brakes

i just rebuilt my calipes and when i pump my brake laver fast it sprays brake fluid out of the master cylinder.i did get the fluid to come out at the calipers but the laver is still sloppy.if i pump it like for times it feels good and it sitls a litle and goes back to sloppy.do i need to replace the master cylender seels or do i still have air in the hoses?thw two sides have nice fluid coming out with no air bubbles.i i rebuild the master cylinder do i have to rebleed the brakes?or can it be rebuild without bleeding agien.

 

Give us some more information about your bike first. Model, year, size ect. It helps to know when diagnosing problems.

 

o sorry.its a 1982 yamaha maxim xj750.

 

Usually we rebuild the MC at the same time as the calipers. If you are getting a strong fountain out of the MC when you squeeze the lever, that indicates that you need to rebuild it because one of the seals isn't working.

 

Pump it slowly! I have found even on a rebuilt M/C if you pump them to fast you will get a strong fountain.

 

And while you are at it.
Check those brake lines!! If you still have the old stock rubber brake lines there will be a date code stamped into them. Original brake lines were good for 4 years maximum. Save yourself the trouble of having to rebleed the brakes for a third time. Replace them when you do the master cylinder.

On to the subject at hand.
If you still have a soft lever after bleeding the brakes. It is a very good indication that you either still have air in the system, or you have worn seals in the MC. Rebuilding the calipers is only one step in restoring the brakes to proper safe operation.

Yes it cost more money. Is your life worth the few dollars you are trying to save?

Ghost

 

Thank you all.if i pump it slow it does not shot aby fluid out its when i go really fast.aslo i did not replace the little copper washers do i need to replace them too?

 

They are called crush washers and they are supposed to be replaced every time you take them off.

 

The Master Cylinder Body is a PUMP.
It has (2) Seals.

The REAR Seal:
Keeps the Fluid from Leaking out of the Bore.
It Pushes Brake Fluid through the TINY "Replenishment Holes" on the Piston where Brake Fluid flows :::> One Way <::: past the MAIN HYDRAULIC SEAL.

The MAIN HYDRAULIC SEAL:
PUMPS Brake Fluid out of the Master Cylinder.
IT ::: SEALS ::: Not allowing Fluid to Re-Enter the MC Bore to Maintain Hydraulic Pressure in the System.

IF, ... The Brake Fluid in the Master Cylinder --> "Fountains-Upwards" out of the Master Cylinder Bore when the Lever is Pulled ::: The Master Cylinder is malfunctioning.

The "Excessive Fountaning" is caused by the REAR (Outboard) Seal applying Pressure to the Volume of Fluid in the MC Bore which has NOT been "Moved-out" by the MAIN Hydraulic SEAL.

Pressure in the System FAILS in Front of the MAIN SEAL
Pressure is NOT applied to the System by the MAIN SEAL
The MAIN SEAL's Failure ALLOWS Pressure to develop within the BORE of the MC, ... >> BEFORE the REAR Seal.

Because the Fluid in the System was NOT Pumped toward the Calipers by the Failed Main Hydraulic Seal ...
Hydraulic Pressure develops within the MC Bore.
The Fluid, ... NOW under Pressure from the REAR Seal, ... seeks the LEAST Point of Resistance to escape.

Fluid is PUSHED-OUT the Tiny Fluid Replenishment Port.

Now, ... Under Pressure, ... it SQUIRTS-UP HIGH.

Indicating that the:
Main Hydraulic Seal is Bad, ...
Compromised
Torn
Leaking
-Or-
Bore is Pitted
Scratched
Compromised with debris.
-Or-
Hydraulic Seal is on Backward
-Or-
CUP is Inverted, Squished, Punctured
Missing


The Brake Fluid in the Master Cylinder is supposes to be FORCED-Out of the MC at the OUTLET

NOT back into the Reservoir.

 

rickcomatic i like your post great info.thank you.the fluid only sprays out if i press the brake fast couple off times.if i have the cover on the MC and it sits over night the brake can be pressed all the way in but if i pump it 4 - 5 times it feels good,and after sitting its soft agien.so do you guys think it is the master cylinder or air in the system?

 

1

 

If you haven't rebuilt the MC, then that is likely at least part of the problem. Right after rebuild, I could rapidly squeeze mine and only see a weak fountain, not enough to spray out and make a mess. And, you might still have air in the lines, too!
You might try adjusting the brake lever screw. If it is too far out your lever will hit the handlebars and it might feel like you have spongy brakes when really it is just not pushing hard on the piston in the Master Cylinder.