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brakes

I have 1973 Chaelon 914 and find that the brakes are not that good . Ihave read where some people change over to either the Bmw front brakes calipers are the 944s calipers. My question how do these work on the car and what about the rear and what am I running into .
Thanks
Old 09-13-2017, 08:53 PM
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What is the problem with the brakes? Soft pedal? You can't lock them up? You can lock them but the car doesn't slow? They overheat with heavy use?

Assuming the brakes are the stock solid rotors (four-lug hubs almost always means they are) then the 944 brakes won't fit. They are made for vented rotors, which are much wider than the 914's solid rotors.

The BMW calipers are larger, but it's a matter of debate about them being an improvement. The stock brakes, when working correctly, are actually pretty good.

A few considerations:
- A soft pedal is caused either by air in the lines somewhere, or by flex and give somewhere in the system. Fresh fluid, well bled, should help with that.
- You should be able to lock the brakes without putting the pedal through the floorpan. If not, there is something wrong with the brake system and that should be addressed.
- Brakes stop the wheels. Tires stop the car. If you can lock the brakes and the car doesn't slow down, upgrading to more grippy tires should help.
- If repeated braking overheats the brakes and causes a soft pedal, and the fluid is decently fresh, a couple of things can help with that. Getting more air on the brakes, changing to vented brake rotors, and going to larger calipers with a higher thermal capacity.

Larger calipers only help with the last. Of course, the fact that they are (presumably) rebuilt before you install them will help with some of the others.


The rear calipers are fairly unique. Unless you want to ditch the handbrake, you pretty much have to keep them. There are other ways to deal with the handbrake, such as fitting a 911 drum type brake, adding mechanical "spot" calipers, and so on. BTW, the "line lock" is not recommended as a parking brake, because it tends to let go at the worst of times.

It is possible to go with vented rotors on the rear by putting a spacer in between the halves of the caliper. PMB Performance offers this, along with lots of other top-quality brake work and parts.

--DD
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Old 09-13-2017, 10:06 PM
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brakes

Dave
What brake system does the 914/6 have both front and rear. Am I going to run into brake pressure problems if I went to different calipers
Old 09-14-2017, 02:50 PM
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The 914-6 used standard 911 "M" calipers in the front.

It used 914-6-specific versions of the 914 rear calipers, with larger piston sizes. (N.B.--the Ferrari 308 used the same calipers but I believe with an even larger piston. And you thought 914-6 rear calipers were expensive? )

There are balance concerns if you start changing to calipers with different sized and/or number of pistons than stock. At that point, you're into re-engineering the brake system, and that is not exactly for the faint of heart.

The short version is that the total areas of the brake pistons on each end of the car determine the distribution of braking force between the front and rear. You do not want the rear to lock before the front, as that generally means the rear tries to become the front under hard braking. So you don't want the rear doing more work than appropriate. Also keep in mind that weight will transfer off the rear wheels and onto the fronts in braking, meaning the rears will have less grip than when not braking. And going uphill or downhill also changes that.

So you can try to work out what the brake balance is, and how making changes will affect that. But there is extra complication from the "proportioning valve" in the rear brake lines. That reduces pressure applied to the rear brakes above a certain pressure level.

It is usually best to find a tried and true recipe and follow it, unless you like crunching numbers and experimenting and swapping parts.

--DD
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Old 09-14-2017, 03:15 PM
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I have a set up from PMB. Money well spent. Period Brembo AMs upfront and 914/6 GT calipers in the back. I like the system, but the pedal is still a little soft. I would go with something from PMB an keep the parking brake. I just got mine fixed!
Old 09-21-2017, 09:47 PM
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Oh, another thing that can contribute to a soft pedal: The floor flexing! The master cylinder is bolted to a section of the floor pan, and especially as the cars get older and are subjected to corrosion, this area can actually move around when you apply hard pressure to the pedal. Tangerine Racing and Original Customs have both made braces that go from the master cylinder to the steering rack, which help to keep the master cylinder from moving.

McMark from OC actually has a Youtube video demonstrating this flexing.

https://www.youtube.com/watch?v=TRz387hvFhU


And one with his version of the brace:

https://www.youtube.com/watch?v=674n722tdwQ

--DD
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