Power Brake bleeding procedure difference. .
 

Hi,

I 'm ready to do the 2th year complete brake fluid flush. Got a motive power bleeder, 2 cans of the blue stuff and lots of towels.

The confusion comes from the Bentley manual vs the motive flow instructions,

BENTLEY Manual suggests having someone to push and release brake pedal slowly while bleeding the pressurized system, and MOTIVE that is a one men job without touching the brake pedal.

According to your experience, which procedure works better?

Leo
911 1982 targa SC

I never touch the pedals until I am done. Rock hard pedal. One man job.

With the Motive no need to touch the brake pedal.

I use the Motive but not with its fluid reservoir. I just use it to pressurize the master cylinder, frequently checking and ensuring the MC is full. It's far easier to clean up when the job is complete if you don't have to worry about the bottle the Motive includes.

old seals in the (old) master cylinder can rip finally when using the pedal-method.

I use an "easy-bleed" system pressurized via a spare tire with max 1.4 bar.
with that, you have pressure and instand reservoir refill and can do all 4 bleeder in a turn within minutes.

ALLWAS REMMBER TO SHUT THE OVERFILL NOZZLE OF THE RESERVOIR (e.g. with a clasp)

Thanks a lot for sharing your experiences.

I will not touch the brakes then.

Leo.

When you use the pedal, you're using the master cylinder as a pump to push the fluid; when you're using the motive system, you're using air pressure to move the fluid. Either way, you're doing the same thing: Pushing the fluid from the reservoir through the lines and out of the calipers. The advantage of the motive system (and or using a vacuum pump at the caliper) is that you don't run the risk of ripping the o rings on the master cylinder rust scales, which by the way, would not be a problem on a new master cylinder.

For normal fluid flushes, the motive alone is fine. However, I've always found that when i open the system completely by removing a caliper or swapping lines, I am unable to get the desired pedal firmness w/ just the Motive. I always have to follow back up by pumping the pedal. My MC has been replaced so i'm not concerned about issues associated w/ passing its operating range.

Recommend old school procedure, I have worked with a Very good Porsche shop, that's the only way they do it. As far as pumping pedal just use good practice, once air bubbles are our of each brake caliper, you don't have to push that hard on pedal. I always go around two to three times on each wheel.
I think if you do it that way it mimics actual brake action that you would experience driving

I used to do the pedal only method, then I bought the bleeder and did the 2 together.
Lately I have just used the bleeder and have found little difference.
BTW I bleed before track events so this is very important.

I've done it a number of ways with the Motive.

But currently, I do a combo. I pump the Motive only to around 10 psi (or less) to put some pressure in the system. Then I mostly let the pressure bleed it, but I'll do some pumps on the brake pedal, but only going down about 1/4 of the way.

That way there is no risk of tearing any seals in the MC, since it's not going past any point that it travels in normal use. But the pumps help speed up the process.

I'm sure most systems can handle more than 5-10 psi, but it makes me nervous!

I've also done it with filling the motive with fluid, or by leaving it empty and just making sure the brake fluid reservoir doesn't get too low. There's advantages and disadvantages to each. Just did one of my cars last weekend, and left the motive empty. Next time I'll probably just fill it with the fluid. Seems like I'm 50/50 on that.

The problem is when the systems can't. Some of the plastic reservoirs are probably older than most of us !

^^^

Some of you boyz are weird - I use 17-18psi for pressure bleeding on any and all vehicle systems I get my hands on (not just Porsche) . . . no problem at all with that sort of pressure, and besides, air leaks past the cap long before it will damage the res bottle (not to mention, if the res bottle is that weak, might as well find out now, rather than on the road somewhere). :)

Not weird, unlike some ;) Just not taking the risk of BF damage, speaking of which, looks like useful stuff, there must be a 101 uses for used BF thread somewhere !

pNutz, real men, wif turbo powaaaaa', drink used BF - helps with age-related, virility issues! :D

Ignorance.......
 

Sean,

If those reservoirs you are talking about could not withstand 25 psi. of air pressure, they should not be used at all!!!! 10~20 psi. is a good pressure range for brake pressure bleeding and clutch saver. You probably have not done one and your anxiety has to be overcome. If this pressure bleeding is scaring you to death, I wonder how you would feel towards driving 100+ MPH in a track in a 30 or 40 year old car. Just my two cents.

Tony

I presume no one had to replace a cracked or failed brake reservoir ever.

What are they made of ?

Hi,

How would you know if the master cylinders o'rings had been twisted or broken?

Leo.

You would have little to no brake pedal pressure (pedal would be relatively easy to push all the way down, even with caliper bleed nips closed).

So this would be a catastrophic failure and not just not perfect brakes?

Finally I did the brake bleeding, My first time with motive bleeder. Flushed two bottles of the racing stuff, didn't touch the brakes, I'm pretty comfortable with the braking action.
When I bought the car, brakes where stiffer, but during hard braking the car wanted to turn a little. A local shop performed the four caliper overhaul, they found a couple of frozen caliper pistons. Since then pedal stiffnes hasn't been the same.
Should a blame dose two frozen caliper pistons for the less pedal displacement it used to have?

The brake system only needs 1 liter for a complete fill. Wasting new brake fluid is well.... wasteful. Spitting out a liter of new ATE Blue is about $10, Motul RBF about $17, Castrol SRF about $65, but that's the result when pressure bleeding to drain, flush and refill.

Sherwood

There is a hose (venting?) on the side of the MC reservoir. Does that have to be plugged/sealed when using the Motive?

The Motive supplies air to the cap area, correct? If so, then yes, the vent has to be plugged or air and fluid will flow out of it.

PS - when pressure bleeding with a compressor, you can attach the air supply to the vent nip and leave the original cap on.

Makes sense. Where does that vent lead to? I suppose one just removes that tube and attaches a clamped one.

How old is that stuff?
If it's older than a year I wouldn't be using it.
Bill K

The vent is for boil over and should come out just in front of the driver's a-arm. I use a set of surgical forceps that clamp down.

I thought an unopened can of brake fluid should be good for a couple of years. I didn't think you could get blue anymore.

The vent tube is now 30+ yo. Is it wise to clamp it?

You say surgical forceps... the typical ones do not self clamp. How do you keep them clamped down?

If you did damage the hose you could cut the damaged part off and re-attach.

The forceps you show do self clamp.

Having spent 10 years as a service writer/manager at GM/fiat/ssubaru dealership, I often got called on to push the pedal for the mechanics. Most of the cars were fairly new but some of them were 10-30 years old.
I noticed a significant number of the older cars experienced a failed maaster cylinder right after the bleed. I put this down to the "full" travel of the MC piston(& cup seal) during the bleed. My sense was that during normal use the brake pedal would only travel part way down the bore. The seal would push any debris only part way down the bore. If you pushed the seal past/over this pile of crud you risk nicking the seal.
If the fluid is flushed, every one or two years, (not just bled), you are ok to use foot power.
IF you don't know the service history on the car, foot bleeding is a risk.
BTW, the shop went to power bleeding and master cylinders enjoyed much longer life.
I have had good results with mighty vac. When I install the lift (& do more brakes), I will go to the motive bleeder.
Chris

^^ What you say is true and that is why you put a block of wood under the brake pedal so it does not go all the way down.