LouZ

I finished up my preparations for an upcoming DE, brakes, filters, oil, etc.
The last step was to power bleed the brake system. Switched from ATE Blue to Gold, pressurized to 20 PSIG, and made the rounds - RR, LR, RF, LF. Then topped off the fluid and buttoned up everything.

I have a '90 C2 with the vacuum brake system, not the C4 hydraulic.

Pedal was hard on the first push. I backed out onto the driveway, hit the brakes, and the pedal went to the floor. Pumping did nothing!

I suspected that I got a little of air while doing the last bleed- I use the dry method of bleeding - no fluid in the power bleeder. I completely rebled the entire system, but to no avail. One or two pumps, and it's right to the floor. Vigorous pumping will bring them up a little, but sustained force on the pedal and it's right back to the floor.

Any suggestions? Could I have air in the Master Cylinder, or worse could it have coincidentally went bad?

Five days to get it fixed for DE inspection!

Any suggestions would be appreciated.

Adrian

Pedal flat to the floor means you have a big hole in the system. This means a serious leak somewhere. If you look at the reservoir it should be low on fluid but it has chambers so look for the lowest or the empty chamber and this will tell you where the leak may be.
Hard pedal means no pressure.
Pedal to the floor means no fluid to pressurise.
Ciao,
Adrian
964C4

LouZ

Adrian

No leaks noticed, level in resevoir doesn't move after 20 to 30 pumps on the brake pedal, and all 4 calipers are totally dry (no blown piston seals).

Arjan B.

Did you bled without a bleeder?? Never bleed with the pedal, otherwise the internal parts of your brake cylinder will damage your rubber seals cause of corrosion. Usualyour pedal never goes that deep.

I think you have much air in the system as I hear your story.

LouZ

Arjan

I used a pressure bleeder, pumped up to 20 PSIG (~1 1/3 Bar). Bled, rebled finally re-rebled, all to no avail.

My suspicion is a blown seal or massive air in the master cylinder.

Is there a way of checking for air in the master or checking for a bad unit?

All help is greatly appreciated.

Adrian

Dear Lou,
The master cylinder could have a failed seal which is just allowing the fluid to run around inside instead of pressurising the system.
Ciao,
Adrian
964C4

Arjan B.

The pressure from 1,3 is just great for bleeding. May be try to bleed with the pedal by JUST PUSH IT THE DISTANCE YOU NORMALLY NEED FOR BRAKE. Push on the pedal, hold it, and let somebody else open the bleed exit on one of the calipers. Just one step at the time. Things should work pretty soon.

Remember!!!! NO PUSHING THE PEDAL TO THE BOTTEM!!!!

Good luck!

Jeff Curtis

One question: did you pinch off the overflow line from your reservoir cap when you pressurized the system??

I know, I know...just gotta ask.

Are you using the Motiv bleeder or another device?? ...okay, that's TWO questions.

You can dry bleed, but I find this annoying, my friends do it because they don't want to dirty up their bleeder - ok, understandable. I have a professional setup that I keep in a milk crate, packs up neat in the trailer and goes where I go. I always have fluid in the container and keep a new can of ATF Blue in the milk crate alongside my bleeder for refills.

Enough about MY setup...just trying to brainstorm here.

I would be surprised if you blew a seal in any of your calipers, master cylinder, etc. - although it's possible.

Go back through your steps, pressurize the system, bleed out of the inside screw 1st, then the outer one, and back to the inner one.

WHY do this?? ...I dunno, I made it up.

Actually, MY theory is use the inner one to get the trash out of the line, instead of running it over to the other side of your caliper then out...then bleed the outer one, bringing new fluid over to that side...bleed the inner one again to ensure you nipped any bubbles and trash in the butt.

Another consideration is that you could bleed out the slave cylinder for your clutch as well. Something may have backed up into the system, etc. - again, I dunno.

MY VOTE is that it's something simple, in the procedure...while I don't prefer the dry method, it works, just keep an eye on your fluid level - you know that.

LouZ

Jeff

Yes, the overflow was pinched (I unpinch to relieve pressure in the "Motive" pressure bleeder)

The exact steps were putting on new brakes all the way around. This necessitated pushing back the caliper pistons to pull out the old and insert the new thicker pads - nothing out of the normal there.

I then pressurized the reservoir, after pinching the overflow, to 20 psig. I drained MOST of the fluid (ATF Blue) from the reservoir thru the RR caliper. Then I filled the reservoir with ATF Gold so I would know when each caliper fully flushed. went in sequence - RR, LR, RF, LF. When done, I filled to the proper level, and NO PEDAL!

You state that there is an inner and outer bleed screw! I have a '90 TIP which has the 4 piston fronts and 2 piston rears, I don't recall seeing 2 bleed screws on either.

As I stated before, I went thru the bleed process 2 MORE times to no avail.

Track DE at Pocono is looming and I need to be buttoned up for inspection on Saturday.

I'm looking at $450 for a new master and a scramble to get it in by Saturday.

I'm open to all suggestions to get pedal pressure and I'll go through them all tonight, I would like to prove out that it is the master cylinder and I'll immediately get one shipped.

As always, thanks in advance.

springer3

I agree with Arjan that you have a massive air pocket. Getting some pedal after a lot of pumping is the give away - you will eventually compress the air enough to get some pedal.

I have a pressure bleeder (home built), and I have inadvertently introduced air in the system on my 300E. It turns out that the back reservoir is tiny, and quickly depletes if you are not extremely careful.

Here is what I would suggest:

1) Have an assistant sit in the drivers seat, and press the brake pedal to about the normal hard braking position (Arjan correctly warns not to go low in the even you have rough spots or corrosion).

2) Fit a drain hose, and open the right-rear bleed screw. Close the screw and have the assistant raise the pedal. Repeat until all traces of air are gone. Be damn sure to keep the reservoir full to the top!

3) Repeat at left rear, then right front, and finally at left front.

If you get no flow, or never see bubbles, then your problem is likely not an air pocket. If you get considerable improvment, a second round of bleeding after you drive the car will get any remaining air out.

Good luck!

Jeff Curtis

Okay, we have a problem...there are INNER AND OUTER bleed screws on the 4-piston calipers...PLEASE take your wheels off and rebleed BEFORE hunting for what we call in the tech. industry - Easter Eggs.

I agree with Springer, you have air somewhere, but you don't have to go through the process of having someone step on the pedal, etc. - I've bled my system AT LEAST 100 times since purchasing my 964 with NO issues.

I use a pressure bleeder and have NEVER had anyone hold down the brake pedal, etc. - not that I don't agree these are valid ways of troubleshooting, with the thought process that the master cylinder will then be in a different position...so on and so forth, but let's start with the basics and go from there.

Troublshoot trying ONE thing at a time...this time...I would like you to find the SECOND bleed screw on each of your calipers, bleed from the inner, the outer, then the inner again.

You are SPOT ON with using gold over blue fluid, one of the best ideas I ever heard of years ago...although I don't drain my entire system when I bleed, just a good amount from each caliper - I bleed so often, (my brakes) that it's not necessary.

Let us know what you find...hopefully it's another bleed screw on each caliper.

Jeff Curtis

Okay, just to show you that...we here...at Rennlist - go that extra mile!

JasonAndreas

So you're the wanna-be hand model from Adrian's book!

JoeW

Same to you, JC! Joe W.

Jeff Curtis

Guilty as charged...the people at Bentley think I have nice hands.