Help troubleshooting my brakes on a 69 coupe

[Bob R.]

Re: Help troubleshooting my brakes on a 69 coupe

I had issues bleeding my 63 and you might want to try the fix we discovered after many attempts to bleed the system. We found the the rod from the brake pedal was obstructing the opening in the master cylinder just a bit which prevented the brake fluid from flowing into the brake lines. We loosened the bolts attaching the master cylinder to the fire wall or booster allowing the piston to fully open. The brakes then gravity bleed easily once the bolts were tightened we had a firm pedal.

[Michael L.]

Re: Help troubleshooting my brakes on a 69 coupe

I guess I don't understand how the MC works. How could it be working on the rears and not on the fronts? I would think that the rod pushes fluid simultaneously from the front and rear reservoir to ensure equal pressure to the front and rear brakes?

In any case I loosened the MC as you suggested and now the brakes gravity bleed easily. I also took the rear wheels off and bled the outer bleed screws that I missed with wheels on. The pedal seems a little better but it's hard to tell if its fixed. If I get another helper I'll try bleeding them again the old fashion way.

[Owen L.]

Re: Help troubleshooting my brakes on a 69 coupe

There are two pistons with seals inside the master cylinder's bore. The brake rod pushes on the rearmost piston which in turn acts on the forward piston.

Master_Cylinder-Diagram.jpg
You can see that the rear circuit is directly activated at every pedal push whereas the spring between the two pistons needs to be pushed far enough before the front braking circuit activates. You could have a hung up forward piston that is not being pushed rearward so is limiting the fluid flow.

mastercylinder_exploded_view_4696a961f5871932b64e06f6cf25467e3d5f2720.gif

[Leif A.]

Re: Help troubleshooting my brakes on a 69 coupe

I guess I don't understand how the MC works. How could it be working on the rears and not on the fronts? I would think that the rod pushes fluid simultaneously from the front and rear reservoir to ensure equal pressure to the front and rear brakes?

In any case I loosened the MC as you suggested and now the brakes gravity bleed easily. I also took the rear wheels off and bled the outer bleed screws that I missed with wheels on. The pedal seems a little better but it's hard to tell if its fixed. If I get another helper I'll try bleeding them again the old fashion way.

Michael,
Get yourself one of these and you can do it all by yourself. There's a magnet on the back of the bottle to attach it to the brake caliper. Open the bleeder, place the hose over the bleed valve, get in the car and pump the pedal about 10 times and then refill the master cylinder. Secure the bleeder and move on to the next one. One person can do all six bleeders in about fifteen minutes. There is a one-way valve in the lid of the bottle that allows the brake fluid to flow from the master cylinder (when you pump the brake pedal) but does not allow air to suck in as the pedal is being pumped. I was skeptical at first, but once I used it I was a believer. Best $20 you'll ever spend.

[Michael L.]

Re: Help troubleshooting my brakes on a 69 coupe

Thanks Owen and Leif good info. I just order a couple of those bottles.

[Leif A.]

Re: Help troubleshooting my brakes on a 69 coupe

Thanks Owen and Leif good info. I just order a couple of those bottles.

In my earlier post, I meant to say attach the bottle w/magnet to the face of the brake rotor NOT caliper. You're gonna love this little bottle.