brakes don't lock, (not that I want them to) Options

[r3dplanet]

Hi.

A couple of months ago another user (Bembry) posted that after replacing all of his brake parts he couldn't get his brakes to lock and his car's braking performance was pretty weak.

That thread ended without resolution and I didn't want to hijack that thread, so I'm starting my own.

A summer project that I wanted to nail down was dealing with the poor braking. The front calipers were messed up and the wheel bearings needed replacement. The rears were allegedly rebuilt by a local Porsche shop a year ago but I've been through two tanks of gas and the rears were leaking through the outer adjuster. So, I jacked up the car (or rather, left it on its jacks) and went to work, beginning with reading all that I could read about the braking system and experiences of other users.

I've just finished replacing older calipers with very nice front/rear rebuilt calipers, new rotors, new pads, new soft lines, new front and rear hard lines. I've bled and re-bled the system with ATE super blue fluid with a Motive pressure bleeder. I waited a few days and bled it again to achieve one tiny air spec and so I'm quite certain that's taken care of. The only thing I haven't touched is the master cylinder, regulator, and midship brake lines. The old fluid was ATE gold and it was very clean on its way out.

After all of this, the car stops exactly no better.

When I stomp on the brakes the car doesn't really stop the way it should and while I know that I don't want to lock up the brakes, I think I should have the option.

The parking brake cable has good feel and its adjusted for a tiny bit of slack at the calipers, so there's no drag.

The venting clearance on the rears are solid at .005 (the smallest gauge I have on any set) and I spent most of a Saturday making very sure of it.

I'm not driving the car because in a panic moment the car won't stop or slow well enough, especially at speed.

I'm stumped.

-marcus

[timothy_nd28]

Mine is the same way, thought this was normal for not having a "oh shit stop". I tend to leave plenty of room between me and the car infront of me.

[dlee6204]

Did you break-in the new pads?

[VaccaRabite]

My breaks will lock up on demand. Stock 4 - though rebuilt and well bled.
You may still have air in the system.
You may need to break in your pads.
Those are the two most likely issues.

Any air in the system will make the breaks feel crappy. After bleeding the lines, pedal should be rock solid.

New pads will also feel kinda mushy. There is usually a break in procedure for pads.

[balljoint]

(IMG:style_emoticons/default/agree.gif)

You need to take your pads to bed. Any changes in that area can affect how the way things meet, fit together etc. Just saw the same thing after temporarily running a very different set of wheels and tires.

[Eric_Shea]

We just went through Marcus's brake system and got him back in the realm of the proper calipers for his car. Here's what I would suggest now Marcus:

1. Bed the pads as suggested.

Here's why; by bedding the pads, you will help bed those new seals in your calipers. They will be aggressively pulling your pistons back causing a softer pedal until the system has been broken in. Get the seals and pads seasoned and your pedal will begin to come up, modulate well and become more effective. Don't be afraid to bed them 2-3 times. Follow the procedure on our site.

2. Re-Bleed the rears if needed after bedding the pads.

3. (This should actually be #1) - I see where we sent off all new calipers but, no killer pads. You may want to spring for a full set of Porterfield R4-S pads. If you have Pagids or Jurids, those should be fine but you will, again, want to bed them properly.

About Pads - I'm OK with most pads with the exception of the ones that are advertised as "Semi-Metallic QUIET" pads. That should read "Semi Metallic Don't Stop Very Well" pads. You can usually eliminate 99% of pad squeal by bedding the pads properly. Organic pads stop better than the semi-metallic and the Porterfields stop better than those. There's a ton of great pads out there but those are the ones I like.

Let me know if you have any success with that method.

[ConeDodger]

+1 for the Porterfield R4S pads. I use them on both my 914 and 240Z and a set of them were on my 911 that just went back to Germany with a new owner. They are quiet and stop well enough to double as both a street pad and my track and autocross pad. They wear well and though they dust up pretty good after a track event, it cleans right up and you were going to clean the car up anyway right? (IMG:style_emoticons/default/biggrin.gif)

[Spoke]

How is the braking not good?

Does the pedal go to the floor when you stomp on it?

Does the pedal feel hard and doesn't go to the floor but the car just won't stop?

Did you change the master cylinder?

It would seem that high performance pads will add more braking resistance, but standard pads should have enough resistance to stop the car if the system can generate enough pressure.

[914Mels]

At one point the master clyinder in our '70 went bad and I bought the 19mm version to replace it the 17mm version. The rest of the system was stock in good condition. Right away I noticed the extra effort required to stop the car and it was almost impossible to lock up the brakes. What help me was swapping out the front calipers for larger BMW units and now the pedal pressure is normal and the brakes work great.

[Vysoc]

Porterfield R4S - Bed them in as directed by Eric, 2 or 3 times.

Vysoc (IMG:style_emoticons/default/flag.gif)

[r3dplanet]

Okay.

So yesterday I drove a few laps around Sauvie Island, a lovely ten-mile loop around a lovely island (p.s. thanks, President Roosevelt!) and ran through the padding procedure. Twice. With a good twenty minute cool-off session in between where I took some time to adjust the clutch and munch a sandwich whilst staring at some berry pickers.

The brakes are certainly much better. But I still can't lock the fronts. Today I'll re-bleed and examine the rotors to see if the bedding went well.

Oh, just to answer the questions thoughtfully provided:

1. The front pads are Porterfield R4S. The rears are new but I don't know what brand.
2. The pedal moves a couple of inches before resistance is felt. It does not go all the way to the floor. More like about halfway down where the feel is very firm. Stomping on the brakes allows the pedal to be pushed another inch or so.
3. I have not changed the master cylinder.

Will update soon.

[Eric_Shea]

What pads?

[r3dplanet]

1. The front pads are Porterfield R4S. The rears are new but I don't know what brand.

[Eric_Shea]

OK... shouldn't be a problem. I would eventually get the same compound all around.

You may want to adjust the pushrod to the master cylinder. Take a 15mm wrench down there with you.

Bed again and report back. You should have a blue grey hue on your rotors.