I am trying to reduce the pedal travel and increase it's feel by going to the J65 MC that had the 1" bore. However, I just went to NAPA and bought a MC for an 86 disc/disc car (which should be J65) and they gave me the same MC I have now, with 18006814 cast in the bottom. Where can I get the real J65 MC?

 

Oooh, ooh, what is the difference in master cylinder sizes?

I was under the impression that the MC was the same on all of these cars and only the prop valve was difference on a few of them.

 

No, the J65 master which came on disc/disc cars up to 89 had a 1" bore. The J50, which came on all disc/drum and all cars 90-92 has a 15/16" bore.

 

Sorry for bringing this back from the death. I realize most say to use the J50 with the 1LE valve with the 1LE setup front and rear.

My 89 has the rear PBRs and I am going with Ed's C4 setup in the front and am going to change the valve to the correct 1LE 14089496.


Regarding the MC what exactly would the 1/16 difference between the bore sizes do ?

I understand the J65 I have has a 1 inch bore and the J50 ( rear drum ) MC has a 15/16 bore. Thx for any replies.

 

A larger bore increases pedal effort and reduces pedal travel.

 

That being the case I don't see why I should should
change to the smaller bore of the J50. I have read multiple times it is the MC used with the 1LE setup.

 

So the final word on this is......there isn't much if any difference between the two ?

 

Pretty much. GM even put out a TSB telling dealers to change one for the other if the customer didn't like the pedal feel.

 

Thx

 

exactly.

the fluid displacement vs pedal travel is almost identical.

you will get a larger pedal diff depending on how soft the bottom of your sneaker is.... lol.