Oversized master cylinder


Old 02-02-04, 05:07 PM
GregH's Avatar
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Oversized master cylinder

'88 Dodge 3/4 ton, 4x4, 4 spd trans, 318 tbi

Due to 40 below weather and no heated shop I had to get a local shop to perform some finishing touches to my latest project.
I picked up the vehicle with spongy brakes and have to return it in the morning.

The secretary was the only one there and said the service notes said they had trouble bleeding the brakes and found the master cylinder was the wrong one.
What they installed was one that looked like it was possibly from a one ton.
My question is, will an oversized master cylinder cause any operational problems or would it work as well as the original smaller one?
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Old 02-02-04, 05:13 PM
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Definately cause problems. Increased bore size changes hydraulic pressure, assuming the bore is different. Your mismatching what engineers designed.
Old 02-02-04, 10:47 PM
mike from nj
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true, the one ton should have a dana 60 rear, and with bigger shoes, and bigger wheel cylinders. they corrospond to a bigger master cylinder. it would also have bigger calipers and front rotors

you could either have a hard pedal, but never stop. or you could have super sensitive brakes. or you might not ever notice it, depends on how different the size is.

the only concern you should have is for the bore size. some aftermarket manufacturers cast their own stuff, and they look nothing like the original stuff, but the bore would be the same.

the brand name and part number should be on the invoice. call around and see if the numbers are right. then worry that if the wrong part was put in the correct box.
Old 02-03-04, 05:19 AM
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I do have the Dana 60 but when I ordered the rear shoes I remember it took the smaller of the two they had.

Right now the problem with the braking is that the pedal goes too far before braking begins.
It could be that the push rod is too short.

I have the old master cylinder and will put it back myself.

I'll let you know what happens.

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