Brakes Job - Soft! What happened?

[tcesar888]

Hello All!

I did the following to my brake system on my '78 911...

- New Rotors (F/R)
- Rebuilt Kit for Calipers (F/R)
- New Pads (F/R)
- New SS Braided Lines (F/R)
- Fluid = Blue!

Note: I believe this is the very "first" brake job in 28yrs on this vehicle...(30K original miles). Its was needed big-time.

I painstakingly cleaned, normalized, and replaced everything (as indicated above). I even bled the system using the old fashioned foot-pump method. Also, drove it a bit and bled it again... No bubbles...

Basically it works ,but feels much much softer than before... Before, it used to be TIGHT - real tight... Could it be that it was so dirty/semi-rusty that now everything is WORKING? I couldn't believe the system even functioned as it was; some pistons were barely movable...

Any thoughts on how I can determine if this is the way its "supposed" to be? Also, are there some undocumented tricks to tightening it up a bit? Adjust my brake peddle?

Thanks!

Tom

[JoeyD911]

Mine were a little soft after the same job, 200 miles or so later and all was normal again. I've read this is not uncommon. Give it some time to settle in.

[tonythetarga]

Tom,
"the old foot pump method" may be a cause of the problem, but there may be a couple other things.
If your pedal was real hard before, that was likely the siezed or partially seized pistons and swelled up brake lines (they swell internally so you can't tell by looking).
Using your foot to pump the brakes for bleeding may have damaged the master cylinder internally. With so little pedal travel over the last number of years, the extent of smooth bore inside the m/c was probably very small. When you move outside that range into areas that have been pitted or are rough from gunk build up, the seal inside the m/c is compromised and won't hold pressure.
Try this; with the car off, pump the pedal quickly a couple times until it gets firm and hold hard pressure on it. If you feel the pedal slowly start to sink, then you are losing pressure through the m/c. It will need to be replaced.

If that holds, then the other problem might be that with fresh caliper seals, the pistons retract a bit too much and you use extra pedal effort to get the piston out far enough to stop the car. You will have to go though each wheel again, remove the pins and one pad at a time and slowly push the piston out far enough so that you can just fit the pad back in. This will help seat the seal in the position you want, to minimize pedal travel when you step on the brake.
My money is on a damaged m/c however.

[JMatta]

+1 on the damaged master cylinder. The internals are old and eveything tonythetarga stated is most likely true. Get yourself a pressure bleeder...worth every dollar.

[KTL]

The fact that the pistons were barely moveable would give you that firm pedal feel when the pedal travels, yes. But if your pedal is soft when the pistons, pads are pressed up against the rotors? Master could be damaged or you could need to bed in your brakes and rotors (the bedding should be done anyway).

When the system is bedded, the firmness of the pedal definitely increases. Try bedding them first before resorting to the master replacement. I don't discount what others said about the master damage. Just hoping it's the other symptoms like new pads, rotors, possible air in system, new piston seals retracting the pistons,..... etc. Start first by doing what Tony said and extend the pistons for each caliper such that you really have to force the pad into the caliper. This will minimize the piston retraction issue. Then go out and bed in the brakes by doing several high effort stops from 60 mph without coming to a complete stop or locking the brakes. Once you smell the brakes, you're done and drive home without coming to a complete stop and don't use the brakes at all if possible. The goal is to let the brakes cool completely. After everything cools to ambient temp., the overall feel of the brakes should be much improved. If not, investigate the fluid by pressure bleeding and then resort to master cylinder replacement.

[911nut]

When I did my SC I pressure bled to flush the old fluid out.
I had a soft pedal when I was done so I went and "hand" bled with my wife working the pedal.
Hand bleed them again. Start with the right rear caliper, than the left rear, go to the right front and finish with the left front. as you bleed tap the caliper lightly with a tooling or rubber mallet.
My pedal was hard before but all my calipers had rust on the pistons between the bore seal and the dust seal so the car didn't stop real well
Afterward my pedal was slightly softer but the brakes became like an arresting hook on an Navy jet.

[oregonmon]

Same thing here, although I did everything you did but I did not rebuild the calipers. I also drove it and re-bled the system.
I think I can rule out the master cylinder because I don't lose pressure. It's like you said the pedal feels softer. Took to my mechanic and he said it feels fine, but he says really I (car owner) would only be the tell the difference from before the brake job. I did switch to Ate gas slotted rotors and Hawk HPS pads, and with the SS lines maybe it's just a different feeling. The only part that concerns me is that I can press the pedal down to the floor if I'd like. I don't remember being able to do that before. I don't ever feel like I'm not going to stop but the feel is definately different.
I'm basically in the same boat as you, would like to see what you find.

[Won]

Somebody has to ask: did you put the calipers back on the right way? The bleeding nipples should be oriented towards the top of the caliper, and it's easy to swap left and right.

[tcesar888]

Originally Posted by oregonmon

Same thing here, although I did everything you did but I did not rebuild the calipers. I also drove it and re-bled the system.
I think I can rule out the master cylinder because I don't lose pressure. It's like you said the pedal feels softer. Took to my mechanic and he said it feels fine, but he says really I (car owner) would only be the tell the difference from before the brake job. I did switch to Ate gas slotted rotors and Hawk HPS pads, and with the SS lines maybe it's just a different feeling. The only part that concerns me is that I can press the pedal down to the floor if I'd like. I don't remember being able to do that before. I don't ever feel like I'm not going to stop but the feel is definately different.
I'm basically in the same boat as you, would like to see what you find.

Thanks! We'll see...

I even tried bleeding the lines with the car was fired-up (with the boot engaged); slightly better; but same-same. I can't quite floor the peddle, but it sure semms like it getting there... I'm gonna run it today and see if it normalizes on its own. BTW, I went with Brembo rotors and Mintec pads...

Tanks,

Tom

[oregonmon]

My only other thought after talking with my Porsche mechanic is that with the different pads is that, they may need to be warmed up and therefore require less pedal effort when hot.
Maybe after driving some, see if your pedal feels different. I have and this could be an answer.

[tcesar888]

Originally Posted by oregonmon

My only other thought after talking with my Porsche mechanic is that with the different pads is that, they may need to be warmed up and therefore require less pedal effort when hot.
Maybe after driving some, see if your pedal feels different. I have and this could be an answer.

I'm hoping its something like that... I'll probably run it for a week and bleed it one last time. I order a Motive bleeder from our host, but it has not arrived yet. I'll try that too. I'll let you know if I find the "answer"...

.tc

[tcesar888]

Check out this thread. Lots of good tips....

Brake Caliper Rebuild Problem

[Por_sha911]

Clarification: are you saying you have a soft pedal or are you saying that the brakes don't grip as tightly as they used to?

[tcesar888]

Originally Posted by Por_sha911

Clarification: are you saying you have a soft pedal or are you saying that the brakes don't grip as tightly as they used to?

Hi Joe,

Its a soft peddle --->>> In "comparison" to what I had. But as I work thru this, it was probably due to a system that was in dyer need of a rebuild.

The brakes grab nicely and feel confident. Initial depress is soft, but the second and third pump it gets tighter...

Hope this explains more...

Thanks,

Tom

[tcesar888]

Originally Posted by Por_sha911

Clarification: are you saying you have a soft pedal or are you saying that the brakes don't grip as tightly as they used to?

Hey Joe...one last thing...

My square/dash brake light remains ON... I know its not my e-brake, becuase I disconnected it long ago. I got plenty of brake fluid...

Any ideas on why the light is still on? This happened only after I completed the brake job...

Thanks again!

Tom

[OzDino]

Originally Posted by tcesar888

Hey Joe...one last thing...

My square/dash brake light remains ON... I know its not my e-brake, becuase I disconnected it long ago. I got plenty of brake fluid...

Any ideas on why the light is still on? This happened only after I completed the brake job...

Thanks again!

Tom

Hi,
First, re the brake light, there is a reset button on the side of the master cylinder that you need to push in. Comes out when fluid is low or the lines are undone.
I did the same on my '77 2.7 Targa and have the same problem. Porsche told me that I should have only done the calipers one pair at a time! Not sure why, the system is split anyway.The system has been pressure bled, hand bled, SS braided hoses and it is still a soft pedal.
I tried a couple of other '77 cars at a cllub gathering and they are about the same although a bit firmer.
The initial longer ravel is due to the square seals pulling the pistons back from the rotors a little when the pedal is released.
That said, I always believed the pedal should be hard after that but seem it is not so. have done about 2500kms since recon and it has not improved. Like your car, mine stops well, but leaves a little doubt as the pedal will flex down/up a couple of inches after stopping. That is foot hard on the pedal to stop and I can still move the pedal down a bit more.... spongy feel.
Hope this helps a little.

[tonythetarga]

Originally Posted by tcesar888

Initial depress is soft, but the second and third pump it gets tighter...

You really should not have to pump at all to get a normal firm stop. Have you tried the test I mentioned for the m/c?

With the car stopped pump up the pedal firm then continue to press hard. If the pedal sinks and continues to sink, you will need a new m/c.

[audi2.7t]

Also, todays new, asbestos free pads need a few hundred miles to wear in.. I recently had my truck rotors cut and pads replaced and it felt exactly how you described...soft pedal which I could push all the way to the floor with some pressure...it cleared up after a couple of days and plenty of heat cycles. If your brake pedal will hold moderate pressure for 10 seconds or so without going to the floor then the pads are the likely cause . Find an empty road and do some heavy stopping from different speeds...also, do some braking in reverse.

[tcesar888]

Super replies! Great info! Thanks again to everyone!

I'm going to go find that "reset" button on the m/c...

Thanks!

Tom

[Por_sha911]

Originally Posted by tcesar888

My square/dash brake light remains ON... I know its not my e-brake, becuase I disconnected it long ago. I got plenty of brake fluid...Any ideas on why the light is still on? This happened only after I completed the brake job.

Did you replace the brake sensors (#15 in diagram below) when you did the pads?

Soft pedal: Have you bedded in the pads? Did you check to see if a caliper was pushed too far away from the rotor? Have you bled the brakes all the way around again?