Hey all,

I was reading another thread on brake upgrades. Some of you have talked about using the Boxster (not S) monoblocks on the 914, once you've changed to 911 struts and rotors.

The agreement seems to be that this would be great for the track but a bit too much brake power for the street. Some have indicated lockup of the tires can occur quite easily. I can certainly see this being a problem (I would think there would also be that scary "just touch the brakes and they grab way too much" feeling).

If that's the case, is there some way of fixing the lock up problem by also adding ABS to the equation?

QUOTE (Dinobx @ Aug 15 2005, 09:58 AM)

I can certainly see this being a problem (I would think there would also be that scary "just touch the brakes and they grab way too much" feeling). ...is there some way of fixing the lock up problem by also adding ABS to the equation?

first, welcome !

it's not "too much power" it's just unnecessary/

next - good brakes aren't grabby. good brakes are easy to modulate, and are typically installed ONLY after substantially improving traction (big wheels & sticky tires) -- why else would you need "better" brakes? they are also typically installed with bigger master cylinders that further reduce mechanical (hydraulic...) advantage. if you stomp on ANY brake pedal you risk lockup somewhere.

finally - ABS is used only with POWER brakes. that's a challenge for a car with bottom-hinged pedals and is one of the biggest reasons 911's went to suspended pedals - to make room for the brake booster. finding and plumbing the vacuum is a bit of a challenge too, although the 911's manage it. if you don't mind doing the fabrication for suspended pedals, plumbing the vacuum, finding an ABS controller from a car with similar weight distribution and wheel rates, and modifying all the hubs for rate sensors, it's a piece of cake.

The only thing used from the Boxster brake system is the calipers themselves. They are attached to the struts/trailing arms with adapter blocks, and 24mm carerra rotors are used.

To put ABS on a 914 would require some major engineering. You would have to add rotation sensors to all 4 wheels. Then additional wiring to support them. You would have to install the ABS control unit that allows pressure to be bled from each wheel when lockup happens. There is also a speedometer type sensor on most abs systems to disable it below a certain speed too. Then you have to add the computer to support all this. IIRC, the ABS controls are contained in the Body control computer, which also contains a bunch of other functions. To use it, you would have to either hook up those addtional sensors, or find a way to trick the computer into seeing the correct voltages on the sensor lines.



After all that, you have an ABS system that is incorrectly calibrated for the car. The 914 weighs quite a bit less than a Boxster.


Plus, most people who drive near the limit don't want a computer helping them with something as critical as braking. Remember, the most sophisticated computer available is the one between your ears.

I figured it would a pretty complicated undertaking. I'm going to be running the car with 7/9x16 fuchs and 205/245 rubber. I take it the boxsters would still be too much brake for those wheels/tires? Unless, of course, one is careful to not lock them up.

If boxster monoblocks have a good amount of modulation and feel built in, then it shouldn't be a problem. Then I'd be able to do some track work as well.

From what I've read in the archives, if not the Boxsters, then the best route would be just standard 911 carrera brakes on 911 rotors both front and rear.

The problem with any 914 brake upgrade is not the front brakes. They are a bolt on all the way up to 996TT calipers (Provided you bolt on 911 front struts first).

Porsche/VW designed the 914 with off the shelf ATE rear brake calipers that had the park brake built in, plus they used a 3" bolt spacing on the rear. Most performance calipers out there have a 3.5" bolt spacing for the caliper mounts. The trailing arms that the calipers attach to are unique to the 914, and the caliper mounts are welded on. So we have to either remove the existing caliper mounts and weld on new ones (not easy to do), or we have to use some kind of adapter to mount the calipers. The Boxster monoblocks are the easiest in this situation, because they use a radial mount, and the stock 914 calipers use an axial mount. That means that we can make a relatively inexpensive, bolt on block to attach the calipers.

That still does not address the issue of the park brake. Some people dont' think we need one at all, some think a line lock is sufficent, and some (Like me) think a mechanical park brake is a necessity. I have explored all of the possible park brake permeutations, and the best (IMHO) is a modified 911 setup. But in that you have to make custom park brake cables.

For street or AX usage on a stock 914, the stock brakes, with all the parts working correctly and a good set of performance pads will serve you well.

But most of us modify the car for higher performance. Then we need bigger brakes.


FWIW... I have only driven my car a little bit since getting it up and running, and I am disappointed in the 944 turbo calipers that are on it. I expected more from it, but the brakes don't even feel as good as the stock brakes on Betty's 1.8L. I am hoping that switching to the 23mm master cylinder will improve the feel.

Hey Clay, Hmmm, very interesting.

The problem with any 914 brake upgrade is not the front brakes. They are a bolt on all the way up to 996TT calipers (Provided you bolt on 911 front struts first).
The only restriction I have here is that I love the look of the fuchs. So my wheels have to have enough room to clear whatever I put in there. I understand that they will clear the 911/Carreras and the Boxsters no problem.

Porsche/VW designed the 914 with off the shelf ATE rear brake calipers that had the park brake built in, plus they used a 3" bolt spacing on the rear. Most performance calipers out there have a 3.5" bolt spacing for the caliper mounts. The trailing arms that the calipers attach to are unique to the 914, and the caliper mounts are welded on. So we have to either remove the existing caliper mounts and weld on new ones (not easy to do), or we have to use some kind of adapter to mount the calipers. The Boxster monoblocks are the easiest in this situation, because they use a radial mount, and the stock 914 calipers use an axial mount. That means that we can make a relatively inexpensive, bolt on block to attach the calipers.
Yes, and from what I understand, Rich can provide the adapter blocks (from another thread).


That still does not address the issue of the park brake. Some people dont' think we need one at all, some think a line lock is sufficent, and some (Like me) think a mechanical park brake is a necessity. I have explored all of the possible park brake permeutations, and the best (IMHO) is a modified 911 setup. But in that you have to make custom park brake cables.
I like the idea of a manual brake. On another thread, someone had posted pics of the 917 brakes with the manual parking brake setup. Very nice. Would love to able to adapt that for whatever rears I choose. It actually looks like you would need to drill and tap some holes at the end of the caliper for a mounting spot for the system the 917 uses.

For street or AX usage on a stock 914, the stock brakes, with all the parts working correctly and a good set of performance pads will serve you well.

But most of us modify the car for higher performance. Then we need bigger brakes.
Good point, mine actually has a V8. It's putting out quite a bit of torque and it would be nice to have that peace of mind feeling that I can stomp on the brakes and have some solid control over the momentum of the vehicle.

FWIW... I have only driven my car a little bit since getting it up and running, and I am disappointed in the 944 turbo calipers that are on it. I expected more from it, but the brakes don't even feel as good as the stock brakes on Betty's 1.8L. I am hoping that switching to the 23mm master cylinder will improve the feel.
Wow, that's interesting. I had contemplated doing the same. I used to own a 944 and have driven the 86 944 turbo and the brakes were nothing short of excellent. But someone had indicated that you couldn't mount them on the 914. How were you able to do that Clay?

The fronts are relatively easy and well documented. They use the same 24MM Carerra rotors as the Boxster monobolocks. Then you use a milling machine to offset drill the mounting holes and they will bolt up to a set of 911 front struts that use the 3.5" bolt spacing for the calipers.


The rears are MUCH more involved. I removed the mounting tabs for the calipers and made new ones from 3/8 plate steel. Then I welded them onto the trailing arms. Properly locating them was the problem, not the actual fabrication.

I would not recommend this method. The payoff is not worth the results. Monoblocks are much easier, and don't require the effort it took to reweld the trailing arms.

QUOTE (ArtechnikA @ Aug 15 2005, 06:10 AM)

finally - ABS is used only with POWER brakes. that's a challenge for a car with bottom-hinged pedals and is one of the biggest reasons 911's went to suspended pedals - to make room for the brake booster.

911s had power brakies with bottom hinged pedals for YEARS. The Cap'n

QUOTE (Cap'n Krusty @ Aug 15 2005, 11:45 AM)

911s had power brakies with bottom hinged pedals for YEARS. The Cap'n

you are correct, sir.

there's a kinda goofy pushrod that runs up to a reversing lever. am i seeing that right that it's installed "backwards" on those cars? or is there another linkage bit to re-reverse the pedal motion i just can't see?

okay - i'll revise my earlier incorrect statement..

911's went to suspended pedals when it became desirable to utilise an over-center spring for the then stiffer clutch...

I keep hearing about locking up wheels with big brakes. I just had GTP Brembos installed. They are fantasic, the feel is smooth, firm, and confidence building. I have exited freeway ramps at 90, and come to a "gentle" stop, with no hint of lock up. The pedal pressure is so sensitive you can haul it down from very high speeds quickly, with no feeling of lock up. This is with 17 x 205 tires. Prior to these I had S Alloy fronts & T rears. I had to push pedal "very" hard, and had about 25% the braking control I have now. I believe locking up would have been more an issue with them, since I had no modulation, just had to stomp on them. I think you could lock up just about any brakes, but I would never go back to small brakes after driving with these.