Spongy brakes

[MT-2500]

Originally Posted by laxman21

So when my brakes pads wear down, my pedal travels more? I don't think so.

Right on track there Laxman21.

To add a little info.

Worn rear shoes out of adjustment can lower pedal travel.

The original post said spongy brakes.
And little lower than he thought they should.
{Which is sometimes normal with a lot of power brakes.}

But full solid with engine off which would point to just brake booster soft and causing more travel .

If a pedal is more spongy than normal the ABS unit and complete with brake system.
If pedal is lower than normal or not full pedal with engine off check andadjust up rear brake shoes.
Many require a ABS scanner to bleedthe ABS system.

[laxman21]

Originally Posted by j cAT

when pads/and or rotor/drums are excessively worn the amount of brake fluid in the pistons is much larger in volume...this now creates a softer pedal as the fluid needs to be compressed more to create the braking pressure.

when I had to brake very large transportation vehicles I used a pressure supplied bleed machine. the guages told this story quite well.

these toy trucks/vehicles weigh 5,ooolbs..when you bleed brakes for 50,000lbs you must not make stupid mistakes and ignore worn braking componets.

Brake fluid compresses about 1-2% at the most and it is greater at high temperatures, so in all reality you won't notice much at the pedal. Maybe 1/2" to 3/4 at high temperatures.


Don't those very large transportation vehicles use air brakes?

[j cAT]

Originally Posted by laxman21

Brake fluid compresses about 1-2% at the most and it is greater at high temperatures, so in all reality you won't notice much at the pedal. Maybe 1/2" to 3/4 at high temperatures.


Don't those very large transportation vehicles use air brakes?

the large transportation equipment will have , on different manufacturers , air brakes as well. however the hydraulic brakes are superior...very much so ! air brakes suffer from mositure . this then causes braking issues especially in cold weather..

also air does compress very well , compared to hydraulic brake fluid .

when you replace the worn brake componets the brake fluid in the lines and pistons is reduced. this then causes a much harder pedal..

air in the system will also do this ..when bleeding it is important to slowly press down on the brake pedal.. pumping quickly causes air bubbles to form...

with the pressure bleeder I used , we always filled the system with the pressure very low on filling...instead of filling the brake reservior we filled thru the brake calipers this pushed back all the air out the system ...

[laxman21]

Originally Posted by j cAT

the large transportation equipment will have , on different manufacturers , air brakes as well. however the hydraulic brakes are superior...very much so ! air brakes suffer from mositure . this then causes braking issues especially in cold weather..

also air does not compress very well compared to hydraulic brake fluid .

when you replace the worn brake componets the brake fluid in the lines and pistons is reduced. this then causes a much harder pedal..

air in the system will also do this ..when bleeding it is important to slowly press down on the brake pedal.. pumping quickly causes air bubbles to form...

with the pressure bleeder I used , we always filled the system with the pressure very low on filling...instead of filling the brake reservior we filled thru the brake calipers this pushed back all the air out the system ...

Air compresses much better than liquids. But I understand what you are getting at.

[j cAT]

Originally Posted by laxman21

Air compresses much better than liquids. But I understand what you are getting at.

that is true I did not correctly explain that fact.

because brake fluid does not compress as easy as air this is why brake fluids work better with braking systems , than air....also to create a large enough force / volume to get the braking forces required you always get a delay with air brakes..