Ok so I am upgrading to a 911 suspension (Seperate Thread http://www.914world.com/bbs2/index.php?showtopic=87337 ). Then I hear brake caliper bolt spacing 3.5 vs 3.0. So WTF is 3" vs 3.5" Am I making a mistake going with 3.0 vs 3.5? I really don’t understand the issues. Do I care?

Thanks for real world opinions!

Regards,

James

The bolts that attach the caliper to the strut are either 3" apart or 3.5" apart. All 914's were 3" spacing. The 911 T's were 3" spacing, the 911 S's were 3.5" and all of the SC's and Carreras were 3.5" spacing. I'm not sure about the '75'76'77 cars, I think they went to 3.5 mid '75. If you want vented rotors and 5 lugs the easiest thing to do is just change the struts, hubs, and brakes to S, SC, or Carrera. There were 2 different ways to mount the strut to the ball joint, a pinch bolt and a wedge bolt. Either type of ball joint will attach to either the 911 control arms or the 914 control arm, but it must match the strut. 911 control arms are not superior to 914 control arms, the only difference is the splines on the torsion bars are different. If you use all the 911 stuff you use the 911 torsion bars.
Bigger calipers are available for 3.5" spacing than for 3" spacing. The biggest calipers for the 3" spacing is the BMW caliper which is about the same as the "M" caliper. With 3.5" spacing you can go up to the "A" caliper, Turbo calipers or with adapters you can use Boxster calipers. There are many more options and many more adapters, 944, 944T, etc., but I'm not that familiar with what all is out there because I already have a set of Boxster caliper adapters so I stopped looking.
If you're not racing seriously you won't need anything more than the "M" or BMW caliper with vented rotors so the 3" spacing will be fine and the 3.5" spacing will just cost you more money that you don't need to spend.
You can put your front 914 calipers on the rear with "M" calipers and replace your master cylinder with a 19mm master cylinder and have a well matched setup that will stop you really well, but you'll loose the parking brake without more adaptations.

It depends on what you want to do with the car. What kind of motor you're putting in etc.

Basically, more stress (big motor, track time, etc) means more brakes.

3" = 'low' and 'medium' brakes
3.5" = 'medium' and 'high' brakes

To expand a bit, in case you were wondering where the 'M' and 'S' brake classifications came from, they are Ate (Itself an abbreviation for Alfred Teves) designations for the size of the caliper.

Mitte - middle/medium duty
Schwer - heavy duty

There are good brakes to be had in both sizes. a /4 on 'normal' street tires can lock 'em up repeatedly with stock calipers, which is -probably- all the brake you need.

The small caliper and unvented disk/hub assembly is quite light which contributes to the 914's nimble feel and good road-holding.

For more power and increased fade resistance (i.e. V8 or trackday) the vented rotor has its benefits. 911 'M' calipers are plentiful and cheap. It's what 914/6's came with up front.

Be aware that /6's also came with bigger pistons in the -rear- brakes, so if you go increasing front caliper size, you're tinkering with the front/back brake bias as well as approaching the hydraulic limits of the 17mm 914.4 master cylinder. This is all manageable, but it is additional stuff to think about.

You -can- put truck brakes on a 914 - after all, the 935 brakes were basically a standard heavy truck brake Ate was asked to make in aluminum rather than the truck's cast iron... But your car won't stop any faster.

And all this presumes you are going 4-lug, 'cause AFAIK, there are no 4-bolt 3.5" bolt spacing struts.

(BTW - that's a real 3.0" and 3.5" measurement, one of 4 or 5 English unit parts that are international standards. Another thread for those...)

With both "S" (aluminum) and "A" (steel) front calipers being 3.5" is there a reason behind the "A" designation?

I recall there was - but I don't remember -what- it was.
I'll consult "911 Story" tonight unless someone here beats me to it ...

James,

Can you tell us the intended use for the vehicle? I don't recall that in either thread... maybe I missed it in the 5-lug thread.

Frère to the rescue again..

The 'A' calliper (The Brit spelling, as I'm kinda quoting...) was originally developed for the Alfa-Romeo.

For those of you playing at home, you'll also recognise that the Weber carburetors were also originally developed for the Alfa, which has slightly shorter cylinder-to-cylinder spacing on their V-6's - which is why Porsche intake manifolds have slanty end runners...

It really would help if you'd like us to give you brake and suspension recommendations.

Sorry, for the delay. Ever notice how working for a living gets in the way of having fun?

What is my intended use for the vehicle? Kind of what a Porsche was intended for… Lot’s of Spirited Driving… Long drives freeway, lots of twisties, as little commuter driving as possible and spirited A/X. A/X is not the focus. Driving the on the highways and mountain roads in the SF Bay area.

My current project plan for the car is to:

Get the suspension dialed
911 front suspension
five lug conversion
16x6 fuchs
Koni adjustables front using 914 insert in the 911 struts
911 under tank sway bar
Stock rear sway bar
Rear 100# springs
Koni adjustables rear
911 brake master cylinder
Thinking about V-Calipers on the rear’s

Freshen the paint – Malaga Red
Upgrade to leather upholstery

Freshen Engine
I have two numbers matching 1975 running 1.8L

Option 1
Rebuild a perfectly stock Fuel Injected 1.8L.

Option 2
Build a type 4 carbureted 150 HP

Option 3
Build the biggest badest carbureted 911 engine I can afford

Option 4
Build a 2.7 to 3.2 911 FI engine with A/C (Imagine A/C in a 914 a 30 year foolish dream) that I can afford


Dr Evil Tranny rebuild (gearing based upon engine above)


Last but not least… Drive Car in a spirited way

IMHO... Install the 72 911 suspension with the 3" M-Calipers and enjoy.

Conflicts a bit with the stated desire to run a 911 underbody front antiroll bar.
Easy path on that is probably suitably new 911 A-Arms with the bar mounts. I suppose new/replacement bar mounts are available for attachment to bare arms tho.

I don't get the attraction of the underbody concept but that's just me.

Of course - 1972 A-Arms are also probably approaching their service life on rubber bushings, which open up its own slippery slope...

I agree with you on the struts & brakes.

It's what he has... he said he has the 72 front end already, got it for a great price if I recall.

Yes - hence the conflict...

Guys, I am planning on installing the through body 911 sway bar (just like the 914). Not the 911 under body sway bar.

Regards,

James

No conflict and a much better way to go. Better selection of bars and better geometry

When I make a change like this I always try to get the best bang for the buck. In this instance why spend money on 911 3" when you can probably get 3.5 spacing for about the same or a little more. In the future you will have more options for those struts including kits with adapters for very large brakes if you ever need them.

I battled this same decision and decided to go right to the max. I'll never need more. 964RS brakes on 3.5 spacing with adapters. The cost was only a few hundred more than going with smaller components You can also see the red Tarret sway bar done at the same time with additional reinforcing added

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I'm not sure I agree on the really big brakes but if 'A' calipers can be had for the same price out the door (insluding the strut package) as M's I couldn't argue. Of course, he already has the '72 M-brake struts sogoing bigger could be considered an upgrade path. Swapping in a pair of built-up big-brake struts 'should' be an afternoon job.

(And I'm sure I wouldn't have painted the brake pipes, but it's your car, do what you like...)

AFAIK, Ira Tarret is the only one who 'gets it' that the 'standard' 8mm droplink hardware is marginal - his stuff is 10mm. (Lost a car to droplink failure, this is a sore subject with me.) The 911 project will be using Smart bars but Tarett droplinks.

FWIW, and out of the scope of this thread, I'm reconsidering my long-held belief on disk slot direction. I've always done it the way you have it, which matches the drilled-rotor pattern on 911's.

However, Brembo is recommending the other direction on cars with trailing calipers. After years of doing it the traditional Porsche way, when I did the slotted rotors on the Subie (trailing calipers) I went with Brembo's suggestion. *Mostly* I think it doesn't matter. The only place it seems to make a visible difference is the angle at which the slot first contacts the edge of the pad. This may be a distinction without a difference - like I said - I'm thinking about it.

I still mount drilled rotors with the spiral in the conventional direction, even tho my drilled-rotor cars have straight vents, not the curvy ones that inspired the pattern originally...

Actually the slotted pattern is opposite the drilled pattern with the slots running "forward". I slotted them myself. The reason being to not have the slot run between the reinforcing and vanes in the rotor creating a weak spot. I do however agree it does not matter from a functional standpoint, only a strength standpoint.

I made sure to stagger the slots on each side to make sure grooves were not close to each other.

As for weight, the calipers are very light. The big negative with big brakes is the large rotors, not the calipers. They are considerably heavier and have more rotating mass and unsprung weight. It's also the positive since they can absorb so much more heat. Building car a is a trade off and you have to decide whats important to your application...ability to shed and absorb heat or light weight.

Here is the difference between my rotors and stock 911. A huge difference in mass and heat absorption ability. Do I need all that? eh, probably not but it cost the same as the smaller ones and they have unbelievable stopping power.


Click to view attachment

Hi, Just purchased my first 914 (1973 2.0L Pheonix red I think) and am looking to replace the brake calipers. I've heard several guys say that you can put BMW 320 calipers on the front, however they make several kinds ie. ATE, Beck... Does anyone have info on this? I'm new to this forum any info is greatly appreciated
thanks
NY914guy

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