I have some air trapped in my brakes and want to try the long tube method to purge. With the tubes in the resevoir and connected to each caliper nipple, I understand the idea of cracking each nippple open and pumping until the cows come come.

What puzzles me is the idea of injecting air back into the system using this method. Until the lines are full of fluid, won't you be sucking air on each pump of the brakes back throuh the nipple from the empty tubes?

I have a motive bleeder but can't seem to get all the air out. It takes a couple pumps to get a hard pedal.

New MC
All new rebuilt calipers, etc
Used the pedal pump and release method
Flushed a 1/2 gallon of fluid throuh the calipers
Rear vented to .004
Driven the car and repeated the bleeding with motive and two people
Yes, the front caliper nipples are pointed up
No speed bleeders

While I'm certainly not an expert in this method, I think the idea is to keep an eye on the brake fluid level while there is air in the tubes. When you start pumping, the air will go into the brake reservoir, but the bubbles will immediately go to the top and out...as long as you don't let the reservoir run dry, you'll eventually have a solid flow of fluid.

Sounds reasonable. I think....

You put lines on each caliper's nipple and run the line(s) back to the resevoir? And open them all and pump? Is that the gist of it?

When you bleed the calipers, make sure that you close the bleeder nipple while your helper is still pressing the brake pedal, not at the end of the movement. You need to close them while the fluid is running out.

If you don't have a helper, use a tube with a one-way valve on the nipple. This way the nipple won't suck back air. Works like the speed bleeders but you can reuse it on all the bleeders.

You can use something like this.
http://www.harborfreight.com/one-man-brake...-kit-37201.html

My old man tought me a trick... with the system sealed, slam on the brake pedal as fast as you can. Then lift up on the pedal as slow as you can. This forces the bubbles toward the calliper. Do this a few times and bleed the brakes again. Repeat until you have all the bubbles out.

Though there are a couple of methods that work well, my personal favorite is reverse bleeding. You can only do this when the calipers have both an upper and a lower bleed port as typically found on race calipers, since you will need to use the bottom port (lowest in the system) to push new fluid into the system. Start with the caliper that's furthest from the master typically starting with the rear circuit. The reserviors of course need to be free of fluid, and you'll likely need to remove some fluid as you go. It's best to perform the procedure again the next morning to ensure all the air is purged.

For systems with traditional caliper bleed port locations and small reservoirs, the pump and bleed method seems to work reasonably well for me, but you have to be thorough. After I think I'm done, I'll do it some more. On my hydraulic clutch (V8 conversion car), it took me no less that four tries over the course of a week to get all the (damned) air out....that ended-up being far more tedious than the brakes. Bet I purged a good 1/2 litre or more through it.

Andys

I'm tired of taking the wheels off and bleeding, so quite a few people just rave about this tube method so I thought it would be worth a try.

The pic below is from McMark, maybe he'll chime in or someone who has actually tried this. Brian, my thinking kind of follows yours but it sure seams you would suck an awful lot of air in before the lines finally are full...perhaps that's OK. After the amount of bleeding I've done so far, I just don't want to go backwards.

Yes, I've tried the vaccum method, but have liked the motive pressure bleeder the best with a final foot from my wife to get the ultimate hard pedal.

After graciously pumping her share (opening and closing the nipples at the appropriate time) I thought I had a nice hard pedal...so I bolt the wheels on and...craaapp...more air.

PS I also have a T, no proportioning valve to complicate things.

If I had speed bleeders then the air in the tubes wouldn't concern me. According to the threads I've read you just open the regular bleeders and pump. Maybe I'm confused. Wouldn't be the first time.
Mark

Here's how I bleed a 914 brake system, from my post back in Mar 05.

Remember the "Search" function is your friend!

Get a spare cap for the brake fluid resevior.
Get a tire valve & stem.
Drill a hole in the center of the resevior cap, the same size as the hole in a wheel (or measure the narrow part of the tire valve).
Pull the valve stem through the hole.
Remove the plastic screen in the resevior.
Fill the brake resevior completely, not to the fill line, all the way full to the bottom of the tube that holds the plastic screen.
Put on your new modified pressure bleeder cap.
Drain your air tank to 10 psi, for cheaper compressors setting the regulator at 10 psi may not work. If you put too much pressure in the system, you'll blow off the blue lines that connect the supply lines to the resevior, or worse.
Take a clip on air chuck and clip it on your new pressure bleeder cap.
Bleed the brakes, starting at the furthest bleeder from the master cyl, and finish at the bleeder nearest the master cyl.
Bleeding sequence (RR-LR-RF-LF) EDITED FROM ORIGINAL POST
Pump the pedal hard about ten times and repeat the proceedure.
Do not get brake fluid on painted surfaces it will ruin them.
If the pressure bleeder cap retains pressure, bleed it down before taking it off the resevior.
This works very well, and makes it a one person job.
Replace brake fluid every two years.
Properly discard used brake fluid.

Thanks for the tips, but as stated I've been using a motive pressure bleeder...which is what you have done DIY.

I've tried the slam on your brakes but not the "lift up on the pedal slow." I just want to make this the last time I pull the wheels to bleed

Theory is: lifting up slow will prevent the bubbles traveling back to their original position.

The long tube method works well. And I've tried the conventional approach as well as the motive power bleeder. Do one corner at a time, though. Not all at once.

My method is to get it going normally, then I crack every single union (one at a time, like it was a bleeder screw) and let it piss all over the floor.
Hell of a mess but works first time everytime.
Cat litter is cheap.

If I understand correctly, you think air is in the system because it takes a couple of pumps to get a firm pedal with freshly rebuilt calipers?

If so, it may not be air in the system. It takes a few stops to get the caliper pistons in the proper position.

This worked great for me in the past. I don’t think I did anything special rather than starting at the rear passenger, then rear drivers, to the front passenger side, finishing off at the drivers front caliper. I used clear vinyl hose from Orchard so I could actually see when the bubbles were out of the system. I used a helper to hold the end of the hose in the fluid reservoir so that it did not pop out and could watch the level of the fluid. Before starting I changed the entire brake system with new blue fluid.

As I was sitting in the driver’s seat watching the bubbles go back to the reservoir, I felt that I was gaining on the system as I could also see what was happening. There were big bubbles but also much smaller ones in the line. I continued until all bubbles were gone before moving to the next caliper. After trying for more than a day to get a firm pedal this finally firmed it up.

That looks like Sir Andy's Car.....

Hi Michael!
So it sounds like you used 1 hose and just moved it from caliper to caliper. Everytime you moved the hose you probably sucked some air intially back into the system, but continued pumping then filled the line and purged all the air.

I've driven the car a bit to set the pads but now want to finish up with a hard pedal.

Yes, I believe that is Andy's car.

I opened the bleeder valve at each caliper then closed it before moving to the next caliper. No air was let back in as I closed the bleeder before moving to the next caliper.

Or you can pull the pads with a spacer thinner than the pads, push the pedal. Remove the spacer, push back piston just enough to get the pad back in.

I have found with a dry system, do the one man bleeder thing with a bottle. Drive it a little, let it sit overnight, then do it again. I have also opened up bleeders and let it piss on the floor,mthat works well too. It's all about how much time your willing to spend. If your a shop, this probably wouldn't work too well.

Will pumping on a closed system really consolate the air bubbles to the top/end of the line? Just asking what all the experts here think.

I have found that a little bit of teflon tape on the threads of the bleeder gets rid of the mystery bubbles...

It won't suck any air in, promise. You'll see fluid moving out from the caliper with each pump and almost no fluid going backwards. Plus the fluid will move down the line in one solid 'chunk'.

Hard to explain, I guess. Just go for it.

interesting conclusion...

A symptom that may not be air...


Aha. Now we're getting somewhere...

Common symptom with rebuilt calipers.
It takes a while for the pistons to properly align in their new square O-rings - they get pulled back too far when they retract.

Someone here was able to address this in the garage by making plywood 'brake pad simulators.' The idea being that you crush the pistons into the plywood, so they extend a little 'too far.' Then when you push them back just far enough to get the pads in, the artificial 'overtravel' has been normalised.

Well, the car has been about 10 miles all together on side roads doing all the brake in steps suggested to bed the pads. Your suggestion and the one earlier makes me wonder now. I have the car to what I thought was a good hard pedal on two separate occasions until I put the wheels back on and drove it--assuming that trapped air bubbles were the culprit. I decided to go ahead and bed the pads to the new rotors before I would try to bleed again.

So if the pistons are being pulled back too far, then the couple of pumps for a hard brake makes sense.

If this is the case, how long does it normally take to normalize? The plywood option sounds interesting as well.
Mark

Just drive it. If no improvement after a couple of days, then you have another issue.
EVERYBODY that rebuilds their calipers goes through this the first time.

Speedbleeder nipples always worked well for me.

http://www.speedbleeder.com/

They are cheap & work great. I'll put these on everytime on every 914 I own. You no longer need the extra person. Just run a hose from the nipple to a cup & pump away. At maybe $15 to do all 4 why not?

Yup...ordered a set last weekend.

The standard rule of thumb was "a hundred miles." That car looks like it might not get driven in traffic much...

The thread I referred to earlier is here: Front End Changeover The brake issue shows up around the middle of page 2.