quick brake pedal travel question

[r67northern]

Hi All,

I know I've been spoiled by new brakes on things like my '06 Rainier, but yesterday in a panic stop my 1990 suburban let me punch the pedal to the floor. That doesn't seem right to me (it did stop though).

I can't detect any leakage past the cylinder if I just hold the pedal down. So should I be able to hit the floor in a panic stop (assume that I'm not a body builder for this question)?

Thanks for the input.

 

[HotRodPC]

Adjust your rear brake shoes and also inspect the linings. Although the rear brakes aren't the biggest percentage of your stopping power, they do affect the pedal travel the most.

A good tell tale sign that your rear brakes are getting out of adjustment, and/or linings getting low, is how far does your park brake travel before you feel it get tight. If it's going real low before starting to feel tight, it's time for rear brake adjustment and inspection.

 

[chengny]

If you check your rears and find that they are within tolerance (and you are sure there is no air in the system), but you still get excessive travel when you hit them hard and fast - and yet, get normal pedal travel/resistance when the brakes are applied slowly and gently - it's probably time for a new M/C.

As the rubber cups (seals) within the M/C get old, they begin to lose their flexibility. Normally ,when new, the lips of the cups respond quickly. They immediately press outward onto the cylinder wall when the brakes are applied - even in situations where the brakes are slammed on.

But when they have lost their flexibilty, and the brakes are quickly applied, they just slide right down the inner walls of the cylinder without creating a seal.

The results are; the plunger presents no resistance to foot pressure, and since no seal is created , limited hydraulic pressure is developed in the system.


No Pedal / Sinking Pedal


CAUSES
A brake pedal that sinks all the way to the floor is the result of the master-cylinder not developing any hydraulic pressure. This can be caused by a severe fluid leak which has emptied the master-cylinder, or by complete failure of the seals inside the master-cylinder.

A pedal that slowly sinks to the floor is the result of hydraulic pressure leaking off. This may be from an internal leak in the master-cylinder or an external brake fluid leak.

NOTE: Rear brakes which are extremely out of adjustment in conjunction with air in the hydraulic lines can also produce this symptom. Always verify that the shoes/linings are properly adjusted and the brakes have been bled prior to replacing a master-cylinder.

 

[r67northern]

Thanks for the input guys, I'll work on tracking this problem down starting with the rear drums.

-Leland

 

[Greybeard]

What they said^^^...assuming the first thing you did was look under it for puddles.

I've had two brake systems rust out on me this year alone. On my 02 Dodge 2500 and my 02 Ford Focus. They worked fine until the panic stop and then slammed to the floor. So if they never regained to what they were before the panic stop I would consider a broken line first. If they went back to working as they did before the panic stop I'd consider at least one of the previous scenarios.

 

[highdesertrange]

great advice so far, can't really add anything. let us know what you find. highdesertranger