Brake Master Cylinder

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s.unsworth
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Brake Master Cylinder

Post by s.unsworth » 11th May 2024 - 4:57pm

Can a Brake Master Cylinder fail internally ? I had a leaking Front Wheel Cylinder in the 1966 Beetle, which was converted to Dual Circuit Brakes many years ago. Got new ATE Front Brake Cylinders and Meyle Front Brake Shoes yesterday. Fitted them today. Adjusted Brakes. Bled Brakes. It`s like the Pedal is going down twice as far as it should then going firm. I get the impression only the Rear Brakes are working. Have tried Adjusting and Bleeding again. No better. Just wondered if Master Cylinder Seals fail with the change from a very limited range of movement to full range ?

Steve U

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purplepeter
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Re: Brake Master Cylinder

Post by purplepeter » 12th May 2024 - 8:42am

Yes, they fail (and can be rebuilt if needed)
But, those are also the symptoms of failure elswhere in the system, so check all hard lines & Flexy's for leaks
Thats the great joy of Dual circuit though, pedal disappears but you still have braking abilty right at the end of the stroke
Apologies if this is a sucking eggs comment, but I take it you bled the whole lot, starting at the furthest point away from pedal?

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purplepeter
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Re: Brake Master Cylinder

Post by purplepeter » 13th May 2024 - 9:26am

Further thoughts overnight!
The m/cyl can only be re-built if the bore is still in absolutely perfect condition, & given the faff & cost of going through the whole process of re fitting then bleeding, I would always advocate just buying a new M/cyl. I'd always also replace the flexy's as a matter of course to try to get the whole system as good as possible & avoid having to work on the brakes again soon.

My other thought, was that on Beetles, M/cyl failure fills the nap hat with brake fluid, so you really need to get as much of it as you can, out of the Nap hat- any method is good, I think the last one I did , I used a combination of stuffing strips of Blue roll into it to try & soak up the fluid, then brake cleaner aerosol & more blue roll, then once I was convinced I'd got as much out as possible, emptied a large amount of paint aerosol into the cavity to try to seal up the inevitable bare metal inside.

s.unsworth
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Re: Brake Master Cylinder

Post by s.unsworth » 13th May 2024 - 10:40am

Thank you. I ordered a New Master Cylinder yesterday. Hoping it will be Delivered tomorrow.

Steve U

s.unsworth
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Re: Brake Master Cylinder

Post by s.unsworth » 14th May 2024 - 7:53pm

New Master Cylinder Delivered today from JP Parts ebay shop. Posted yesterday Royal Mail 24. Made in Denmark £27.51 Posted Free. Even has all the Connections in the same configuration as the old one. Thnk I`ll take the opportunity to make some new Kunifer or Copper Pipes anyway.

Any opinions on types of Brake Fluid please ? I have Pagid DOT 4 but hear DOT 5 does not damage Paintwork ?

Steve U

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purplepeter
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Re: Brake Master Cylinder

Post by purplepeter » 16th May 2024 - 8:09am

You can't mix Dot 4 & Dot 5 so you'd have to thoroughly clean out the entire system

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broady_6
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Re: Brake Master Cylinder

Post by broady_6 » 16th May 2024 - 8:44pm

I have been converting classics to DOT 5 over the past couple of years. Not because it doesnt damage paint work. Brake fluid should be kept well clear of paint work.

But because DOT 5 is silcone based and not hydroscopic. The main advantage of this is, if the car sits for any length of time, it doesnt soke up moisture and corrode the internals of the brake system. With mineral based fluid regular use and this heat tends to boil off the moisture. But as our classics usually dont get used all that regular. I for one vote for DOT 5.

But as peter says you must clean out all the old DOT 4. To do this ive used a pressure bleeder. set to 10psi, Id open each bleed nipple in turn and leave it blowing for 5 minutes on each one. Then ive fill the res with brake and cluttch cleaner. Id "bleed" a bit of this into the system. And then let it sit for a while. Once its had a chance to disolve the DOT4 ive blow that out, and then flush once more with brake and clutch cleaner.

On cars where I have been working on the brake system anyway, ive simply dismantled wheel cylinders or calipers and cleaned them with blue roll and cleaner. and blown lines through. Both methods have worked perfectly and ive got a number of cars happily running DOT 5 with no issues. Even having done a few track days and got the brakes very hot. Performance remained.
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s.unsworth
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Re: Brake Master Cylinder

Post by s.unsworth » 20th May 2024 - 10:30am

That`s good to know. Will think about changing to DOT 5 at some point. I would have thought just flushing a load of DOT 5 through the whole system would be enough to clean the DOT 4 out. Maybe get a Garage with proper Fluid Change Equipment to do it.

Steve U

s.unsworth
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Re: Brake Master Cylinder

Post by s.unsworth » 3rd June 2024 - 11:12am

Are the Hand Held Vacuum Pump Brake Bleeding Kits any good ? I never got the Pedal feel back how I would like it to be after fitting new Meyle Front Brake Shoes, new ATE Front Wheel Cylinders, new Dual Master Cylinder and both Front Metal Pipes. Our MOT Tester even had a go at Bleeding the whole System again. Suppose next step would be 2 new Front Brake Hoses, although they do look fine. 1966 Beetle does not need an MOT but I still prefer to have one !

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broady_6
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Re: Brake Master Cylinder

Post by broady_6 » 3rd June 2024 - 7:11pm

I have both a vacuum and pressure bleeder. I much prefer the pressure bleeder. Its hard to tell how youre doing with the vacuum version as it also draws air in round the bleed nipple threads.
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s.unsworth
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Re: Brake Master Cylinder

Post by s.unsworth » 9th June 2024 - 1:49pm

Fitted 2 New Front Brake Hoses this morning. Bled Brakes. Useless. Pedal is still nowhere like how it should be. Think I am going to need expert help e.g. Professional Bleeding by a Garage. Never had such a problem before. Could the New Master Cylinder be faulty, or incorrect ? How many different Dual Circuit Master Cylinders can the be for a Beetle ? How could I find out if it is Faulty ? Buy another and try it ?

Could it be that the Brake Pushrod needs adjusting for the New Master Cylinder ?

Update - tried Adjusting the Pushrod. Made the Pedal feel better but still only Braking on Rear Brakes ! Faulty New Master Cylinder ? Faulty New Front Wheel Cylinders ?

Steve U

s.unsworth
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Re: Brake Master Cylinder

Post by s.unsworth » 12th June 2024 - 8:54pm

I`ve sorted it today. Thought about Vent Route for Air to get out of the Master Cylinder - Via the 2 Hoses from the Fluid Reservoir. Realised the Routing was not good. They went down from the Reservoir, flattened out but then uphill a bit where they were held in a Clip along with the Fuel Hose to keep them all out of the Steering. I took them out of the Clip and held them so they only went up from the Master Cylinder to the Reservoir. Got a load of Air bubbling up. Used one of those Rubber Hoses with a bung in one end and a slit in the side that acts as a NRV ( £2.69 from euro car parts ) to Bleed the Brakes again - All fixed !

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broady_6
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Re: Brake Master Cylinder

Post by broady_6 » 13th June 2024 - 7:20pm

pleased to hear it :D
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