As part of my rebuild I completely replaced the brake system:
calipers and rear pressure valve rebuilt by PMB
new ATE 19mm master cylinder
new hard and flex lines
new disks and Porterfield R4-S pads

I went through many (many!) episodes of bleeding, with different methods. The pedal feels very firm from the first push, and does not pump up. Rear clearance is set at .004". I went through the PMB bedding process, and have driven around a bit.

But the braking force seems weak. When I get on the brake pedal, I do not feel any "bite". Another 914 friend drove the car and also agrees.

Any suggestions?

Brake feel is highly subjective.

The obvious thing is that you’ve gone to the 19mm master cylinder. That involves a trade off between having less brake pedal travel but that comes at the penalty of higher brake pedal force to achieve equivalent brake line pressure vs the OEM 17mm master.

The other is to make sure you aren’t comparing expectations between modern power assisted brakes to a pure manual brake system.

The most objective question is: can you lock up the front wheels? If not, something is wrong.

19mm master cylinder, push the pedal harder, they will bite.

I did the same thing and also couldn’t get much brake pressure. I noticed while bleeding, there was air in the rear proportioning valve and still some in the calipers. I cracked those hard lines, let them pour out, tapped all four calipers with a rubber mallet to get more air bubbles out and re bled again and was able to get pressure. Once driving I did the aggressive braking procedure, after once or twice I finally got them to lock up and about after a week or so of regular driving did another bleed just in case. Was definitely a head banging process but I figure if the car moves it needs brakes so well worth it

The system is notorious for holding bubbles. You will have to dive it a bit bleed again, and perhaps repeat a few times.

Two suggestions:
Add a master cylinder brace to prevent floorboard flex.
Adjust the rear brake regulator to begin regulating at a higher pressure.

Bad plan

The regulator / proportioning valve doesn’t affect initial bite as brake line pressure is ramping up on moderate or even on hard brake brake applications.

The regulator only limits pressure to the rear brakes after pressure has built to the cutoff or knee point. After that point it continues to build pressure to the rear brakes but at a lesser rate than the front. By the time the regulator comes into play (on street use), weight has been transferred to the front axle and the front brakes are doing the vast majority of the work.

The regulator is there and adjusted to prevent lock up of the rear brakes and the inherent vehicle instability that comes with rear brake lock.

Messing with rear brake bias is fine for racing application but shouldn’t be taken lightly for street applications.

Here is the data on how the rear brake pressure is regulated:
Click to view attachment

48 kg/cm2 is 683 psi - that is significant brake line pressure before any reduction in rear brake pressure build rate even begins.

Can you lock the brakes up if you stand on them?

If yes then they are working.


Pad type can change the feel of the initial "bite" however I find that the rebuilt calipers feel a little soft at first but will become more responsive over time as the new rubber in them work hardens.

I find going REALLY aggressive with the bedding procedure helps with this as well. You really want to cook those things.

And Tangerine has a nice kit to do so!

This question needs to be answered. If the front brakes can’t be locked there is something wrong.

What MPH would the front lock-up test best be done ?

30- 40 mph is sufficient. Dry pavement. Safe area to do so.

You want the vehicle to have enough momentum so that it will take quite a bit of line pressure to lock the brakes but not end up stopping the vehicle completely.

A light squeal or heavy scuffing from the tire is all it takes to confirm No need to keep it locked for any time/distance that would cause a tire to flat spot.

I've done it enough times to know that it works really well.

I’ve been a brake design engineer long enough to know that it is a really bad plan. I’ve also done enough brake testing (with fully instrumented vehicles) and regulatory signoff to back up the theoretical side of design engineering.

Rear brake line pressure needs to account for varying road and tire friction, vehicle load variance like a fully loaded front trunk (full fuel + luggage) with no load in the rear, and not locking up while cornering with lateral load, etc.

I’ve posted the data. Below that threshold pressure, the regulator is not doing anything - it passes pressure straight through. There is nothing there that will affect initial bite that is occurring well below 683 psi of line pressure.

I just went and tried Locking them up tonight (haven't done it before, and was never impressed with my brakes), but darn if they didn't lock up nice when I gave it the old what for. Just the fronts of course.

Thanks for all the replies.

Yes, I can lock up the fronts. It takes a good shove, and maybe the left locks before the right.

I hear you about bleeding and stubborn air. Like I said, I went through several episodes with different techniques. And I will do more, with all the chanting and banging on components I can think of.

I went through the bedding process again today, and maybe the brakes feel a bit better.

And I realize that 1960s engineering, and small, single piston calipers can only do so much. But I still think I should feel more bite and urgency when I get on the brakes hard.

I love the motive pressure bleeder. I don’t know how I lived without it all these years

I have essentially the same setup as you and get really good bite. After I bedded in the Porterfield pads following Eric's procedure, I could smell the brakes strongly inside the cabin and see smoke rolling from under the fenders. In other words, I really gave them hell but they never faded. After that, I could feel a distinct difference in bite.

OK - so we know there isn’t a major defect or massive air in the system if you can lock the brakes.

The desire for more “bite” is a fair feeling to have. However, what we do know for sure is that you can generate lock but you don’t like the effort (pedal force) required to do it.

The problem will be trying to tune a system via the internet.

My first recommendation would actually be to install the Tangerine reinforcement to make sure as much force gets to the master cylinder as possible.

My second would be to recognize that you went to the 19mm master cylinder which is working counter to what you want to achieve - which is having less pedal force get you to an equivalent line pressure. The problem here is 1) finding a 17mm master 2) reopening the hydraulics to install it and having to redo the bleed.

Finally, I suspect you are indeed expecting a manual brake system to perform like a power assist brake system we all have become so used to. A manual brake system is largely linear. More pedal pressure is needed to generate more brake output pressure.

Vacuum assist and modern electronic brake boost systems can provide non-linear output that cannot be matched by a manual brake systems. I’ll find a graph to show what I’m talking about.

Note how a vacuum booster initially has lots of output at the front of the curve (green and magenta regions) but then tapers off (blue) - I suspect this lis the sort of “bite” you’re looking for.

Click to view attachment

Look at the yellow region in the bottom left- there is almost a vertical region in the performance curve. Very little increase in pedal force is getting a lot of output. This “jump in” can’t be duplicated by manual brakes.

It takes several bleeds to get air out of a totally fresh system. Put speed bleeders in and stomp the pedal in conjunction with a motive pressure bleeder at 10psi

Even when all the air is out, Eric at PMB says it will take several hundred miles of driving for the piston seals to wear-in. I had the same thoughts about my pedal as you. Eric was right.

You didn’t mention if you bled the MC first. Definitely should.

If you can lock them up and the pedal isnt doing unpredictable things then you should be good to go as far as system assembly and bleeding.

As I (and Ian) mentioned, the rebuilt calipers take a while to break in and sometimes it takes a lot more then you think to properly bed the pads.

Go find an empty road and run through the bedding procedure again, maybe even a couple more times and this time REALLY give it to them, do not go easy, this is not how you would normally drive, brake as aggressively as you possibly can without locking them up from freeway speeds down to barely rolling. Multiple times, to the point they start to fade before letting them cool off.

I think people underestimate the aggressiveness needed here. If you are not smelling burning brakes and possibly seeing smoke you are not getting them hot enough.

With the Porterfield R4 being a race pad it takes even more to bed them in (Eric recommends the aggressive (near lockup) stops from 80mph) and per Porterfield they don't achieve optimal friction until they are above 450F.

Ultimately it may be that you just prefer the feel of a street pad, but I suspect you need more time to fully bed the pads and break in the calipers so I would run through that again and give it some time before you make the decision to swap pads.

Pressure bleeding is the best way to bleed the Brake's on a 914.

Hmmm…
I’ve been running the Porterfield R4S’ for years and bedded them as prescribed by Eric. But never felt they were as efficient; most of my driving is local and under moderate driving conditions; is it possible that I don’t achieve that 450 temp ?
What would be a better choice if so.
Interesting topic !

Different car but maybe a useful data point - I had some unknown old and what appeared to be metallic very hard pads on my race car with Willword calipers. I called Willwood to get their recommendation for a pad. I gave them car weight, HP, typical track cycles (speeds braking from down to corner speeds how many times per lap and how much time between applications).

I was surprised when they recommended an aggressive street compound. They said my loading was just not enough to get sufficient heat into a race pad to generate good friction. My point is Race oriented compounds need a lot of heat to get into efficient friction ranges. The new ceramic street compounds are very good at generating initial bite with minimal loading while providing good wear characteristics.

Not sure what type of compound the R4S is, but you might be asking it to do something it is not designed for

R4S is a street / performance compound so not outright race pads. R4S also have a good history for most but certainly may not be for everyone.

having said that I don’t disagree a bit with prior comments of re-bedding and or consideration of a pad change as a possible improvement - it all depends on driving style.

Each pad has its own friction curve. Some (race pads) have low friction until the get hot. Others have high friction when cold but fall off drastically when hot (prior to actual fade).

One thing that has frustrated me for years in the aftermarket is the unavailability of the curves. They are easily obtained on a brake dyno. The problem is the data is so specific to a particular pad, rotor, caliper combination so the data doesn’t necessarily apply the same between a Nissan and a 914 for example.

For example the Porterfield is listed by PMB as 0.41 mu (friction coefficient) but doesn’t tell you what temperature that is at. No pad has a singular average mu at all temps. This doesn’t reflect on PMB - like I said the pad suppliers just don’t provide good data.

That leaves us with trial and error.

I really used to like Ferodo back in the day but Only God knows what they are like today with all the EPA regulatory restrictions limiting raw materials.

FYI - get ready for things to get worse. Copper is being regulated out of pad formulas for OEMs. It has caused a lot of chaos trying to find new friction compounds that work as well as those that had copper in them. This will eventually trickle down to the aftermarket. If you have a particular pad that you love - stock up now.

I can't let this pass without comment. This isn't coming as some random restriction to stick it to auto parts manufacturers. Copper is toxic as hell to aquatic life which is why it is great for household plumbing because not much can live in it. Copper content in storm water in some metro areas exceeds safe limits for marine and freshwater life and a major source of that copper has been found to be brake dust running off of streets. AFAIK, the regs will reduce the amount of copper in brake pads but not eliminate it completely. Yeah, it's a PITA to have to reformulate brake pads again, but living with degraded natural systems we depend on for food and oxygen is no picnic either. Just saying...

What's a recommended for light daily driving ? I have 911M front calipers, 914 rear calipers. Both front and rear rotors are vented type. Current pads are Porterfield R4S

https://www.porterfield-brakes.com/images/p...06_02_41_04.pdf


If sticking with Porterfield ceramic pads, looking at their brochure the R4-1 compound looks like it would have quite a bit more friction and at lower temperatures.

but, it may be you just prefer the feel of a non ceramic pad that dont need the time to warm up.

I have never been unhappy with OE compound pads (Bosch, Pagid, ATE) for daily driving.

Thanks, again. I will try bedding again with some extreme force, driving to loosen up the caliper piston seals, and more bleeding.

I am also inclined to swap pads to something stock/street oriented. Suggestions welcome, especially if anyone can compare to the Porterfield R4-S pads.

I used to sell KFP pads because I liked their performance, but not enough customers bought them so I stopped selling them. Their street pad compound 1935 has excellent cold bite and the full race compound withstood the heat I could generate with stock calipers and wide slick tires.
I tried using their autocross compound on my street 914 until I scared myself with an emergency stop that almost wasn't successful because the brakes were cold.
I bed my street pads with repeated heavy braking to warm them up to just smoking temp and then allow to cool. It isn't very convenient to repeatedly brake to a stop on public roads so I only go down to 10-15 mph but still gradually increase the brake temperature over a couple miles of driving until I smell the compound baking out and then I drive home without using the brakes at all.

I had R4-S on my 944T that I bedded properly twice and the stopping power was marginal. I could not lock up the fronts unless I jammed the brakes as hard as I could. I switched to stock (Textar) pads and the brakes were much better. I also have R4-S on my 911 and I'm not convinced they are better than the stock pads were.

I ordered a set of Textar OEM style pads for F and R today. Let's see if they have better cold friction.

I just ordered the Pagids from PMB, Here’s the infomercial from the site :

“ Pagid brakes are found in the calipers of vehicles from Ferrari, Porsche, and Callaway as standard equipment, and the company's real emphasis is on performance. If you have a high-performance vehicle, particularly one of European descent, Pagid brakes are most likely available to fit your car. In addition to shorter stopping distances, Pagid brakes have noticeably reduced fade after multiple stops. But the big advantage to Pagid brakes is their cold friction capability—in other words, the amount of brake feel you get even when the pads are cold. Many performance pads don't stop well until they're warm, but Pagid brakes are built for real-world driving conditions. That means you get short, firm stops in all conditions. Whether your car sees primarily commutes to the office, or you get to spend time on the track, Pagid brakes are a worthwhile upgrade to your factory system.

These are my favorites for value and overall performance. I currently run them in my 914-6/GT car with S-Calipers up front and GT calipers in the rear. “

Mentioned before but the stock system was designed with a 17mm MC. The 19mm one is used on the 914-6 which has 48mm front pistons instead of the stock /4 42mm. In the back, the pistons are 38 for the 914-6 vs. 33mm for the /4. This is a pretty big overall surface difference!

Being that our beloved 914s aren't assisted on the brakes, I would think switching to 19mm while keeping the stock calipers must make the pedal feel pretty scary.

This is a thread I thought I would need to start. I'm having the same issue. Bought my 74 in Feb 21, pulled all of the brake parts except the steel lines. I sent the calipers to PMB along with the regulator. Bought an EZ MC from 914 rubber. Over the next 6 months (!) I was able to get it all together and start bleeding. And bleeding And bleeding. Over 2 quarts in all, lots of bumpy roads, hammer blows to the calipers and about 350 miles total. Finally the brakes were OK but would not lock up regardless of pedal pressure.

Then as I was putting the car away for winter I noticed that all 4 calipers nice new gold coating was pitted and looking like they were several years old. Crap. PMB sent replacements which I installed in January.

Bleeding wasn't as bad since I had fluid in the system, but still, after about 10-12 bleedings and 500 miles I still don't have brakes I would like to have. Soft pedal, doesn't pump up, push rod clearance is good, no leaks, Porterfield pads, venting clearance of 3mm.
When bleeding I can hear the regulator working, click click with the pedal travel, don't know if that's normal but it seems like that would indicate that it's working.

On my last spirited drive with lots of hard braking I pulled into the shop and took temp readings on all of the rotors. The were all within 2 degrees of the others.( 120-122F) That tells me all 4 are trying to stop the car.

I am really tired of screwing with these brakes. Bummed that I'm going to have to replace the lines from the reservoir to the MC if I go with an ATE MC. I'm thinking the Chinese EZ may be the issue.

Any input is welcome.

Other than that, life is good! Still a couple of good driving months left on the North Coast!

Hmm, what?

Hmm? What? 125F means you aren’t measuring before they cool down or they are not even working. That’s not even 40 degrees above ambient. Even 125 C isn’t hot for spirited driving or we have vastly different definitions of spirited driving.

The only objective measure is can you lock the fronts? If not - something is wrong.

Guys: Oops, not 3mm, .003". Clearance between rear pads and the rotor at rest.
I was thinking 120 degrees was kinda cool too. I took the reading at the outer edge of the rotors less than a minute from stopping. No way I can get these to lock up. I'm seeing some brake dust and it does stop eventually but not like the should.
PMB Says it's the 914 MC, 914 says they don't know.
If I put in the Ate I've kinda been screwed because the EZ involves cutting away the feed lines so I'll have to replace those too. I'm game for whatever, just want to get them right once and move on.

Hmm. I have PMB plated calipers that I rebuild myself per their instructions. Same for the pressure regulator. Porterfield pads and a 914R MC WITHOUT the EZ option (I never liked the look of that "improvement"). So, essentially the same setup as you other than the EZ option.

I initially bled my brakes using the gravity method that Eric describes on the PMB site, making sure to bang on the MC, regulator, and all calipers with a rubber mallet. I let the car set a couple weeks and followed up with a Motive power bleed and the pedal became rock hard. After bedding the brakes on the initial drive, I gave it another round with the Motive but don't remember getting much, if any, more air out. I do think the gravity bleed helped set me up for an easier power bleed.

I think I just got lucky but 6,000 miles later, the pedal is still firm and brake feel is excellent at all speeds although I still wish I had a 17mm MC. The other day I was driving at 70 mph on the frontage road and thinking of this thread and decided to punch the brakes hard. I heard the front tires chirp on the pavement within a second and let up and kept driving.

To be honest, I'm not a fan of the 914R MC and would go ATE if I had it to do again, but it does a good job of stopping the car and I'm happy with the overall setup. I've been paying a lot closer attention since this thread started, wondering if I had just gotten used to sub par performance but I'm confident I'm not. Even our resident brake engineer, @Superhawk996 has driven the car and didn't comment on the brakes. He may have been too preoccupied complaining about the steering

I really don't know why I had luck with my setup where others are having trouble. The only things I've done are get a good bleed on the system and bedded the brakes like I hated them (Of course I couldn't see it, but I'm pretty sure they were glowing red hot).

Thanks All: Good comments all around. Still not sure where to head. I've not tried bedding them by heating them up really hot. That'll be easy enough to do, or at least see if I can get them hot enough.
I've bled this car using every method known to man, and am back to the two person pump and hold method. Have not seen air the last several sessions.
My next step is probably to put another MC in. Going to have a friend drive the car this weekend and get his input.

Speaking of potential environmental hazards, nobody mentions asbestos. Last I knew it was still being used in brake linings. I hope someone can correct me and it is not in use any longer

Sounds as though the consensus is having the ability to lock the front brakes. Ok, but I have no mention of the rears locking, is this a design feature?

The pressure regulator is there to prevent rear wheel lock up so you don't wind up facing backwards while you are trying to stop. It was the early version of ABS @Superhawk996 That gets under his skin.

@bbrock

I replaced the pads with "stock" Textars, front and rear. I had to enlarge one hole in the rear pad backing plates.

I took a first drive today, starting with some gentle braking, and then cruising with light dragging for a while. I then went through a series of repeated moderate to hard braking, first a few times from 40 to 10, then 50 to 10, and finally 60 to 10.

My initial impression is that the Textar pads have more grab, but at the end of the session I could not get the brakes to lock up.

While I don't believe it is illegal to use in brake pad friction, it hasn't been used in decades...The last holdout that I'm aware of was a Ford police pad, but I believe that went away in 2005 or so. (I've been in the brake manufacturing business for 20 years)

All: This is all great info. So, an update, last Saturday I took the car out and braked (broke?) the living daylights out of it, 60mph to just about stop over and over and over. Got em really hot, got a little lockup on the right rear. Temps were high but my reader crapped out after two wheels.
Today, did a Motive pressure bleed, no fluid, just 15lbs air pressure in the jug. Enough to pinch the rotors a bit but not enough to blow the EZ fill lines apart. Didn't see any appreciable air bubbles.
Took a drive and did the same thing, got em hot, got lockup on only the right rear with the pedal right down at the floor.
Temps when I parked were in the 480's on the fronts and 380's on the rears.
I just don't understand the soft pedal with everything being new.
Some thoughts:
Should I 'exercise' the pistons to work the seals into the bore? Pull the rotors and have them turned? ( they were new less than 1500 miles ago, Pellican's better grade)
I put 195/60's on the car. Could the contact patch be too much for the brakes?
Some ideas: Exercise the calipers and bleed again.
Pressure bleed with the Motive and a full jug and run another quart through even though I'm into the fourth quart already.
Have the rotors cut to leave a pattern to help bed the Porterfields.

Going on two years and getting tired of screwing with these brakes.

Any input is welcome.
Thanks guys

For $35 you can try a set of Textar pads for the front...that solved the problem I had with Porterfield on my 944.

Man I feel for you. I'd be fed up too. Can't think of what would cause the soft brakes other than still have air in there somewhere, or the MC is just not doing its job. One fail safe way of eliminating air I've read that sounds like a giant PITA but is said to work is to pressurize the system and go around and crack open hard lines one at a time to make sure all air is out. Can't remember if there was a sequence. I'd guess MC and pressure regulator would be the prime suspect areas for trapped air.

Also, rear brakes shouldn't be locking if the regulator is adjusted and working properly but if it were me, I wouldn't chase that gremlin until figuring out the soft pedal. Could be related I suppose.

BTW, I'm running 195s on my car and can lock up the fronts on dry pavement.

New caliper seals cause a long pedal which will pump up in operation, then return to long pedal again. It takes time for the seals to bed in - a couple hundred miles of driving is usually sufficient.
Enough air in the system to cause the same feel is unusual once the system has been properly bled. Contrary to popular myth, the rear regulator does not contain enough volume to be difficult to bleed.

Single rear brake lock up could indicate a corner balance issue.

Firewall flex is a significant factor in pedal feel.
Have you installed a master cylinder brace? It can make the difference between a pedal that reaches the floor before lockup and one that doesn't.

I would try a conventional bleeding method…one person on the pedal, one person at the calipers. If this is a late car, make sure you’re bleeding at the top bleeders. With the higher pressure doing it this way, you create substantially higher fluid velocity which will carry more air with it.

Another trick you might try…pull the front pads out and replace with something about 1/2 the thickness, then pump the pedal up to run the pistons out a bit…then push them back in. Sometimes pushing fluid towards the master, rather than towards the calipers can find and expel more air. Of course, put the pads back in after this.

Lower HP/slow cars can be a bitch to bed in when using a high temp pad because by the time you get it back up to speed after the first brake application, they’ve had some time to cool off. In some cases like this, more of a “normal” street pad will work better since it’s designed to work properly at lower temps and doesn’t require the rather rigorous bed-in that a higher temp range pad typically needs. A lower temp pad that IS bedded in will many times out perform a higher temp, higher friction level pad that is NOT bedded in.