Me vs. Brakes: The Road to a Solid Pedal Options

[Bwingate]

I have been fighting mushy brakes since I got my 914. They are better but not great. I suspect there is a lot more bleeding to do, including finding the proportioning valve to bleed.

The PO said that they had the master cylinder changed by a local "Porsche expert" I suspect it was replaced with the 17 mm master cylinder. Can I confirm with an external inspection whether it is a 17 mm or 19 mm MC?

So my plan is:
1) Bleed MC
2) Bleed proportioning valve
3) Possible replace soft lines
4) Bleed each wheel again.

I saw something on this site that made sense, but I had never seen it before: Clamp off all the soft lines and test the pedal. If the pedal is solid, then the problem is at the wheels; if the pedal is soft, then it is the MC. Then unclamp each wheel one at a time - the "bad" wheel will be soft, the "good" wheels will have a firm pedal. Is this a bad idea?

[technicalninja]

Clamping is OK if you're planning on replacing the rubber lines anyway.

Clamping CAN damage the inner lining. Most of the time it doesn't but the older the line the more prone to failure.

Lines that are over 10 years old, NO WAY

Lines that are 20 should be automatically replaced.

The 17mm masters are "hens' teeth" rare.

99% chance it's a 19mm which should be fine.

These are a bitch to bleed out correctly. Lots of threads on here showing techniques that help.

[Geezer914]

Get a pressure bleeder, best way to bleed the brakes. Replace the old brake lines first.

[infraredcalvin]

Get a pressure bleeder, best way to bleed the brakes. Replace the old brake lines first.

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[Cairo94507]

Pressure bleeder first for a couple trips around the car. Remember you start with the furthest nipple from the master cylinder and work your way closer to the master cylinder as you go. Right rear, proportioning valve rap with rubber mallet, left rear, right front, left front. Then switch to the old-school method of having an assistant pump the brake twice and hold it down while you release the valve and let air out and then lock it down and do it again until the air in that line is out. Work your way around the car, don't forget to top off fluid as you go, then after clean fluid is coming out with no air, one more trip around the car. If you have a brake proportioning valve, don't forget to bang on it with a rubber mallet a couple times to dislodge air trapped in it as you go around the car. (IMG:style_emoticons/default/beerchug.gif)

[Bwingate]

Thanks everyone -

I have a pressure bleeder, used it and like it. I am also a big fan of speed bleeders for one man bleeding. I used to do all the maintenance on my bikes (air and water cooled BMW's) and did most of the maintenance on my bug. I'd like to think I'm pretty good at bleeding brakes, but this car is fighting me hard.

As I was concentrating on the rear brakes, I only bled them. I got some improvement but mostly I think that was from getting the vent distance closer. I did this a lot - 3 or 4 rounds, 2 quarts of fluid. I then did the front a couple of times and maybe a little more than a pint of fluid.

I avoided the master cylinder just because it was hidden away and didn't feel like figuring out how to get to it. I'm going to have to attack the system component by component until I'm happy.

The brake lines are old - don't know how old. I will have some lines on order from PMB, so they will be replaced soon, and then I'll have to do this all over again.

[technicalninja]

The vent clearance has to be tight!
If the rotors are dirty from sitting get the system up, run the car around a bit (re-bedding pads and cleaning up the rotors) and hit that vent clearance again.

The square cut caliper seals get old and sometimes will not allow for proper piston retraction. You end up with brakes that slightly drag and wear pads out quickly.
Same age points as lines.
20-year-old calipers SHOULD be rebuilt.

I've got a new "add" that I'm going to do when I put mine back together.

Get everything proper and have a reasonable pedal.

"Kick the dog shit" out of the pedal to ACTIVATE the rear pressure regulator three or 4 times.
Re-bleed rear.

ABS bleeding tip: Find a pea gravel parking lot and ACTIVATE the abs circuits!
Clears those bubble gremlins right out.
Don't do this when the owners of the parking lot are present!
Clean up the ruts...

[FL000]

When I upgraded my master cylinder recently I decided to bench bleed it on an actual bench prior to installing it in the car (and “bench bleeding” it while installed).

I was surprised at how long it took to get every last air bubble out of it, and I was able to rotate it in every possible direction to ensure nothing was trapped. Made me wonder how much air may still be in my me that is only bleed in the car.

I will say I have a very firm pedal now, but I also have a larger m/c so not sure ultimately which of the two improved it.

[moto914]

Had a hard time myself, last time. Just kept this thought; They will work great, but there's still un bled air in the system. Sure enough that was the case. Use all the tricks in the book. After successfully installing the master cylinder the periodic fluid changes will be normal and easy.

[930cabman]

Don't give up, getting these just right can be tricky. Over and over and over is sometimes what it takes.

Just think, it could be you vs the law (IMG:style_emoticons/default/aktion035.gif)

[friethmiller]

(IMG:style_emoticons/default/agree.gif)
For me, I had air between the bleeders on the rear brakes ('74). Took me several iterations to get all out but after that, my peddle was great. Just took time.

[fiacra]

Motiv pressure bleeder, three quarts of brake fluid, periodically tap proportioning valve with a soft mallet, and tap the MC and calipers as well. I also bled both top and bottom bleeders. I know people say just to bleed the top bleeders because air should rise in the system, but I don't think it hurts to do both (someone can correct me on that if need be). Take it for a drive on a bumpy road, do it all again. That's what it took for me to get all the air out of the system after replacing my MC. Took a bit of time, but it worked perfectly. The brakes are better than ever.

This system bleeds very differently than our Bugs/Ghias do. They are much easier.

[technicalninja]

It does not help to remove air bubbles from the caliper by bleeding the bottom bolts.

Bubbles rise to the top inside the calipers.

Opening the bottom bleeder alone might ALLOW air to enter the caliper body.

Now, if you want to actually DRAIN the caliper (like when you are flushing brakes) the bottom bleeder is instrumental.

On single bleeder system (almost everything else in the world!) if you want to clear the old fluid out of the caliper you have to do one of two things.

Remove caliper/pads. Open bleeder and push piston back. Close bleeder. slowly pump brake pedal to drive piston/pistons out. Open bleeder, push pistons back.
Lather rinse repeat until you THINK you've got the old fluid out.
You're going to do this two or three times for each caliper and there's four.

Or rebuild the caliper...

Those bottom bleeders should be MANDATORY on everything IMO.

[76-914]

It does not help to remove air bubbles from the caliper by bleeding the bottom bolts.

Bubbles rise to the top inside the calipers.

Opening the bottom bleeder alone might ALLOW air to enter the caliper body.

Now, if you want to actually DRAIN the caliper (like when you are flushing brakes) the bottom bleeder is instrumental.

On single bleeder system (almost everything else in the world!) if you want to clear the old fluid out of the caliper you have to do one of two things.

Remove caliper/pads. Open bleeder and push piston back. Close bleeder. slowly pump brake pedal to drive piston/pistons out. Open bleeder, push pistons back.
Lather rinse repeat until you THINK you've got the old fluid out.
You're going to do this two or three times for each caliper and there's four.

Or rebuild the caliper...

Those bottom bleeders should be MANDATORY on everything IMO.

Yes, bubbles rise to the top and debris/trash fall to the bottom. I bled about a tablespoon of nasty assed brown fluid from the bottom calipers on the rear after replacing the front calipers. I had power flushed the entire system but the lowers retained the old fluid until bled. I should have taken pics.

[Dave_Darling]

The brake master cylinder is under the car. You remove the "gravel pan" that attaches to the front suspension crossmember and the chassis.

It may be very informative to have someone mash the brake pedal while you look at the master cylinder itself. The firewall has been known to flex when the pedal is pushed, resulting in even more of a mushy feeling. If you don't have someone to stomp the pedal for you, set up a camera to capture a video.

Hint--you don't want it to look like this:

https://www.youtube.com/watch?v=CUdPmitJ9XQ


--DD

[ctc911ctc]

Get a pressure bleeder, best way to bleed the brakes. Replace the old brake lines first.

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Super easy, the only way to go,

[r_towle]

Lots of experience here.
Mine is use another human.

I have vacuum and pressure bleeders.
The proportioning valve requires 750 lbs to open.

Rear brakes require you first properly adjust the venting clearance (there are articles with pics on this topic)

Then you need a human to build enough pressure to get past the valve and bleed both rear brakes, 2-5 times

Then do the front.

Rich

[steuspeed]

I had a lot of trouble getting a hard pedal after I replaced my MC 17mm. I have bled many different cars and never had a problem. I did not bench bleed the MC. After many old school pedal pump bleeds, I final borrowed a pressure bleeder. It got better, but still from memory, not as good as before. Maybe it's the Porterfield RS4 pads I installed at the time? Maybe they don't have the initial bite when cold?

[Superhawk996]

Maybe it's the Porterfield RS4 pads I installed at the time? Maybe they don't have the initial bite when cold?

Correct

You don’t get peak friction level from R4S until pads are 250F - 300F.

[moto914]

Get a pressure bleeder, best way to bleed the brakes. Replace the old brake lines first.

Motiv pressure bleeder

The nice thing about Motiv pressure bleeders is they will hold a pressure. You can go from one bleed point to the next. One thing to note; They pressurize at the brake fluid fill reservoir. The brake fluid fill reservoir should be only minimally pressurized. You can rig a Motiv pressure bleeder to connect to the caliper, and pressurize there also. (can handle more pressure there )
While pressurized some points of interest, can be slightly loosened and re-tightened to make sure only fluid escapes, and not air.
(maybe at a high point where the soft and hard lines connect)