Gravity Brake Bleeding

[7783911]

I just completed a complete re-build of the 4 calipers and need to bleed the system


I had intended to use Motive but it was a defective unit and sent back

I have my trusty 20 year old MityVac which was plan B

Then I read about gravity bleeding but I am not sure I understand the part where the drain bottle attached to bleed valve is placed...is it on the ground or is it higher up?

I did install speed bleeders too so could just do old fashioned pump the brake method?

Thoughts?

[wjdunham]

I've gravity bled a couple of 911's after a full brake system upgrade. If I recall, I placed the fluid catch above the caliper but below the level of the brake fluid reservoir. It's takes a bit more time but the results were excellent. Tap the calipers and brake lines lightly with a rubber mallet to release any trapped air bubbles.

Bill

Originally Posted by 7783911

I just completed a complete re-build of the 4 calipers and need to bleed the system


I had intended to use Motive but it was a defective unit and sent back

I have my trusty 20 year old MityVac which was plan B

Then I read about gravity bleeding but I am not sure I understand the part where the drain bottle attached to bleed valve is placed...is it on the ground or is it higher up?

I did install speed bleeders too so could just do old fashioned pump the brake method?

Thoughts?

[SCadaddle]

Don't believe you will be able to gravity bleed through a speed bleeder. They require pressure to let the fluid past them. What I did in your shoes a year or so ago was to leave all the regular bleeders in the calipers, gravity bleed them one at a time, then quickly replace the original bleeders with the speed bleeders and crack them open one at a time pump the brakes a few times and I was good to go. You can place the catch bottle above or below the caliper as long as the line from the caliper to the catch bottle has it's high point above the caliper for the gravity bleed. Speed bleeding won't matter as they are one way valves.

[mat911ku]

heard a lot about the gravity bleeding, tried it on a simple system like my bicycle with hydraulic brake and it simply just didn't work. Gravity bled 3x with soft brakes, did a pressure bleed 1x and it worked. Since that experience, would not try gravity bleeding.

[7783911]

Thanks Bill/Scadaddle

Good insights

last caliper just mounted...used a low profile ratchet (craftman) i found in my tools bin
worked like a charm! and fits in the small space no problem

https://toolguyd.com/craftsman-max-axess-mechanics-tool-set-with-pass-thru-ratchet-and-sockets/

[Cloggie]

I do only gravity bleeding on my Turbo brakes.

Main thing is to be patient and remember, you need to lower the caliper end for a while to allow fluid to flow through the longer lines, fill the caliper and then bleed out.

I use only silicone brake fluid so I do not want anything that creates any bubbles - like a pressure bleeder - and this has worked for me for 20+ years

D.

[7783911]

I ended up using the mityvac to try it out (worked on my old TR6 years ago..sigh)

But once all 4 are done I may go around one more time as articles suggest and try the gravity method..but i have to replace the speedbleeders with the OEMs?

[David Inc.]

If you flushed all the fluid and air with the mityvac just give a pump or two at each corner through the speedbleeder. You'll be golden.

[7783911]

Yes, figured that after I posted...try the gravity next time I do a flush/fill

[stownsen914]

I’ve used the gravity method for years, both for initial fill after major brake service and periodic bleeding with excellent results.

I didn’t have much luck with speed bleeders, The concept sure sounds great. For me, they would suck air through the threads on the retraction portion of the stroke. Couldn’t get them to stop doing that, so went back to the regular bleeders and gravity bleeding.

[porsche930dude]

To bleed i put a clear hose on and run it up 8 or 10" and back down to a cup on the ground. Then have someone very slowly pump the pedal a few times till there is no more bubbles and go to the next one. It seems to work for me.

[creaturecat]

i've always had good luck with the gravity bleed method.

[7783911]

I have the old bleeders, maybe I will try it tomorrow, psgr rear first, driver rear 2nd, psgr front and lastly driver front...is that the correct order.

To do rears I jack up the front to raise the reservoir, for fronts do i need to jack driver side front up to do psgr front? I assume driver front I leave as is as long as the catch bottle is below reservoir but above caliper?

sorry for all the questions..this is a new method for me

[stownsen914]

I usually do it flat. To the other question about height of the catch can, I do try to put it close to the height of the caliper. While not technically important, I find it convenient for holding steady loop in the hose attached to the bleeder. Makes it easy to see any bubbles that are coming out during bleeding.

[7783911]

Ok, so I understand, bottle is same height as caliper, the hose goes from bleeder up in an arc and down to bottle so there is a small loop

The Reservoir Height question relates to gravity and I assume may improve bleeding rates

Thanks for your patience

[7783911]

Worked like a charm....!

[tx63conv]

Define patience. Is it 1 minute per caliper, 1 hour, 1 day. Am I looking for no more bubbles in my clear line?

I have done speed bleeders, old fashioned friend pumping and then mighty vac. I have been successful with each but I have a new project that I cannot get bled after trying all three. I believe I have a leak somewhere but that is another thread.

[stownsen914]

When I gravity bleed a system, let's say a yearly full system flush (1 liter can consumed) ...

Probably takes something like 15 minutes per corner after I crack open a bleeder. In the case of a full flush I'm aiming to get all the old fluid out so it does take a bit. I usually do some other mindless task nearby while I wait.

If it's a bleed and not a full flush, I may just look for bubbles in the bleed line.

If you're having a hard time bleeding a stubborn system, a few old tricks to try:
- Tap the master cylinder gently with a non-metallic mallet to encourage air pockets to migrate
- Tap the calipers, same idea as above
- In between bleedings, pump the brakes a few times - also helps push any trapped air around in hopes it will migrate

[trond]

i always gravity bleed and no point in using vacuum or pressure, just open bleed nipple. But I like to also replace fluid inside calipers too, and usually take them off and use the vacuum bleeder to suck out out all old brake fluid from reservoir, and from calipers (with disconnected brake line)

[7783911]

Trond

I just blew the old fluid out since I was doing seals/boots and cleaning pistons. What I failed to do was "precharge" the caliper with new fluid before installing...every project teaches you something to remember next time ...

bob