Master Cylinder bore

[Alexi3rdgen]

Hey,

My '89 LX-i is having brake issues. After driving for a bit, the pedal gets really soft and goes all the way down to the floor. This is the quintessential signs of a failing master cylinder, but when i went to the parts store, they had a 7/8" bore, and a 15/16" bore master cylinder. How do I know which one I need?

Wes

[Oldblueaccord]

it usually stamped right onto the metal part.

15/16 is mine.

wp

[AZmike]

15/16" is the size that you need.

[Xulfiqar]

I swapped mine for a 1 inch cylinder with dual diaphragm brake booster from a CB5 accord - feels excellent

[acranox]

Check out the whole brake system before you replace that master cylinder. A leak at any line or any caliper can cause these symptoms. Follow each line from the master cylinder to each wheel looking for leaks, and if you've got rear drums, take them off and inspect the wheel cylinders for signs of leaks.

I'll also tell you this, I had a parking brake cable freeze up, and the right rear brake was dragging. After 20-30 minutes of driving the pedal would go to the floor. I fixed that problem, and I haven't had a problem since. I believe the brake fluid was overheating, and causing bubbles to form in that line, causing the soft pedal, but there wasn't a leak, and the master cylinder was fine.

[Legend_master]

I swapped mine for a 1 inch cylinder with dual diaphragm brake booster from a CB5 accord - feels excellent


Did you have any issues bolting the Brake booster up or did all the parts line up. If so that sounds like a great brake upgrade.

[Xulfiqar]

Did you have any issues bolting the Brake booster up or did all the parts line up. If so that sounds like a great brake upgrade.

the booster is a 9 inch unit but its dual, you will have to insert a 10mm spacer in the master cylinder cup to make it engage or its too short and you would need to use a larger flare nut for the primary piston outlet in the CB5 unit.

[AZmike]

I swapped mine for a 1 inch cylinder with dual diaphragm brake booster from a CB5 accord

What was your goal by doing this?

[Xulfiqar]

when I converted to all wheel discs - and coupled with the fact that my M/C was shot - and the 3 gee cylinder with 9 inch booster was not available, it seemed quite sensible to me.