Cure for Sticky Calipers

Or An Ode to the Lowly Grease Gun

My latest project involves an Italian motorcycle from the Seventies (yes, apparently I do have too much time on my hands). It’s a 1978 Moto Guzzi V50 that I bought in relatively good condition with 14k miles. It’s very complete and pretty much unmolested– meaning the fenders haven’t been buzzed off or removed. Of course, it’s still over 40 years old so… well, there are issues.

Moto Guzzi V50

The first issue I dealt with was stopping. Moto Guzzi’s unique “integrated braking system” is a linked arrangement where the foot pedal operates the rear and front brakes. The hydraulic plumbing to achieve this involves a pair of hoses on the rear brake cylinder- one attached to the rear caliper and one attached a single front caliper. The front master cylinder is then connected to the other front caliper.

I’ve ridden Guzzis with linked brakes before and the arrangement has always left me less than impressed. Mostly because I’m not used to it, partly because it’s so “non standard.” Grab a handful of front brake and… you slow down. Slowly. I’ve owned BMWs with partially linked systems, but the front brake lever is linked on those bikes. Almost every other motorcycle in the world stops via the lever on the handlebar, not the pedal— but that’s an argument for another day.

This poor little Guzzi didn’t just have a wimpy front brake, it was basically worthless. The foot brake seemed to work fine and hauled the bike down from speed quite admirably. But the front brake (remember – we’re only operating one front caliper) seemed to hardly have any effect. Can it really be that bad?

I thought surely not and began to investigate. Fresh brake pads all around– this was my first clue that someone had been unhappy with the stopping. Uneven patterns/wear on the front rotors also pointed to the culprit. The inboard face of one rotor was even rusty! I used a prybar to push the pads back a tad on this caliper, then pulled the brake lever. One pad responded promptly, the other was motionless. I had a frozen piston.

The Brembo F05 brake caliper. Back then the pistons (5) were made of steel.

Brake calipers that have been static for extended period of time have a habit of corroding. Especially the Brembo calipers found on BMWs and Italian bikes of the Seventies and early Eighties. Back then Brembo used steel pistons riding inside alloy calipers. These dissimilar metals cause corrosion and the steel piston is the loser. It corrodes and will seize in the bore of the caliper.

Brembo stopped using steel pistons sometime in the late Eighties.

These newer calipers seldom have trouble with corrosion or seized pistons.

Fortunately only one caliper was affected, so I removed it from the front fork and began tearing it down. It was immediately obvious that one piston was really stuck. Removing it wasn’t going to be easy. The common method of using compressed air was my first attempt. A simple blow gun often works, or with some fittings and hose higher pressure can be applied. It did not budge.

My toolbox includes a set of brass adapters in various metric sizes. The kit is intended for connecting an oil pressure or temperature gauge– but I have found it invaluable for working on hydraulics. In this case I used the M10 x 1.0 threaded fitting on the little Guzzi’s caliper where the brake line banjo bolt normally connects. The adapters all have a 1/8″ pipe thread so it’s easy to connect a schrader valve or fitting.

Since compressed air didn’t do the trick I moved up the viscosity chart and pulled out my trusty grease gun. This throwback to the Industrial Revolution is a tool most people no longer own or need. Cars haven’t had grease zerks for half a century, and the average Gen Xer wouldn’t know what to with one if they did! But in situations like this, a grease gun can be your new favorite tool. Your typical grease gun hose (or “whip” as it’s called) just happens to use 1/8″ NPT thread– the same thread as our brass adapters!

Threading the whip into the adapter took longer than pushing out the stuck piston. Barely half a pump… Pop! Now I was able to separate the caliper halves and proceed with replacing the seals and pistons.

The grease gun exerts a great deal more pressure than any air compressor. And since it’s a liquid (or is it a goo?) instead of a gas, it isn’t compressible like air. So even the most stubborn brake piston will yield to the mighty grease gun. Of course there’s always a downside… the caliper will be full of grease!


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