So I know this has been talked to death thousands of times and when I do a google search there's reems of information, but rather than spend the entire evening reading through many posts that really aren't relevant, I thought I would pose the question and see what turns up.
Recently I had a four wheel alignment and corner balance done by a really great and well known shop out my way (who are very familiar with track cars for my local track-Summit Point) and when I asked the primary mechanic today what things he might suggest for my sbc Sheridan standard wide-body conversion, he said upgrading my rear brakes would be pretty important for that track.
Soooo, yes there are lots of ways to go to be sure but I was wondering about retaining the standard rear 914 brake (and e-brake) but using the vented 911 SC rotor? Do I recall Eric made/makes a spacer for this or is/was that for converting 914 fronts to rears?
A lil confused this particular application.
I like the idea of retaining the stock 914 rear calipers if I can but I really want to go to vented rotor (as opposed to drilled).
Thoughts?

I added spaced 914 rear calipers and 911 rear vented rotors cut down by Eric Shea. My progress thread has some info and pics on my upgrade.

You need a spacer between the rotor and the hub to properly space the rotor in the caliper.

One thing I ran into with the spacer is when the spacer is placed between the rotor and the hub, the rotor loses it's centering capability on the hub. In this case the little screw that holds the rotor is important to setting the rotor in the center of the hub.

Also the 911 rear rotor screw placement is not in the same place as the 914 hub. I had to drill and tap a new hole in the hub.


Spoke's Progress Thread

Exactly what I was hoping for!
You wouldn't remember what year the rotors are from would you?

Don't know why year the rotors are. I bought them from Eric and he cut them down to fit the 914 caliper. PM Eric about your questions.

Makes me wonder if a spacer between the caliper and the attachment point could be used to center it? This would retain the rotors "centering ability", no?

Will do it!
Thanks again

Certainly '69 to '73 and surely later but I can't remember when they changed.

Makes me wonder if a spacer between the caliper and the attachment point could be used to center it? This would retain the rotors "centering ability", no?
[/quote]

No. Rotors do not center themselves. The caliper can be spaced to center on the rotor if needed. You need the spacer between the caliper halves to allow the caliper to go around the rotor the thicker rotor. The caliper is in the correct position.
What is the use of the car that makes you think vented rears are needed? Doing a lot of repeated high speed braking? Or is this just something you want to do ? Does not hurt anything other then adding more unsprung weight in the rear. Or is this just something you want to do?
Yes a 69-73 911 rear rotor thatare 20mm thick will work.
What calipers and rotors are on the front ?
Or is this just something you want to do ?

[quote name='bdstone914' date='Jun 29 2017, 11:51 PM' post='2501617']
Makes me wonder if a spacer between the caliper and the attachment point could be used to center it? This would retain the rotors "centering ability", no?
[/quote]

No. Rotors do not center themselves. The caliper can be spaced to center on the rotor if needed. You need the spacer between the caliper halves to allow the caliper to go around the rotor the thicker rotor. The caliper is in the correct position.
What is the use of the car that makes you think vented rears are needed? Doing a lot of repeated high speed braking? Or is this just something you want to do ? Does not hurt anything other then adding more unsprung weight in the rear. Or is this just something you want to do?
Yes a 69-73 911 rear rotor thatare 20mm thick will work.
What calipers and rotors are on the front ?
Or is this just something you want to do ?
[/quote]

911 SC calipers and rotors on the front.
On the advice of a local and well known mechanic that services alot of cars that use Summit Point Raceway it was suggested as an upgrade where repeated high speed braking will occur, not to mention the extra 250lbs I'm lugging around (sbc).
Good data the spacers (already using caliper spacers on the front of course) and the rotor years.
Ty

Spec for the rest
Hankook Ventus V12 evo 225/50ZR16 front
Koni red front
Stock sway bar front
Turbo tie rods
911 SC rotors and calipers front
Stock torsion bars (soon to be changed to 21's)

Fuzion ZRi 245/45R16 rear
Koni yellow with perches
220 springs
Stock sway bar rear
Boxed trailing arms
Rear chassis stiffening kit.

Porterfield all.

Here's a thread I started to ask vented rear rotor questions.

Rear Vented Rotor Questions

Great thread! Exactly the info I needed :-)
TY

I used spacers (flat washers) under my V-calipers it centered just fine. 2mm cut, 4mm total off the OD of the rotor. My rotors were off of a '75 911.
Only PITA is the cast rotor is hard as hell to cut, at least on lightly used rotors, but still do-able.

Eric did you ever come up with a hardware solution?
Mine came from you with no pins or pad springs.

I've made pins, but it would be nice to have springs, even if I have to modify them a bit.

I v'ed my rears about 5 years ago, I used the dust shield bracket as the spacer.
Disk needs to be cut down by 4 mm or it will hit the caliper.
See my photo on the left.
Mike

The 6 vented calipers are always an option. I'll check to see if I have a set Eric did up for me.

You might want to go the 911 rear caliper route with that setup. You lose the built in parking brake but it's a better balance.

Ask the mechanic why he recommends upgraded rear brakes. Is there some specific thing that he feels should be remedied on your car at that track? Does the car need more rear brake bias, more rear brake effect, more rear brake heat dissipation, or something else?

--DD

Good question!
The main circuit at SP has only 10 turns but many high speed straights, the secondary circuit (one that's a bit slower but better for my level) has 27 turns!
I think my mechanic was concerned that my car having a sbc and carrying more weight (2380 dry) that I may experience some significant brake fade. On the main circuit there's plenty of run off but on the secondary there's walls.
As an aside, PO removed the valve.
Oh, corner weighted at 490 front both, 700 rear both.
I think the main concern is brake fading due to heat buildup on the stock solid rear rotor. This is a mechanic well known for his tuning to this track and he reports, 914's that are well modified have experienced this problem at SP.
I guess I'm wondering if a standard vented, drilled vented, or cross drilled vented is what I want to do. I hear drilled vented rotors have been known to spider crack with alot of oscillations in heat.
As for the caliper, I'd like to keep the stock teener rears if I can. I guess that'll be a wait and see thing.

I didn't see rear vented 6 rotors at PMB's site?
Confused.

Cross-drilled are a waste of time for almost all cars. (Rotors with cast-in holes can be OK, and drilled can be OK for a track car that gets torn down and minutely inspected every event, but very much not for a street car.)

To manage heat problems, ducting air to the rotor and caliper can help immensely. I remember Chuck Forge had clamshells around the whole rotor that were fed by an air scoop pushing high-pressure cold air onto them. You couldn't see any of the rotor.

--DD

--DD

That's very good to know as the non-drilled vented rotors are a good deal less expensive.
Like the idea of ducting...the Sheridan body I have would make for a good duct opening just fore the rear wheels, no?

Sooo, I reckon the Sebro 20mm will work allright
http://www.pmbperformance.com/catalog/item...576/9661559.htm
And using the stock caliper, from what I've read I'll have to have Eric cut em down a bit, then use a spacer for the caliper and a spacer betwix the rotor and the hub?
Um, and I have to re-drill a centering hole to, eh?
Have I missed anything?
Seems like an easy and cheap mod.

On mine, i just shaved down the rotor diameter 2-3mm. I didnt need any spacers but I am using 911 hubs. If you are using a 4 hub, you can re drill holes for the set screw but its not needed. Once you put on the wheel and tighten the lug nuts, everything is held secure. Rotors wont "fall off" when you remove the wheels since the caliper holds them on.

Thanks for chimming in on that. I had read a thread where someone claimed that they needed to drill and tap a new guide as they felt the spacer between the rotor and hub had compromised the ability for the rotor to self center. I had thought that kinda odd as the lug studs center the rotor....
Mebbe because you hadn't used the spacers, you didn't encounter that problem?
Either way, not difficult to solve.

Put on new rubber flex lines if you havent done them recently. Its so much easier to do now and they sure dont get better with age.

Chuckle. Way ahead of ya Bro! I just finished up a total brake rebuild and included the rubber lines.
This vented rear idea is kinda after the fact :-(
At least when I go to crack open the calipers for the spacer they'll be freshly rebuilt, eh? Less than a hundred miles!
And I just now got em well bedded :-(

6's did not have vented rear rotors. They are 911 rotors.
What calipers and rotors are used up front? That is where most of the braking happens.

That's what I thought too. Poster to thread must have been thinking about fronts.

As to my front calipers and rotors, per earlier post in thread, 911 SC

We're not addressing braking power or balance per se (in this thread) but rather rear brake cooling capability in a car who will see track time where repeated high speed braking will occur at a track where 914's have a history of rear brake fading.
And judging from what I'm reading and researching, the 911 vented rear using the stock 914 caliper seems to be a cost effective solution. It'll remain to be seen if the 914 caliper will suffice using a rotor that doesn't overheat and boil the fluid...

I have a 1 or 2 sets in the shop but haven't got back in to check. I think that one was built for vented rotors as I had Eric do up a few in this configuration. I do know I can have them built up if they are not currently in that configuration, but I do need to check (I'm thinking I have one that is already set up.
Mark

The bolts are the issue, I believe. Hardware is 7 mm fasteners with strength grade of 10 or 11.
Early/4 rear calipers have Ribe fasteners '73 and up are standard bolt heads.
Late calipers have upper and lower bleeders, only one on early cars.
Can't speak of/6 never played.
Mike

My car is named Lil Bastard. From my profile picture you can see why.
No purist here. I'll toss the Ribe's (I have the earlier style on my 73) and git some high grade Allen's.
I s'pose Eric will have the caliper spacers.

V-calipers use the 911 rotor. They also must be cut down, at least they do on the /4 V-calipers.

Yes, just like when you use a 914-6 rotor/914-4 caliper on a 5 lug conversion.

914-6 GT cars had vented rotors. They were special made rotors. They have a 911 part number. I do not have the parts number right off hand though. Years back they were in stock in Porsche Germany.

Eric Shea had once quoted ~$250 for the pair (old quote), but they fit 914-6 GT calipers. They might still be too large diameter for v calipers.

901.352.041.12
Rear disc - 2

According to the 914/6GT spare parts list.
Mike

Need to ask... what are the V calipers? Stock 914 rears or something else?

Eric makes/made 914-4 calipers with a spacer for vented rotors.

V'ed calipers have a spacer to widen the gap for the disc to run through, wider gap allows wider vented rotor. Because of the calipers size the outer edge of the vented SC disc must be cut down for the rotor to fit without hitting the caliper.
Mike
Both /4 and /6 rear calipers can be v'ed. 914/6 v'ed become 914/6GT and Ferrari Dino calipers.

always a fascinating discussion

- must be 300 ideas about this on the internet with more permutations than my old brain can handle

to further upset the cart - see the recent Pelican brakes advert for Part # 911-352-907-00-PMB set of the "M" style calipers showing 914 style e-brake levers - would be a helluva deal if true

http://www.pelicanparts.com/More_Info/911-...SVSVSI=357.htm#

I think it's just a mistake. Some of the pics have an ebrake, some don't.

Well fuch me, I'll be callin in the mornin bout that 4 shore lol

All the pix I saw had the e-brake?

Addendum-AH, I see when I click to see the full image set that yes, some do not have the e-brake. Also, some appear not to have the spacer. Definitely be calling for clarification!

Well crap.
I just realized the PO had converted the rears using a 4-lug to 5-lug spacer :-(
This means if I want a vented 911SC rotor I have to change out the hub and the spacer as well as adding a spacer to the stock caliper and having the 911 rotor cut down (not to mention longer pins and caliper nut/bolts :-(

I wonder how effective ducting from my Sheridan Standard Widebody would work for efficient rear brake cooling. Certainly easier and more cost effective to do that at this point.

I'm bummed.

Do 911 5 lug hubs even bolt up to a 4 lug stub axle?
I thought you had to change the whole assembly - trans stub, axle, cv's, etc to use a 911 hub.

I think he means adapter, you can get 4-bolt to 5-bolt adapters from VW bug shops.

Well the good news is that I was wrong!
Indeed it's a 914 hub, but it was re-drilled to a five lug so that means I can use the 911SC rotor AND the 5-lug spacer I have.
Back on track this project! Woot woot.
http://www.pelicanparts.com/techarticles/9...onversion_7.jpg

Where is Erc??

MIA

Tricky part about Summit Point (main) is the T1 entry. With my 911SC, I would just brush 120mph and have to brake to 45-50 ish for T1. Do that 15-20 times a session. A SBC could be pulling closer to 140mph (depending on aero and driver) but still need to brake down the same.. so scrubbing close to 100mph.

The related issue is that you then have T5 -entry to the carousel. While you might enter at 100 ish, you have to brake down again, to 40ish... and by the third hot lap, THIS will be where you really want effective brakes with large heat soak ability, or LOTS of cool air...

imho, messing around with home made this and that vs a proven and supported product that, while giving up the E-Brake, allows you and a passenger / instructor to be confident of high speed stopping seems to be putting a cart before the horse...

At minimum I would encourage you to run SC rotors and calipers front and rear along with ducting to get air on them.


While the prices might be crazy, at least look at the Lots of general good brake info here.. http://www.vehiclecraft.com/Brakes/930_upgrade.htm