Carl,I just checked the bolts between the Raybestos master and the old Mopar one. While the head of the bolt on the new one is 10mm, the bolt itself is still 1/4-20.I can't tell that the new cap is any lower quality than the old one. My old one is pretty crusty and has been over tightened in the past and it's pushed in at the top.The top of the master cylinder is very well machined and very flat. The cardboard gasket is much thinner though and doesn't fit as well in the lid, so that may be what's causing your leak. The gasket from the old lid fits in the new one fine.Nick--On Mon, Jul 1, 2024, 6:46 PM Carl Bilter <cbilter@xxxxxxxxx> wrote:--Thanks for the suggestions Ron. Thought of using an old cap but they all have a bigger center hole for the larger 7/16" hex head bolt that was used in the past. I'm stuck with the 10mm bolt. And that bolt is likely only a grade 2, don't dare overtighten. I could try a thicker gasket and sealing the gasket to the cap.Carl------ Original Message ------From "Ron Waters" <ronbo97@xxxxxxxxxxx>To "'Carl Bilter'" <cbilter@xxxxxxxxx>; chrysler-300-club-international@xxxxxxxxxxxxxxxxDate 7/1/2024 7:55:16 PMSubject RE: {Chrysler 300} Brake master cylinders for 56-61 Chryslers - heads up--A couple of thoughts, Carl.
Could you reuse your old cap ? Can you fabricate a gasket of thicker material, then use Indian Head gasket sealer to attach it to the cap ? Let it dry overnight, then cover the master and tighten the bolt. Retest.
Ron
From: chrysler-300-club-international@xxxxxxxxxxxxxxxx On Behalf Of Carl Bilter
Sent: Monday, July 01, 2024 7:15 PM
To: chrysler-300-club-international@xxxxxxxxxxxxxxxx
Subject: {Chrysler 300} Brake master cylinders for 56-61 Chryslers - heads up
I hesitate to write a post that sounds like whining, but I think it is a valid heads up and a statement about the current availability/quality of master cylinders for 56-61 300s (and other Mopars).
After much searching, and much to my delight, I found a listing on ebay that offered a "made in USA" brand new master cylinder for the above mentioned cars:
Turns out that the seller is Andy Bernbaum, with whom historically I have had good experiences.
So I ordered the part, and when it arrived, much to my disappointment, the part did not match the photo in the listing, as it does not say "made in USA" on the boot or anywhere else on the part.
No manufacturer box or instruction sheet was included either indicating country of origin. The part was absolutely IDENTICAL to the Chinese made master cylinder that I had recently bouight at O'Reilly Auto Parts for $10 less! It will fit of course, but will be no better quality than the part I already have. So I am returning the part.
The problem I'm having with the new Chinese made master cytlinders (all of them) is that they leak from the cap! No matter how tight, or how full or not the reservior is with fluid (I'm using DOT5 silicone), the cap/gasket will not seal well. I do not have this issue with my older American made masters cylinders or even the Chinese master cylinders from a few years ago. The casting looks ok as does the gasket material. I chalk it up to poor quality. I may try doubling up the gasket? Running out of ideas. The cap bolt is also metric spec now (10mm hex head) - all of them - rather than the familiar 7/16" that was used even just a few years ago. And yes, I bench bled the master per instructions, and actually, the Raybestos master (Chinese) says to not bench bleed or you will destroy the piston seal; so you bleed on the car (and waste fluid).
The plug in the bottom port will tend to leak some as well, despite using thread sealer, but that's not a new issue and some of the older American made units will do that as well.
Other than leaking, the Chinese made masters seem to function well.
Anyone else having this issue? Solutions?
Carl B
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