Brake Bleeding Problem

Rod Schneider · 03-18-2013, 01:21 PM

I recently purchased a dual circuit brake conversion set from Classic Speed and Parts for my 66 911. Installation went well, but I'm having big problems trying to bleed the brakes. (The kit I got has an "aftermarket" master cylinder) I've tried vacuum bleeding, pressure bleeding, and the old "push the pedal and release" method. The pedal still goes to the floor, although the front brakes do have a little firmness to them. I've tried to bench bleed the master cylinder, but that is difficult since the reservoir cannot be hooked up until the master cylinder is installed.

Any ideas? Did I make a mistake by not buying the ATE master cylinder? At this point, I'm tempted to go back to the original system, although I've already cut off the pedal push rod for the new master cylinder, so I'd have to come up with a new one..........
Thanks,

LJ851 · 03-18-2013, 01:35 PM

Do you have free play at the pedal? It sounds like the bleed port in the MC is not being uncovered when the pedal retracts.

When you pressure bled did you get a nice steady stream of fluid coming out of the bleeders?

Rod Schneider · 03-18-2013, 01:39 PM

I do have free play at the pedal-about 4 or 5 millimeters or so. I do get a good, solid stream at the calipers when I pressure bleed. Thanks.

LJ851 · 03-18-2013, 01:46 PM

If you have free play and can pressure bleed all the air out and still don't have a pedal, i would replace the MC. Sounds like a bad one.

nickelplated5s · nickelplated5s's Garage

Try bleeding the front and rears at the MC. Obviously just crack them when you try it.

3rd post! The '11 F350 is in the shop again so I spent the weekend getting the 69 running. It's dry here in OR so I'm going to go put new fuel in and drive it again today. Tune up parts coming. Need tags and might have to get rid of the old CA plates. Kudo's to the PCA NW for being gracious to a newbie last weekend at their time trial.

911pcars · 03-18-2013, 02:19 PM

Hint. If there's air in the master cylinder, you should observe bubbles slowly bleed out of the intake port and into the reservoir as the pedal is exercised. Observe as a helper does that.

There are more MC's transformed to paper weight status by pressing the pedal to the floor and ripping seals as they traverse an unused section of MC bore.

Using a pressure bleeder to force fluid out of the caliper bleeder valve doesn't confirm the MC is able to push fluid into the system.

Sherwood

Rod Schneider · 03-18-2013, 04:02 PM

Well, I just ordered an ATE master cylinder from our host. Hopefully, it will work, otherwise I'll probably go back to the original single circuit brake........

Rod Schneider · 03-25-2013, 01:21 PM

I replaced the master cylinder with a new ATE from our host, and still had no luck getting a good pedal, even after a LOT of bleeding. After a lot of head scratching, I installed a short section of capped off brake line onto the master cylinder in place of the line going to the rear brakes. Suddenly, I had a good, hard pedal. Hmmmm, that means the master cylinder must not be the problem. I reconnected the rear brake line, bled some more, still a soft pedal. Suddenly, it hit me--there are TWO bleed valves on each rear caliper! I'd been bleeding the outboard fitting only! Sure enough, I pressure bled the inboard valves and now I've got a great, firm pedal.

(I've also got the most thoroughly bled system I've ever seen, must have put nearly a gallon of fluid through the system over the past few days...........)

911pcars · 03-25-2013, 04:46 PM

Quote:

Originally Posted by Rod Schneider

"............(I've also got the most thoroughly bled system I've ever seen, must have put nearly a gallon of fluid through the system over the past few days...........)

Good to hear the system is okay. Prepping for a pressure flush/bleed with only 1 liter of brake fluid is pretty optimistic. The time-saving pressure bleeder gets expensive when you use up multiple bottles of $16-$20/liter fluid. I'm pretty sure guys using Castrol SRF ($65/liter) or equivalent use alternate methods.

Sherwood