Hey Bill V, quick question...

The Turk · 04-09-2006, 10:50 AM

Hi Bill,
I got all the parts ordered (from our host) for the 993
caliper upgrade on my 75 911.

My machinist buddy plugged the rear caliper holes yesterday
and wants to drill the new holes today, I just need to confirm
the location.

I'll be using the 78-89 930 rotors with 1996 993 calipers.

Are the new holes M12 diameter drilled 12.5mm below the flats of the caliper 3 inch on-center ?

Bill Verburg · Bill Verburg's Garage

Yes, but since slight differences in methodolgy can lead to errors, please trial fit them.

The Turk · 04-09-2006, 02:54 PM

I was going to measure the 12.5mm up from the flat spots that are next to the steel brake pad plates on the inside of the caliper and center the 3" holes between the plugged holes.

Does that sound right ?

Bill Verburg · Bill Verburg's Garage

Yup

The Turk · 04-09-2006, 03:03 PM

You're a man of few words...

Thanks for all the advise you've given me on this project.

The Turk · 04-12-2006, 06:37 PM

Hi Bill,
I decided to take your advice and trial fit the rears calipers before drilling, I just received the rear rotors today so it will probably be a few days or a week before I can get to it.

In the meantime I started on the fronts.

So here's my question of the day.

After tearing the front apart it looks like I've got the 3" struts
(odd for a 75 ?) since my machinist buddy will be making the
adapters to use with the 993 calipers, is this a problem ?

Let me know what you think, thanks.

Bill Verburg · Bill Verburg's Garage

3.5" will be stronger and stiffer, but as long as you are making them from scratch, 3" ought to work fine.

You should make a few sets as I'll bet there is a niche market for them.

The Turk · 04-12-2006, 11:18 PM

That's good news.

When my brake project is complete, I'll post some pictures for 3" and 3.5" 993 caliper adapters as well as the modified hubs that the my friend Joe built for the 993 rotors, he has a small job shop and said he'd be interested in offering some for sale at more reasonable costs than currently are available.

Thanks again for all the help.

The Turk · 04-15-2006, 12:46 PM

I think I figured out why no one is making the 993 caliper adapters for the 3" struts, the caliper touches the 3" mounting point before it's all the way down over the rotor, there's about an eighth inch of pad overhang.

Looks like Pelican will be getting more of my money...

By the way, the front hubs turned out great, I'm going to start on the rears while I wait for the new struts to arrive.

KTL · 04-15-2006, 01:56 PM

Don't cheat on the 12.5mm measurement and go less than 12.5mm.

The result is that you end up having to clear the interior crown of the caliper. Ask me how I know.......

And of course don't get carried away by going too far beyond the 12.5mm. You'll end up with thinner walls on the mounting holes since you are approaching the outer limits of the existing caliper mounting ears.

DUK · 04-15-2006, 02:00 PM

Pictures Gary, pictures...

The Turk · 04-16-2006, 11:19 AM

Hi Kevin,
I'm a little confused (as usual) I'm getting ready to drill the holes, I was planning on going exactly 12.5mm, with the 78-89 turbo rotors why would I go less or more ?

Bill V,
If you’re out there feel free to jump in also.

Hi Duke,
I'm not much of a photographer...But here's a couple of pictures, the front caliper is just sitting on the rotor.

KTL · 04-16-2006, 07:51 PM

Gary,

If you were to go less, the inside of the caliper gets closer to the outer perimeter of the rotor. Going less is an attempt to get the caliper to clear the pesky Fuchs wheels without needing spacers. Problem is you end up shaping the inside of the caliper to clear the rotor = PITA.

Going more would reduce the likelihood of having clearance problems inside the caliper. Problem with that is then you run into clearance problems with the Fuchs wheels. That is, the 16x7 16x8 911/930 Fuchs. The 951 16x7, 16x8 and the 930 16x9 clear no problem.

My theory is the the goal is to reduce the amount of work done on the caliper. That would mean setting the holes at 12.5mm or more. If you have wheels or spacers that negate the potential clearance problem? You're gold.

jpahemi · 04-16-2006, 09:31 PM

Gary:
Once you have found the exact drilling of the 993 rear calipers, could you make a template so there finally is a standard measurement for those venturing in this in the future??
j.p.

The Turk · 04-16-2006, 10:02 PM

J.P,
Everything I've read says to use 12.5mm measured from the flat spot that is next to the steel brake pad plates if your using the 78-89 turbo rotors, I down loaded a template from this BB.

I'll let you know how it turns out.

The Turk · 04-16-2006, 10:12 PM

Kevin,
I'm using 3 piece BBS style wheels so I'm not sure if there's going to be clearance problems of not, I'm thinking about some new wheels anyway, maybe Kodiak STX or RT.

KTL · 04-17-2006, 12:06 AM

There will be no clearance problems. I have three different offsets of BBS RS three-piece wheels. 16x8 ET 11, 16x8 ET 28 and 16x9 ET 15. All of them clear the rear with no problem whatsoever, plenty of room to spare. So 12.5mm or more will be no problem for you.

Here is the template I made with AutoCad.

993 Caliper Mods- Grinding and Drilling

The Turk · 04-17-2006, 04:15 PM

Hi Kevin,
Unfortunately my wheels aren't real BBS, they are a true 3 piece with an aluminum centers, looks like it's going to be pretty close.

Thanks for the CAD drawing, I had found that a while back when I was researching this project and already had it saved

So is there any pad overhang when drilled at 12.5mm ?

KTL · 06:15 AM

Gary,

A true 3 piece wheel should have adequate clearance radially, since the typical 3 piece wheel halves do not have the prominent interior taper like the Fuchs. The problem you may have is clearance between the backside of the wheel face and the caliper, due to the depth of the wheel hub. I'll post a picture of some Compmotive wheels I used to have. The hub is quite shallow on those and i'm sure the wheels cannot clear large brake calipers.

And no, there's no pad overhang when drilled at 12.5mm. The fit is just right.