2nd Gen Non-Engine/Transmission Soft brake pedal after starting the truck

[TboneMan]

Hi all,



For the past week or so, I have been experiencing a strange phenomenon. The first time I use my brakes after starting my truck (after it has sat for a couple of hours) the pedal seems VERY soft. The brakes engage, but I have to pump the brake a time or two to get the "normal" pedal feel.



I do not experience this after the initial brake application.



The brake fluid reservoir is about a 1/4 inch below the full mark. I am keeping an eye on this, but I figure that if I had a leak, I'd experience soft pedal all of the time.



Any help would be greatly appreciated.



p. s. the 2001. 5 had front and rear disk breaks standard.

 

[dieselshu]

soft brake

Are getting any codes or check lights?



Dave

 

[TboneMan]

I have not check for codes, and I do not have any luminated idiot lights.

 

[RustyJC]

Does the brake pedal slowly sink to the floor if you hold constant pressure on it (classic sign of a leaking master cylinder)?



Rusty

 

[TboneMan]

RustyJC, I will try this technique tonight when I head home from work.



I am assuming this should be done after the pressure has built up.

 

[TboneMan]

As a follow-up... . I held the pedal down (with far more pressure than I normally use for braking) and the pedal held.



Any other suggestions?

 

[scotmartin]

Maybe it's an internal leak in the hydro-boost system?? Can someone pipe in who has had more experience troubleshooting this system?



Scot

 

[Rman]

how long has it been since a change? Hydraulic fluid has a natural ability to retain water (there's a fancy term for this, it's eluding me at the moment) Perhaps you have some trapped water in the lines and when starting you purge it. As the brakes get used, this water can evaporate leading to trapped air. Bottom line is change fluid regularly. The common interval is 2 years. I do it once a year to be on the safe side. Check your brake lines too, the rubber can swell and cause sponginess.



Hydraulics are really simple systems, pressure here means pressure there kind of thing, but air and water can cause weird things to happen. Sounds to me like your getting air in your lines from some where. Then you purge it out when depressing the pedal for the first time.

 

[TboneMan]

Change the brake fluid???? You're suppose to change that too?:--)



No I have'nt change the brake fluid (82,000 on odometer), but your explanation makes some sense. I have been figuring I'd need some new pads soon (these are the original). I guess I'll take beast in for a brake checkup.

 

[Rman]

OH MY! I would definitly start there. Go get some good brake fluid (I just use the DOT4 valvoline at autozone) and flush the system really well. Then bleed them and start over with troubleshooting. I bet it solves your problem. They make handy do it yourself tools, but hell i just use the wife to press the brake pedal. Don't let that master cylinder get empty, keep filling it as you drain the fluid. Bleed from the longest to the shortest brake line.

 

[Tardog]

And as another member has mentioned , when bleeding the brakes with the "pump the pedal method" never push the pedal down past where it normally gets used as this has a potential of scoring the seals in the Master C from years of crude and rust?

 

[Rman]

tardog is correct, the water that may have accumulated does corrode the cylinder, normally the bottom. This pitting and deterioration will foul the seals, causing the MC to leak and ultimately having to be replaced. Rebuilding by honing the cylinders and replacing the seals is possible, but i always end up leaking again much sooner then buying a new one.



Brake systems are simple, but must be maintained just like the engine and transmission.

 

[illflem]

Originally posted by rhickman

Hydraulic fluid has a natural ability to retain water (there's a fancy term for this, it's eluding me at the moment)

hygroscopic

 

[Rman]

thanks bill, i knew someone would chime in with the winning answer.