993 brake conversion on Carrera - questions

[Maxhouse97]

I have been researching this mod for over a week. Someone said every 10th post on here is about brakes and I think they are right. I have an opportunity to acquire calipers and rotors from a stock 993 C2S (non-Big Red). My car is a narrow-bodied 87 Carrera. I wrote Doug at VCI with some questions and have posted his answers below. I still have a few more questions (and looking for a second opinion).

1. What rotors should I use in the front? Here are the choices as I see them:

- 993 - used by Slider79SC w/custom hub and longer wheel studs (VCI says no)
- Late 930 - Bill V mentioned using these
- Aftermarket - used by KTL (309x32mm rotors with adapter hats (I used Wilwood HD rotors), and JeremyD

What are the pros and cons for each? I do not want to pay for VCI's front rotors ($375 a piece). 930 and 993 rotors are pretty close in price ($150-170). Don't know how much the Wilwoods are. I think they are two piece. I am looking for the best bang for your buck.

2. Can anyone (shop or otherwise) machine the rear calipers for me in order to fit the 930 rotor (widen the throats and redrill holes)? Not something I want to do. VCI said they don't widen throats, which I guess means they would advise to stick with stock Carrera rotors and deal with the pad overhang. I would like to go with the 930 rotor due to the larger thermal capacity. 965 calipers are mucho $$$ and defeat the purpose of using the "free" 993 parts I am getting. Any other options here?

3. Quick explanation on hats and rotors. I am assuming a hat that is referred to as separate from the rotor is from a two piece rotor. Can you reuse these hats when you change rotors? Are the replacement rotors expensive? Seems as if the OEM rotors (993, 930) are all one piece. I would think OEM would have the advantage of availability (as our cars age) and lower cost. I view rotor as a wear item. Am I wrong?

I think that is all for now - thanks.

Tony

Email from Doug at VCI:

1. Can I use stock 993 rotors up front?
No I don't know a way to do this. We make a rotor for the application.
About $750 for the pair. The adpaters are 275.00 for the pair.
> How about in the rear? I assume the recommendation to use 930 rear
> rotors has to do with their different offset. Again I would like to
> use as many 993 stock components to cut down on initial and
> replacement costs. I have also been told that even with the machining
> of the rear calipers that you have to remove about a third of the new
> pad when replacing them. This sounds like something to avoid if
> possible.
It's not for 930 rear rotors, but for Carrera rear rotors and yes you'd
have to deal with pad overhang of a bout 1/4". We don't machine the
throat of the caliper - too risky for us.
> 2. What would you charge to machine the 993 rear calipers in order to
> fit the 930 rotors if unable to use the rear 993 rotors?
550.00 for the pair, includes adpaters. Again, it fits Carrera rear rotors.
> 3. Why do I need solid metal lines? Do these brakes not use flexible
> lines? I currently have SS lines on my stock Carrera brakes.
The solid metal line goes from the caliper to the tab where the flexible
SS line starts. It dosen't go directly to the caliper in other words.
> 4. Would I use your VCI-6600 adapters for the front? I assume its
> $249 for a pair (pr)?
Yes, they are $275.00 now.
> I have Boge struts on the front - will this make a difference?
Nope
> 5. What exactly are adapter hats (referenced above on "Front")? Are
> they a one time purchase?
I don't know. There's no hat to adapt standard 993 rotors. Thats why we
make a set of our own, hats and rotors. VCI-3510 $749.00
> 6. What other parts would be beneficial to acquire from the 993?
You can only use the 4 calipers.

[JeremyD]

These are the rotors I use


Wilwood Rotors HD
12.19" (309,7) 1.25" (31,8) 8 x 7.00" (177,8) .313" 8.41" (213,6) 6.53" (165,9) 12.7 RH 160-3870
12.19" (309,7) 1.25" (31,8) 8 x 7.00" (177,8) .313" 8.41" (213,6) 6.53" (165,9) 12.7 LH 160-3871

Wilwood Directional GT
12.19" (309,7) 1.25" (31,8) 8 x 7.00" (177,8) .313" 8.41" (213,6) 6.53" (165,9) 12.7 RH 160-2526
12.19" (309,7) 1.25" (31,8) 8 x 7.00" (177,8) .313" 8.41" (213,6) 6.53" (165,9) 12.7 LH 160-2527

The hats are custom - but can be made pretty easily from Measurment. You might try KTL - he measured alot of this - I bought some from Dave Walsh at probraking

As far as the rears - I took them to a place that welded al and ask them to fill in the holes - I then bought a drill press and drilled them out. A little anxious but they worked after I made a template.

Don't forget the bigger MC

I got mine from Dave Walsh - Probraking.net

[JeremyD]

yes you can reuse the rotor hats - although new nuts and bolts are recommended



993 Caliper and 930 rotor vs stock Carrera




Finished rear

[911crazy]

Hi. I also had a 87 Carrera and when I fitted the 993 calipers to my car I used 993 front rotors on the front and 930 rear rotors at the rear so that the park brake would still work.

I had the rear caliper mount holes welded up and re-drilled them with the spacing that Bill V was kind enough to post on the forum. The small tabs inside we ground off by me using a dremel tool after I had covered the pistons and closed any ports that were open on the caliper.

For the front rotors to fit the front hubs had to be machined down at the outer portion. I do not recall how much but you can easily measure it. An objection to this is that some feel that the hub my now develop a crack from the wheel mount bolts. I did not experience any cracks and I did do track days with the car. The mount adapter I had to figure out the dimensions and I will check to see if I still have that data.

I talk of the car in the past tense as it is sold because it was a targa and I want to get into the track days with more enthusiasm. So I am looking for a coupe now.

Cheers Craig

[Bill Verburg]

Originally Posted by Maxhouse97

......
1. What rotors should I use in the front? Here are the choices as I see them:

- 993 - used by Slider79SC w/custom hub and longer wheel studs (VCI says no)
- Late 930 - Bill V mentioned using these
-.......

I never said that you can use late 930 front rotors on a n/b of any year. They can only be used on w/b w/ late turbo hubs.

you can use front rotors and hats from a '78-80 930 on a n/b w/ 911 hubs. This is the best way to go but is expensive

[Maxhouse97]

Jeremy - What do replacement front rotors for your setup cost (including the new nuts to reuse your hats)? Why did you decide to go that route instead of using 993frs? I assume it has something to do with the offset adjustments and machining the hub.

Craig - why did you go with 993 rotors on the front (I can sense a pattern here?

Check on the bigger MC.

Also like the idea of taking the rear calipers to a machine shop to fill in the holes and drill the new ones - I guess I could give them the template describing where to drill. Probably much cheaper than sending them away.

Once you break down this mod, it does not seem as scary as it initially did...

[Maxhouse97]

OK Bill my bad I got my late and early 930 rotors mixed up. Any thoughts on the pros/cons of each choice for front rotors?

[Bill Verburg]

As i said best is '78-80 930, 993 on a modified 911 hub is probably cheapest, Most of the people i know that have used aftermarket rotors haven't been happy.

At this point I think the easist is to get a GTP-L kit or the Zuffinhaus 917 kit, it might be a litle more expensive but you will avoid a lot of little headaches

[JeremyD]

Originally Posted by Bill Verburg

As i said best is '78-80 930, 993 on a modified 911 hub is probably cheapest, Most of the people i know that have used aftermarket rotors haven't been happy.

Well after 13,453 miles I changed out my Wilwood rotors. That's also close to a dozen DE days.

They still had plenty of wear left - I just warped one when my cooling scoop was lost and I didn't complete a sufficient cool down lap.

I think that's pretty reasonable for a rotor that costs ~$100

My car is heavy being a cabriolet - I have some pretty good HP - and I use porterfield R4 pads.

[Maxhouse97]

Thanks! I have seen the GT-L kit but was trying to use the 993 hardware to keep costs down. Steve W lists his kit as:

Pricing for the GT-L kits runs $2390 for the front and rear 2 piece and $1890 for the rear 1 piece option that retains the emergency brake.

Is that $1890 for all four corners (with one piece rear rotors)? That does sound enticing.

Gotta weigh the cost vs trouble of modifying 993 parts. Hmmm.

Two piece floating front rotors sounds expensive when it comes time to replace them though...

[Maxhouse97]

Nope - answered my own question - $2300 or $1800 for two wheels, so either a total of $4600 or $4100...

Ouch. Gotta pay to play

[KTL]

I have the dimensions of the Probraking rotor hat at home. I'll try to get them this evening. I also can give a thumbs-up for the Wilwood HD front rotors. Mine performed perfectly for two seasons ~ 10 track days and then a third season on Motodelta Chris Streit's '70 911S 3.3L GTS4 full-on race car. Chris finally decided to replace them this season since they had a good bit of cracking, and plus they're cheap at his dealer cost.

If I had it to do again, I think i'd go with the 993 fronts and Boxster rears. Reason i'd go with the Boxster rears is because you can get some slick adapters from TRE Motorsports that puts the caliper in a very nice location and makes the install a true bolt-on, with I believe the Carrera rotor if you narrow the pad pins on the monobloc caliper? Although keep in mind the Boxster rear pads are MUCH more expensive than 993 rear pads.

http://www.tremotorsports.com/product.cfm?Node=10317

http://www.tremotorsports.com/product.cfm?Node=1329

http://www.tremotorsports.com/gallery.cfm?Node=10321

I don't like the redrilling and widening the throats of the 993 rear calipers because of the extra work to widen the throats and you have to make sure you locate the new mounting holes well- too high and you're hogging the caliper a lot to clear the monster 930 rear rotor. The 930 rotor works well, but the thing that bugs me most is the need to shave pads- kind of a waste of good pad material. 930 rotors are getting quite pricey too. But it is a very good rotor. I'm kind of being a hypocrite here because this is coming from a guy using the VCI rear caliper setup with the Carrera rotor and it's overhang (I have the complete VCI 951/964 brake setup on my car). The other caveat of using these calipers, both 993 and VCI, is the mounting of them. It's a very tight fit to get the mounting bolts installed. You need to have a floppy-head socket wrench or socket handle, plus a very thin, short 19mm or 3/4 in. socket. I "made" the socket by grinding it down very much on my bench grinder

Just remember when you go with the 993 setup that only 951 16x7, 16x8 Fuchs and 930 16x9 Fuchs wheelswill fit over these calipers w/out using spacers. The barrels of of the "regular" 911 Fuchs are too narrow and won't clear the big 993 calipers. I had to use small spacers on the rear for my 16x8 911/930 Fuchs to clear the caliper. If you use BBS RS 16 in. wheels, or other similar multi-piece wheels, they clear fine. I believe most any 17 in. wheel will clear these brakes no problem.

[JeremyD]

My solution for the rear caliper bolts on the 993 rear calipers

The problem is no room - as in can't get anything to fit -

My solution - cheap 19mm socket that I epoxied in a 8mm bolt and nut

[Maxhouse97]

Good info. Never thought about Boxster/Carrera rears…

I have 17” wheels for the street, so I am not worried about clearance. Working on a solution for track wheels (currently have 16x6,x7 Fuchs for the track but am willing to go the 951/spacer route).

How would the brake bias/balance be with 993 calipers/rotors up front and Carrera rotors/Boxster calipers in the rear? Would I have to worry about the thermal capacity issues that Boxster front calipers on Carrera front rotors create? The main reason I am doing this at all is to increase the thermal capacity of my braking system. How much of a load/heat do the rears create in our rear engined cars? Can the rear Carrera rotors take the heat?

[Bill Verburg]

Originally Posted by KTL

......If I had it to do again, I think i'd go with the 993 fronts and Boxster rears. Reason i'd go with the Boxster rears is because you can get some slick adapters from TRE Motorsports that puts the caliper in a very nice location and makes the install a true bolt-on, with I believe the Carrera rotor if you narrow the pad pins on the monobloc caliper? Although keep in mind the Boxster rear pads are MUCH more expensive than 993 rear pads.

http://www.tremotorsports.com/product.cfm?Node=10317

http://www.tremotorsports.com/product.cfm?Node=1329

http://www.tremotorsports.com/gallery.cfm?Node=10321

I don't like the redrilling and widening the throats of the 993 rear calipers because of the extra work to widen the throats and you have to make sure you locate the new mounting holes well- too high and you're hogging the caliper a lot to clear the monster 930 rear rotor. The 930 rotor works well, but the thing that bugs me most is the need to shave pads- kind of a waste of good pad material. 930 rotors are getting quite pricey too. But it is a very good rotor.....

the problem w/ using the Boxster rear w/ the 993 front is you still have the smallish 911 rear rotor, you end up w/ a lot more front bias than is usual for a 911. If you are going to do that you might as well use 3.2 Carrera rears save a bunch of $$ and have a bit better bias.

If you don't want to modify the 993 rear caliper throats get a set of 965 rear calipers, you still need to do the mounts but the throats are sized for 28mm 930 rotors.

honestly, the 3.3 930 rear rotor w/ a 993/965 caliper is the best match for a big front.
here's a view from the trans of a 930/993 rear setup

[ChrisBennet]

Just a data point:
I have 993 front calipers with VCI front hub adapters for the 930 floating rotors ('78-80 930).
The VCI supplied Coleman rotors would probably work fine for a street car but they didn't last at the track. The Porsche rotors I replaced them with just go and go and go...
I used 930 rear calipers and rotors and removed the bias valve ('86 Carrera).
-Chris

[Maxhouse97]

Stupid question – can you move stock Carrera 3.2 fronts (calipers and rotors) to the rear? Would this help the bias problem with 993 fronts?

That being said, Bill V I am starting to like your option more and more. 993 front rotors w/ 993 front rotors and 930 rear rotors w/ 965 rear calipers. All OEM, and only have to modify mounts for the 965 rears (adapter for 993 front calipers). Now I just have to find 965 rear calipers for cheap – would you stay away from remanufactured ones (Cardone, Bendix)? I used them on the front of my Carrera and they were the same bodies as my stock ones – right down to the ATE stamp. Could save lots of money this way.

[KTL]

Bill,

I like the 993 fronts alot because they are a straight bolt-on with the correct adapters. Although there is some a-arm clearance with the 309x32 big rotors. Nothing major like the VCI setup. You can grind on the ball joint front and rear to help the rubbing problem. I agree about the 993 44/36 fronts being large-ish with the Boxster 30/28 rears and agree you don't gain much of anything at all with them besides easier pad changes and more pad selection. I do notice also that the Brembo dust seals are slightly more resilient to heat than the Ate dust seals. But those factors are obviously less important than bias. You are of course right that for the $ spent, you're not really gaining anything much at all with the Boxster rear since you still use the same thermal mass with the Carrera rotor and become more front biased. My recommendation for these is incorrect, as I was thinking about the current setup I have with the small basic Brembos.

I guess that's why I like the smaller 964/951 Brembos though, because you gain some needed front thermal mass with the 299x28mm 951 rotor (although i'm not a fan of it's clearance to the ball joint/A-arm) and improve the bias. Here's why I believe so, and please correct my miscalculations!

The stock Carrera HBR is 2.419 w/ PLV in place, quite front biased, no? Doesn't seem that I can compare to others since it uses PLV..... How do we make a proper comparison?

The 993 front 44/36 = 5077 sq mm and 34/30 rear = 3229 and HBR = 1.572. Using 30/28 rear would result in a 1.919 HBR. Is this less front biased than stock?

A small front Brembo has 40/36 =4549 sq mm, small rear Brembo has 30/28 = 2645 sq mm. Therefore HBR = 1.720

My 1986 951 VCI setup has 38/36 = 4304 sq mm and rear 30/28 = 2645 so HBR = 1.627 If I used the Carrera rears w/ 2771 sq mm you get HBR = 1.553 a bit less than 993. Bad? Dunno according to the numbers, but I do know I have had NO problem locking/flat spotting the rears if i'm not careful with either the 993 or the VCI setup. Both have PLENTY of clamping force!

I suppose i'm a bit eager to recommend the Boxster rears because i'd like to use them in lieu of my current VCI 30/28 rears with the not-so-desirable pad overhang. And of course they're a more appropriate fit for my situation as far as bias is concerned since i've got the smaller Brembo fronts. I might as well use the Carrera calipers since i've got them. Only thing I like about the VCI rears right now is the pads are surprisingly a bit cheaper!

Thanks!

JD,

Nice idea with the socket and M8 nut-bolt idea. I bet it's a snap for you to R&R the bolts with a ratcheting 13mm wrench?

Tony,

Keep in mind also if you go the Timmons/Slider 79SC route, that the use of the stock front 993 rotors requires a suitable wheel (my 951 16x7 wouldn't clear, but Slider thought the 951 16x8 might- your 17's shouldn't be a problem) to clear the calipers and you also need to ensure you've got enough negative camber & fender clearance. The Timmons machined hub setup pushes the wheel outboard a bit further.

[KTL]

Originally Posted by Maxhouse97

Stupid question – can you move stock Carrera 3.2 fronts (calipers and rotors) to the rear? Would this help the bias problem with 993 fronts?

993 front and rear are good bias as Bill mentioned. 993 front w/Carrera front at rear is a no-no, as it's too rear biased.


That being said, Bill V I am starting to like your option more and more. 993 front rotors w/ 993 front rotors and 930 rear rotors w/ 965 rear calipers. All OEM, and only have to modify mounts for the 965 rears (adapter for 993 front calipers). Now I just have to find 965 rear calipers for cheap – would you stay away from remanufactured ones (Cardone, Bendix)? I used them on the front of my Carrera and they were the same bodies as my stock ones – right down to the ATE stamp. Could save lots of money this way.

You have to be certain they can give you the 965 rear, since they're rather rare. I'd bet they wouldn't know the difference between a 993 and a 965. Other than that, I wouldn't worry about getting reman.

..

[Maxhouse97]

Yeah just checked with advanced – they had two different calipers for a 1993 911 – one for the C2 and one for the Turbo. The Turbo one was about $80 more – with no core to swap it would be about $220 each. I figure I could always return them… Sure beats $800 new.