12" Rear Disc Brake Mod

not everyone get the brake upgrade for performance. i'm sure some, if not half the buyers will do it for show.

until i find a way to adjust the proportioning valve, i guess i'll be set with the brakes i have now.
i still keep meaning to measure the actual stopping distance with my current setup.

I'm also glad they're available. If I ever find an adjustable proportioning valve that's easy to install, I might look into these brakes.

Another (easy) option for increasing rear braking power is to upgrade to a higher friction pad compound. The pads for the rear are smaller, so this offsets the cost of the more expensive compound. Once the pads are heated up, you'll get a little more performance out of the same rear rotors and calipers.

Being that the rotors are solid in rear, I don't think they handle heat very well. To see how fast they go into fade, try engaging the E-brake when at high speed. You'll notice from 75 mph they will slow you down as they heat up, but after 4-5 attempts, they're totally useless. This is why I'd be interested in a vented rotor of the same diameter for the rear. No increased stopping power, but you get longer stopping power.

Matthew, there are some bolt on slotted/drilled options for the rear:

EBC

ATE

I predict these brakes will lead to a proportioning valve solution. Look at how far our knowledge had come since we started out on regalgs.org. There was a time when we weren't sure the SLP headers would work, we didn't know about sway bars, we didn't know about the f-body brakes let alone the CTS-V brakes.

Quote :

We've never been disappointed by Porsche brakes, and the Panamera lineup continues the impressive trend. The Panamera S and 4S both wear massive vented and grooved 14.2-inch rotors (1.42 inches thick) with six-piston aluminum monoblock calipers up front. The rears are 13.0-inch (1.10 inches thick) in diameter wearing four-piston calipers. The Panamera Turbo bumps up to vented and grooved 15.4-inch rotors (1.50 inches thick) with six-piston aluminum monoblock calipers up front. The rears are 13.8-inch (1.10 inches thick) in diameter wearing four-piston calipers.

Link

Just when I thought a 14" rotor in front and 12" in back was overkill . . . but that Pan Amer Turbo weighs 4,344 lbs!

The larger rear brakes on the turbo could be for show - but I'm thinking they're functional, this being a Porsche and all.

I think they are somewhat for show on the Panamera, but for the 911 and Carrera GT, all the weight is in back, so bigger rear brakes can really be of use on most Porsches.

But brake technology is one of the areas where most car makers really do more show than go. This is because brake components are one of the more visible systems on a car. You'll see stock Brembo or Wilwood "big brake" systems on Vettes, V Cadis, and SRT vehicles, as well as all the exotics. Most consumers feel these systems (which add thousands to the price and extra unspring mass) will stop the car faster, but actually they don't. Most big brake kits don't add any additional friction. What they do is manage heat very well, extend pad life, and they look cool. They are needed sometimes for track events, but not for daily driving, even serious driving. There is the option for larger rotors, but you can do that with any old floating piston caliper (like ours). Manufacturers put these big 4 or 6-piston brake calipers on their sports cars A) to look good because buyers will pay for it, or B) because they think their buyers will be doing club track events. Hmmm... I think I know the answer.

Another thing that is mostly for show are drilled rotors. Read the Vette forums and you'll see a lot of track racers abandon their drilled rotors for solid or slotted because the OEM ones will crack or warp. General Motors puts them on anyway, because people have the opinion that drilled rotors cool better, because they've seen some very good rotors out there with holes in them.

There is a way to use big rear brakes safely and effectively, though. The Pontiac G8 GT has big 12.75" rear discs, and only 12.64" on front. The car has phenomenal stopping ability. I think what Pontiac did here is really examine the car's performance in way more detail than you see on most sedans, especially GM sedans. They probably found a way to proportion the pressure just right for this set up and still be safe. There are ways to proportion a "kneepoint" curve so that the rears start off with more pressure, then receive less as you shift weight more to the front of the car. One way is to use a rear height sensor (like used for our ELC suspension) to moderate the rear proportion. Stop-Tech talks about it in this paper: http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml

I think there may be some substance to the idea that Porsche-style big rear brakes may not be a good idea on anything but rear engined cars. Here's a chart showing Brembo and StopTech big brake mods to an Audi S4:



Note the "Big Red" conversion (stock brakes from a 911 turbo) is a popular bolt-on upgrade for the S4, simply because they fit. But it's not actually a good idea, as the car becomes unbalanced, causing the rear to slide out when braking in a turn.

Interesting, to the left on the graph are two similar Brembo (F50) front big brake kits. Both kits use the exact same calipers and pads, but in this case using smaller rotors caused an improvement in stopping distance.

It's interesting, but aren't they trying to move product?

Sure they are, but it's also interesting that their entire business is based around upgrading the front wheels only, being extra sure to preserve or improve the factory F/R bias. They could come out with big rear kits and sell them, but they don't. Instead, they do objective testing to show exactly why preserving balance is more important than using the unfounded approach of guessing what should go on the rear based on what a Porsche uses, or whatever other method.

Here's an example of their testing procedure: http://www.zeckhausen.com/Testing_Brakes.htm

StopTech does offer a couple of rear kits for cars with heating issues (like 350Z), but the calipers are not very big, offering the same or less braking force to keep the bias forward oriented. The idea is to use thicker, vented rotors in back, and the calipers have adjustable piston size to custom tune each car's F/R balance.

I think if we could get a vented rotor design for the rear it would help with the warpage issues.
Agree or dis-agree

Here's a few more factoids -

2004 CTS-V

4 piston Brembo calipers front and rear

front rotors - 14"

rear rotors - 14.4"

Link

2009 CTS

front rotors - 12.4"

rear rotors - 12.4"

Link

2009 CTS-V

front rotors - 15"

rear rotors - 14.7"

Weight Distribution, F/R (%): 53/47 (manual); 54/46 (automatic)

Link

Porsche Panamer -

6 piston front calipers, 4 piston rears

front rotors - 14.2"

rear rotors - 13"

Weight Distribution - 52/48

The Porsche Panamer and the 2nd gen CTS-V are the two fastest sedans on the Nurburing. I don't know this for a fact but I strongly suspect that means the big rear brakes are for more than show.

The bottom line is, we won't know until we try. Looking at the above cars, I believe the 12" rear brakes are worth trying if you've got the money and the ability to tune the braking system right.

Quote :

I think if we could get a vented rotor design for the rear it would help with the warpage issues.
Agree or dis-agree

Rick, I have vented and cross drilled Brembo rotors on my rears (same as front) and have have no warping issues at all. Come to think about it, I never had warping issues with the stockers but it wasn"t driven hard until after the mods...

They fit as stock replacements with stock calipers?
I didn't know those were available. You do mean vented and not just cross-drilled?
Do you remember what company you order them from. I can only find fronts not rears.

Supposedly you can do some kind of rear brake upgrade in the grand prixs (very similar to our brakes) that involves something about grand am front brakes. That might be a way to get a vented rear rotor. Not sure what the deal is for a caliper there, if you use grand am front calipers in the back (which is my suspicion) you lose e-brake functionality, not recommended...

Rickw they are stock replacements that work with stock calipers. From Brembo. Cross drilled and vented.

For those of you wanting to do a brake upgrade here is a minor one.


Bonneville GXP brake brakets part # 18026216 Order 2.
and GXP Rear rotors (11.7" compared to stock 11")
and Pads of your choosing.



The rear brakes are the same on a Riviera.

ewolfe0050 wrote:

Rickw they are stock replacements that work with stock calipers. From Brembo. Cross drilled and vented.

It appears, after searching a bunch of Brake sites, that they no longer make the one for the rear.
That's why I asked if you possibly remember what vendor you got them from.

It was a local speed shop here in town called Auto Cre8tions. Unfortunately they are out of business now.

Rick, there are some bolt on slotted/drilled options for the rear:

EBC

ATE

I currently have EBC slotted and dimpled rotors all the way around with about 12,000 miles on them and am beginning to feel the hint of pulsation at high speed braking.
What I would like to find is a true vented disc for the rear, not a flat slab of steel. I think a vented disk will help with the heat warpage issue.
I'm not near replacing these yet, I will remove, clean, check runout, index or shim as necessary to bring them within .003" as I did when installing them new. But again just trying to find a company that makes a true vented rotor for the rears.

I agree, the rear vented discs would be nice. Would need a set of wider calipers, too. I don't know what makes more sense - a great rear system, or replacing the rears with Brembo solids every 25k ($15 per side).

If that's all the Brembo solids cost then that would be cost effective.

after re-reading this thread, I have slotted and drilled rotors on the back not vented. I do not know of any company that sells the "vented" rear brakes for our cars... Have you guys really been having that many warping problems with your rears?

After only 12K miles I'm starting to feel pulsation again but I have yet to measure runout on them yet.
When i do I'll find out if it's the rears, fronts or both.
But one good thing is catching it early. I should be able to index or shim them to bring them to within .003" and get much more life out of them.
When I ran stock type cheap rotors the front and rears would warp.

My OEM rears died at just over 50k miles. The next set lasted a LONG time. Third pair were Brembos, now with 25k miles and slight judder, but I think it's not getting any worse, maybe going away.

EDIT:

Here is a rear big brake kit for 95 Rivieras. Supplied by Precision Brakes Company for HorsePowerFreaks.com:

Rotors: 12.8" dia x .87" thick (wow!), 2-piece w/ alum hats, available in same finishes.
Calipers: 4-piston Wilwoods, probably the same, available in red, maybe other colors.

Kits include necessary brackets and hardware, stainless steel brake lines, and brake pads (likely are Wilwood BP10, a high performance street pad).

Probably not the exact set, but close:



Price: $1,649.34

Order from: HorsePowerFreaks.com

I've read the sets are made to order, so may take a while to get these. Not a bad price for what you get. I would bet lots of money this 'kit' is not designed specifically for Riviera, so it probably not proportioned correctly. Take care - might need some testing/tuning to get things dialed in for safe high speed operation.

More info found here: http://www.stangnet.com/mustang-forums/576316-precision-brakes-company.html

Has anyone done this? Can you put a set of front ones on the back, or at least put some on that don't have a completely retarded design? Forgive me if this is a stupid question, I'm not very familiar with brakes.