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  Chicagoland MG Club:Driveline
Go Brit Baby! - Tech Sessions

Steve Merical Hydraulics - Give Me A Brake(s)
January 12, 2002

We had 8 people show up for the hydraulic tech day on Barney Gaylordís í58 MGA. After working in my 40F (or below) degree garage the last month it was a real pleasure to work in the warm confines of Barneyís heated garage.

After running silicon fluid for some 10 years with good results, Barney switched over to DOT 4 fluid a few years ago. Lately heíd been noticing some leaking from the master cylinder and dark color fluid draining from brake cylinders while bleeding the system. Time for a MG brake system rebuild.

After putting the car up on stands and removing the wheels the real work began. First, we went around to each wheel and the clutch slave to bleed the old fluid out of the system. We did this with the aid of an EZ bleed system that uses the air pressure from a tire. This system is very handy especially if you are working alone because there is no need to pump the brakes. Then Barney put some alcohol in the EZ bleed to flush the system and then used an air compressor to blow the lines clean to prevent contamination when he goes back to using silicon brake fluid.

The master cylinder was taken out of the car and the cylinder pistons were removed so we could evaluate the bores for the rebuild. The bores looked pretty good so they were lightly honed to smooth up the interior walls. Cylinders hones are a good tool investment. They only cost about $20 and Iíve used them 3 times in the last year. The hone attaches to a drill just like at bit and then youíre in the honing biz.

The master cylinder was repacked using a rebuild kit from Moss. MGAs use a single master cylinder for the brake and clutch. You need to be careful and put the proper rebuild parts in the correct bores of theMGA master cylinder installed cylinder.

Then it was time to attack the individual brake cylinders and the clutch slave cylinder. These were also honed and repacked using a rebuild kits. The í58 MGA has brake drums all around. No discs brakes on this model. There are 2 cylinders on each front wheel and a single cylinder for each rear wheel.

Itís important that you get a smooth clean surface when honing cylinders. A smooth surface is critical for the new rubber plungers to contact with. If you find pitting that doesnít clean up after honing, you need to buy a new cylinder. Trying to rebuild a cylinder with pits will lead to a leaking fluid after a short time.

All the cylinders were installed and the clutch hose and brake hoses were replaced. The fresh system was then bleed with silicon brake fluid. Iím sure Barney is hoping for another 10 years of reliable braking service with silicon fluid. The added benefit of the silicon fluid is that it doesnít remove paint like the Castrol LMA Iím using in my MG.

The savings on doing a rebuild like this is 100s of dollars. Rebuild kits are inexpensive when compared with new cylinders all around. The master cylinder is especially pricey. The key is having cylinders that are in fact rebuildable.

Steve Merical - - 630-443-4985

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