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Old 09-27-2020, 05:56 PM   #1
msg
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Brake leak at the master cylinder and booster - remove and fix?

I had recently installed a new master cylinder to a booster and run all new lines and done a bleed. The truck isnt in running condition yet so I havent been able to test the brakes. All is well except this very slow leak that doesnt seem to be coming from anywhere I can see except a trail from the master cyl to the booster connection. Is it overfilled maybe?
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Old 09-27-2020, 07:46 PM   #2
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Re: Brake leak at the master cylinder and booster - remove and fix?

Hmmm, could be coming from the rear of the MC where the pushrod goes in?
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Old 09-27-2020, 07:56 PM   #3
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Re: Brake leak at the master cylinder and booster - remove and fix?

Bad master. Swap it out.
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Old 09-28-2020, 02:18 PM   #4
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Re: Brake leak at the master cylinder and booster - remove and fix?

What a pain, I bought that new at Summit but it was a Dorman vs AC Delco, not sure if AC Delco is that much better but would be closer to OEM I would think.

Here is what failed

https://www.summitracing.com/parts/DHB-M76162

and I was going to get this AC Delco as a replacement. The specs look the same.
Seem right? I cant get any tech help at Summit.

https://www.summitracing.com/parts/a...1878?rrec=true
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Old 09-28-2020, 02:27 PM   #5
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Re: Brake leak at the master cylinder and booster - remove and fix?

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... not sure if AC Delco is that much better but would be closer to OEM I would think. ...
I think the one dollar difference would be well spent.
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Old 09-29-2020, 10:08 AM   #6
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Re: Brake leak at the master cylinder and booster - remove and fix?

Bought the AC delco last night and returned the Dorman. Waiting on a bench bleed syringe today from a local parts store and Ill do this all again. The brake fluid had leaked into that area of the booster so I cleaned it out but now Im concerned about what damage may have happened to the booster. I didn't notice the leak until 4 days ago after I had to re route brake lines from a previous install a few months back when the master cyl was new. Any tests that I can run on the booster before I put the master cyl on? Also some grease in the booster area there I removed just to clean out the brake fluid, so I would need to re apply some kind of grease.
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Old 09-29-2020, 10:15 AM   #7
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Re: Brake leak at the master cylinder and booster - remove and fix?

I'd measure that booster pin against the master cylinder depth before I'd install it again.
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Old 09-29-2020, 10:23 AM   #8
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Re: Brake leak at the master cylinder and booster - remove and fix?

Thanks Rocknrod, so I need a tool like this then?

https://www.youtube.com/watch?v=llA9t_Ao6Cw
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Old 09-29-2020, 10:38 AM   #9
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Re: Brake leak at the master cylinder and booster - remove and fix?

I use one like that.
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Old 09-29-2020, 12:37 PM   #10
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Re: Brake leak at the master cylinder and booster - remove and fix?

I can order one but before I do I thought to try and follow what this guy did to measure with a straight edge and a caliper which I do have.

https://www.youtube.com/watch?v=rYYzPIGoxfY

Around the 33:43 time stamp he gets to it with the how to measure. 1st thing I see is that the pin on his booster protrudes out and so far mine is still in the well nearly 5mm. Shouldnt it be further out? I depressed the pedal and let it release and thats the measurement I got.
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Old 09-29-2020, 01:48 PM   #11
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Re: Brake leak at the master cylinder and booster - remove and fix?

few more pics of the setup inside before pressing the pedal
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Old 09-29-2020, 01:49 PM   #12
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Re: Brake leak at the master cylinder and booster - remove and fix?

and here is one with the pedal fully depressed
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Old 09-29-2020, 02:22 PM   #13
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Re: Brake leak at the master cylinder and booster - remove and fix?

Found a pic of when I removed it and what it looked like. The pin looks recessed at the same level. Strange because for the years that I drove it after a local shop did the conversion for me I never had any braking issues. But since my restoration I have learned that they didnt run the brake lines correctly. They ran them really close to the headers. And there was no proportioning valve all that time, and Ive learned since that they should have installed one since its front disc rear drum.
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Old 09-29-2020, 04:08 PM   #14
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Re: Brake leak at the master cylinder and booster - remove and fix?

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few more pics of the setup inside before pressing the pedal
Wow, I never did anything like that in the last 48 years. I have read and done this though - https://techtalk.mpbrakes.com/how-to...r-cylinder-gap
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Old 10-01-2020, 01:10 PM   #15
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Re: Brake leak at the master cylinder and booster - remove and fix?

I didnt put a gasket on before, these dont have one do they?
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Old 10-01-2020, 01:42 PM   #16
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Re: Brake leak at the master cylinder and booster - remove and fix?

Not between the master and the booster, no.
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Old 10-01-2020, 01:49 PM   #17
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Re: Brake leak at the master cylinder and booster - remove and fix?

I didnt think so. Seems like if I had before all that brake fluid would not have dripped out but in towards the booster. I bought the cheap knock off and now need to return iot and get the real deal. Its a plastic straw in the center and the instructions are for a metal pin. Should have known. But they do mention the gasket and having the engine on when setting the push rod but my engine isnt there yet. Does it matter on the distance to have the engine running?
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Old 10-01-2020, 02:49 PM   #18
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Re: Brake leak at the master cylinder and booster - remove and fix?

I've never heard of a gasket. I did it just like this in the past and was happy - https://techtalk.mpbrakes.com/how-to...r-cylinder-gap
Now, maybe I didn't know I was supposed to be unhappy.
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Old 10-01-2020, 02:56 PM   #19
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Re: Brake leak at the master cylinder and booster - remove and fix?

I did a parts search and found one - https://www.ecklerscorvette.com/corv...E&gclsrc=aw.ds

I have just never used one in the past.
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