This journey started out simply enough. My son's 70 914-4 pulled to the right under braking so we figured it needed rebuilt front calipers and ordered a set from PMB Performance. I put new pads in them and installed the calipers. It's when I tried to bleed the system that things got "interesting".

My initial attempt involved using my power bleeder. When that didn't result in a good pedal I consulted this group and got turned on to the "long tube method" which seemed to be going well on the rear wheels, but when I moved to the front I had no pedal at all. After consulting this group again I concluded that I had experienced a catastrophic master cylinder failure.

So at this point I've installed a new 19mm MC. I initially tried bleeding using the power bleeder, and then bled the system again using the long tube method. Again, this resulted in the same behavior even though it's a new MC. During bleeding I felt normal push-back on the pedal on each rear wheel, but had no push-back on either front wheel.

The latest stab at this was to gravity bleed each wheel. I made sure I used a tube that had at least as much tube on the ground as the length from the MC to the right-rear wheel cylinder. All 4 cylinders bled just fine with the fluid level rising to the level of the MC as expected. While bleeding each wheel cylinder I also used a hammer to tap on the MC and the wheel cylinder that I was bleeding.

So I'm totally frustrated at this point, but I've also had a flash of "insight". Since the no-pressure situation seems to be associated with the front calipers, did I miss doing something when I installed them? All I did was to put the new pads in place and then mount the calipers and connect them to the brake hydraulic system.

Any thoughts or help would be appreciated!

have you replaced the front soft lines?




that's all there is to it, which is why I'm wondering if your soft lines could be bad.. I replace the softlines with any caliper rebuild on any car. if you have the stainless braided soft lines, this is important because you can't tell by looking if the lines are clogged.

I've got new soft lines for the car, but for some reason didn't install them. I think it was because I had problems removing the old soft lines and was in a hurry at that point trying to get the car on the road for last spring's Route 66 Classic.

Sounds like you are starting at the wrong end. I thought you needed to start in the front at the closest wheel. Drivers side basically then move to passenger front. Drivers rear & then passenger rear

Maybe I am back asswards . Wouldn't be the first time

I'm with Jamie on starting on the fronts first. DS First, then PS, then rears.

a little bleed brake graphic

Um... guys bleeding order is one thing I know for sure. The Haynes 914 manual, the VW Idiot's Guide and every other publication I've ever seen on brakes all agree that you ALWAYS start from the wheel cylinder which is farthest away from the master cylinder.

Now I don't know why they all they say that, or if it is actually important to do it in that order, but I also remember that my VW repair class instructor drilled that into me over 30 years ago and I've never forgotten it.

Ernie, are you sure the push rod is centered in the MC bore and that the length is not so long as to not allow the pistons to return properly?

Secondly, which MC did you buy? If it's the Euro Parts one the MC could be bad outta the box.

I crack the fittings at the MC and let them drip for a while to fill the MC before attempting to bleed. I use a vacuum pump to bleed the brakes .... never had much success with a pressure bleeder.

And then there is that proporitiong valve that is a bitch to bleed all the air out.

Other than that, I gots nuthin!!

I didn't change anything about the push rod and the MC that was in it was a 19mm ATE so I figured there was no need to even look at it. AFAIK it is properly centered because I found that if I didn't have it centered I could not get the MC mounted to the wall.

The new MC is an ATE.

Okay well I do it front to back as stated. I've never had a problem bleeding them that way . That is how I was told to do it many times & seen 914 guys do multiple times. Anyway it may be worth trying if nothing else is working

New master cylinders are a PITA to get bled. I usually spend a lot of time on the front left wheel when I've got a new master cylinder, just because it's the shortest run of tube and just pump and pump.

The idea of starting with the farthest wheel has never really held much weight for me. I bleed where I need to and adhere to the 'traditional bleeding order' only on occasion.

Another trick is to leave the bleeder only open slightly, so that you can build up some pressure with each pump and let it slowly bleed off. This will help the bubbles compress and expand, hopefully knocking a few free.

I've also found that when bleeding a complete system, it helps to bleed for awhile, then shut the whole thing down and leave it over night, then come back to it.

I would definitely change those soft lines before any further bleeding attempts. Who knows that may the reason the caliper locked up in the first place. When the lines collapse if can cause a caliper to lock and be a PITA to bleed if you get it to bleed at all.

Bleeding always starts at the furthest point from the MC the RR then to LR, RF, LF. Most of the time you try to bench bleed a MC before installing it. On these I would imagine the best thig is to bleed the MC before hooking up the brake lines.

totally. Replace those hoses because there is as good a chance that was the original cause of the problem as the calipers.

And while I bleed old school just like you were taught, there is some value in what Mark said about doing what's necessary or what makes sense for a given situation. And in this situation I'd work on the left front as he suggested until you get the MC bled. Otherwise pull it out again and bench bleed it.

I did not bother with bench bleeding with any of the masters that I have put in.

If you have one of the AutoMotive pressure bleeders, they work GREAT. UNLESS you have speed bleeder valves on your calipers. The bleeder valves have a check valve, and the pressure bleeders do not have enough pressure to operate them properly.

The Long Tubes method works GREAT. Unless you have standard bleeder screws. if you use speed bleeders, it is an absolute snap. When I do long tubes, I don't try and do all 4 at once. I only do one at a time, or I find I don't have enough pressure to remove bubbles. This is with an ATE master, BTW. If you have standard screws, I think it still pays to have a second person to close the valve when you let off pressure. Otherwise, it takes forever longer.

Also, your calipers may be stripped out where the bleeders screw in. I had that with 2 of my calipers. Instant leak. Only cure is a new caliper.

So, do you have standard bleeder screws, or speed bleeders?

Zach

I never have either. But the first and last time I replaced a 914 MC with a brand new 19mm unit I wish I had, because I had the same issues Ernie's having now. It took forever to get that entire system completely bled. Like weeks...

with all the suggestions. I presume since the back brakes are bleeding, the "proportioning valve" is not malfunctioning? Is it possible the problem is there?

I don't see how. The circuit that goes to the fronts is separate from the circuit that goes through the prop to the backs.

I think he just has an air pocket in the forward master circuit that he needs to get bled out, after replacing his soft lines.

Zach

remember that the "proportioning"valve for the rears is not a Proportioning valve in the normal sense. It will flow properly during bleeding, but limits the amount of pressure on the rear calipers, to increase safety under panic situations.

The P-valve will act like a T for bleeding purposes, however, people have issues, getting the air out of then sometimes..

I have no more advice than what was already provided here, but I have had my struggles with it as well.

I hope that helped.

Thanks for all the suggestions - I'll be back at it again tonight after work. Just 2 questions at the moment:

1. It was my understanding that gravity bleeding and tapping on the MC should ensure that there is no air in the system. Apparently this isn't an accurate statement?

2. Assuming that I actually have to "bench bleed" the master - how do you do that? I've not been able to find anything that says how that's done. Also, can it be done without removing the MC from the car?

I'm really hoping that the soft lines are the issue. I'm just having a hard time believing at this point that it is the MC because the behavior I'm seeing now with the new MC is exactly the same as when I had the original MC in place (assuming my memory is correct - last Spring was a long time ago). The "catastrophic failure" that I experienced was just like I've got now - normal push-back on the pedal when doing the rear wheel cylinders, no push-back when doing the fronts.

I hate to even ask Ernie, but you have set the rear venting clearance correct?

Gotta ask the easy stuff sometimes.....

I have standard bleeder screws and I bled each wheel individually when using both the long tube and gravity feed techniques.

I've not touched the rear calipers at all except for operating the bleeder screws to bleed the system.

Ernie ... as stated before, I crack the fittings at the MC and let them drip to fill the MC. After that I bleed as normal (rear to front).

If the venting clearance on the rears is way off, it will feel like you have no brakes at all.

Oops, missed that! Thanks, Ron!

I hate to even ask,,, but Ive seen this problem before on my son's jeep... are the bleeders in the up position?? My son's jeep they were only a little off center,,,they where on the wrong wheels...never would bleed right.. switch them back..no issue!!

I know I can be dense at times (ok, maybe often), but I have no idea what you are talking about. AFAIK the bleeder screws don't have any position options - I just finger screwed them into the holes provided. Can you explain further?

I think he meant that the calipers had bleeders at the top of the caliper....not the bottom.

I think he means... "are they on the "TOP" of the caliper?

some have bleeders at the top and bottom but only the top bleeder should be used.

That makes sense. I'll have to check that out tonight - I simply moved the bleeders from my old calipers to the available holes on the new calipers. Just going from memory - I noted that the front bleeders are lower on the caliper than the rear bleeders and much easier to reach. On the rears I have to remove the wheels so that I can get to the bleeders because they are on top. On the front I can just reach up from under the car. Sheesh... could it really be that simple?!?!

sorry, I think in short hand,,,Drives my boss crazy..

And yes it could be that easy.. I bleed my jeep 8 times, the brake shop 3 times more before we switched sides with the calibers. We had mounted them upsidedown.. Bled out first time after we switched them...My son just mixed them up and it wasnt readily noticeable..

I havent worked on -4 brakes for a long while but most porsche's bleeders are at the very top of the caliper..

The later 4s have two bleeders on each caliper.

Greg D. gets the prize!

I ran home at lunch to take a look - I just had to know. This is a 1970 - early calipers. Here is a photo of the passenger side installed. If I had picked the other one first out of the box all would have been well (what's that line about given a 50/50 chance I'll get it wrong every time?).

So tonight I'll be switching the calipers to the other side and changing out the soft lines, then bleeding the fronts again.

There is your air trap Ernie! That will fix you up right away when you switch sides on them!

Ha HA! That will do it, to be sure! You will never get the air out of the top of the caliper.

This looks like it is going to be an easy fix for you.

Zach

you'll never do that again!

yep, you can't bleed air at the bottom, damn physics!

still, change the soft lines... seriously

Oooops... we sent you right calipers for the left and left calipers for the right. We'll need to get a rush replacement order going! Sorry about that!

Ok its a sad day when, I get it right!!!!! Of course I did it first!!! Does that still count???

Most of us learn from our mistakes....I have done it before (not on a 914) and I will never do it again.

Oh Ernie ... it's the rarified air ...............

I'm very happy to report that switching the calipers from side to side and replacing the soft lines has resulted in a wonderfully hard brake pedal - just like it should be.

I cannot thank you all enough for all the helpful suggestions. The wonderful thing about this place is that you have folks who actually try to help and who don't ridicule you or laugh at you, but instead laugh with you at both the problem and the solution. Through this experience I've learned 2 more ways to bleed brakes that I had not known, and I've got nice fresh fluid in the brake system and that's a good thing. AND most important, someone else will learn from it (search is a wonderful thing) so all-in-all it's a great experience!

Just two things left to do. The brake lights and brake warning light are both constantly on. I understand that pushing the "button" on the MC switch will take care of the warning light and the brake lights are on because pushing the brake pedal down that far will "flip" the brake light switch so I have to remove the pedal board and get that done. Should be a piece of cake.

Oh yeah - anyone know how to preserve a used (but good) MC so that it will still be usable when I finally need it?

Again... Thanks to All!!

Filll it with light oil .... hydraulic jack oil .... maybe 3 in 1 oil. Get the brake fluid out and put it in a baggie to seal air out.

Oil? On the rubber seals in the brake system?

My thoughts, exactly. I was thinking brake fluid. Pour some into the MC openings, then wrap it in a shop rag that is soaked with brake fluid and put the whole thing in a zip-lock type bag.

Brake fluid is hydroscopic and will absorb water which will eventually lead to pits in the bore (even the Silicone shit). If you can draw a vacuum on the baggie ... then head on!

And exactly what are the seals made from in a hydraulic jack ... they sure as the hell aren't Viton ... try Buna N or something similar.

You might want to call ATE and ask them what they use, 'cause it certainly isn't brake fluid.

Well, that shows what I know about this stuff. That's why I ask!

I was wrong about the silicone stuff ... it's not hydroscopic so you could use it. Clean with alcohol and fill with silicone stuff ($7 a pint?).

Seals are no longer rubber, they are elastopolymercrosslinkedplasticrubber yada yada yada and do not swell as the "old" pure rubber seals (prior to the 50s?) ... they are also quite chemical resistant.

Seals primarily wear out due to abrading on the bore walls and the contaminants that accrue in the system ... corrosion inhibitors such as zinc, copper and ferrous particles from the piston movement and springs rubbing against the bore and WATER / Oxygen. Old fluid can exhibit as much as 6% water from heating and cooling cycles and we know what that does to cast iron.

Oh well ... just a few thoughts is all.

I call "Cut/Copy/Paste"

You can't spell or pronounce 1/2 those words.