Question on bleeding brake fluid.

[rnln]

I need to bleed by brake fuild. I used to bleed brake fluid on many cars before, but not a P. On P, I know that brake fluid and clutch fluid are on the same system and refill the same resevor.

My question is that if I bleed brake, do I have to bleed clutch?
If I do, do they have to be in order? Which one to do first? Brake or clutch?
How much fluid should I buy? I don't want to stop in the middle of the process to run to the autopart store.
Thanks in advance.

[tshih]

For the 87 Carrera, I use 2 Liters Valvoline synthetic DOT4 and a Motive Pressure bleeder. Pump the hand pump pressure to 10 psi and start bleeding the calipers each about 200 mL. Then open the clutch slave cylinder after connecting a clear hose to the bleed nipple, go hand pump the clutch pedal back and forth (10 cycles for the clutch should be enough to bleed the clutch. Close the bleeder valve and disconnect line and you're done for next 2 years of street driving.

[KCPSG]

As tshih said:
Thats pretty much exactly as I did it, I also change from the super blue to the red fluid when I change the fluid so I know when all the old is out of the system.

[KCPSG]

Also if you have a Motive bleeder, don't forget to use something like vise grips to crimp off the overflow hose which will dump right near your front drivers wheel well.

[Por_sha911]

Do your brakes first and then do the clutch. The bleed nipple for the clutch is a little smaller than the brakes so if you are using a vacuum bleeder you will have to be sure that you have a tight fit to get good suction. I used ATE SuperBlue this time. Next time I'll use ATE Golden. Same fluid, just diff color so I know I've got a clean line. You probably will need only need one liter but I buy two to be safe. This is a great time to also change out your brake light switches (2) on your master cylinder if they haven't been done in a long time. They are fairly cheap and its a good PM to be sure that your brake lights are coming on as soon as you hit the brakes (I want the bozo behind me to notice that I am slowing down asap).

[rnln]

Thanks guys,

I read some talked about "gravity bleed". Can someone explaining me the steps?
Thanks.

Por_sha911,
I just did switches. And replacing fluid is because of the switch. When I replaced my switch, I probably let air comes in the system. My brake pedal is softer now. This is why I want to bleeding the system.

[cstreit]

Gravity bleeding doesn't really cut it for trapped air. Bubbles will "stick" to the walls of your calipers, etc.. and not come out that way. What it does is allow you to SLOWLY change out your fluid. You just open the bleeder and let it drain out making sure the resevoir doesn't empty.

Best to use the old fashioned method of pump, hold, bleed, repeat!

[911Atlanta]

Pressure pump followed by a few hand cycles on the pedal results in a great hard pedal.

Slave nipple is hard to reach, but you can do it - lots of good info on this board about it.

If you take off the calipers for a refresh/rebuild, be careful when replacing them. Right fits on left and vice versa, but if swapped the bleed nipples will be pointing down rather than up and you'll never get a good bleed.

Good luck !

[Wil Ferch]

Cstreit:
I disagree fully !!!

Gravity bleed will make it less likely to *create* bubbles, and offers a nice, high firm pedal. Another plus...many who use the pedal/hold/pump method often drive the MC seals past the normal range of operation, so the seal enters the "not-often-seen" rough bore casting of the MC. Result?....your "well maintained" system now begins to leak because you tore part of the seal apart while "maintaining" your car..... how ironic. Gravity method doesn't get close to this risk....

Downside...it is a bit slow....

Wil

[Huh]

Gravity bleeding is a good technique if you are just replacing old fluid with new. If you have removed all brake fluid from one line, for expample, then you can get air bubbles caught on the edges. I have never had any problems driving MC seals past normal range on pump/hold/pump. I am not sure how one can do that because the car isn't on so you aren't using power assist. I have a Vacula that works off of the air compressor. It is easy and quick. A mity vac is probably one of the best for a one person job or the ones that screw onto the master cylinder and force the air out vs. vacuum sucking.

[Wil Ferch]

Mity Vac..if used via tubing connection on the bleed nipple...can still pull small bubbles...

Pressure has its own set of problems....pinching vent lines, possibility of spraying stuff around. I guess "to each his own"...but don't dismiss gravity as meaningless or ineffective...it works well for normal bleeding procedures. Also, if you don't pump the pedal "at all", there is 0% chance of driving the MC plunger in too deep.

- Wil

[911pcars]

Wil and I are holding onto this skill that might be lost for the next generation of DIYs unless some of you youngsters learn about it.

Gravity bleeding is non-traumatic to the system. It is both the zen and the zenith of brake bleeding. How else can one reverently observe the offending air bubbles exit the hydraulic passages, actually dissolve into the atmosphere through a clear pvc tube connected to the bleeder screw, never to increase pedal travel again? Other bleeding methods are both wasteful and thus harmful to mother nature (1 liter is sufficient thank you; not 2 or 4). A mallet smack makes short work of bubble particles that cling longingly to the caliper's internal workings.

And finally, if money is a consideration (mindful of the thick wallets so prevalent on Porsche forums), pouring or force-feeding 4 liters of HD Ford or Valvoline BF into the system to install 1 liter is one thing. Try doing that with SRF a few times.



Sherwood

[RoninLB]

pressure bleeding can put air in solution.. thus bubbles.

Pressure bleeding, if done, should be very low psi.

rnin has this subject going on in the other BBS.. no problem.

[rnln]

Originally I replaced my brake light swiches and the pedal got softer, braking is still ok but further distant.
I planed on bleeding the system on the weekends after drving couple days, it seem like the system ush air up and out by itself :lol: Pedal is firm as normal now :lol:
Thanks all for help.