completed fwd to awd conversion, now spongy brakes

[ballen1]

fellas, i just completed my fwd to awd conversion, after completely pulling the complete rearend, and disconnecting the rear brake lines, i now dont have the stopping force i once had before the conversion. i bled all the lines front and rear at the bleed caliper, but it didnt help. I have to pump the brakes at least twice before pressure builds in the lines. when i first apply the brakes the pedal goes all the way to the floor. i have tried everything i know. what else can i do to remedy this problem??, my brakes were fine before i disconnected the rear brake lines.

thanks for your help guys.

billy

 

[92redman]

How did you bleed the rear lines? I found that the best way is with a Mityvac pump with the brake bleeding kit. If do it the old fashioned way, a lot of times air will get sucked back in the lines as the flow of fluid comes to a stop. If you are going to use a partner to press the pedal, you need to close off the bleeder before the fluid stops or it will suck in air(this is why I recommend either a pressure bleeder or vacuum pump).

 

[mavisky]

there's still air in the lines somewhere, it's the only explanation honestly.

 

[ballen1]

i havnt yet used a mighty vac, but i will get one and use it, i'm now at the point i'll try almost anyting.

thanks for the suggestion guys, i appreciate it.

billy

 

[pneumo]

You should also check to make sure the lines aren't twisted.

 

[Sotarts]

Either air is still in the lines (it happens, to many people, all the time) or you've twisted/pinched/broken something, perhaps losing fluid.

 

[turbotsi92]

I would say air in the lines as well, but if you use that bleeder system, and still no brake I would check the master cylinder. If it goes bad, air will leak back through it.

 

[napkinthief]

did you go from drums to rotors in the back, if so...
did you upgrade your master cylinder to make up for the extra braking power needed for rear rotor pistons?

 

[Todd TCE]

By my notes this should be a 1.0" MC.

The other common size is 15/16 and will provide a softer, longer feel.

You might also want to be certain that the parts are securely bolted up, the calipers slide freely, and the pistons of the rear move correctly. Too much movement on the rotor or an excessive amount of pull back on the piston can lead to longer travel of the pedal as well.

 

[Drifte]

also make sure the calipers arent on the wrong side (if thats posible). I did that once on a civic and couldnt figure out why i couldnt get any pedal pressure. sure enough, i had the calipers on backwards.

 

[DiamondStarM]

bleed the brakes with the car turned on, the brake booster will help push the rest of the air out

 

[TSiWarrior]

Car to do a post on the fwd -> awd buildup? My freind is considering doing it and he wants some info.

 

[ChvyKc]

Car to do a post on the fwd -> awd buildup? My freind is considering doing it and he wants some info.

http://www.dsmtuners.com/forums/showthread.php?t=95132

Already been done (I think that it use to have pics with it though before they did the changes to the site.)

 

[EclpzLvr97]

did you go from drums to rotors in the back, if so...
did you upgrade your master cylinder to make up for the extra braking power needed for rear rotor pistons?

Is this true?...because in the several times I've read the write up on a drum-to-rotor conversion, I don't remember ever reading about a need to upgrade your master cylinder....(I think he's got an air pocket causing the problem)

 

[DSM Jeff]

When the lines were disconnected, did the master cylinder drain all the way? Or while bleeding the brakes, did the fluid get too low? Air could be trapped in the master cylinder. I'm guessing the car orginally had disc brakes and not drums, but if it did have drums the master cylinder and proporting valve could be different. Are you losing fluid when you are braking? Possible leak? Lines twisted? Check to be sure brakes are moving freely and are tightened? I would say inspect the master cylinder, bench bleed it and bleed the entire system front and rear.

 

[Defiant]

Build a power bleeder:
http://www.bmw-m.net/TechProc/bleeder.htm