Gravity Bleeding - Effective ??

AirCooledExcellence · AirCooledExcellence's Garage

Hi All,

I've just finished some brake work on my car and am now ready to bleed the system. As it's up on axle stands and all wheels are off I thought I'd try Gravity bleeding.

Is this method as effective as pressure/vacumn bleeding?

Cheers

dean · 02-20-2003, 04:06 AM

No

Wil Ferch · 02-20-2003, 04:08 AM

Yes !.... produces very high and firm pedal....downside is it takes a bit of time...
--- Wil Ferch

Jim Sims · 02-20-2003, 04:12 AM

Only if you move the master cylinder reservoir up until it's 15 feet in the air. Seriously, when using the gravity method you only have the hydrostatic head or weight of the column of brake fluid providing the pressure or driving force to push the brake fluid through the system. There's only a couple of feet of head (elevation) at most between the brake fluid reservoir and the balance of the system. Which probably only generates about 1 or 2 psi. I doubt this would move the brake fluid very quickly and it might not move the fluid rapidly enough to flush bubbles. A vacuum bleeder can provide up to 14 psi or so depending upon one's altitude and a pressure bleeder even more. I'd recommend getting a "Motive" pressure bleeder. Jim

Wil Ferch · 02-20-2003, 04:28 AM

To All:
I see a lot of words like "which probably" in the previous posts...have you nay-sayers *actually* tried it...or is this supposition??
I have used this method...it's both cheap and effective ( less than $1.00 for the clear vinyl hose)..but yes..it's a bit slow. Fronts go fairly fast, but rears take some time.
It doesn't take a lot of hydrostatic head to move fluid through the system. As to pressure provided, I don't know the specific gravity of brake fluid, but as a reference... "water" is rated at 2.3 ft height / psi.
---Wil Ferch

RoninLB · 02-20-2003, 04:36 AM

Quote:

Originally posted by Wil Ferch
Yes !.... produces very high and firm pedal....downside is it takes a bit of time...
--- Wil Ferch

Yep it does work.. even in the Boundary Waters area of N. Minnesota.. like Jim said, it's slow.. after the first bleed drive around the block and re-check all calipers for air.. you can also make an adapter to use a tire for air

n8marx · n8marx's Garage

I'll bite. Why were you bleeding brakes in the BWCA? Doesn't seem like a canoe would fit very well on the 911!

RoninLB · 02-20-2003, 06:44 AM

Quote:

Originally posted by n8marx
I'll bite. Why were you bleeding brakes in the BWCA? Doesn't seem like a canoe would fit very well on the 911!

Naw, no canoe.. I was on Hy 12, it heads NW from Grand Marais.. the area is unknown to most everyone, outside of Min.. that's good.. I left as soon as the walleye fishing season opened.. was in rain/drizzle for a week.. Grand Marais has a great town pool/sauna.. the girls in town kept stareing at the 911, LOL..

john walker's workshop · 02-20-2003, 07:54 AM

i use a variation of the gravity method all the time. pretty quick and easy actually. keep the reservoir full, attach a 12"length of hose to a bleeder nipple, open the bleeder, pump the pedal several times to get the fluid flowing out the hose without any bubbles, shut the bleeder before removing hose. do the next one. piece of cake. only takes one person, and the fluid stays in the hose after bleeding, so air doesn't go back inside. you don't even have to rush back to the wheel to shut the bleeder off. it's like holding fluid in a straw with your finger on top.

n8marx · n8marx's Garage

Ron,

I've had my 911 up to Grand Marais a couple of times myself. I felt like a rock star with all of the staring going on. Great area. I make it to the BWCA about twice a year on average. Cool to see your car there.

pwd72s · 02-20-2003, 08:31 AM

cool tip...time I have plenty of...thanks guys.

RoninLB · 02-20-2003, 08:43 AM

Quote:

Originally posted by n8marx
Ron,

I've had my 911 up to Grand Marais a couple of times myself. I felt like a rock star with all of the staring going on. Great area. I make it to the BWCA about twice a year on average. Cool to see your car there.

thanks for the hospitality.. I guess you know the area better than me.. the 911 slept at "Trails End", LOL.. was looking to sleep with some wolfs, never happened.. did check out some guides.. took notes of the 4 I liked.. a very special place.. but don't tell anyone, I don't.. you gotta see the tourist traffic at places 1/10 as magnificant... the girls at the visitor center were like cats checking out a solo guy in a 911, LOL.. one did make a sneaky phone call to another girl to "get down there quick before he's gone", LOL.. she came down and made small talk.. but I was on a mission, LOL... the ride was the 1st cross country for the 911 a few years ago.. left home 1,500 mi after a complete rebuild.. kinda like "lets see what your made of".. it was either going to clock 15,000+mi or blow up trying, LOL.. so it relaxed me to know I didn't screw up the rebuild..

AirCooledExcellence · AirCooledExcellence's Garage

Well I gave the gravity method a go this afternoon and have ended up with a really nice firm pedal.

I do have a pressure bleeder (gunsons) but when I attach the air supply it seems to 'fizz up' the fluid and I was worried that I was actually pumping gassy fluid into the lines!

I bled through about a pint of fluid today, ATE Super blue going in tomorrow!

Cheers

Superman · 02-20-2003, 09:30 AM

Yes. It works great. It's also fairly important to push the caliper pistons in for this procedure. The reason is that if you don't, the old BF in the calipers will essentially not be renewed. Only the BF in the reservoir, MC and lines.

911pcars · 02-20-2003, 10:27 AM

Gravity is good. Open lines to a fluid tube allows air bubbles to rise up and out without introducing air inside the lines. You can even bleed remaining air out of the master cylinder by pumping the brake pedal without fear of sucking in more O2.

I recently purchased (4) gravity bleeding containers from Harbor Freight (~$4 ea.) for simulaneous bleeding, but one is all that is needed. A plastic container with PVC hose attaches to each bleeder screw. A magnet on the container allows placement above MC level. Longer hose might be necessary, but available at the hardware store. Use safety wire and pliers to prevent hose from slipping off the bleeder screw and to create a tighter seal.

For those who complain about the high cost of HD brake fluid, gravity bleeding uses the minimum amount necessary to fill the system and bleed. Those using pump and squirt techniques find a lot of new fluid ends up not in the system. Pressure bleeders must load the pressure container with more fluid than necessary which wastes fluid as one shouldn't store opened containers (it absorbs moisture). This is a waste. If you're using Castrol SRF @ $70, that's costly waste - even at "only" $10 for a liter of ATE, an extra liter in and out to expel air is an equivalent of a good meal.

I'll revisit this page w/some pics when I get around to changing the fluid.

Sherwood Lee
http://members.rennlist.org/911pcars

Wil Ferch · 02-20-2003, 10:57 AM

Sherwood:
Weren't you and I ( and a few others I recall)... some sort of charter members for the "international brotherhood of gravity bleeders"...or somesuch...a while back when this topic surfaced on Rennlist??
---Wil Ferch

911pcars · 02-20-2003, 11:16 AM

"Weren't you and I ( and a few others I recall)... some sort of charter members for the "international brotherhood of gravity bleeders"...or somesuch...a while back when this topic surfaced on Rennlist??"

Wil,
We still are... as long you still bleed in the correct manner. I forget the name of our loose-knit brotherhood of self-admirers, but we should schedule a convention sometime to compare the latest nuances of gravity bleeding. We could have 60-0 mph runoffs.

How about "BFD" (Brake Fluid Dummies ... or Dilettantes or ...) ?

Sherwood