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Posted by: porsche4me Jan 5 2011, 03:55 PM

Hello - looking for opinions --and info --- are all 70-76 rear rotors the same ???

are all trailing arms the same ??? - are all the rear calipers the same ??

- I have a 914 race car that has no brakes mounted - the body is a 76 --- front suspension is 71 and I bought new rotors for all 4 corners. I have 6 stock front calipers (new and old) + the 2 early ones on the car --

-- and 6 rear calipers (new and old all of them need rebuild) -

-- I have heard people put front calipers in the rear , but should I put early or late front calipers in the rear --- I have both ---- dont care about the e-brake ..... thanks for ideas -- I need to buy pads ASAP ---- going to do Porterfields --- but dont know which ones to buy for the rear ------

Posted by: URY914 Jan 5 2011, 04:18 PM

I have fronts on my rear.

I couldn't tell you what year they are.

Posted by: porsche4me Jan 5 2011, 05:04 PM

thanks for the info --- do you have to buy pads ????? what kind do you buy ???? what year is the car???

Posted by: DanT Jan 5 2011, 05:05 PM

had fronts on the rear of this car...took out the stock bias valve and replaced with a "T"
you need to space the calipers on the rear rotors about 1/8" to center them on the rotor.
worked perfectly with Porterfield R4-Ss upfront and stockish pads in the rear.
but I was running M calipers up front with SC vented rotors...
It will be hard to balance the braking running stock front calipers both front and rear...you will probably have to use an adjustable brake bias valve to get the balance anywhere near close.


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Posted by: porsche4me Jan 5 2011, 05:11 PM

Thanks for the info ---- I DO NOT have any rear calipers that are useable --- but I have 3 or 4 pairs of fronts (early and late) that are good ------ I will run stock early fronts with porterfield pads in the front. The car has an adjustable proposional valve next to the shifter ---- the rear factory valve is gone and a "T" installed in the brake line.

Posted by: Randal Jan 5 2011, 10:58 PM

Ditton on another teener running the same calipers on the rear as utilized on the front.

In the case of "222" used 914-6 calipers. These essentially fixed the front lock up when autoxing.

Also using a T valve to allow equal proportion between the front and the rear.

Credit due to Brad Roberts on this fix.

FYI we put a bias valve in The Beast, but never had to adjust it one way or another.

The Beast also runs the same calipers on the back as the front, i.e., Carrera callipers and works effectively.

Posted by: Brett W Jan 7 2011, 08:59 AM

I as running the stock 73 front calipers on the back without spacers or machining. They just bolted right on. I ran a 19mm valve, brass T and the 320 Calipers up front. Braking balance was super nice and you could really feel it pull down hard.

Posted by: Eric_Shea Jan 7 2011, 02:57 PM

I don't recommend this at all.

1. Your bias is set by piston size, from the factory.
2. Your "Pressure Regulator" is not a proportioning valve. It acts exactly like a "T" (until you come to a panic stop).
3. You will be putting a larger piston in the rear... not the place to be "overbraked" on a car with polar moment inertia.
4.

No you weren't. They don't fit. Only "early" front calipers will bolt on (70-72).
5. The best piston to use in the back is a 38mm if you have a 48mm up front. This will give you the correct bias. This can be accomplished by removing the spacers from a 911 rear caliper and going solid or, by spacing back a 911 rear caliper 4.5mm off the ears and use a stock 911 vented rear rotor.
6. I would want to be front bias heavy vs. rear bias heavy in any 914, especially a race car. My friend here in UT was overbraked in the rear with a T at Sears. He lost his 914-6 and nearly lost his life.

Summary, the best solution for this application is a rear 911 caliper. It is cast from the exact same mold as the early 914 front caliper but has a proper 38mm piston so... you'll get:

a ) A larger 38mm piston but not too large as to where you can lock up your rears before the fronts (if you have a 48mm piston up front).
b ) Bolt on availability.
c ) Use the same pad compound front and rear... no mysteries, no experimenting.
d ) A larger #31 pad vs. #30 (same as the 914 front swap again but with a better piston for bias)
e ) The option to use a vented rotor if you space them back a bit.

Posted by: quadracerx Jan 7 2011, 04:34 PM

I was wondering the same things....and if they have already been answered...Im sorry....I miss stuff sometimes....LOL

1) Are all 70-76 rear rotors the same ???

2) Are all trailing arms the same ???

3) Are all the rear calipers the same ??

Thanks....

Steve

Posted by: Eric_Shea Jan 7 2011, 07:13 PM

Yes.

Yes (the first few years incorporated a small tab to hold a e-brake cable on a -6.)

Yes (basically... I could list a ton of differences but, suffice to say, they all have 33mm pistons and interchange.)

Posted by: quadracerx Jan 7 2011, 11:25 PM

Thanks Eric...answers alot for my ongoing project....one last question for you...are the front calipers the same from 73-76? I have a leaking caliper on my red 76...but have spare fronts from "good old rusty...my 73. hope the answer is yes again cause I dont want to make the red car undrivable.....

Steve

Posted by: porsche4me Jan 8 2011, 09:55 AM

This great info for the under-informed like me----- I have done the street car thing for years , where all of the car is either early or late ---- but this race car thing in kicking my mental butt ----- Here is what I have --- the racing series will not allow me to run 911 brakes or any crazy after market stuff ----- I have 2 sets of early front that are in good condition -- I have 1 set of late fronts that are good ---- I have 3 sets of rears (early and late that are all in need of rebuild that I don't have time for)

The race car has an adjustable proportional valve next to the shifter ---- So my original question is ---- can I run front calipers on the front and the rear --- with same or different pads, with the proportional valve --- and if so, early or late in the rear ( I think this was answered -- Early! right?)

Thanks again - it take a couple of time for me to get the understanding I need to move forward with knowledge

Posted by: Racer Chris Jan 8 2011, 11:19 AM

In spite of what Eric telling you being all true, you can certainly use early fronts at the rear on a race car that has a proportioning valve. Many racers before you have done it successfully. (I don't though, because I prefer to use heavily modded rears).
It will be important to heavily bias the balance to the front brakes and test in a safe environment until you know the fronts will lock up first if you go beyond threshhold (at the limit of control) braking.
Braking in wet conditions will not transfer as much weight to the front. Therefore the bias can be adjusted rearward when racing in the rain.

Posted by: Eric_Shea Jan 9 2011, 10:24 AM

Dual bleeders = the same... late model calipers. 73 and 76 should be the same.

I agree with Chris. Most of the time, people use a larger "Front" caliper and leave the rear languishing. There is no proportioning valve for this equation. My goal is to get a "balanced" system and your p-valve should be able to do that for you.

Odd set of rules that would allow you to put a larger 914 front caliper on the rear but not a 911 caliper of the same casting but, stranger things have happened.

If you deicde to do this for a race car only I would highlight and underline Chris's text: test in a safe environment until you know the fronts will lock up first if you go beyond threshhold (at the limit of control) braking.. This is generally why I recommend against this, there's a lot of armchair racers that are reading this now thinking "hmmm if it's cool for a race car, I'll be really cool and have it on my street car". This takes a lot of work and knowledge of not only your braking system but your cars dynamics. It can be detrimental to your car and your life if you don't get it right.

Use early (single bleeder) fronts. Later models do not have the proper offset.

Posted by: porsche4me Jan 9 2011, 08:56 PM

Thanks guys - here is more info --- race car only --- www.chumpcar.com -- the rules are about value -- race a cheap car for 14 to 24 hours in a row --- very grassroots racing ---- the 914 is acceptable but no real "go fast" parts ----- I traded the 2.0 liter complete fuel injection for a set of 40 webers ----- and a set of VERY nice ss heaterboxes and a monza exhuast for a very used Kerry Hunter with a super trap ---- So stock fronts in the rear-cool 911 - or big reds NOT COOL---- i would get huge penalty laps for those --- I bought lots of new parts (rotors - bushings - pads - cables ) that are not part of the car value equation.... cage , safety , tires and wheels are not in the value..... brakes are limited to 2x (2 times) original parts ---- not OEM nos but fair market price ----- My car is piced together from 3 parts cars and a stripped out race car shell ---- for a $100...

Posted by: campbellcj Jan 11 2011, 11:10 PM

I am using this setup as well on my track car with reasonable results, although I may change/upgrade some time this year. 911SC "A" calipers and rotors up front (really the whole front suspension), front 914 calipers moved to the rear. Pagid pads. I do have an adjustable prop valve as well.