I am trying to rebuild my drum brake system on my 69 cutlass. My question is about the wheel cylinders. The options at the store were 15/16 and 7/8 inch bores. The 7/8 was the only one they kept in stock and were about $8. The 15/16 was over $40 and they had to be special ordered. Looks like mine are a 15/16 or 1". What size is best? Does it make a difference with what size I use? Any change in brake performance? Thanks

 

The cylinder bores are different sizes and they shoudn't be mixed up ie the wrong overhaul kits could leak and/or fail prematurely...you need a wheel cylinder hone to do the job right...you might want to check a few parts stores for the price of a complete wheel cylinder...been a while since I bought any overhaul kits---but $40 seems pricey even by todays standards

 

He is looking at cylinders, not kits.

Norm

 

I too have a 69 cutlass and redid my entire brake system, the only things I did not replace were the brake booster and the 4 brake backing plates. My car is a canadian manufactured Cutlass Supreme, it has a 12 bolt "C" style rear axle. When shopping for parts it seemed like the larger bore rear wheel cylinders were the ones my car required. All the other cutlass models would take the less expensive ones, the supreme was the odd one. I bought the ones for my car ($40). All the other brake hardware was the same accross the cutlass lineup. I removed the drums and the existing wheel cylinders were the other (cheaper) ones. They had a different exiting angle on the brake line fitting port. I returned the expensive ones and got the cheaper ones. They fit fine and seem to work as well as can be expected for a anitquated design.

 

The size that is "best" is the one the car came with. Having said that, for a given pedal pressure, a larger wheel cylinder will provide a higher braking force, so it IS possible to increase brake force by using a larger cylinder. The problem is that drum/drum systems do not have proportioning valves, so changing the front/back size relationship can lead to premature lockup.

As for availability and price, Partsamerica.com (the online arm of Advance Auto Parts) shows three available sizes: 7/8", 15/16", and 1 1/16". All are in stock at the stores and the prices (for complete cylinders, not rebuild kits) run from $10 for the smallest to $20 for the largest. It's been a while since I worked on a drum/drum system, but I seem to recall that the 1 1/16" is for the front, the 7/8" for the rear of coupes and sedans, and the 15/16" for the rear of wagons. Someone needs to check me on that, however.