Brake upgrade, 320i? Options

[Porschef]

Curious as to know who if anyone is running 320i ATE calipers on their otherwise stock
brake system, and their impressions...

Thanks

[CptTripps]

I had them on my last 914. I was expecting "more" but the reality was "same-ish".

Have Eric re-build your stock calipers and call it a day. (IMG:style_emoticons/default/biggrin.gif)

[rick 918-S]

I had them on my last 914. I was expecting "more" but the reality was "same-ish".

Have Eric re-build your stock calipers and call it a day. (IMG:style_emoticons/default/biggrin.gif)

(IMG:style_emoticons/default/agree.gif) What tires and wheels are you running? There is no reason to mess with the brakes unless you are increasing the weight of the car by hundreds of pounds beyond 2 passengers and increasing un-sprung weight, Tire diameter and contact patch. Completely rebuild the stock brakes from the master cylinder, rubber lines and calipers and you will be fine.

I used BMW 2002 4 piston calipers on the front and stock rear calipers on my Alien with 19mm master cylinder and proportioning valve delete. I have a massively heavy engine along with added un-sprung weight, increased tire diameter and contact patch. This is the only reason to increase clamping force.

IMHO: 320 brakes are not an upgrade. The pads ride higher on the rotors. As I recall the top edge of the pads are off the rotors. Plus they require machining of the mounting flange. Lots of work for not net gain.

[0396]

Why rebuild your old 914 stuff when you can really upgrade to Eric's new calipers for a little bit more.
Well that's me, others might have a different outlook.

[Niklas]

WHy not buy brakes from a 320i ?
I did on one of my cars. Works perfect.
They are cheaper. And are just bolt on.

[nathansnathan]

There's a great writeup in the Lupuwali classic thread forum on the maths behind master cylinder vs caliper piston size that specifically talks about this.

brake faqs

What's the detail on bigger calipers? Why don't they help?

The entire idea of the brake system is to provide a mechanical advantage to the force applied by your foot. This is provided in several ways. When you push the pedal, there's a leverage effect based on the distance between the pedal pad and the master cylinder pushrod. The longer this distance, the greater the leverage (and the farther the pedal has to travel to move the pushrod the same distance). The distance between the center of rotation of the rotor and the center of where the brake pad grips provides more leverage, again, the farther the distance, the greater the leverage. Finally, the ratio of the area of the master cylinder piston and the total area of the brake caliper pistons also provides leverage. The greater the difference, the greater the leverage. However, the smaller the master cylinder, the farther the master cylinder piston has to move to push the same volume of fluid. The larger the caliper pistons, the greater the amount of fluid is required to move them the same distance.

So, make the master cylinder smaller, or the caliper pistons larger, and you get more force at the pads for a given foot force, but you have to move your foot farther.

The area of the stock 17mm master cylinder piston is 227sq.mm. The front and rear systems are separate, so you count the front and rear brake areas separately. The stock front caliper piston is 42mm, so the area is 1385sq.mm. So, the ratio of the MC to one caliper piston is 6:1.

The popular 19mm MC has a piston area of 283sq.mm. The ratio with stock front calipers is 4.9:1. We've reduced the ratio, so there's less force at the caliper for a given foot force. However, there's also less travel required by your foot, and the brakes feel "firmer", mostly because you have to push harder to get the car to stop.

So, clearly, ratios of 5-6:1 are reasonable, but the 17mm provides more force for a given effort, where the 19mm requires more pedal force, but not so much that the car is unsafe.

If we moved up to the 23mm MC (415sq.mm) and the ratio drops to 3.3:1. This would require super-human leg strength to lock up the tires.

Now, looking at the BMW 320i caliper "upgrade", or the 911 caliper (same size pistons), both use 48mm pistons, for an area of 1809sq.mm. With a 17mm MC, the ratio is 8:1, with a 19mm MC, 6.4:1, and 4.4:1 with a 23mm MC. A really large ratio means greater force, but the pedal travel is so long that the brakes feel "mushy", even with plenty of bleeding. The 48/19 ratio is better than the stock ratio, but only by 6%. Buying new front calipers and a new MC only made it 6% better than stock. Also, pedal travel will be longer with the 48/19 arrangement than with the stock 42/17 arrangement, which many people find so dissatisfying they insist on switching to the less powerful 42/19 setup just to get better feel.

So, moving to BMW/911 front calipers and a 19mm MC means you spent a fair amount of time, effort, and money to get something really close to stock brakes. This is why this "upgrade" is not a worthwhile idea.

OK, smart guy, what about all of those people who insist it makes a big difference?

It does make a difference, there's no arguing that, the difference is just fairly small. 99% of the time, people saying it makes a big difference are generally switching from tired front calipers that need to be rebuilt. Fitting freshly rebuilt stock front calipers and good pads would very likely make just as big a difference as the one they feel with the "upgrade". The other 1% of the time, well, people often engage in wishful thinking. This is something of a subjective thing, brake feel, so people are going to "feel" something that may not be there. Some people insist that appying green magic marker to the rim of a CD makes it sound better, even though there's absolutely no reason for that to work at all, and no objective test has borne that out.

At some point, even a small difference can make the difference, as it were. If the cost to do the upgrade is worth it to you, then do it. You're not harming anything except your wallet.

[jeffdon]

I am running 320i calipers, with a 19mm MC. Pedal feel is great, and I can modulate right to lock up if I want. They mounted right up to my 72, just had to do some minor wheel clearancing with a grinder. Guess I am lucky.

With the 19mm MC and stock calipers, I had many "oh sh*t" moments where I thought I was going to hit someone in front of me. Never did, but came close.

[computers4kids]

I had them on my last 914. I was expecting "more" but the reality was "same-ish".

Have Eric re-build your stock calipers and call it a day. (IMG:style_emoticons/default/biggrin.gif)

I had them with a 19mm on both a 2ltr and shortly on a v8. They were not enough for the SBC and no noticeable improvement on the stock setup.
Your best bang for your buck would be rebuilding the stock calipers and adding some Porterfield pads. (IMG:style_emoticons/default/lol-2.gif)

[Porschef]

The reason for my inquiry is that I have not been able to lock up the wheels on my car either. I have owned cars without brake boosters, so the feel is not unfamiliar. I don't know the history of the front calipers, the rears were redos from AA. I don't know the size of the MC, 17 or 19 mm. My pedal is not spongy, and feels consistent.

I'm running KFP pads. Rims are factory Fuchs.

I always get a kick out of the pad size on these cars. My 92 Civic Si had front pads twice the size, rears about the same. So my thinking was that an increase in front brake size might make a difference.

Yes, a call to PMB is planned...

[69telecaster]

I put them on my '70, with the 19mm MC, and I removed the proportioning valve. Balance seems good, and while I've never locked them up, the car stops very quickly with the wide tires. The pads are about 15% bigger.

[eric9144]

Eric Shea is cringing right now I can feel it...

I did the 320i "upgrade" years ago when I regularly auto-x'd my car--19mm master, stock rears, for street they seemed to bite a bit better...however...at auto-x it could get real scary real fast.

The brake bias is all off when using stock rears, so the front end tends to over brake and the rear end wants to come around on you...sometimes that can be good (auto-x) and sometimes not good at all and downright scary. The other big drawback is that you've now introduced larger pads to the same rotors which cant shed the heat very well so under heavy use you have a pretty good chance of boiling your brake fluid and loosing your brakes all together (me @ my 1st sudo-time-trail event, VERY SCARY).

Proportioning valve wont help in this scenario--only way to bias out the back end properly is to do /6 rears or PMB's alloy /6 calipers...and quite frankly if you're going to do that then skip the 320's and do something that makes more sense.

If you're going to cheap out, dont do it on your brakes, your life may depend on them.

[Eric_Shea]

(IMG:http://www.914world.com/bbs2/uploads_offsite/static6.businessinsider.com-1110-1389219910.1.jpg)

[boxsterfan]

Proportioning valve wont help in this scenario--only way to bias out the back end properly is to do /6 rears or PMB's alloy /6 calipers...and quite frankly if you're going to do that then skip the 320's and do something that makes more sense.

Sounds like what makes most sense is to get your stock system in order with good pads. Not sure what "makes sense" if you are planning on upgrading to a larger type IV motor (for me a 2270) in the future.

If I am just changing the motor out (all other stays the same....wheels, suspension, etc...) and not adding in any more weight to the car, then what makes sense?

(IMG:style_emoticons/default/confused24.gif)

[Porschef]

(IMG:http://www.914world.com/bbs2/uploads_offsite/static6.businessinsider.com-1110-1389219910.1.jpg)

Say no more....or not (IMG:style_emoticons/default/laugh.gif)

[eric9144]

Sounds like what makes most sense is to get your stock system in order with good pads.

YES, you would be suprised how well a well sorted stock set up works and this is going to be the most cost effective route for sure.

Not sure what "makes sense"if you are planning on upgrading to a larger type IV motor (for me a 2270) in the future.

If I am just changing the motor out (all other stays the same....wheels, suspension, etc...) and not adding in any more weight to the car, then what makes sense?

(IMG:style_emoticons/default/confused24.gif)

This is what 'made sense' in my scenario, not inexpensive so if cost is a concern look away now (IMG:style_emoticons/default/smile.gif)
I'm only the second owner of my 914 and it's in remarkable original shape, so for me I wanted to make sure any upgrades were totally reversible for value--all upgrades had to be 'bolt on' or be super minimally invasive.
After collecting parts for 5 or so years this is what I ended up with, all 'bolt on' and retains the 4x130 so I can keep my stock Fuchs (IMG:style_emoticons/default/beerchug.gif)
(sorry for crappy cell phone pic)
Front - Billet '4 Bolt' "Club Hubs" with 911 vented rotors and aluminum Brembos w 3" spacing (Everything here is a direct bolt on replacement to stock suspension)
Rear - 911 vented rotors (will be machined for 4x130 "4 bolt" pattern, then mounted to stock rear hubs--tapping the set screw is the only permanent change and it's easy to hide if I roll the change back to stock) with 914/6 GT rear calipers with parking brake--PMB didn't have the alloy version of those or I would have saved money and weight and used them instead.

In terms of cost alone this may not 'make sense' to you, but IMHO if you want the most braking possible while retaining all the stock equipment you can this is the way to go. Now if only I can find time to get these onto my car... (IMG:style_emoticons/default/dry.gif)