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Old 18-08-2017   #1
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brake master cylinder repair

I am on vocations with my 500 and seems that my master cylinder is almost dead. I knew that it had a small leak from the seals and had in mind to replace the master cylinder but it came faster than i thought, ofcourse who cares about brakes when he drives a 500 but ok i will repair it. I just want to ask since i am not in my base right now is there any option to repair the seals only without changing the master cylinder? Maybe it has some common seals with other fiat cars that i might be lucky and find here, so perform a quick repair and then order a new master cylinder.
Thomas
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Old 18-08-2017   #2
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Re: brake master cylinder repair

Normally, being that a new master-cylinder is so cheap, the unit is replaced rather than repaired (for which there is never a guarantee of success). The internal bore of a 500 master cylinder is 19mm and it has 2 '0' ring seals, 1 either end of the piston. I don't know off hand what other master-cylinder has the same bore, but a garage with a parts reference catalogue might be able to sort out some seals for you. Where are you on holiday? it might be just as quick to order a master-cylinder.
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Old 18-08-2017   #3
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Re: brake master cylinder repair

well I will order one and I will have it here before I live but I am looking for a plan b also. I was lucky with the starter before I live. I'll go tomorrow to the local shops around and see what I can find, but I will also place an order.
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Old 19-08-2017   #4
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Re: brake master cylinder repair

Good luck, not much to add but as others have said replacing is easier than repairing.

I've attached two schematics showing the internals in case you want to fix it, maybe it can help:



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Old 19-08-2017   #5
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Re: brake master cylinder repair

Hi Thomas,

If you check www.falga.com/en/oldcarparts,
then click on Download pdf under Brake Gasket,
you'll see illustrations of the various brake seals used on classic Fiats,
plus parts no's and model applications. Unfortunately the website says the Co. is closed for holidays from 5th-27th? August.....

From memory, Fiats used either of two types of seal in the master cylinder,
a lip type and a 'D' cross-section type.(might be one of each or 2 of one type, can't remember!). The seals you require might be the same as used in 19.05mm (3/4 in.) wheel cylinders. So if you can't locate a master cylinder seal kit, you might check out wheel cylinder seal kits or even buy a wheel cylinder and 'borrow' it's seals. As you will see in the above pdf from Falga, these seals were used in a wide variety or Fiat models including some more modern than the 500.

Hth,

Al.
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Old 19-08-2017   #6
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Re: brake master cylinder repair

Good day to all.
Thanks to your help, links and manual pages, i manage and found locally two new seals
I will put'em on this evening and see what happens. I guess it will be just fine until i rebuild the whole front section including brakes. The leak is that big that fluid run into the floor inside the tunnel and then out from a hole it found!
I will keep you updated and put some pictures for ref.

Thomas
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Old 19-08-2017   #7
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Re: brake master cylinder repair

Quote Originally Posted by F123C View Post

From memory, Fiats used either of two types of seal in the master cylinder,
a lip type and a 'D' cross-section type.(might be one of each or 2 of one type, can't remember!).
I removed the master cylinder piston and there is one of each type inside, unfortunately the one that leaks is a lip type and i don't have it
I will go Monday morning at the local shop and see if he has it. Of course a new master cylinder will be ordered.

Thomas
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Old 19-08-2017   #8
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Re: brake master cylinder repair

I do not think that you should have a lip type seal in your master cylinder. Sounds like a bodge to me that has caused the leak problem.
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Old 19-08-2017   #9
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Re: brake master cylinder repair

Have no idea, all i can say is that it looks pretty original to me plus it is mentioned at the catalog posted by Al in the previous post.
http://www.falga.com/docs/oldcarpart...ake_gasket.pdf
I will give it a try if i found one and see how it will go. Monday morning car has to be ready, ill go for camping with it!!
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Old 20-08-2017   #10
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Re: brake master cylinder repair

Hi Thomas,

Sorry to hear you didn't manage to get the correct seals.
I know how disappointing and frustrating it can be when the new parts don't fit, especially when you're under time-pressure with your upcoming trip!

That size of master cylinder seal is afaik quite common.
I previously referred to it as 19.05mm but I now think it's 19mm bore and the seal is 19.05mm. Sorry for any confusion I may have caused.

With reference to what Toshi 975 says above, I seem to recall seeing original Fiat master cylinders fitted with 2 of the 'D' type seals and replacement (but Italian made) cylinders fitted with one lipped and one 'D' type seal.

I remember some Fiat dealers (back in the day) keeping a supply of loose seals in storage jars.

That lipped type seal was also used on much later Fiats (various models) in other areas such as hydraulic clutch cylinders (possibly slave cylinders), so you might find it is still being used, even nowadays. Hopefully your supplier can locate a suitable seal for you.

Don't forget to clean any scale/rust etc. from inside the master cylinder bore as you'll be using the full stroke of the piston if you bleed the brakes manually. (I'm sure you're well aware of this!).

Regards,

Al.
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Old 20-08-2017   #11
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Re: brake master cylinder repair

I have also plan D in progress, i cut a strip out of a beer can and place it under the seal inside the piston groove to make seal expand a little and seems to work but i will put it only if i don't find a new seal. I also ordered new cylinder to fit when i will return home, i think it is time to build a one person bleeder. I will come to this later.
Thomas
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Old 20-08-2017   #12
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Found this schematic that clearly has two type of seals like my piston. Just for ref guys. p/n 4184521 is a double leap seal "H" cross section.
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Last edited by gordinir8; 20-08-2017 at 21:17.
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Old 21-08-2017   #13
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Re: brake master cylinder repair

Quote Originally Posted by gordinir8 View Post
I have also plan D in progress, i cut a strip out of a beer can and place it under the seal inside the piston groove to make seal expand a little and seems to work but i will put it only if i don't find a new seal. I also ordered new cylinder to fit when i will return home, i think it is time to build a one person bleeder. I will come to this later.
Thomas
Hi Thomas,

I hope you enjoyed the beer, I used to get 'great' ideas when I drank beer. I no longer drink....

I've heard of a bodge where the seal is dipped in diesel fuel for a few minutes, causing it to swell, then refitted. But idk about the advisability of this trick...

Looking at the schematic you provided, it seems to me that the 'H' type lipped seal is there just to prevent a leak, it's not under pressure unless there is leakage past the 'D' type seal, which is what is pushing the fluid when the brake pedal is applied. A suitably sized 'O' Ring or a carefully cut rubber disc or a rubber grommet would probably work for a reasonable time providing the other seal and cylinder bore was good. Those 'D' type seals are strange things, they don't seal very well unless something causes them to expand axially (i.e. their diameter to become larger), sometimes a special cup washer is used, other times fluid is diverted under the seal to expand it outwards or it is squashed between two metal faces to expand it. These methods can be seen in the excellent schematics provided by 'turbo500' in post#4 above.

I'm sure you'll soon have the little car going again.

Or should that be 'stopping' again.

Regards,

Al.
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Old 21-08-2017   #14
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We are back in the air I think. I went to the local farm tractor store and he gave me a very similar seal that he removed from a tractor master cylinder piston! Put everything back and up until now I have no leaks. So little car is now ready for more adventures.
Thank you guys for your help and chat.
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