How am I supposed to get THAT out? When that question comes up, an argument takes place in my brain. Half of my brain tells me I can’t do it, the other side is all can-do. The pessimist side telling the optimist side I can’t do something is like telling a dog he can’t sniff trees and fire hydrants. If you are like me, I like figuring difficult things out.
I’ve been refreshing a 78 Midget that hasn’t been on the road in well over a decade, maybe two. Now that I have the painting done, I’m taking my time putting it all back together, renewing components as I go. Today’s project was to revive the front brake calipers. Initial inspection revealed that the brake pads didn’t have very many miles on them. Apparently, since replacing the pads the outside half hadn’t moved. Now it was frozen. Sitting for an additional 10+ years didn’t help this condition. Here lies the problem. How do you get that piston out of there when it is fully pressed back into the caliper half? There isn’t anything to get a hold of. I even popped the first seal out so I had at least a little something to grab, but nothing doing, that caliper was stuck in there tighter than a seat on United Airlines. Not only that, there are warnings in the manual not to separate the two halves, and there’s a reminder of that fact in the Moss catalog if you try to buy the little o-ring needed to put them back together again. So, in my mind there has got to be a way to get that piston out. The inner side has a hole where the pressure line connects, you can use a 5/16-inch dowel rod to push that piston out. And there may be a special tool out there but I don’t have it and don’t want to buy one for just one job.
If the caliper was still on the car I could just restrain the inner piston and just use brake pedal power to push the outer piston out. In fact I thought of that, but when I pulled the master cylinder out of the storage box it was so rusted and corroded up it looked like it had been lying on the ocean floor for 75 years, complete with barnacles. I had ordered a replacement but I didn’t expect to see it for another 4 or 5 days. That just wasn’t a viable option at this stage of restoration.
Then it occurred to me that I could still use fluid pressure to pop that piston out so that I could clean and renew the seals. I inserted a 5/16-inch dowel rod through the pressure hole and tapped the inner piston out till it was even with rotor slots in the caliper. Then I removed the caliper from the vise and set it on my bench with the pressure line hole facing up and topped off the brake fluid.
Next, I used the copper washer from the pressure hose, a regular washer and fine thread 3/8-inch X 3/4-inch bolt to plug the pressure line hole. Now I had a caliper solid full of fluid and sealed off so nothing could escape. I put it back in the vise.
I used two c-clamps and applied pressure evenly on both sides of the inner piston by tightening the clamps simultaneously. The idea was that by compressing the piston on the inner half it will put pressure on the outer half to push it out
It took some serious pressure but it finally started to move. Success! Take that pessimist side of my brain! Victory.
By Jere McSparran