914-6 Brake Upgrade Options

[SouthernMan]

Here's my story.

I have a 914-6 that's been garaged for the past 22 yrs. It was originally race / crossed and I made it road worthy in the late '80's. The tweaked 2.4S engine is out for a quick review. The chassis has HUGE, from what I understand, factory issued race flaring with 12" rear wheels and 10.5" front wheels. I'm looking into upgrading the brake system and putting the original equip. in mothballs. Cheaper to burn up available equip.

Research has lead me to many - many options. Everything from 930 to Boxster. All of these seem to require aftermarket brackets and upgraded master cylinder. I want to do this correctly the first time.

I just spoke with the guys at 911pcar.com, the advice was to run this by you, the specialists on this forum that know whats - what with 914's and 914-6's. Wait, the direct quote was "ask the guys on pelican because they've already done what your brain is just starting to try and think of."

My 914-6 currently has OEM stock brake system. Too spongy for huge rubber tires.

Please pass some knowledge.

Thanks,

-- SouthernMan

Bill V needs to chime in on this one. He is your brake guru.

[campbellcj]

There are many options, as you know. One question is whether you need to keep to Porsche factory equipment and/or period-correct parts for race classification reasons, or if you are open to use any available stuff (i.e. Wilwood or whatever).

In addition to here, this topic has been discussed on 914world.com - A Porsche 914 Community / Forum / Club and in fact here is one recent thread with some info and pics:

914World.com - A Porsche 914 Community / Forum / Club

[campbellcj]

I forgot to chip-in with what I've currently got; although I am still running skinny tires so my needs aren't as extreme as yours. I simply swapped to 911SC "A" (steel) calipers and vented rotors up front, with a 19mm master cylinder, and moved the stock 914-4 front calipers to the rear. Braided lines, adjustable prop valve, and Pagid race pads.

That has worked fine with skinny DOT-R tires -- plus my car is very light at barely 2,000 lbs wet -- but I am planning to (or at least seriously considering) going to flares and at least 2" wider rubber in which case I will most likely do a Boxster caliper + Carrera rotor setup. I already have the Boxster caliper adapters and have heard good things about that setup.

[Dave at Pelican Parts]

Lots of causes for sponginess, some of which will only be peripherally addressed by upgrading the system.

Air in the lines is the #1 reason.
Air in the proportioning valve is the #2 reason.
Air in the lines is the #3 reason.
Old and tired flex lines are the #4 reason.
The floor-board flexing when you push the brake pedal is probably #5.

There are fixes for all of these; bleeding the air out is great for #1 and #3 (and #6-20 ). Aftermarket proportioning valves don't tend to trap air as readily as the stock one, so they may not need to be directly bled. Floor-pan reinforcements can help the flex, as can bracing the master cylinder.

Upgrades to the system can change the brake balance, and will certainly change the heat capacity for the system.

--DD

[cstreit]

Assuming there are no issues in the system (air in the lines, etc as above) sponginess is more related to the proportions of the master cylinder to the brake calipers than anything else.

For example if you went to a master cyl that was 50% bigger your pedal would be SO hard it would be unusable.


Tell us, are you planning on racing the car or just want a better feel while driving it on the street?

Some tips:

1. Better heat capacity = Bigger rotors (not related to calipers per se)
2. Firmer pedal = Better master/caliper ratio

[Bill Verburg]

I'd just use 911S or 911SC brakes on it, they pretty much bolt on and will work well for a very light car like that.

next step up is 3.2 Carrera fronts w/ 911 rears

then 930's but these are way more than you will need

Btw, I have a complete SC setup with poterfield race pads for sale. Calipers have been rebuilt and rotors are in good shape. PM me if interested.

[SouthernMan]

Perfect, this is a great start. Keep it coming.

I plan on putting the car back together, making it street worthy. Even though this thing is engineered and now tweaked for a thrash'n I have no need to bash it on the track. However I will push it a bit

The garage space where it's been living is being changed so it's time to give it the TLC and parts it deserves. I'm not sure if I'll move it to new storage or sell. But I know I want to sort it either way.

911 SC brakes on front and back... they bolt right up? Master does the same?

The 930 brakes up front and moving the OEM fronts to the rear.... that's a interesting thought. Will that bolt, swap with not adapters? Or maybe 930 all the way around?

Where would the Boxster system rate on the performance enhancing? 930's better? 911SC better yet?

The current brake system does have steel braided lines and I spent too much time bleeding and playing with the OEM stuff when it was road worthy.

-- SouthernMan

[Dave at Pelican Parts]

Assuming your 914-6 is an original Six, or is using the 914-6 front suspension, the only calipers that will bolt up will be the original 914-6 brakes, also known as 911 M calipers. These have a 3" mounting bolt spacing.

Swap to later 911 struts with a 3.5" brake mounting bolt spacing to use S calipers or A calipers.

Nothing really bolts up to the rear. Well, nothing that keeps the parking brake, which is essential for a street car IMHO.

The 19mm master cylinder from a 911 without power-assisted brakes will bolt up to the 914. It is also sold as the 914-6 master cylinder. It will move more fluid to help keep up with larger brake caliper pistons. It is also sold as an upgrade to the stock 914-4 brakes, but that is a misconception--it merely changes the pedal feel, not the actual braking force.

There are adaptors that can be purchased or fabricated to attach just about any caliper to an M strut, an A strut, or the 914 rear suspension. They all require at least some research and often some extra work.

There is a 20mm master cylinder and a 21mm master cylinder that also fit the 911 and 914 application, but I don't know where they came from.

Any of the 911 brake options is going to provide as much stopping power as a street tire can handle. The only real difference in most cases is how well they handle the heat of repeatedly dragging the car down from triple-digit speeds on the track.

--DD

[Bill Verburg]

Originally Posted by SouthernMan

.........

911 SC brakes on front and back... they bolt right up? Master does the same?

yes, you will need a 3mm spacer to move the rear rotors outboard and you will use a 911 19.05mm m/c, in front you of course need to use 911 3.5" struts

Originally Posted by SouthernMan

.........
The 930 brakes up front and moving the OEM fronts to the rear.... that's a interesting thought. Will that bolt, swap with not adapters? Or maybe 930 all the way around?

it's an interesting thought but terrible idea

Originally Posted by SouthernMan

.........
Where would the Boxster system rate on the performance enhancing? 930's better? 911SC better yet?

you need to do a lot more studying, Boxster brakes are used on 3.2 Carrera rotors, the net result is marginally better than just using a full 32. Carrera setup

as Chris mentioned you need to formulate a clearer idea of what you want to improve, the usual categories are;
1) thermal performance - are you boiling your b/f now? glazing pads?
2) brake torque - you need tires to take advantage of an improvement here
3) feel - too much travel? not enough bite? spoginess?

a hierarchy would go something like this
late GT3, 996t, 993t, 930 or 993, 996, 3.2 Carrera or Boxster, SC or S but as you go to bigger and better you also gain weight a 450 hp GT3RS can afford to haul the extra weight of it's brakes around because it has the power and needs them, not so on a 914 2.4, you want to use the smallest lightest package that allows you to compete w/o issue for at least a day and preferable a couple of days w/o any maintainance being necessary.

[Bill Verburg]

Originally Posted by SouthernMan

.........

Nothing really bolts up to the rear. Well, nothing that keeps the parking brake, which is essential for a street car IMHO.

what you do is use 911 rotors w/a 3mm spacer, you keep the stock L caliper halfs but w/ 911 rear M spacers and bolts, the pistons are the same as in an M so essentially you build a thicker L caliper

Originally Posted by SouthernMan

.........
The 19mm master cylinder from a 911 without power-assisted brakes will bolt up to the 914. It is also sold as the 914-6 master cylinder. It will move more fluid to help keep up with larger brake caliper pistons. It is also sold as an upgrade to the stock 914-4 brakes, but that is a misconception--it merely changes the pedal feel, not the actual braking force.

.....

There is a 20mm master cylinder and a 21mm master cylinder that also fit the 911 and 914 application, but I don't know where they came from.

.....

--DD

the only ones i've seen in that size range are the 911 19mm mentioned and there was a 20.5mm used for part of the MY69 911 run.
the 20.5mm m/c is
901.355.012.04 (Porsche #)
3.2120-3901.3 (ATE #)

and has not been available, to my knowledge, in decdes

[trekkor]

Just as an FYI:

I use the stock brakes with race pads on my track car.
No need for more brakes.

Car slows down from 100mph+ with zero issues.
I use small air cooling ducts to the calipers.


KT

[J P Stein]

The stock 914/6 brake package is sufficient for street/mild track use.....when up to snuff. You may have the infamous 17mm master cylinder in there which will cause "sponginess". New, modern pads, a new 19mm MC, rebuild the calipers, round file the proportional valve (an adjustable one in it's place), flush the system and you're good to go.
Any brake system sitting for 20 or so years is not trustworthy.

BTW, those stock 914/6 rear calipers are worth gold.....don't get talked out of them.

BTWII, you'll find 914s, mild to wild at www.914world.com

[campbellcj]

I ran stock 914-4 brakes in my current car for a while as well as in a prior car for several years, with Porterfield race pads and everything replaced or rebuilt as necessary. I never had serious fade problems -- our local tracks are not really intense on brakes -- but decided that as I increased the power and grip of the car, it was prudent to increase the brake torque and heat-sink properties. Of course the new front brakes were a 'given' with the 911SC 5-lug swap.

[Flieger]

Use these. Sell the original 914-6 brakes to Eric to recoup the price. He is a big 914-6 guy and a brake expert on early calipers.

Brembo AM-Caliper: The "ULTIMATE" M-Caliper Up-Grade!!

[Flieger]

Zuffenhaus makes new 930/917 brakes if you are concerned about age. You will need the new struts for those, however.

[trekkor]

My car on track.
Red light is an in-car brake light.

Stock brakes.


KT

[Dave at Pelican Parts]

Stock 914-4 brakes with solid rotors, or stock 914-6 M calipers/vented rotors?

Regardless, they're working....

--DD

[trekkor]

914-4 with solid rotors and proportioning valve.


KT