For those of you that upgraded their brakes to a 6 pot front and 4 pot rear setup or larger, did you need to upgrade the master cylinder? For those in the know, please chime in, as I'm having a problem with my setup. I've bled them several times but they are still "spongy" and do not grab as they should. What other problems can there be, besides air in the system? Thanks in advance for your help..

 

Pedal feel will not be where it use to be. Should not be spongy but will go closer to the floor with the 6 pot front and 4 rear

 

I agree as you have to move more oil when you have pistons with a larger area than the OEM set up.I think a larger master cylinder could overcome that little problem.
I have always thought the SRT has spongier brakes than the NA and I think the larger pistons are the cause of this. The longer travel makes it feel spongy.

 

Thanks for the info guys! Has anyone replaced their master cylinder? And if so, would one from an SLK55 work? How difficult is the task?

 

Subscribed.

 

I agree with 180 about the difference between the two cars brakes. The pedal feels more firm on my NA compared to my SRT. I have had the brakes bled twice on the SRT and finally decided that's just the way it is. I don't drive it very much so it always takes a stop or two to get used to it. It will definitely stop however. Drove it really hard in some twisties this summer and never experienced any fade or low pedal.

 

After market braided lines got rid of my spongy brakes after my conversion. I used the stock master cylinder with my conversion.

 

i do have the aftermarket braided lines. They were installed before the big brake upgrade. First step will be to see if there is air in the system. As stated, I've bled the system a couple of times with no success. I'm gonna take it to a professional this time and see what they say. I'll keep you guys posted....

 

Are you using the old buddy system to bleed the brakes or some sort of vacuum assist system? I had better results using the buddy system.

 

I had best results with speed-bleeders.

 

Both times buddy system. The next time will be taking it to a professional to have them take a look. How hard would it be to upgrade the master cylinder? I was thinking looking into the unit from an SL55.

 

The OEM master cylinder was fine when I did mine years ago.

 

Try bleeding your brakes when it's as cold as you can stand it and still do the job. It will feel better in the summer. Still not as crisp as the NA but much better.

 

Thanks, will try that at the beginning of the new year. Will probably need to get new rotors as well as I've noticed mine are wavy and there's a vibration when I brake from a speed of 50+ mph.

 

Brembo brakes here. There is no pedal resistance until I am down 20%, then they work fine. Bled last week, not sure if it helped. Glad I saw this thread so I don't keep chasing the issue

 

A bit late with this question but what is the reasoning in the above statement.

 

As a guess, in a closed system, cold fluid would take less room than warm. So when it warmed, it would create extra pressure in the brake lines.

 

It is not a closed system, the lines are open at the reservoir. So any excess fluid due to expansion would return to the reservoir.
The lines are open so that the system can make up any losses of fluid, only when the master cylinder pistons move and seal the openings in the reservoir can it be called a closed system. One piston actually moves before the other in our system and many others because of a spring between them.

 

Sir, you are correct. Maybe the better feel was just due to the actual bleeding process getting all the air out! It sounded good in theory but in fact as usual you don't miss a trick. Glad you're on here.