Spongy brakes after upgrade

[Spool'n Spyder]

I have a 96 Spyder with the rear drum brakes. I swapped the rear drum for rear disc with stock lines. Everything was fine. Then I swapped the front single piston to 91 Dodge Stealth dual piston and stock lines. Now I have spongy brakes. I was told that I needed to upgrade my master cylinder for a true 4 wheel disc vehicle, so I swapped in a 97 gsx master and still have spongy brakes. I have bled the brakes with the one man bleeding system (bottle with a hose) from Advanced. I have searched every where and tried all the answers everyone else came up with. What else could it be?

Thanks, Nathan

 

[sjgYFZ200]

Eh, I'm not a big fan of those one man bleeders. Although it's probably not your problem, you might want to do it again the old school way

 

[1Gtuner1G]

You are using DOT 3 brake fluid correct?

 

[jasoncitrano]

I agree, not sure if I trust the "one man bleeders" get a wrench and do the old fashioned 1, 2, 3, PRESS and HOLD! always got my brakes rock hard! if thats your problem...Also check for leaks somewhere, check the brake proportioning valve also

 

[oldman]

Maybe those stock lines you swaped in are expanding under pressure. The calipers could be in question as well.

 

[RamenPride]

probably still have air in the lines, not sure how good those one-man bleeders work. bleed them again using a mity-vac or speed bleeders if you're going to do it by yourself, or grab a friend and bleed it the traditional way

 

[nine5raptor]

The air in the line, as stated above, is the most likely culprit. Rebleed to fix.

The other option is: Does the sponginess start after braking for a bit? If so, replace all of the brake fluid. It is VERY hygroscopic and when the brake fluid heats up, the water can boil out of it. The steam will act like a non-linear spring in the brake line and create the sprongy feel.

...I think I am going to use the word 'sponginess' more often...

 

[Spool'n Spyder]

I am using DOT 4 brake fluid. The calipers seem to be working fine (they grab when I push the brake and release when I let off the brake). I cant find any leaks anywhere. I am one who likes to do my own work but my weird hours and not having someone around to help has lead me to the shop. I have an appointment at Midas in the morning to see if they can bleed them out. I hope that works, cause it sux to have an awesome upgrade and have worse brakes than when I started.