This is a topic that’s sure to spark debate, but after hearing repeated troubleshooting stories and witnessing ongoing confusion, it’s clear there’s an underlying design issue with Wilwood 260-8556 master cylinders. What’s particularly noteworthy is that, more often than not, it’s the calipers that end up taking the blame.

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The Wilwood 260-8556

Our learnings through remanufacturing one offs which can be the very rare and sometimes the supposedly un-rebuildable designs and what we learn in studying engineering of new parts helps us see where O.E.M and aftermarket manufacturers sometimes go wrong. From time to time, we see components from reputable brands come through our doors that have failed. Normally, we say that’s not our domain-fixing other companies “engineered-in flaws”, but sometimes we know that our unique perspective and knowledge will allow us to improve on an otherwise flawed design. Particularly when it’s glaringly obvious. Particularly in the case of this Wilwood 260-8556.

The perfect design

For 25 years, we’ve had the luxury of disassembling, studying, documenting and re-assembling brake components from O.E. manufacturers from all around the world. We’ve remanufactured cylinders off vehicles from the 1930’s through to the very latest. With this, we’ve seen engineering trends that each manufacturer follows. Like the perfect recipe families pass down through generations. It’s a recipe of “best practice” in something as simple as, what makes a cylinder work. But just like a recipe, when someone substitutes an ingredient, it just doesn’t turn out quite the same.

What we found

Just like Grandma coming over and seeing you’ve substituted an ingredient in her recipe, our many years of experience allows us to recognize the wrong parts and engineering practices used in brake components. Whether that be in a Booster, Caliper, Wheel Cylinder or in this case, a Master Cylinder.

I caught up with Darren in the workshop to find out why this aftermarket master cylinder manufactured by a reputable manufacturer had failed.

What was the symptoms?

As you heard it, Wilwood hasn’t followed “Grandma’s recipe”, for some reason. Wilwood has forgotten the basic fundamentals of “good practice” in compensating master cylinder design, which shocked us. There were two symptoms. It was leaking from the rear of the cylinder, and the vehicle was losing its brake pedal.

The leak was a stationary leak and that’s pretty easy to see why, it’s also the cause of the second problem. The rubber is simply just poor quality and too hard! As you could see in the video.

Wilwood’s second problem

The second problem is the compensating cylinder is not compensating or in other words, not recuperating correctly. This makes it almost impossible to bleed the air out of the system and causes the vehicle to lose its pedal overtime. This is mainly due to the incorrect style and hardness of the primary pressure seals. The fluid that is under pressure, on return, can’t move around the seal and return back to the reservoir. Not only did the original designers make the seals too hard, but they also added ribs that stop the seal from collapsing on return.

Straight from the gospel

Here’s some words straight from a 1970’s PBR “Guide to hydraulic brake service”.

Compensation

All master cylinders must be able to compensate for variations in the volume of fluid required by the system. Wear of the lining material may change the volume by allowing a piston to move further out of the bore, thus requiring more fluid. When you fit new linings, they push the piston back into the bore, so you need less fluid.

Expansion through heat, or contraction because of cold can cause an increase or reduction in volume. If you don’t let expanding fluid return to the fluid reservoir, releasing the brakes causes pressure to build up.

Conversely, if the contracting fluid doesn’t draw more fluid from the reservoir, the lines and cylinders develop a vacuum. This vacuum either retracts the pistons or pulls air into the system from the atmosphere.

Recuperation

All master cylinders must recuperate. Recuperation is necessary if the master cylinder is to act as a pump, for two main reasons. Firstly, when you bleed the hydraulic system, you use the master cylinder to pump a large volume of brake fluid through the system until all the lines are completely full of fluid and free of air.

Secondly, occasionally a component in the brake system will fail and suddenly, the master cylinder must provide much more displacement than normal, to meet the additional braking pressure build-up required. Although different master cylinders use various methods to achieve recuperation, the vacuum in front of the primary seal draws in fluid after the system uses more fluid and the piston returns to the bore with less fluid than it started with.

Whenever this vacuum exists, fluid from the reservoir flows through the inlet port to refill the cylinder bore. This condition also occurs when the piston return is faster than the fluid return caused when pumping the pedal.

If you “pump up” the pedal and temporarily force excess fluid into the system, the excess flows back to the reservoir through the compensating port or valve when the cylinder piston fully returns.

What does it all mean?

Basically, when you release the pedal and the cylinder is in the “off” position, the compensating port stays open and lets fluid move between the reservoir and the brake lines. When you press the brake pedal, the piston moves about 0.76 mm, and the primary cup or seal covers the compensating port, pushing fluid to the brake lines. If the piston returns faster than the fluid, a depression forms in front of the primary cup or seal and makes the cup collapse. This allows fluid to flow from the reservoir via the inlet port, through a series of small holes in the piston head (or over the piston) to fill the depression.

This process replenishes the brake lines with fluid as the components wear and the wheel cylinders need more fluid. The above action also allows the master cylinder to act as a pump for the purpose of bleeding the brake lines.

So if you go and mess with Grandma’s recipe, you should expect it wont work properly. But instead of a dish that didn’t work out, we’re talking safety here!

What’s the fix?

See in the illustration above how there are two fundamental functions occurring? This only happens when you use the correct parts, and now you understand why you have so much trouble with a Wilwood master cylinder, or maybe you’re blaming the caliper?

On release, see how the seal or cup collapses, allowing fluid to exit the reservoir via the supply port? In the case of this cylinder, the type of seal they’re using can’t possibly collapse (as seen below). The rubber is too hard, and to make it worse, it has ribs or supports under the lip, further preventing this action.

The other major oversight (but isn’t always necessary if the fluid can pass over the piston) is the lack of recuperating holes in the flange of the piston. When the seal or cup collapses, it un-covers the holes allowing the fluid from the reservoir to pass through, back into the brake lines.

There’s still just one more missing element here! Along with making the seal softer, we added flutes to our primary seals, as you can see in this snippet from the PBR book. The seal on the left is a true primary seal with recuperating grooves or flutes.

You’ll see below how the Wilwood 260-8556 cylinder is missing the flutes on the primary seal and the seal construction is unsuitable.

In Summary

Sometimes trust in a brands ‘name’ exceeds the fact it’s simply, just not made correctly. This causes all sorts of headaches and blame on other components because, why and how can it be the master cylinder? It’s new, right? We can’t understand how the engineers ignored the basic fundamentals of correct master cylinder functionality. But it’s definitely not the first time we’ve seen aftermarket ‘new-anything’ not work as it should. In this case, it’s not even a cheap knock off…It’s the ‘real-deal’ in aftermarket brake parts. If you have one of these Wilwood 260-8556 master cylinders that is causing problems we have the solution for you.

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