Never ending master cylinder leaking issue

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.

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.

Click to expand...

I got a new one from MACS 18 months ago, no problems

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.

I would try to find a new one, not a reman-ed...

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.

Click to expand...

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.

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.

I would get it sleeved in stainless save any more problems especially on cars which aren't driven daily

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.

My reman leaks at the rear too. No drips but a slight wetness around the firewall.

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..........

Two reliable options:

1. Adapt a brand-new modern MC; preferably one internally designed for DOT5, then source up brake calipers and pistons that can be rebuilt with absolutely new seals.

2. Accept that DOT 5 is akin to stainless brake lines: You can't mix-and-match the old with the new and expect it to work without redesigning an entire system.

-Kurt

I looked at option 1,, problem is they want 400$ for this type of MC rated for dot 5.

option 2 is still on the table, might have to tuck tail and run... the problem is you hear success stories... why are some people lucky and some not....

that leads me to wonder and try an experiment....

I looked at option 1,, problem is they want 400$ for this type of MC rated for dot 5.

Click to expand...

What car does it fit, and have any made it to the junkyard yet?

-Kurt

Do you have a power brake booster? If so, they have been known to leak vacuum at the master cylinder opening effectively pulling brake fluid past the seals just like you are describing.

If you have manual brakes of course this won't be the case. I'd then suggest disassembly and hone the cylinder with a new hone set lubricated with wd 40 ,then clean thoroughly and reassemble.

Interesting, there should not be a vacuum on the back side of the master because of the weep hole, even if the seal is leaking for the booster it should just be inside the piston that holds the push rod which is solid metal. If that is true then maybe there should be a felt gasket between the booster and back of the master to force any vacuum to be defused faster.

Thing is on mine I did notice extra fluid even when bench bleeding I was hoping i was imaging it on the bench but I just knew it was going to leak and after install it was confirmed.

Urg so frustrating.

Do you have a power brake booster? If so, they have been known to leak vacuum at the master cylinder opening effectively pulling brake fluid past the seals just like you are describing.

If you have manual brakes of course this won't be the case. I'd then suggest disassembly and hone the cylinder with a new hone set lubricated with wd 40 ,then clean thoroughly and reassemble.

Click to expand...

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..........

Click to expand...

Your thinking seems to have some validity to it. It's almost a year after your post, did you try it?

My mechanic switched my Torino's Dot 3 to Dot 5, stating it would be a better choice for a car which doesn't get driven a lot...something to do with moisture...is this true? And when he did the switching over he just bled the new Dot 5 through the lines while installing brake cylinders...what happens if there's any Dot 3 left in the system which would mix with the new Dot 5?

yes i made additional posts

http://www.7173mustangs.com/thread-the-gift-that-keeps-on-giving-part-3

http://www.7173mustangs.com/thread-master-cylinder-experiment

Here is what i found: soaking the parts in dot 3 for a while then reinstalling the parts and using dot 5 Did have a positive effect things did stop leaking. i could not find a measurable difference in the parts with the measuring equipment i have however my weeping leaks stopped.

what i found was when a new system used dot 5 directly the rubber parts did not swell as they would have with dot 3, that left extra tolerance in the new seals and you ended up with small weeping leaks of brake fluid.

this makes sense as dot 2-3-4,5.1 is known to swell rubber as has additives to reduce swelling. dot 5 originally had a major problem it did not have enough swell additive in it and there was a big recall on the first batch some years ago. however there is still something missing from dot 5 as car manufacturers scrambled in 2006 with factory recalls to change rubber orings in master cylinders my Acura had a recall like this because of Dot 5.

now the best is stick with Dot, 3,4,5.1 if you have a brake system in good shape.

if you plan to race the car then go to dot 5.

dot 5 has a higher boiling point but lets water pool up in the system causing point areas of corrosion.

dot 3,4,5.1 all absorb water, and then overall the system gets moisture inside.

Dot 5 has the advantage of not eating paint. so its a real toss up. dot 5 gives you a different pedal feel as well.

was switching over to dot 5 a good thing for you? well maybe / maybe not

if the fluid is switched out like every 5 years then you have no problem with moisture. most classics do sit around but the fluid is usually newer then a daily driver so corrosion from water is much less a concern. was he right to change you,,, again could be a yes or no situation. dot 5 can cause major problems in some cars.

yes the dot 5 fluid could be better in fighting moisture in the brake system, but a system in good shape won't have much moisture in it anyway.

i used to be a big dot 5 guy now i wouldn't have been i would of gone with dot 4 or 5.1 instead with the knowledge i have now.

if a system is rusty inside then you want to change the brake lines anyway switching from dot 3 to 5 does nothing for you.

if you flush the dot 3,4,5.1 out every couple of years then they will pretty much last forever, that gets the moisture out.

the preferred method of switching from dot 3 to dot 5 is to flush the system with 100% alcohol, getting all the dot 3 out that you can.

however this can damage the rubber seals. you can flush out the dot 3 with dot 5 you just have to use A LOT of dot 5 keep flushing the lines until the purple dot 5 is nice and clear of contamination from dot 3 and then bleed the entire thing flushed through again just to be sure.

you can change back to dot 3 again you need to flush the system a couple of times and use lots of fluid to push all the silicone out.

the mix between dot 3 and dot 5 produces a kind of varnish gel over time and that can clog up the prop valve or a restriction may build up inside one of the hoses. it can make caliper pistons stick in the bore.

i think when you switch over from either there should be a major flush then 6 months or a year later in the spring when you get ready to drive again flush the entire system one more time to make sure. the fresh fluid is a good thing anyway.

now it comes down to do you currently have a leaking dot 5 system, if you do then i would think about switching back to dot 3 or 4 or 5.1

if you do not like the pedal feel of dot 5 then also think about switching back.

if you don't have any issues then i say leave it alone and keep an eye on it during maintenance for a couple years.

right now spring is coming so i will be testing my experiment for year 2 to see how things are holding up if i start to see weeping leaks again i will be switching the dot 5 out finally and putting in most likely Dot 4 brake fluid.

one thing to make sure is did the mechanic switch you from dot 3 to dot 5.1 that is a different story as that is compatible it is glycol based.

some times people hear dot 5 but they don't know there is dot 5.1 and those are very different.

i want i update this thread please see.

http://www.7173mustangs.com/thread-master-cylinder-experiment

Hi,

I had the same problem with the master cylinder,

again and again it was leaking and I thought it is leaking from the rear seal.

After I had removed everything again and cleaned,

then I noticed that it doesn't come from the rear seal but from the lid seal

I have cleaned the sealing surface and readjusted the clamp, now it is dry

I hope this helps you

Juergen