Brake Bleeding issues, 'again' Options

[pthughes]

Hi All,

Seeking sage advice, as I am finally admitting defeat somewhat. I have read over and over all articles on bleeding, from here and all the part site tech articles. As one should. But, I am stumped.

First, I have a 1976 2.0. I lost 2nd gear (I should say it welded itself onto the shaft), so with the help of Dr. Evil's dvds, got that tranny rebuilt, and then moved houses. For the last 3 years, the car has sat up on blocks, as I slowly between health issues rebuilt the entire suspension, steering gear, shocks, etc.

All 4 calipers were gone thru, the rears being totally rebuilt. Also in is a new 19mm master cylinder from 914 Rubber. I say this, as, well the car has been undriven for 3 years. (hey, I have turned it over and sat in it monthly, with sunglasses on, and a beer). (I have also continually checked for caliper leaks, drips, and anything coming from the MC. Nothing)

So, with excitement, filled the brake fluid. First, I bled the left front lower bleeder, gently pushing the brake pedal. Filled fluid again, and used the Motive Speed bleeder. (which I thought is impressive, btw.) Right rear, bottom, then top bleeders, worked my way around the wheels in the correct order. (I should say here, I have triple checked the rear brake pad clearance, and it is spot on) I did this bleeding process about 4 times, overall.

Spongy pedal, not getting any firmness until more than 1/2 way down. Pump the brakes, I get a wee bit firmer, but it seems to fade ever so slowly.

Grabbed my father, and switched to him pumping and me bleeding, thinking a human touch would work. Twice around the car. Same. But, he did enjoy sitting in the car, although there was a slight issue getting him out. (He's 83, and well, while you can fall into these 914's, you really cant reverse that and fall out.)

Read some more. Located the brake proportioning valve, and glared at it. It looks like its been in a dusty barn for 30 years. With some reading advice, I gave it multiple gentle bangs or taps, whichever you prefer to hear. Back to bleeding, knowing this had to do the trick.

Nope. Pedal is still about 1/2 way down before I get firmness, and a little harder if I pump 2-3 times.

So here I am. I could bleed some more, but I think I am missing something. I do have the absolute clearest brake fluid in my lines on the West Coast, but I do not have firm brakes. Technically, to me it feels like a large bubble is somewhere, although I cannot get even the tinniest bubbles out of the system anymore.

I will likely hang under the car tonight, again checking all connections. (Brake fluid reservoir does not deplete, nor can I find any drips, but, hey, why not.)

As an old VW guy, we used to adjust the MC rod down by the brake pedal. Cant seem to find anything on that for the 914. 'Could' it be a faulty proportioning valve? Should I bang on it more, replace it, or rebuild it? (I dont know if such is possible for either option). Am I missing something in the bleeding process?

Basically, a full brake rebuild has left me with spongy brakes which I would say leave the car unsafe to drive.

Any thoughts would be greatly appreciated. I am no real hurry, because I also have to wrap my head around adjusting a newly built shifter onto the long rod, which has also got me in stitches. But that's another post (IMG:style_emoticons/default/wink.gif)

Thanks all - I wish someone tells me I have or am doing something wrong to get this remedied.

[mlindner]

I had the same problem....after many tries, I applied some compressed air to the top of the brake fluid reservoir. Put a rage around the air nozzle and cap opening. Few pumps later, nice hard peddle. Best, Mark

[emerygt350]

I find bench bleeding mcs very satisfying. And easy. Haven't had to do it on the 914 yet.

On the positive side, if you are bleeding your brakes all the time your fluid is nice and fresh.

[Van B]

How much pressure in the motive bleeder?

Not sure the OP is coming back, but I’m using 15psi in the motive right now and it’s working like a champ! (IMG:style_emoticons/default/smilie_pokal.gif)

I know my 996 manual says to use 15psi, and so does the motive instructions. I saw on Ian’s video he prefers 5psi…. But he also uses soap vs the carcinogenic lubricants I prefer lol (IMG:style_emoticons/default/poke.gif)

[pthughes]

I am back..had a golf weekend, had to get away from the car!

Some updates:
Discovered the right front caliper was sticking, couldnt spin the rotor, locked up tight from the pads. So, pulled the caliper, pistons out, cleaned again, etc. Just back on the car, so unk yet how that will turn out.

The Motive I was using first at 5psi, then bumped it to 10psi. Read some worries about going higher.

Did multiple bleeds while tapping the calipers with a hammer, I think this released a few tiny, tiny bubbles

I bench bled the MC while it was in the car, using a video on You Tube from a guy I cant recall! Basically install it, then crack the left front caliper and gently push the pedal to get fluid rolling, until no bubbles. (I did this first, way back)

Saw the post on gently opening the top line on the rear regulator - I have been pondering trying this, although it looks like quite a pain and may require pulling the regulator off the frame to get to the top line.

I am pretty much now going to re-bleed again, and see how that sticky caliper reacts, since there is air in the lines now.

I will circle back after a few more rounds of bleeding.Thanks to all of you, great advice!

[Van B]

Those wonderful and hugely beneficial videos are by our very own @iankarr

Regarding the motive, I just did my whole car at 15psi no problem. With the exception of your reservoir, the brake system sees waaaaay more pressure than 15psi. So unless you have a leaky res, those “worries” are unfounded IMO.

[iankarr]

Thanks much! Glad you find the videos helpful.

[pthughes]

Thanks much! Glad you find the videos helpful.

I love the videos, watched so many of them. What a resource you have created!

[mgphoto]

Saw the post on gently opening the top line on the rear regulator - I have been pondering trying this, although it looks like quite a pain and may require pulling the regulator off the frame to get to the top line.

This is actually very simple, with the car jacked up there is lots of room for a wrench, use a line wrench, nothing has to be removed, 5 minute procedure, just messy.

[Superhawk996]

I've been trying to resist the urge to respond to this thread.

There is no need to be cracking fittings and letting fluid drain on your parts or paint. (IMG:style_emoticons/default/chair.gif)

Here's best practices for brake system design:

1) Master cylinder and reservoir should be the highest point in the system. On this account, VW/Porsche FAILED on the 914. It can be made to work, but as noted it leads to a system that is difficult to bleed. The master cylinder is down in the pedal box area nearly at floor pan level. The rear proportioning valve is well above the floor pan and HIGHER than the master cylinder.

2) Caliper bleed screws MUST be at the top of the caliper. Can't count number of times I've seen people trying to bleed out the bottom bleed screw. Won't work. Just physics air rises.


As former automotive brake engineer:

Use Motive bleeder and vacuum on the bleed screws (Mighty Vac or HF pneumatic vacuum bleeder. You want lots of brake fluid velocity to pull along entrained air bubbles . This is accomplished by having a high pressure differential between inlet and outlet. i.e. pressure over the reservoir combined with vacuum at the bleeder. Again - use physics to your advantage.

Since air rises, jack up the end of the car you're having trouble bleeding. So in case of trying to get air out of the proportioning valve --- get the rear in the air. Rear brake calipers higher than the proportioning valve. That way air will continue to want to rise toward the rear calipers on it's own accord. Once you get the air to the rear calipers it will come out the bleeders. No need for spilling brake fluid.

If you're trying to fill a system that is completely dry for the first time (like after complete MC & hard line replacement), apply vacuum to a caliper bleeder and pull the air out before you try to introduce brake fluid into the system. In the modern OEM plants, this is done as a two part part process called Evac & Fill. System is 1st put under vacuum and leak checked. Then, brake fluid is introduced under pressure. The whole system fills, air free in a matter of seconds. Good bleed every time - at line rate.

[Van B]

If you're trying to fill a system that is completely dry for the first time (like after complete MC & hard line replacement), apply vacuum to a caliper bleeder and pull the air out before you try to introduce brake fluid into the system. In the modern OEM plants, this is done as a two part part process called Evac & Fill. System is 1st put under vacuum and leak checked. Then, brake fluid is introduced under pressure. The whole system fills, air free in a matter of seconds. Good bleed every time - at line rate.

This right here is what makes the airlift vacuum tool such a prize for refilling coolant! I loooove that thing!

PS: lol at you trying to resist temptation! Buddy, that's like going out with the boys and trying to only have educated and informed conversations... not. gonna. happen!

[ClayPerrine]

I've been trying to resist the urge to respond to this thread.

There is no need to be cracking fittings and letting fluid drain on your parts or paint. (IMG:style_emoticons/default/chair.gif)

Here's best practices for brake system design:

1) Master cylinder and reservoir should be the highest point in the system. On this account, VW/Porsche FAILED on the 914. It can be made to work, but as noted it leads to a system that is difficult to bleed. The master cylinder is down in the pedal box area nearly at floor pan level. The rear proportioning valve is well above the floor pan and HIGHER than the master cylinder.

2) Caliper bleed screws MUST be at the top of the caliper. Can't count number of times I've seen people trying to bleed out the bottom bleed screw. Won't work. Just physics air rises.


As former automotive brake engineer:

Use Motive bleeder and vacuum on the bleed screws (Mighty Vac or HF pneumatic vacuum bleeder. You want lots of brake fluid velocity to pull along entrained air bubbles . This is accomplished by having a high pressure differential between inlet and outlet. i.e. pressure over the reservoir combined with vacuum at the bleeder. Again - use physics to your advantage.

Since air rises, jack up the end of the car you're having trouble bleeding. So in case of trying to get air out of the proportioning valve --- get the rear in the air. Rear brake calipers higher than the proportioning valve. That way air will continue to want to rise toward the rear calipers on it's own accord. Once you get the air to the rear calipers it will come out the bleeders. No need for spilling brake fluid.

If you're trying to fill a system that is completely dry for the first time (like after complete MC & hard line replacement), apply vacuum to a caliper bleeder and pull the air out before you try to introduce brake fluid into the system. In the modern OEM plants, this is done as a two part part process called Evac & Fill. System is 1st put under vacuum and leak checked. Then, brake fluid is introduced under pressure. The whole system fills, air free in a matter of seconds. Good bleed every time - at line rate.

(IMG:style_emoticons/default/agree.gif)

I will add that a pressure bleeder will make your life infinitely easier.

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.allzim.com-1143-1649265926.1.jpeg)

Brake Bleeder tools

It provides the push that will clear the air out of the brake lines. The only time I had a problem bleeding brakes on a 914 was when I had a complete brain fart and forgot there are both an outboard and an inboard bleeder on
Boxster calipers. (IMG:style_emoticons/default/headbang.gif)


I use the pressure bleeder to move the fluid through the lines to push out the air. Then I use the " have the toolwench pump the pedal" method to make sure everything works correctly.


Clay