I Thought a New ATE Brake Master Failed out of the Box

[ctaylor738]

I am doing a complete (master cylinder, reservoir, hoses, calipers, wheel cylinders, relined shoes) brake job on a 1966 230SL.  Yesterday, I finished putting everything back together and pressure bled the system from the reservoir.  Everything seemed normal until I pushed on the pedal and it went straight to the floor.  I pushed some more fluid through but got no additional air from the bleeders.  Pumped the pedal while pressure bleeding.  Flow from all four bleeders is fine.  This is not like there is some braking.  When the pedal is pushed, the shoes do not move and the pads do not tighten against the rotors.

When the pedal is pushed, you can see movement of fluid in the rear chamber of the reservoir.  

The reservoir and attachment kit came from the dealer, and the master is the correct ATE unit from AutohausAZ.

I can't come to any conclusion other than the new master is bad.

Anyone have other ideas?
 

[badali]

I put a new master cylinder from the classic center on my 230 this past year.  I pre bled it before I put it on.  I bled each wheel and it works fine.  I used the 2 man method to bleed the brakes.  It sounds like your master cylinder has bad seals if you are sure there is no air in the system.
Brad

[Atazman]

My guess is that you still have air in the system.  Even if you have a bad master cylinder, I believe there would be enough "seal" inside the master to create some resistance when pushing the brake pedal down....... resulting in some pressure at the individual wheel bleeders.

Pump the brake pedal several times (slowly).........hold down........and then bleed the longest line away from the master.  Repeat this procedure several times, and then proceed to the next wheel.  It takes a lot of bleeding, and a lot of fluid to completely fill the system and get rid of the air.

Initially, when you start your bleeding, you will have very little resistance to pushing the brake pedal down.  Just keep pumping that brake pedal and opening the bleeder............eventually you will feel resistance in the brake pedal, and the brake fluid will start "squirting" out the bleeder.

Let us know what you find.

[ctaylor738]

I don't think this is an air problem.  I ran almost two quarts of fluid through the system with the pressure bleeder and bled each wheel three times.  The only path from the reservoir to the bleeders is through the master cylinder so I don't see how there would be so much air in the system to have zero braking function.   

I bought another new master cylinder yesterday.  My plan is to first try to foot bleed off a fitting on the master.  If that doesn't fixi it, then put the old master (which worked OK) and reservoir back on, bleed the system and see if that resolves the problem.  If it does, then I'll put the new(est) master on. 

[menesesjesse]

Chuck
I replaced mine and had a similar issue.  I ended up bench bleeding the master cylinder first and then had a second person help me bleed the brakes.  I tried the vacume bleeding but the 2 person was better.  I replaced all my lines along with wheel cylinders.
Jesse

[ctaylor738]

Today.

Used the foot method off the master cylinder, no change - no pedal.

I put the original master/reservoir back on and re-bled the system.  No change - no pedal.

Then I clamped the line to the left caliper.  Presto - good pedal.  Why, I have no clue.

[badali]

If that caliper is not leaking fluid there is allot of air in it. Also make sure the bleeder is in the top hole and the line is in the bottom hole.  If it is not you will never get the air out.

[ctaylor738]

No hiding from this one - my screw-up.

RockAuto sent me two rebuilt right-side calipers.  I mounted one upside down (bleeder on the bottom) on the left side.  I don't understand why I could bleed this caliper, getting both air and fluid out, and then have it cause the pedal to go to the floor.  If the master is good and the system is bled, where would the fluid directed to the left caliper go?

Once I clamped that line, I had a very firm pedal.

[menesesjesse]

If the bleeder is upside down I believe a bubble if air forms and the fluid just takes the path of least resistance and not forcing the air out since it is above the fluid.  Good news is that you have it figured out.

[ctaylor738]

OK, think I get it.

I got lots of fluid and air out of the left caliper when I bled it. 

But from what you say, there must have been a large amount of air left in the caliper.  So when I pushed on the pedal with the bleeder closed, all that happened was that the air compressed?

[Atazman]

Good report.  Thanks for letting us know what happened.

[badali]

Make sure you put the bleeder in the top hole and the brake line in the botton hole.  (Gravity)  No mater how much you bleed them the air will not be completely out unless it can escape at the top.

[ctaylor738]

So the correct caliper arrived and I put it on and completely re-bled the whole system (RR, LR, RF, LF) and probably ran 1.5 quarts of fluid through it with the pressure bleeder, which you would think would be enough to displace any air.  But still a pedal that went too far down w/o resistance, and then was still soft.

So with the help of friend Dave, we used the foot method on all four brakes twice around and got a fair amound of additional air out.   Solid pedal, but there was still too much pedal travel.  I discovered that the plastic stop on the brake light switch had basically disintegrated and this was allowing the pedal to come too far back, increasing the travel before the brakes engage.  This part is NLA.  I was able to adjust some of this out with the eccentric bolt that connects the linkage right by the firewall.  When the notch is in the rear position, slack in the pedal is minimized.

[66andBlue]

Hello Chuck,
did you see this post? http://www.sl113.org/forums/index.php?topic=12083
Perhaps Woody or Dave G. still have one?
Put a new one on last weekend with Joe A. - not easy when the plastic is cold and hard!

[Cees Klumper]

I bought a replacement for this stop at Van Dijk in The Netherlands several years ago. They have them remanufactured, not cheap, but the end to an annoying little problem.

[Shvegel]

Is there some way you can verify the master cylinder is returning all the way either by observation or by measuring the shaft protrusion from the booster and comparing it to the depth at the back of the master? I once went nuts trying to figure out the same problem only to find the master wasn't returning past the fluid reservoir ports.