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Master Cylinder FAQ




How does a disc brake master differ from a drum brake master?
A drum brake master will differ from a disc brake master in two ways. The amount of fluid that a drum brake master has to move is less than disc brake. Drum brake masters have 10 lb residual valves at the outlet to keep a residual pressure on the drums. If you use a drum brake master for disc brakes you would move an insufficient volume of fluid and the disc brakes would drag because of the residual valves.
What will happen if I use a master cylinder for drum brakes and it doesn't have a residual valve?
You will have a spongy pedal and you'll have to pump the pedal to get good brakes.
I have manual brakes and I have an extremely hard pedal. Why?
Check the bore size of your master. If it is larger than 1" then you will have a very hard pedal.
What bore size do you need for manual brakes?
If you use anything larger than 1" then you will have an extremely hard pedal.The smaller the bore the more pressure that is output to the wheels.
What is the difference between a power brake master and a manual brake master?
A power brake master will have a larger bore diameter than a manual master.
Can I use a shallow hole master in a manual brake application.
No. The piston hole must be deep so the manual push rod does not fall out.
Can I use my manual master on a booster?
Can I use a power brake master without a booster?
Usually not. The bore size will be too large giving a hard pedal and the piston hole will be shallow allowing the push rod to fall out.
Why is one fluid chamber larger than the other in a disc/drum master?
As disc brake pads wear the caliper pistons will move outward. The fluid level in the master will drop more rapidly than the drum portion so you need more reserve.
Should I buy a rebuilt or new master?
Always try to use a new master. Rebuilts tend to have a high failure rate.. The best way to rebuild a master is to stainless steel sleeve it.
Can I use a disc/drum master for four wheel disc brakes?
Usually not. For 4 wheel disc brakes to function properly you will need a master that has a longer stroke.
How can I tell if my master cylinder is bad?
You will have very spongy brakes. Also when you hold your foot on the brake pedal it will sink slowly toward the floor.
Why should I eliminate my single piston master?
Safety. By going to a split system the possibility of a complete brake failure is virtually eliminated.
Can I rebuild my master myself?
Yes, but you must have the correct rebuilding kit. Also check the bore to be sure it is not pitted or corroded.
I purchased a replacement master and It does not look like the original. Can I use it?
Probably yes. Many aftermarket replacement masters will have a different casting look but be the same internally.