poor pedal after pad swap?

[keithq69]

I have a 69 Camaro that I just bought recently.
The car has the DSE booster and master setup on it, about 2 years old.
The front brakes are 13" C4 and the rear are 11" Ford brakes on a 9".
The brake effort was good and the pedal feel was decent. After the last lapping day I needed new pads.
I bought a cheap set off a customer to get me through the rest of the season since I'm planning on C6 Z06 brakes over the winter.
After the new brakes were installed the pedal went to the floor. The brake feel us terrible. Although the stopping power is decent the pedal is so soft now.
I had my mechanic bleed the brakes with his vacuum system to make sure I had no air in the system, he also upgraded to Dot 4 fluid.
The pedal is no better now, is it possible that the master cylinder is damaged? Could pushing the pistons back have caused problems with something?
Any suggestions would be appreciated.

Keith.

[Apogee]

Certainly pad compounds can and will slightly impact pedal feel, but not to the extent that you're describing. My guess is that your MC is taking a dive and bypassing fluid (does your pedal slowly sink with steady pressure?) or yous still have air in the system. I know you said it's been bleed, but 9 times out of 10 in situations like this, it's air in the system. Since nothing has changed hydraulically, the feel should be more or less the same as before. Also, while higher temp rated brake fluid is a good thing in general, it too should have very little effect on pedal feel or travel.

Tobin
KORE3

[BonzoHansen]

Could pushing the pistons back have caused problems with something? I have seen that cause issues. I always open my bleeders before I push back pistons.

[keithq69]

Thanks for the replies.
If I stop at a light, with the pedal pressed down until its firm it will go soft and drop after 20 seconds or do.
The initial travel of the pedal is too far also.
The master that is on there now is apparently the late 80's to early 90's S10 with a 1" bore. It's a cast iron master. I called DSE today to confirm what master it is.
Would going up in size on the master help with the pedal travel?
I know the larger master will increase pedal effort but it seems to me that I have too much assist already.

[TheJDMan]

I'm running C6 Z06 brakes with a manual 7/8" Wilwood MC. I'm using Hawk Ceramic pads and even with no power assist the brakes are outstanding.

[kawaden]

what are the discs like? did you machine them? if they are grooved or lipped it will take the new pads some time to wear into the old disc and the pedal will feel bad until they do.

[keithq69]

The rotors are good.
I don't really understand how the rotor and bedding of the pads can affect the pedal feel. I know they will affect how the brakes feel in their stopping but once the pad is up against the rotor hard you have hydraulic pressure.
You can't compress the fluid and that's why you get a hard pedal.
If the brakes weren't stoping then I would be looking at the pads and rotors. I can get them to lock if I push hard.
The pedal just feels mushy.

[JD'sTT55]

I'm with Tobin on thinking its either air trapped in the system somewhere or the master cylinder itself. As you described the pedal dropping after holding steady pressure after a stop sounds like the master cylinder is leaking or bypassing internally and needs replaced. Although replacing the pads shouldn't have caused the issue I have had issues after forcing fluid back into the master cylinder and now attach a hose to the bleeder screw and loosen it to allow the brake fluid to run out as I press the pistons back in their bores. I do usually have to bleed a little air out when done but that's better and easier than replacing the master cylinder.