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Cadillac & LaSalle Club Forums => Technical / Authenticity => Topic started by: Jeff Rose CLC #28373 on January 11, 2018, 08:45:37 AM

Title: Gasket for brake fluid
Post by: Jeff Rose CLC #28373 on January 11, 2018, 08:45:37 AM
Hello all.
1955 master cylinder cap is leaking. It is the cap with the remote filler line. It is the cap itself leaking, not the filler line. I have tightened it down as much as I dare but I am still losing fluid while just sitting under static pressure. It is a rebuilt cylinder but it didn't come with a new gasket. I tried the old one but it doesnt seem to have any life left in it. I have not had much luck finding just the gasket on-line and would like to find it locally if possible.
I was wondering if just a copper crush gasket would work. I can match the size with a shop at the local airport.
Any thoughts?
Jeff
Title: Re: Gasket for brake fluid
Post by: Jay Friedman on January 11, 2018, 11:33:29 AM
In my experience those gaskets are either rubber or cork.  Here is a new cap for sale for a master cylinder without a remote reservoir that has a gasket and you can see what it looks like.

https://www.ebay.com/itm/1955-61-Chevrolet-Master-Cylinder-Cap-Numbered-8-126A/190800307056?hash=item2c6c95a370:g:msYAAOxyQj9RImgV&vxp=mtr 
Title: Re: Gasket for brake fluid
Post by: TJ Hopland on January 11, 2018, 01:14:42 PM
Copper takes a fair amount of pressure to 'crush' so I would not think that would be ideal for this application.   Cork seems like it would have been an original type of material. 
Title: Re: Gasket for brake fluid
Post by: Jeff Rose CLC #28373 on January 11, 2018, 02:25:53 PM
Ah, that explains a lot. Thanks. What was there was of a thinner plastic coated paper type material. I don't know if it leaked before because it was dry when I got it.
Will go the cork route..... thanks.
Jeff
Title: Re: Gasket for brake fluid
Post by: Roger Zimmermann on January 12, 2018, 01:56:23 AM
Obviously, I don't understand something. How can be the filler tube be under pressure? Do you overfill that reservoir? It must be open to the atmosphere.
Title: Re: Gasket for brake fluid
Post by: Jeff Rose CLC #28373 on January 12, 2018, 10:24:02 AM
No. Just static pressure of the fluid in the line from the reservoir on the firewall down to the master.  It would leak with it just sitting in the garage.
Jeff
Title: Re: Gasket for brake fluid
Post by: Roger Zimmermann on January 12, 2018, 10:50:08 AM
What happens when you are removing the cap? Is the fluid overflowing? If yes, something is wrong in the master cylinder. The residual valve should assure that a very small pressure is present in the closed circuit. If this valve is misfunctioning, the fluid is  (maybe) draining back from the Hydravac into the master cylinder, elevating the fluid level in the reservoir.
If I'm right, that cap must be vented. If everything is functioning as intended, you don't even need a gasket for the cap.

I have the impression that your problem is not the gasket but why the fluid level is such that the fluid is bypassing the cap.
Title: Re: Gasket for brake fluid
Post by: Bob Kielar on January 12, 2018, 11:59:50 AM
Hello Jeff,
              Sorry I'm late to the party. Here are some pictures of the cap and gasket from my 55 Fleetwood. The gasket is not cork personally I would not use cork for the fear of a piece going in the reservoir the edge is kind of fuzzy maybe just gasket material that is old. If you look at the cap there are small holes on the top square where you put a wrench on did you check this? My reservoir leaked one time I had it to full now I fill it to about a inch or inch and a half from the top never leaked again.

Keep Cruzin,
Bob Kielar
Title: Re: Gasket for brake fluid
Post by: Jeff Rose CLC #28373 on January 12, 2018, 12:12:33 PM
Nope, nope. I have been unclear and I am sorry.
Not the reservoir cap, the cap on the master itself.......
Reservoir on the firewall has the tube that runs down to the master. The tube on the master goes into the master's cap that is fitted with a hole to allow the tube to go into it. This is the cap I am talking about. It leaks (not where the tube goes into it) at the cap itself. It is 2 feet below the reservoir so just having fluid in the reservoir is causing it to leak. There is no leak above the master.
Bob, what us your gasket made of?
Jeff

I need 4.5530. My cap is 4.5525 and the tube is 4.5470 (the inset)
Title: Re: Gasket for brake fluid
Post by: J. Gomez on January 12, 2018, 12:24:35 PM
Jeff,

It is/was probably made of a rubber/fiber gasket material, 1/16" maybe  ??? I have made one for my '56 cap with no issues as long as it is not over tight.

Good luck..!
Title: Re: Gasket for brake fluid
Post by: fishnjim on January 12, 2018, 07:58:49 PM
It won't be cork.   Needs to be impervious for DOT 3, cork is too porous.   Rubber swells.   
They used some sort of pressed gasket material from the day* but that doesn't help.   Should be able to find a proper gasket they rebuild these regularly.   
I found some from another make that fit my other car, so don't just look for 55 Cad.  They used these is a variety of years and makes.  Search by your's manufacturer and part numbers; moraine, bendix, wagner, etc.   I searched via internet and found at some hot rod place.    Check with a rebuilder or parts store that sells rebuilts.   Try the Cad parts guys too, like Fusick, et al.   Might be available in a kit.
* - probably outlawed today by OSHA or EPA.
Title: Re: Gasket for brake fluid
Post by: Roger Zimmermann on January 13, 2018, 02:09:43 AM
A drawing is replacing a confused explanation much better! You may now get better answers!
Title: Re: Gasket for brake fluid
Post by: Jeff Rose CLC #28373 on January 13, 2018, 07:34:36 AM
I thought I explained something well and it appears I didn't........... Funny, my wife says the same thing!
Title: Re: Gasket for brake fluid
Post by: Glen on January 14, 2018, 01:05:20 AM
I thought I explained something well and it appears I didn't........... Funny, my wife says the same thing!
I understood it the first time.   Maybe our brains work the same way. 
Title: Re: Gasket for brake fluid
Post by: Jeff Maltby 4194 on January 14, 2018, 01:49:03 PM
Cooper cap gasket like in my 49 rebuild kit.

https://www.ebay.com/itm/1953-1954-1955-BUICK-CADILLAC-PONTIAC-CHEVY-GMC-BRAKE-MASTER-CYLINDER-KIT-USA/382336867244?fits=Year%3A1949%7CMake%3ACadillac%7CModel%3ASeries+62&epid=74469114&hash=item59050d9bac:g:~VkAAOSwfi9ZsREw