|The MGA With An Attitude
REMOVING A SEIZED PISTON
FROM A HYDRAULIC CYLINDER - HT-105
At 05:13 PM 1/12/04 -0500, Don Fodor wrote:
>".... drum brakes all around. .... cannot get the pistons out. They are rusted in place solid. Any ideas on getting them out?
Yup. First see Tool for removing hydraulic pistons.
Fill the cylinder with oil to expel all air. Install a fitting with a grease nipple in one port, and plug any remaining port on the cylinder with another screw. Pump up pressure with a grease gun. If that doesn't push the piston out on the first try, drop the slave cylinder into the nearest trash can (unless it's some rare or exotic part that cannot be replaced).
>".... do you think the bores and the pistons themselves will be too rusted and pitted to rebuild?
Probably. When the piston is rusted into the cylinder bore, the bore will likely be so badly pitted that it cannot be honed out to a clean bore. In that case a new slave cylinder will likely be cheaper than sleeving the old one. For drum brake slave cylinders, the piston itself is never a problem. Even when badly rusted, just polish it off with a little emery paper, and it will be good to re-use. The seal is effected between a clean cylinder wall and the rubber seal cup. For disk brake calipers the opposite is true. The seal is affected between the clean piston and the rubber seal nested in the cylinder wall. In this case you can replace the piston and clean the cylinder bore with emery paper.
>"Would it be best to toss them and buy all new wheel cylinders all around? ....
If you have a few minutes to spare, it's easy to give it a try with a hone to see if it will clean up. If it does clean up (no scratches or pitting remaining), then a rebuild kit to rebuild all four front slave cylinder is only about $25. The brake cylinder hone is $6.95 from J.C.Whitney (Jan 04). This will last through a few dozen cylinder honing jobs, and replacement stones are a few dollars. Be sure the brake cylinder hone will fit into the 7/8" bore of the master cylinder (quite common). If possible, consider finding a hone that will fit into a 3/4" bore (less common), so it would be good for the smaller bore of the 1098cc MG Midget master cylinder (which may sometimes find its way into an MGA).