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Never ending master cylinder leaking issue
#1
Ok so I have been through 5 master cylinder replacements in the last 10 years.

I need some help.

Specs, 71 power disc/drum 351c Mach 1

I have gotten masters from:
Doorman
And
Alcardone

Every single one of these leaks from the rear seal on the master.

I have gone through new masters and refurbished ones they all leak from these 2 companies. I'm using dot 5.

So can anybody recommend a company other then these 2 where I can get a master from that doesn't leak?

I looked at Wagner and I swear they are using alcardone units because they have the same yellow paint markings and just throw them in a different box.

One thing I noticed I don't think the bore is honed correctly on the doorman or the alcardone units the bore is smooth, I would think there should be a cross hatch.

I would like to stick with a stock appearance but let me know your experance.
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#2
72HCODE;185792 Wrote:Ok so I have been through 5 master cylinder replacements in the last 10 years.

I need some help.

Specs, 71 power disc/drum 351c Mach 1

I have gotten masters from:
Doorman
And
Alcardone

Every single one of these leaks from the rear seal on the master.

I have gone through new masters and refurbished ones they all leak from these 2 companies. I'm using dot 5.

So can anybody recommend a company other then these 2 where I can get a master from that doesn't leak?

I looked at Wagner and I swear they are using alcardone units because they have the same yellow paint markings and just throw them in a different box.

One thing I noticed I don't think the bore is honed correctly on the doorman or the alcardone units the bore is smooth, I would think there should be a cross hatch.

I would like to stick with a stock appearance but let me know your experance.

I got a new one from MACS 18 months ago, no problems
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#3
I just replaced mine for the first time last week, because of the same kind of leak... Got it from NPD. So far, so good but only time will tell.
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#4
I would try to find a new one, not a reman-ed...
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#5
72HCODE;185792 Wrote:One thing I noticed I don't think the bore is honed correctly on the doorman or the alcardone units the bore is smooth, I would think there should be a cross hatch.

The bore should be smooth, but not shiny. If the bores are too rough they will quickly wear out the piston seals.

I would make sure the push rod lines up squarely with the master cylinder, misalignment will push sideways on the piston, causing it to wear.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#6
Checked the rod before install looked ok, the piston for the booster looked straight.
I made a gauge tool from the manual to check the piston length as well and it was correct length.

At least the new hoses I made aren't leaking.
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#7
I would get it sleeved in stainless save any more problems especially on cars which aren't driven daily
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#8
Gave it a few days and the new master is 100% weep leaking from the rear seal.

The remans leak less then the new ones.

For the npd master do you have the part # , was it really made by npd or was another manufacture on the box.

I found a tps unit I might try.
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#9
My reman leaks at the rear too. No drips but a slight wetness around the firewall.
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#10
I've been researching this subject and I'm really coming to a conclusion that i will need to Switch from Dot 5 to Dot 3.

So far i have yet to find a rebuild kit for our type 1" bore masters that supports Dot 5 fluid.

I've used silicon oil for years in other applications and i find a lot of bad information on the Web in regards to Dot 5.

but there is one truth, Silicon oil does not cause rubber to expand. The seals in our brake system were designed to swell up slightly in reaction to Glycol in dot 2/3/4/5.1

here is where i'm coming to an interesting finding:

If you have a system bran-new rated for DOT 3 and you filled the system with DOT 3/4 then years later during a rebuild switched to Dot 5 after a cleaning with alcohol, there is a good chance the Seals will have been internally altered and swelled by absorbing the Glycol.

If you have a new brake system and used Dot 5 in a DOT 3 rated system from day one, then the seals would of never been exposed to Dot 3/4/5.1 and thus never Swelled in the first place leading to continued brake leaks at various seals.

sometimes people seem to get lucky and the tolerance is very close between the seal and the bore and they do not experience a big leak but they may have a small leak and not know it.


but here is the rub... Flushing DOT 5 is REALLY hard. also, I still don't like the idea of Dot 3/4/5.1 and its reaction to paint....

this is leading me to wonder......

what if i took a known leaking Master that i only ran Dot 5 in from day one.... popped the rear seal and took the piston out, cleaned it and soaked it in DOT 3 for say 1 week. then Cleaned it and reinstalled it back in the master then bench bled with DOT 5 would the seal be swollen and stay altered and thus stop leaking.

hummm..........
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