I recently replaced my Brake Master Cylinder on my 1974 914 1.8. Now that it was time to bleed the brake lines , as well as the Master Cylinder, I'm running into some problems. I've heard that bleeding brakes on a 914 is no easy task, but after reading all the posts that I could find and following those procedures...I find myself with a pedal that still just goes down all the way.

I had first bleed the front left caliper to get all the air bubbles out of the lines from the main reservoir. I created a closed loop from the bleeder value to the reservoir. After quite a while, I seemed to have no more small bubbles in the clear line.

I then proceeded to bleed the right rear, then left rear , front right, and finally front left....using a helper to pump brakes etc. Also making sure to apply enough pressure to activate the proportioning valve in the back. Fluid goes through all the lines to their respective bleeder valve (using top bleeder valve on each caliber) , as well as no leaks anywhere on the new master cylinder or other lines.


Am I missing something? Should I be also bleeding the bottom bleeder valves??? If I don't have any leaks and there seems to be no signs of additional air bubbles....shouldn't the pedal start feeling firmer through the process? All lines are stock , as well as the new master cylinder (no larger upgrade done). I have never had problems bleeding brake lines before... but as everyone seems to say...the 914 is a unique beast.

you may first make sure that the feed lines are forced into the master cylinder and banked against the two washers. next make sure that the rear venting clearance is correct between the rear pads and the rotors, Next crack all of the bleeder nipples and let it gravity bleed for an hour or so, then tighten all nipples. (make sure that all calipers have at least a bleeder nipple on the top. then if you have a pressure bleeder hook it to the reservoir and pump it up If not have an assistant go through the usual pump and hold starting at the right rear, left rear right front left front. You can also attach a clear hose on the nipple and run it into a bottle with fluid in it, and have the assistant pump several times while you observe any air bubbles in the line.

Did you put the metal washers under the rubber grommet on the master cylinder?

Not sure what you mean? I thought I did place all the washers etc. just like the set-up was on previous master cylinder. Are you talking about part# 90135593600
washers underneath grommets? Since the ATE Master Cylinder was brand new and had the grommets attached already, I would imagine the washers would be in place. Wouldn't there be some kind of leaks if washers would be missing? At this point, I have no leakage any where near the Master Cylinder.

When you mention feeder lines banked against the washers, I'm not sure about those washers because the MC was already assembled and had the rubber grommets inserted . The lines fit snuggly in place on the top of the MC and no leakage what so ever. Would it leak if those washers were missing?

Also, is there a time that one ever opens up the bleeder valves on the bottom of the calipers?

Also, is there a time that one ever opens up the bleeder valves on the bottom of the calipers?
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Air goes to the top. Only need to bleed the top nipples.

You can open them but no need to.

"Would it leak if those washers were missing?"
Yes, but not always right away. If it was an ATE, they are usually included in the box in a little plastic bag.

Makes quite a mess, but I've always had very good luck cracking the brake line at the proportion valve, same method as a bleeder valve. Once the PV had some fluid in it the rest was a snap.
I had a toyota truck that needed the same trick on the PV.

To get the best bled you want high fluid velocity to help transport bubbles though the system.

How to get that:

Use a vacuum bleed on the TOP nipple. Mighty-VAC will work but you have to keep pumping it back up. I prefer HF cheap pneumatic vacuum bleeder that keeps a nice constant vacuum on the bleed nipple.

Have and assistant to perform the manual PUMP & DUMP while you open and close the nipple.

By having high pressure in the system from a depressed brake pedal "pushing" and the vacuum on the bleed nipple "pulling" you will get high fluid velocity.

NOTE: you will continually see bubbles when using the vacuum bleed as the vacuum will pull some air past the bleed nipple threads when you open the bleeder. Don't try to use visible air bubbles (or lack of) as the definition of a good bleed. Good pedal firmness and minimal pedal travel are the measure of a good bleed.

I always bleed every bleed nipple. Can’t see why Porsche would have put a bleed nipple there if not needed. As previously mentioned, you need velocity to expunge all the Sir - raps foot pumps up and down while leaving each nipple slightly cracked (one at a time) should achieve that. Good luck.

914 front calipers are not handed (Rt & Lt). So therefore you need two bleed screws.

Modern calipers are handed - therefore only one bleed and always at top.

Bleeding all won't hurt but is unnecessary.

Is there a way to check if the washers that the feeder lines bank against are actually in place? Without removing the entire MC? It's been a while that I performed the install of the new MC (small project turned into many projects), I had should a hard time getting those feeder line ends to go into the MC and seat well. I can't remember that I had two washers that went inside the top of the MC. No leaks whatsoever going on when pumping brake pedal.

No. That's part of the problem. Everything seems fine until it isn't. One member here had his MC leak out over the winter. The problem was it was parked above his 914-6 on a lift and ruined the paint. Only way I know is to pull the lines and grommet. Sorry.

I had to pressurize the brake reservoir forcing fluid through the master cylinder. Had a buddy pumping the brake peddle and I had the air hose with rag around it to make a soft seal.....worked the first time. Best, Mark

Thanks for all the insight and suggestions. I think I am making progress. Did what everyone suggested and now have pretty good resistance on the brake pedal. I will try driving it around and repeat the process a few more times until it gets to the point that it won't get any better. I hear that the oem braking system on 914s would not necessarily allow one to stop on a dime.


On a side note, I was wondering if people had luck with replacing their front calibers with new aftermarket BMW 320i calibers? Is it an exact fit or would mods have to be done to the 914?