I have a '73 914/4 that was converted with 2.7/Webers, 911 front suspension, 16 x 7/8 Fuchs, fiberglass fenders and stock rear brakes with studs.

I have installed 911SC front calipers and would like to upgrade the rear brakes to vented rotors. What are my options?



I tried investigated 911SC rear calipers and rotors and discovered a couple of problem areas:

1. The outer diameter of the rear hub is greater than the inner diameter of the brake rotor.

2. The offset (negative) of the caliper mounting bracket is too little.

By using a spacer between the hub and rotor, I believe the 911SC rear brakes will fit.

Has anyone done this?

Thanks in advance

Eddie

'73 914/6 2.7

M front calipers?
Boxster rears will work, but will probably overpower the fronts.

You can just put a spacer in the caliper and run a vented rotor. but you'll need some pretty good pads on the back to keep up with the front rotors..

Just an option

Andrew

1) Odd, the vented 911 rotors went right on mine......lemme guess, you used late redrilled hubs. The stud install can cause the hub to bulge out adjacent to each stud. File or grind off the bulges..or get the early hubs.

2) Shim out the M caliper to center it on the rotor. The hub is used to center the rotor axially.....that's why it's a tight fit.

Stock rear calipers don't cut it with A or S fronts.

BTDT.

911 "Rear" M-Calipers. These are an exact match for the current fronts you've installed (A-Calipers).



They don't work. The nose hit's the hat on a rear rotor. You'll need the rear M-calipers to properly fit a vented rear rotor.



A 5mm spacer between the caliper and the mount and a longer bolt will do the trick. You will need to figure out what to do with the parking brake.



Interesting option but I tend to agree with JP, kinda weak match with the A or S-Caliper. It would be a cool option if you had a set of M-calipers up front. Plus, they're kinda expensive (me thinks). Check the classic threads for a 911 e-brake conversion I did. It shows the completed assembly with the vented rotor and 5mm spacer. Here

Hi Eddie; welcome to the board (post #1; dunno if you were a long-time lurker?)

Since the Bradhole hasn't seen this one yet...I will go ahead and ask the question "why do you think you need vented rear rotors"?

We all know that vented rotors and 911 e-brakes are cool...but a much easier and cheaper solution would be to put stock 914 front calipers on the back and install a "tee" in place of the stock proportioning valve. That is the setup I have, with race pads etc., and the car has plenty of brake...almost "too much" in fact.

Another good solution... the 914 fronts have the same piston and pad size as the 911 rears (me thinks). Still have to contend with no parking brake just like the 911 rears though. It's basically the same setup I mentioned with a solid rotor. One thing to think about might be the cost of vented rotors vs. the 914-6 solid rotor (they're a bit more plentyful and cheaper).

Also, the caliper may rub unless you turn the rotor down a bit or modify the inside of the caliper... but that might just be with 914 "rear" calipers that this problem has been prevalent. Others can weight in on that... some have rubbed, some haven't. If you do encounter that problem, I'd modify the caliper once rather than modify the rotors each time you buy a set.

I have a set of early hubs laying around if you want to go that route.

Geoff

I have run S front calipers with stock rear calipers without hassle. I have also used 914/6 rear calipers with the S fronts. Yes, you need a spacer to center the rotor & caliper. The thickness depends on if you use the bracket for the splash shield. Piston sizes: 33 914/4 rear, 38 914/6 & early 911, 42 914/4 front & late 911 rear

I have some spacers made up for the 914/4 rears to fit early vented rear 911 rotors. They need longer bolts and seals to finish up.

DaveP

The 911 (and 914/6) rear "M" is 38mm up to '83 and 42mm (with a proportioning valve) for the '84 to '89 Carrera.

The 914 front is 42mm, and the has less rear bias than the 911, so correlation to the 911 is not so obvious.

For reference, the front 914/6 and basically all 911 (M, S, and A) have 48mm pistons.

I think 911 rears or 914 fronts (on the rear) with a tee is probably the best way to go with 48mm fronts, and testing to see if a prop valve is needed.

Edit - I type too slow!

Here is my suggestion with the rears. I have 87 911 bilsteins up front with 911 hubs and vented rotor with S alloy calipers.
On the rear I have 914-6 caliper that have been spaced with spacer that came from a set of early 911 calipers.
This allows you to use 911 rear vented rotors that have been turned down 3/16" on the O.D. yuo then space the the hat with a 3/16" 5 lug spacer so the calipers don't drag. Made a big improvement over the stock solid rotor set up.

Davep:
I ran stock 914 rear calipers with S fronts for year or 2 ....even after I realized they were just along for the ride (adjustable porp. valve wide open, venting gap .005)). After that period of time, the -6 rotors still had their machining pattern visable. I went to M rears and vented rotors. Now the rear brakes contribute to stoppage.
Not a "hassle", just didn't work for me.

BTW, IMO, a brake "upgrade" must include a larger heat sink(thicker and/or vented rotor) or a larger dia rotor (bigger mechanical advantage).

Wow! Thanks for the great welcome to the board. Great responses!

I'm new to this board. I have not had a Porsche for years. Helping my buddy with his '73 Carerra RS conversion gave me the bug.

The Carerra RS started out as a '79 911SC. Spectacular car!

I recently purchased this 914 "as is". No extra parts were included. The car was not used for quite a few years. The rear calipers are siezed quite firmly. All the rubber brake lines were nearly swelled shut.

The 911SC front and rear brakes are "hand-me-downs" from when the 911 Carerra RS was upgraded to 930 4-piston brakes, so the price is very attractive. They are in great condition ... freshly rebuilt with nearly new Porterfield R4 pads and extra rotors.

I'm still determining the exact make up of the car. I do not have the title yet. I was told it is a 1973, but most of the paperwork that came with the car indicate the model year as 1971. It does have a sideshifter transmission. The rear hubs were drilled for the 5 stud conversion.

I have a couple of sets of rear 911SC rotors. Maybe I'll try the other set to see if the inner diameter is slightly larger.

I'll also measure the hub to see if the stud conversion distorted the outer rim. Regardless, a spacer will be required ... 5mm?

What is a good source for brake lines and spacers?


Thank you very much for your help!

Eddie

Eddie914. Post your VIN# and my avatar will magically tell you the year.

Geoff If you still have the early rear hubs how much$ ??
CCLINFIVELUGCONVERSION

JP, you are correct. I remember now that it was an early car with M 911 fronts that I ran with the stock rears. I think when I put the 911S front in another car that I had the first set of 914/6 rears to install. They worked MUCH better at Watkins Glen than the stock brakes. No more brake fade!

DaveP