Every now and again we get a pair of late 912 rear calipers in-house. These rare calipers share the 38mm piston diameter with the 914-6 and all 911's (for practical purposes) through 1983. These also have the same #31 pad size associated with the 914-6 and 911 calipers. So... larger pistons and larger pad size.

What are these good for? If you've moved to 5-lug up front and you're now using anything from an M-Caliper (stock 914-6), an S-Caliper (911S, RS, 930), an A-Caliper (911SC through 1983) or a Wide A-Caliper (911 Carrera) these would be a bolt on caliper that would retain the braking bias those cars were set up with (48mm pistons up front and 38mm pistons in the rear).

These are true late 912 calipers vs. 911 rear M-Calipers. What's the difference? They don't have the 10mm spacers. They have the same Ribe R6 cap head fasteners just in the shorter length to accomodate the spacerless application. Because there's no spacers, these fit over a solid 914 or 914-6 rotor (keeps weight down). With the 3" mounting ear spacing, these bolt right on to a 914 rear control arm.

***There is no handbrake option if you install these. This is why they are recommended as race calipers only*** You can add a spot caliper or, install the early 911 handbrake assembly to your arms but, these are really a great solution for the track car that needs proper rear bias and a larger pad without worrying about the DMV and their rules and regulations. You'll probably want a 19mm MC as well.

Comes with everything you need (pins springs and bleeders) with the exception of pads (we can help there too...)

Our normal restoration price is $249.00 plus cores. These will sell fo $199.00 for the pair with no core required. Shipping is $9.85 Flat Rate to anywhere in the US. Ask for International shipping. Crappy picture below:

Click to view attachment

So are these better than using front 914 calipers on the rear?

I was thinking the same thing! Just cuz that's what I currently have...

Much. (Sorry for the delayed reply. I didn't realize I had questions.)

These have the proper 38mm piston to keep the bias in check. The 914 front has a very large (by rear standards) 42mm piston and it really messes with your bias. Dangerous in fact. The 911 didn't get this piston in the rear until 1984 and it was the first year for a proportioning valve in a 911.

Have the proper bias (same as a 911 or 914-6) right out of the box with the same pad size as the 911 and the 914-6.

I do NOT recommend 914 front calipers on the rear of any 914.

These are still for sale BTW.

Eric,

Thanks for the reply and I see your point about proper bias being crucial. However, isn't the front/rear bias dependent on what calipers are used up front?

I currently have "A" calipers up front and 914-4 fronts in the rear, and the bias is just about right from what I can tell. I do actually want to adjust it a teeny bit more toward the front though, so I am about to install an adjustable prop valve.

My car is nowhere near stock and I am using full race pads (Pagid), very stiff suspension, Hoosiers, etc. so my setup should not be construed as good for the street or for other cars/drivers...

Eric,
You have a PM.

Yes. That's pretty much explained in the second paragraph of my first post.

A-Caliper = 48mm pistons. Same as M-Caliper, S-Caliper, etc. All used in conjunction with the 38mm rear pistons on 911's and 914-6's from 1969 through 1983. Chris, if you get into "any" situation where your rears lock up (other than straight line) you risk spinning like a top. Polar moment inertia (check out Elfords book on that subject in a 914). I have a friend who lost his factory six at the track and Dr. Evil will gladly discuss this with you as well. Just some words of caution.

Calipers are SOLD.

Thanks all.

E.

You can also bias brakes with pad compound. ie: stickier pads up front and not so sticky in the rear... .

..........Question for ERIC SHEA.....With any or all of the calaper combinations you discussed....do any of the combinations ALLOW the removal of the stock... brake bias/brake pressure requlator?...or do to a specific combination,is the B.B. P.requlator... removed to achieve maximum breaking ability?...M.M.

That's not a great idea. It takes a LOT of hit or miss and experience with pad compounds to play this game. Dan is the only guy I know that has done this successfully and he races his 914 regularly in wheel to wheel competition. Do me (yourself) a favor, make a quick list of all the brake pads you know of for our 914's. Now list them, in order, from stickier to not so sticky. Ready... go!

The question is; why? When the proper caliper with the proper piston size for best biasing, made off the same casting, with the same pad size is available to bolt on to the same mounting location; why put an irregularly large pistoned caliper back there?



Not on my car. Removing it does not acheive maximum braking ability.

The pressure regulator is SO WAY MISUNDERSTOOD by the 914 crowd. One day, back when we were smashing rocks together for fire sparks, someone said; "If you take the proportioning valve out you'll have better brakes." I bought into it for a while as well, until I did some further reading. There's a page dedicated to it in the factory manual and it's a great read. The funny thing is, the Alfa boys have the exact same valve and if you cruise posts on their board regarding the subject, they would think you were crazy if you wanted to take this out.

That said; the pressure regulator is not a proportioning valve or a bias valve of any sort so it stands to reason it has a purpose beyond balancing our braking bias (which the factory did extremely well with piston sizes... hence the chatting herein). There are two things that you should read to help you put this together in your own mind. They helped make it click for me and I've never gone back to recommending a "T" fitting or an aftermarket bias valve to anyone ever again. Those two things are:

1. Vic Elfords book on Porsche Handling. There's a section about "mid-Engine" and it touches on 914's. We get all pumped up when we tell others our cars are "mid-engine" and superior to God in handling. Vic points out that they are rather good but, the 924-944-968 package is better because, polar moment inertia can cause our little 914's to spin like a top once they get started. Having the weight at the ends (engine in front, tranny in the rear) is much more predictable and controllable. It's a good book to have and a great read when learning all that you can about your Porsche.

2. The page from the manual explaining what this little bugger really is. As stated before, it's not a proportioning valve or a bias control. It (as you rightfully stated) regulates pressure. It ONLY does this when it experiences a panic stop of 535lbs. of line pressure. It shuts the rear circuit down and slowly brings it back in to prevent the rear wheels from locking up. This keeps as much control as possible in the rear of the car in such an instance (no screaching, locked up tires back there).

Bottom line; the pressure regulator sits there and acts just like a "T" fitting, passing all the fluid you can deliver to the rear calipers unless there's an emergency where they may lock up. Then it springs into action.

The only problem is, it sucks to bleed. But it sucks even harder if you're the one bleeding.

I hope that helps someone.

Eric, are the 4 and 6 pressure regulators the same then?

Nope, they have different values but I think it is very small. I think(someone will have to check) the -4 has 17 stamped on the housing and the -6 has 19 stamped on it. I do not know if this refers to the diameter of the opening like the 17mm and 19mm master cylinder have. Things that make you go hummmm! I will get out the shop manuals and see what they say on the spec's.

I find that when I autocross and when I am on the track I am either on the gas or fill tilt boogie on the brakes. One thing I know for sure is I don't want the pressure regulator "shutting down" ANY of the brakes at ANY time under these driving conditions. No matter how well the thing is engineered, there are proper parts for each application and one should know what they are doing when messing with any of them. I, for instance, don't believe the stock pressure regulator is good for a race application. I don't need to know ALL the rates of grip for pads to know the difference of what works for me and what doesn't. If you don't do your own setup and know what is working for you and what doesn't, you need to have someone else tell you what to do. If you build, tune and test your own equipment then you can do the math yourself instead of relying on someone elses opinion of what is going to work for you.That's why I didn't list which compounds would work for any given situation. Because I don't know. You need to do some work to make that happen.

I do know that Dan is not the first one, nor is he the only one to do this succesfully. Many folks that race their cars tune brake bias with pads. Need proof... go to a GGR AX event and I'll show you.

That said, if you do not do your own work or can not test and tune your own equipment then one of the few folks I would trust with my brakes is Eric. No one person can know everything and race applications are very car/driver specific so that throws a monkey wrench into the whole game.

I actually subscribed to the school (5+ years ago) that it made sense to remove the regulator thingie and use a tee. I have found empirically through numerous track events that I can in fact get the balance "very close" with my particular setup and pads. I am actually using two different compounds front and rear, as Mike alludes to. That said, the car is not as stable as I want under extreme straight-line braking, even with an LSD and so I am going to try an adjustable prop valve and see what the result is.

Just an idea - there is some interesting stuff in this thread and maybe we can get an admin to copy/move it over to the Garage or Paddock since we aren't normally supposed to discuss tech details in the classifieds!

I was using differing pad compounds back in the early 90s and I was not the first by a long shot. My 2.7RS motors 6 had identical JFZ 4 pot calipers front and rear...I ran Pagid orange up front and cut down, stockish pads in the rear....worked great.
Is this for everyone, no way. Takes time patience and a well calibrated butt.

Listen to Eric's wise advice for a street car, he is right on the money.