The brakes on my 914 are useless, the master cylinder was leaking so I have replaced it and bleed the brakes..........and they are still useless although not spongy. I understand these cars are not servo-assisted like modern cars but it doesn't matter how hard I press the brake pedal the wheels never ever lock. Am I expecting too much?

they should lock. are you new to the car?

Yes, they do so you should be able to lock them up so if you cant, and the pedal is still soft you have 2 issues most likely, one is that its not full bled out, there is air in the system, sometimes its trapped by the rear proportioning valve , or just in the calipers.
and 2. you may be needing to set the venting clearance on the rear pads, they are not self adjusting like in the front. a power bleeder like a Motiv might be helpful or the bleeder screws that dont require you to be opening and closing them with every pump of the pedal.

Phil

sorry for got to add this...

Most of the time you do not want to lock up the brakes as then you tend to lose control of the car. Obviously you lock up the brakes when you come to a stop.
For maximum stopping capacity you need the pistons to be free, not binding in their bores, so a caliper rebuild is a sure means to achieve this. New or freshly machined rotor surfaces will provide maximum surface area and a suitable friction surface; glazed surfaces and/or rusted rotors are not going to provide a suitable friction surface. Brake pads must not bind in the calipers, must provide the high coefficient of friction and must not be glazed. Pads, Pistons & Rotors; it is all in the combo.

Sometimes old brake lines can be spongy
Use good pads also…. Not the old ones that are in the car
But bleeding is the most likely

4 wheel disk brakes, 2100 lb car.
It stops fast

Replace all flexible brake lines.
New master if needed
New pads

You will be surprised how well it stops

And you might want to review this site and get some advice from the brake guru

https://pmbperformance.com/

As someone that just took his 914 to Watkins glen and headed into turn 1 at 90 miles per hour, let me tell you, they work. By the end of day two I wasn't hitting the brakes till 200 feet. Before the bus stop I was waiting till 100 feet (but I was taking that corner at much higher speeds).

My fronts are untouched, the rears are PMB rebuilt. All stock. I did put braided hoses on it. Safety and all that. I also have strong legs and I am 6' "1.

You have to really give the brakes a push though.

Emery… you trying to get back in the dating game?

When working correctly they will stop on a Dime...and give you 5 cents change!!
They work well...IT took a while to get mine right. but stoping well now

Rule of thumb is to replace soft lines if you don’t know when they were last replaced. They swell shut and don’t allow fluid to flow.

Years ago I did a session at Watkin Glen, then headed down into town on that long hill. That was possibly the only time I had brake fade. The next year I had the 911S "A" calipers with vented rotors and no more fade.

I've been away from the 914 for decades and just coming back. Might be things have changed, but if your pedal feels good but the car feels like is just gonna keep rolling, you might try different pads. What always worked best for me was the cheapest ones: full organic. Not metallic or ceramic or semi metallic, but full organic. Not good for racing and they make a mess, but they grab the rotor better.

Air in the lines somewhere. Crack the line at the proportioning valve. Bleed from the right rear first. Bleed from the upper valve if you have dual valves. Add a length of hose so it's end is higher than the fender. Bubbles rise.

Let me add #3, which was important for getting good braking in my car:making sure the master cylinder mount is solid, and if necessary, making a brace so the MC does not move when pushing hard on the pedal.

I agree with the others. I can easily lock up the wheels. I have the 19mm master cylinder (17mm was stock), so the pedal is fairly stiff, but a good stomp on the pedal is all it takes. The bigger the master the harder the pedal will be.

I never worry about whether the brakes will work… they always do. Even if the rears are non-functioning, the fronts alone are more than adequate to stop the car quickly. Not recommended, of course!

I’ll second the idea that rubber flex lines may have swelled. Happened to me on my Karmann Ghia.

Good luck!

This is what I’m thinking, the pads I’m running are probably more meant for track work. I’d imagine you deal with some hills...

OK thanks guys, so now I know that a 914 does actually stop it's back to the drawing board with some of your suggestions. Cheers.

So give us an idea of what you have on the car.
I'd use Porterfield pads, either stock rubber or PMB braided stainless flex lines.
If your 17mm master is not leaking, use it. I moved to a 19mm as a new 17mm is either very expensive or unobtainium depending on when you look. 17mm uses less leg effort and more pedal travel but stops the car WELL. 19mm will use less pedal travel and more leg effort to stop the car EXACTLY THE SAME AS THE 17MM.

Try a Motive power bleeder to get the calipers bled. It helps!
Do not remove the proportioning valve. This was common back in the 80-90s and there are still some people that swear by it. I've seen the wreckage that results from the rears locking before the fronts first hand.

When you get it dialed in, the 914 STOPS.

Zach

Yes, I made the mistake of removing the prop valve when I put boxster brakes on the front of mine. That ended up locking the right rear when doing emergency stop drills at an HPDE class. I'll send my old one out to PMB and have it rebuild and reinstall.

The 19 is more pedal effort...it will lock up the front brakes full stock depending on the stickiness of the tires.

To answer the title question, I put on wilwood front calipers on 911 3.5" struts and 914-6 rear calipers. With track pads I could go from 100-20 in what felt like 75' it was amazing!

But realistically everything in working order, fresh fluid and good pads they will stop well. I ran Porterfield RS-4 pads with a mild caliper upgrade for years.

As others have said already, a stock 914-4 brake system is plenty of braking power. Something isn't right with your system.

Air in lines most likely
Spongy rubber lines possible
Rubber line internally failed not allowing pressure to caliper(s)

Lots of things could impact braking performance.

Mine had the same feeling, solved after bleeding and some care to the system a second time, it changed a lot. It feels really agile now.

In any case, I had to replace hoses, piston refurb, fluid, pads, rotor grinding, cleaning, bleeding, changing the main piston and such.

Enjoy the ride
Click to view attachment

If you don't know the history on your brakes, I'd suggest sending the calipers and pressure relief valve off to PMB for restoration, new MC and new soft lines. Blow out the hard lines or replace if they are rough. Then bleed properly and bed pads properly. They will stop just fine.

I bought a 1970 a few years ago that had sat for years. The rear soft lines were plugged/swollen shut. No fluid moving through them at all. The fronts barely worked.

Also recommend the PMB soft lines. They are excellent quality.

Here's the link for 73-76. Not sure what year you have but they have both early and late

Link:

PMB Lines

Am I missing something??

Why 4 flex lines, I’m kinda sure there are only two up front...

You have two in the rear as well. They are kind of a pain to change out with the engine in the car but I've done it.

My rears off my 70.

Click to view attachment

There are two that go from the chassis to the swing arms. From there it is hard lines

Jeez, I better up my game. I think they were changed not too much prior to when I got the car but who knows if that included the rears...

Thanks

You mean like here?


Click to view attachment

My brakes have been rubbish but i know the rears arent fully working so they are being restored. I'm also putting 5 simple grooves in all 4 discs to de-gas the pads which should also improve things.

After 50 years of hard life, these take a beating. The rears are a bit harder, but totally possible with the engine/trans in place

Those rear lines are why I took it to my Porsche guy to do my PMB stainless braid. It took him an hour to do all four. It was money well spent.

Here is a pic of mine where it attaches to the chassis.

It is easier to cut the old line off as close to the "nut" as possible, then you can get a socket on it.

Click to view attachment