Review of StopTech Brakes, Carbotech Bobcat Pads, and Porterfield R4-S Pads

[jeff97vr4]

The StopTech 332mm brake kit is installed and working well. However there were several challenges along the way. After driving the car a bit to make sure the new engine and the brakes were working properly, I tried to start the bedding process. There was a very strong shudder from the brakes that could be felt in the brake pedal, the steering wheel, and the seat. The shudder went away as the pedal pressure was reduced and the car would stop normally. I tried this a few more times with the same severe shudder with high brake pressure that stopped as the pressure was reduced.

I removed and examined all of the brake parts; rotors, calipers, adapters, and pads. I didn’t see anything that looked unusual are that was wearing or hitting another part. The factory calipers, rotors, and Porterfield pads were re-installed to ensure that something else wasn’t the cause of the problem. The brakes worked normally with the factory parts. I called StopTech and talked to Matt Weiss about the problem. He suggested measuring the runout on the rotors, which I did. The runout was within the 0.004” tolerance he specified. Also, I assured him that the surface of the rotors did not have excessive pad material transfer from and incorrect bedding.

The pad extended about 0.2” past the OD of the rotor. The step in the pad from the rotor was clearly identified form the wear pattern. I discussed this with Matt and he felt it was more than he had ever seen. I speculated that the step may be responsible for the shuddering. The radial runout of the rotors was about 0.012” and the step would have tried to interfere with the runout during higher brake pressures. He suggested grinding some of the material to remove the step and try the brakes again. I did that and the shudder was considerably reduced. In addition, there were two different pad shapes, two had no cutout at the center outside diameter and the other two had a cutout. I have attached pictures that show the two differences with a scale to show the extra material present.

To test my theory that the pads were causing the shudder in the brakes, I ordered a set of Porterfield R4-S pads and installed them. The brakes are now working very well without any shuddering or vibration. I’m not sure why I choose the Bobcat pads since I was using R4-S pads on the front and rear and would still have the R4-S on the rear. I was not thinking about the balance of the brakes. StopTech big brake kits are designed to be used with the stock rear brakes and using different pad material would certainly change the balance. Whether the difference is significant could only be discovered by trail and error. Philip highly recommended the Bobcat pads and it seemed like a good decision at the time. I was very happy with the performance of the R4-S pads and still am. I should have stayed with what was working very well.

I wrote to Philip at SuperCar-Engineering about the Bobcat pads. He said I probably didn’t complete the bedding process and that the shuddering would go away if I continued to drive the car. The violence of the shuddering was such that I didn’t want to continue experimenting, especially since the R4-S pads worked correctly from the first test. I also asked if the pads could be returned and was politely told that since I had already installed them they couldn’t be returned for full credit, but he was willing to offer a 50% credit. I didn’t care enough to send them back. I would not recommend the Carbotech Bobcat pads under any circumstance. I think their quality control is really lacking to allow two different pad shapes to be sent in the same box. While I can’t prove the extra pad material caused the shuddering, it seems to be the cause from the limited testing I got to do.

On top of all this, and probably because of this, I discovered that the pistons in the calipers were reversed. The small piston that should have been in the leading position was actually the trailing one. If I hadn’t been looking at the calipers so critically I would not have been aware of the incorrect assembly. I did remember that during the initial inspection of the brake kit that the calipers had been mislabeled. I confirmed this with Bob at StopTech and he guessed that the crossover tube had been installed on the wrong end of the calipers. He was genuinely sorry and wanted to fix the problem. He did ask if I was willing to remove and correctly install the parts without shipping them back to StopTech. He described what needed to be done. I was happy that he made the offer because it was faster to make the correction in my garage rather than shipping the parts out.

Philip suggested that the reversed pistons might have been the reason for the shudder with the Bobcat pads and I should try them with the pistons in the correct locations. Since the R4-S pads worked with the pistons in both locations, I didn’t see any reason to continue spending time on the Bobcat pads.

I now have about 3000 miles on the brakes and am very pleased with the performance. The cost of the kit was worth the improved performance and looks. The brakes do not get as hot now as the stock size with R4-S pads did. There is less brake dust on the front wheels. The braking is very linear from the initial bite to activating the ABS. With the stock sized rotors, I couldn’t activate the ABS over about 35 mph. Now the ABS can be activated at highway speeds with lower brake temperatures than before.

Jeff

[pyun]

these are the carbotech bobcats brake pads specifically created for the stop tech kits though right? i picked up a set of carbotech bobcat brake pads for my n/a (non-stop tech kit) so i hope they're not as much of a hassle that you experienced

[jeff97vr4]

Originally Posted by upyun

these are the carbotech bobcats brake pads specifically created for the stop tech kits though right? i picked up a set of carbotech bobcat brake pads for my n/a (non-stop tech kit) so i hope they're not as much of a hassle that you experienced

StopTech big brakes use a standard Porsche pad and that is what was delivered. The steel backing plate was the correct size, the pad size was off. I would check the pad visually against the old pads to see that size is correct.

Jeff

[lightweight]

wow nice post....thanks for the info!

[jeff97vr4]

You're welcome

[mikes2nd]

breaking in pads are very important

it sounds like your porters were broken in already.

[jeff97vr4]

Originally Posted by mikes2nd

breaking in pads are very important

it sounds like your porters were broken in already.

Actually "breaking in" is called bedding. The R4-S pads were not bedded in, they were new out of the box. There was no shuddering on the first firm stop to check the installation before bedding could start.

The Bobcat pads completely unacceptable - it wasn't the installation or the StopTech brakes.

Jeff

[krisx5]

Did you just have oem stock rotors before or did you have drilled or slotted stock size rotors? I'm looking to buy a stoptech kit with stock sized slotted rotors which comes with ss brakelines, axxis ultimate pads, and fluid. So, do would you suggest stoptech to anyone?

[barf]

Originally Posted by krisx5

So, do would you suggest stoptech to anyone?

I would!
The Stoptech kit is awesome...I am using mine with the Carbotech Panther Plus pads (front) and the Bobcats in the rear. My brakes are definitely powerful, smooth and predictable. Actually I'm expecting the real advantages of this will show up when I hit the next track day.

[jeff97vr4]

Originally Posted by krisx5

Did you just have oem stock rotors before or did you have drilled or slotted stock size rotors? I'm looking to buy a stoptech kit with stock sized slotted rotors which comes with ss brakelines, axxis ultimate pads, and fluid. So, do would you suggest stoptech to anyone?

I had Porterfield cryoed and slotted rotors in the stock size. Porterfield R4S pads front and rear. I am not sure which kit you are talking about. In spite of the assembly problem with the StopTech calipers, I am pleased with the improved brake performance with the 332mm X 32mm rotors and calipers. I'd recommend StopTech to anyone.

Jeff