it works... it would really suck if that didn't even work!

FunRunner01

It just seems the brembo rotors will never feel like the OEM, they are spongy, but responsive.

midiwall

Hmmm... "spongy, but responsive" seems like an interesting mating of terms.

If they're responsive, then I dunno that your sponginess is coming from the rotors. I wouldn't think that a solid hunk of steel like that could produce a "spongy" feeling. Ya' know? The same kinda' goes for the pads.


Man, I'm still thinking you've got something going on with your brake fluid. Maybe it's water, not air. Brake fluid will actually attract water, and water won't compress the same what that brake fluid does, it's "softer", and THAT could be a source of the spongy feeling.

Given that this is a 2001, have you ever had the brake fluid _replaced_ (not just flushed, but completely drained and replaced)? The general feeling is that brake fluid is good for about 2 years, that seems to be the threshold on when it breaks down so much from moisture that it reduces it's effectiveness.

FunRunner01

Well, the truck stops great, it is just toward the bottom of the pedal, not the top. they did a power flush and went over the whole braking system checking for problems, even to the point of measuring pressure put on each caliper by the master cylinder. I am at a loss....

Is there a way adjust the brake pedal so it bites earlier on? Is this not a good idea?

midiwall

No, there's no mechanical adjustment like you're thinking of... What you're looking at is a symptom of a problem that could lead to really bad results so it's gotta get fixed.


Okay, working from the symptom, let's look at what's physically happening.

The symptom is being caused by the lack of pressure in the braking system. This means that:

1. The fluid isn't standing up to the pressure of the system
   • The fluid is old
   • The fluid is contaminated with water or air
   
   
2. There's not enough fluid in the system
   • Make sure that the reservoir is full. Have a buddy help you by pressing down on the brake pedal while you watch the fluid level.
   
   
3. There's too much motion at one or more of the endpoints of the system
   • This would possibly be from worn pads or shoes, or maladjusted rear brakes
   
   
4. The system itself has a leak and is allowing pressure to escape
   • This could be in a line, in a brake cylinder, caliper or at the master cylinder
   • If you have anti-lock brakes, check the lines as they enter/exit the distribution block

It sounds like you've covered a lot of these points, but if the symptom is still there, then so is the problem.

It MAY be the master cylinder - my symptoms were VERY similar to yours and while it turned out not to be the MC, the MC may be the source of yours.

fwiw, I still have my new MC (part #47201-3D380) - it's never been out of the box. I paid $157 for it including shipping and if you wanna try it, it's yours for the same. Just lemme know.

shovelhead

Does your truck have antilock brakes? That can open up a whole lot of problems if the system isn't flushed correctly

FunRunner01

My truck does have antilock brakes, but the powerflush and adjustment helped alot, it just seems that it has a different feel than the OEM setup, not bad just different.

My rig does pull to the left during hard braking now, that is weird, but it can easily stop, even fully loaded. I think I just need to realize it is going to be different.

Mad Chemist

If its pulling hard to one side, you may have a caliper thats sticking on occassion, may or may not be related to your other "issues." I just switched to slotted/drilled rotors last week, no brake flush though, system wasn't opened up, and the pedal still feels the same, with improved stopping power. I'm just wondering whether the way it feels now is the way its supposed to be, and you're just noticing the difference after getting used to the "old" setup. Might be worth letting someone else drive your rig and see what they think. Good luck Shannon!

Figit090

Been offroading lately? Even if you haven't, you could check all the tires for correct and even tire pressure (i would) ...if one's lower it would cause uneven stopping.

midiwall

FYI.... that's not Shannon. Shannon is Funrunner, this is FunRunner01.