In search of the OEM Master Cylinder bore size (Page 1/1)
Signupacct SEP 26, 02:13 PM
Ok

I would like to post this as a separate thread since it hopefully will provide the best answer(s) to this question on this forum and perhaps elsewhere.

I searched all OEM documentation and websites to confirm the bore size.

Perhaps there is someone out there that can help determine OEM specs on the bore size.

and it is commonly discussed that the bore size will affect the performance of the brakes, too smaller and mushy and too large and less brake force to the pads etc.

So thanks to fierogt28 for pointing to Rock Auto site for an opportunity to make some deductive determinations. Here is a copy of the post that is elsewhere and under a different title and thus may be missed:
fierogt28 you are on my Christmas card list.

I finally can see at least what the specs are for the bore size on the RockAuto website. Though I have not been able to find any OEM documentation that specifies that OEM is 1 inch.

But the preponderance of the evidence in that most of the units listed at Rock Auto are 1.0

Raybestos, AC Delco and Centric all list as 1.0 inch

With AC Delco being the 1 inch it is likely that is the OEM bore size.

the NM1988 which is Duralast which I have here is 1.4 inch. It goes back to Autozone.

It is listed as NM1988 by FVP and DFC and Quality Built are all listing at Rock Auto as 1.4 inch


Joe k

[This message has been edited by Signupacct (edited 09-27-2024).]

1985 Fiero GT SEP 26, 07:49 PM
I don't know the exact numbers, only that there are 2 different numbers, all brake master cylinders for the Fiero have a "quick pick up" larger diameter bore initially, and a smaller diameter bore after that for the rear circuit. The front circuit is the same bore as the smaller rear bore. Check out the ogre's Fiero cave for more info, even though he is no longer a participating part of this forum, his information is very precise and I'm sure he has that number on his site.