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-   Porsche 924/944/968 Technical Forum (http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/)
-   -   WHY can't I bleed these brakes? (http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/415418-why-cant-i-bleed-these-brakes.html)

Z06C5R 06-18-2008 02:52 PM

WHY can't I bleed these brakes?
 
This car never ceases to amaze me... I completely flushed the brake system on all 4 corners, in the right order, using the right procedure, etc, etc. After running at least 2/3 of a 1L brake fluid bottle through the system, I STILL have a ridiculously long pedal and pathetically little braking power.

I started at the right rear, then LR, RF, LF. I pumped them until clean fluid came out using the standard buddy-system procedure and always keeping the reservoir above 1/2 full, and yet they're no better than when I started. WHAT is going on here?!?

hpservertech 06-18-2008 03:15 PM

Bleeding brakes is such a pain to do, even with the buddy system. What I used to do before I got a Motive bleeder was to get them as best I could, then at night when there was little to no traffic, drive it to the shop....taking my time....and let them get it all the way done. Never more then an hour of labor charge and much easier.

And that's after replacing at least a dozen master cylinders on various cars over the past 20 years.

Z06C5R 06-18-2008 04:29 PM

I don't see why it doesn't work... I've bled brakes tons of times before, and it's ALWAYS worked fine. Hell, even the clutch on this car worked, it's just the stupid brakes.

DSPTurtle 06-18-2008 04:38 PM

There is the old trick of get 'em hot and bleed 'em again. Sometimes they just need to be warmed up a little. At least that is what worked on my old 914.
Then again, you never did tell us why you started messing with the brake system in the first place... was there another issue that now the new pads are no longer hiding?
At the end of the day, when I am totally frustrated, I just open all four bleeders without touching the pedal and allow them to drain through. I keep adding fluid to the resevoir while they just keep dripping for awhile. Your mileage may vary.
Is it possible that your "buddy" does not understand the finer point of hold it to the g damn floor until I tell you that the f'ing bleeder screw is tight??? I have had a few of those in the past too :)

Z06C5R 06-18-2008 04:43 PM

Trust me, I lecture them extensively on why NOT to move their foot even a fraction of a mm until I tell them to, LoL.

I decided to replace the pads because the stopping power and feel they were providing was sub-standard in my book, and they were only a few mils from the wear sensors anyhow.

EDIT: Tried the hot-bleed, no result. Going to see if I can obtain a vac-pump tomorrow and try that.

earlr85944 06-18-2008 05:58 PM

were the brakes spongey before bleeding? could be a bad master cyl, leak in system or worn brake hoses (sometimes they expand when worn)

v2rocket_aka944 06-18-2008 05:59 PM

brake master prolly.


hope to god it isnt the brake booster.

absolutely the worst job ive ever had to do on the 944.

Z06C5R 06-18-2008 06:25 PM

Yeah, great - Because I'm just psyched to put yet another paycheck into this supposedly "well maintained" pile of dung...

But seriously, they weren't spongy before... Certainly not like now for sure. I can't see how putting new pads in would make it more worse. How would I diagnose a bad master by means other than brake feel... I'm assuming I'd be having inconsistent pedal height / travel, no?

DSPTurtle 06-18-2008 06:46 PM

If you get in the car, you have to pump up the brakes and then press hard on the brake pedal. If it slowly sinks to the floor the master cyl needs to be replaced. I did the SS brake lines on mine a few years back to replace the worn out hoses. Talk about being a ***** to bleed out the air after that!!! Don't waste you money on the vac pump. I had a mitty vac that I got from our host. I smashed it against the wall after the first use... it actually made the brakes worse each time I used it! YMMV :)

Z06C5R 06-18-2008 07:07 PM

Well, the pedal holds damn firm after a few pumps if the engine is off, but I haven't tried it with it on.

If no mityvac, then what? Is it even possible to bleed these crappers fully w/o a pressure bleeder? Damn this car really irks me!

earlr85944 06-19-2008 02:38 AM

yes the old pump crack open method does work

flash968 06-19-2008 07:01 AM

never ever ever pump brakes - if you are going to do it manually, do it one stroke at a time

closed - push moderately to floor - buddy opens on downstroke - you hold at bottom - buddy closes - release

Lapponia 06-19-2008 10:29 AM

How did your old brake fluid look like before change? Was it ink? I can see many brake fluid container in pictures here at Pelican and that is a sure sign of BAD oil and prob water in it.
This issue has been up here several times an I remember one a year ago or so. Your brake master cylinder seals are prob shot because you bottomed the piston in its cylinder when passing a little fang of rust deeper in at the cylinder wall. Its rust....belive me, I had it and was prepared when i changed the seals. Had to polish/rub whole inside of cylinder top to bottom with very fine emery cloth, cleaned and lubricated both piston and cylinder. There WAS a blob of water in the cylinder and there was this fang of rust which I could remove. Gave same treatment to clutch master cyl and slave. Bleeding was very straight forward with wife (buddy) at the pedals the old fashioned way. Had no problem what so ever after that. BTW, I changed all bleeding nipples and caps at the same time.
------------------------------------------------------
Lapponia 1984/944 na

Z06C5R 06-19-2008 10:45 AM

Well, after attempting my 4th bleed (this time with a newly acquired mityvac) with no result and comparing the brake pedal feel to a few other cars, I've determined it to be a bad master.

Funny how trying to do something simple and easy like replace brake pads results in a broken master cylinder. Am I having fun yet?

Aufenbahn 06-19-2008 05:48 PM

Did you install new rotors also? If the new pads are perfectly flat and the old rotors are not perfectly flat, you won't get a good feeling pedal until the pads wear-in to the shape of the rotors. Just a thought...

running_cold924 06-19-2008 05:52 PM

never push the brake pedal farther than normal, as if you were braking. master cyls develop dirt and gunk where the brake pedal isn't pushed past. when you push it past these, the rip the seals on the inside and the it needs new seals then. it won't properly work or even bleed your brakes.

2Tight 06-19-2008 06:13 PM

Quote:

Originally Posted by v2rocket_aka944 (Post 4011240)
brake master prolly.


hope to god it isnt the brake booster.

absolutely the worst job ive ever had to do on the 944.

Guess you haven't done a clutch yet?

hpservertech 06-19-2008 06:37 PM

Why do you think it's the master cylinder? I doubt it that. Still sounds like you have air in the system.

DSPTurtle 06-20-2008 07:59 AM

I agree... keep bleeding till you can't bleed no more. Did you open all four bleeder and just let them drip yet?

Tidybuoy 06-20-2008 09:59 AM

My sugggestion is to spend the money an buy a power bleeder. It's $45 at Pelican and is one of the greatest tools. If you have a power bleeder, your more likely to flush your brakes periodically like you are supposed to because it makes the job so easy.

Besides, getting a power bleeder, get brake fluid that is a different color that what you have now (like super blue). Simply fill the resivoir, attach the pressure bleeder to the master cylinder and pump to 15psi. The start with the passenger side rear and open the brake bleeder (using a tube to catch the fluid). Keep the bleeder valve open unitil the fluid changes color.

Now check the resevoir and top off (no need to put any fluid in the pressure bleeder). Attach the power bleeder and pump to 15psi. do the next wheel (driver side rear).

Follow the above steps for the passenger front and driver side front last.

If you really want to be thourough, do the whole process again. Nothing beats a power bleeder - you will get all the air out. and if you still have a soft pedal, it's probably your master cylinder.

Vern


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