Brake Master Cylinder

[s.unsworth]

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

[purplepeter]

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?

[purplepeter]

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]

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

Steve U

[s.unsworth]

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

[purplepeter]

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

[broady_6]

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.

[s.unsworth]

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]

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 !

Steve U

[broady_6]

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.

[s.unsworth]

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]

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 !

[broady_6]

pleased to hear it

[s.unsworth]

Please can anyone tell me what Length of Thread should be present in the Yoke of a Correctly Set Beetle Brake Master Cylinder Pushrod ? If the Pushrods are all exactly the same, and the Length is always the same Measurement of 5.433", then the Length of Thread that can be seen inside the Yoke must always be the same.

Steve U

[purplepeter]

It varies because of the Brake pedal position being adjustable & in older cars, the possibility of corrosion/paint coatings between the cylinder flange & body

[s.unsworth]

I`m stuck because some idiot ( I know who it was. A supposed VW expert since Retired and Sold his Business ) Welded the Clevis Pin to the Brake Pedal. I suspect the Threads are gone in the Yoke of the Pushrod but I can not remove the Pushrod unless I take the Pedals out. I knew he had done that after we got the Beetle back from him but it was never a problem, until now. I`m guessing he did it because the did not have a Clip for the Clevis Pin, or the Grove had worn away, because he did other stuff like used Nuts and Bolts to fasten the Handbrake Levers to the Rear Brake Shoes, Pressed Ball Joints in wrong so they were damaged and too tight to steer, fitted an Alternator type Bely for the Dynamo ( too long ) fitted a non matching size Clutch Centre Plate and Pressure Plate. Other stuff that I could easily fix myself but not this one !

Steve U

[purplepeter]

Do you have too much movement on the pedal or too little? I'm wondering if you might be able to shim the m/cyl?
I think, theoretically you can adjust the pushrod in- situ (theres a locknut on each end that then allows you to turn the yoke)
Other than that it's probably time to take the pedals out & see if you can dress his weld enough to get the pushrod out
I think I've still got the pedal assembly out of a '67 model year beetle, but it's in the depths of my garage, so I'd have to go exploring- Let me know if I need to look?

[s.unsworth]

Thank you.

I last had the Pedals out in the early 1990s when I was welding in a new Floorpan Half and Heater Channel to the Drivers Side. I don`t particularly want to take the Pedals out again. That may be the only way to fix this though. It had another new Heavy Duty Floorpan Half fitted by the man who welded the Clevis Pin to the Brake Pedal while he was doing a Body Off Rebuild. He also converted it to Dual Circuit Brakes as part of the same Rebuild. Never been a problem until now. It does not have an Adjusting Nut and Locknut on the Pushrod now. Just the Yoke and 1 Nut. I can wind the Nut up and down the Threads of the Pushrod but not wind the Pushrod in or out of the Yoke.

Steve

[s.unsworth]

I`m thinking maybe open nearest Bleed Screw ( Drivers Side Front ) so Pedal will go all the way down. Somehow try to remove the Pushrod from the Yoke whilst letting the Pedal return, run a Tap through the Threads of the Yoke and a Die Nut down the Threads of the Pushrod. Wangle it all back together again.

Or just take the Pedals out !

Steve U

[purplepeter]

I've just had an archimedes moment on your behalf! So rushing to tell you whilst i remmber!
If you can find out the gap required between push rod & M/cyl (On Type 3's its 1mm)
You might be able to achieve it by adjusting the pedal stop bracket

[s.unsworth]

Thank you but the problem is I think the Threads are gone inside the Yoke / on the Rod. Some idiot welded the Clevis Pin to the Brake Pedal, so I can not remove it to re thread or replace unless I take the Pedals out.

Regards,

Steve

[purplepeter]

You might not need to remove it
If the aim is to adjust the relationship between pushrod & cylinder, then adjusting the position of the pedal might achieve it
Pedal stop bracket is a 13mm bolt going down into the floor behind the upright stem of the pedal (bracket itself is slotted to allow adjustment)

[s.unsworth]

I started looking for Slip on Locknuts ( yes they do exist ) https://www.wixroyd.com/media/files/dat ... ck-nut.pdf

Ended up using Mole Grips on the Threads and 15mm Spanner on the single Nut. It will do for now.

I still need to fix it properly sometime. Can`t accept having the Pushrod Clevis Pin Welded to the Brake Pedal forever. Maybe I could get someone Grind the Weld off in situ with a Mini Grinder ?

Steve

[937carrera]

I don't know what the access is like, but I would have thought you have a couple of options to deal with the clevis pin:

As you suggest, use a Demel or similar to grind off the weld
Drill lengthways through the clevis pin, proably using a 90 degree drill drive adapter. I suggest you acquire some cobalt drill bits, they make a big difference

You will need to have a decent "eye" and flexibility to get in there. Much easier out of the car. Is it so hard to remove the pedal box ?

[s.unsworth]

I gave in and decided to take the Pedals out. Found that undoing the 2 Bolts under the Pedals allowed me to pull Master Cylinder Pushrod out of the Master Cylinder, so no need to completely take the Pedals out, which would involve disconnecting the Clutch and Throttle Cables. Yes, the Threads are gone in the Yoke of the Pushrod. Unfortunately they are an odd size, which are not in my Set of Taps and Dies. Thought they would have been M10 but NO !

Metric Fine M9 x 1 Have ordered Taps and Die in that size. If I can not re make the Threads then the Pedals will have to come out completely to remove the welded in Clevis Pin and fit a new Pushrod - properly !

Steve