Re: {Chrysler 300} Brake master cylinders for 56-61 Chryslers

On Tue, Jul 2, 2024, 1:57 PM Carl Bilter <cbilter@xxxxxxxxx> wrote:

Hello all in 300 land and thanks to everyone on their feedback re. the leaking MC lid issue.
Special thanks to Nick Taylor for his helpful info on the lid bolts and gaskets.

I am hopeful that the gasket is the issue, we'll see in a day or two. As a followup, I did a comparison study. If this solves the issue, Bob may find this "e-newsworthy."

I have three new master cylinders (all made in China) and the old one that was on the G previously, which is approx. 20 yrs old, made in USA, and sourced by the P.O likely from his local NAPA.
The new master tops all have very good, flat surfaces on the castings which should provide a good seal.
All the lids are essentailly identical dimensionally and nearly the same in weight, and so likely comparable.
The gaskets and lid bolts are not all the same.
The gaskets' composition seems to be of similar materials, just different colors.

Here are the MC stats:

1. Raybestos MC36063 from Rock Auto: lid weight 3.8 oz. Gasket thickness is .051" Lid bolt is 1/4" coarse thread (1/4"-20) with 10mm head
2. Brake Best Select NMC90016 from O'Reilly Auto Parts: lid weight is 3.6 oz Gasket thickness is .058" Lid bolt is 1/4" fine thread (1/4"-28) with 10mm head
3. Bernbaum (MC is identical to the O'Reilly)
4. Old master cylinder: lid weight 3.6 oz, Gasket thickness is .070" lid bolt is 1/4" coarse thread with 7/16" head

This photo shows that the old gasket (left) is notably thicker than the new Raybestos one (right) It also has perhaps just a marginally larger diameter (it fits better in the lid):

This photo shows the differences in the lid bolts. The O'Reilly bolt (top) is threaded all the way to the top, with no provision to prevent over tightening
Raybestos bolt in the middle, old MC bolt on the bottom:

I've installed the old gasket and old 7/16" head bolt in the new Raybestos MC lid; we'll see what happens.

Carl B.

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Re: {Chrysler 300} Brake master cylinders for 56-61 Chryslers - followup on lids and gaskets