Mushy brake pedal

[vcrpro3]

Just did a disc conversion on my 87 New Yorker. Went from small original front disks to 89 Daytona vented 11 inch disks on front and changed from drums in back to solid rotor discs. I originally had rock hard brake pedal on original s/u but now have pedal that goes to floor with little effort after multiple bleeding at all wheels and at master cyl. Help please

[raccoon]

how about hte proportional valve? did you replace that with the rear disc brake one?

[vcrpro3]

No, did not do that. Got all parts off of an almost identical 88 New Yorker, bought from a friend, that i had done the same conversion on some years back w/o changing the prop. valve on. No probs on that car and it had the same original brake system as this one.

[RoadWarrior222]

I'm thinking it's something to do with drum brake cylinders holding about 1/4 cup or less of fluid, and disk brake ones holding more like half a cup full... so I woulda thought I would have needed a higher volume master cylinder.

[cordes]

If you're not leaking any fluid, I would say that the MC is bad. Just going to the 11' brakes in the front and solid disks in the rear shouldn't necessitate a larger MC to get the car to stop normally. There is the potential for you to use all the travel in a panic stop, but it should stop pretty normally.

[black86glhs]

This happens often after doing a swap. The seals can get turned or get nicked during bleeding. Normally they ride in the same area of the MC bore, until the bleeding procedure. Brian is 98% on his diag of the MC is bad.

[vcrpro3]

Come to think of it (it has been a few years... well over 10... since i changed over the 88 NY'er and the LeBaron to 4 wheel discs), i do remember something about using a minivan MC.

---------- Post added at 10:55 PM ---------- Previous post was at 10:48 PM ----------

The 1987 LeBaron originally had the exact same brake setup (small front disk/drum rear) as this 87 NY'er. The only difference being in the LeBaron, the rear disk is the vented Daytona setup-in the Yorker, it is the solid rotor version...and again it definitely had a minivan MC put in. I did not remember this until i saw all of your replys... i must be getting Al's heimers......

[mark]

I recently did some work on a friends yukon. she said the pedal was soft and mushy.
a front wheel bearing was sloppy. once that was replaced brake firmness came back. her bearing was not letting the rotor square up to the pads so it was like |/| and had a soft and low pedal.

[vcrpro3]

If i bypass going to a minivan mc and go to a mc specified for a full size van or pick-up, how much overkill would that be? bounce off steering wheel or pick teeth out of windshield overkill?

[cordes]

If i bypass going to a minivan mc and go to a mc specified for a full size van or pick-up, how much overkill would that be? bounce off steering wheel or pick teeth out of windshield overkill?

It would be more of a hard to press pedal situation than anything. The big brake cars had a 24mm MC. I don't see a reason to go bigger.

[vcrpro3]

Put minivan mc in,Took NY'er in for some new tires and alignment. While car was in air had mechanic bleed system--lots of air in rear, now firm pedal and stops on a dime!!!

[shackwrrr]

Bigger master cylinder will decrease braking pressure, while increasing braking effort.

[turbovanman²]

If i bypass going to a minivan mc and go to a mc specified for a full size van or pick-up, how much overkill would that be? bounce off steering wheel or pick teeth out of windshield overkill?

Yes, the pedal will be alot harder and take more pressure to stop but when pushed hard, hold on.

Bigger master cylinder will decrease braking pressure, while increasing braking effort.

Depends on the setup,

[shackwrrr]

Yes, the pedal will be alot harder and take more pressure to stop but when pushed hard, hold on.



Depends on the setup,

Depends if Pascal knew what he was talking about

http://www.grc.nasa.gov/WWW/k-12/Win...principle.html

[turbovanman²]

Depends if Pascal knew what he was talking about

http://www.grc.nasa.gov/WWW/k-12/Win...principle.html

Ummmmmm, sure.

[shackwrrr]

Ummmmmm, sure.

What? Dont understand?

[turbovanman²]

What? Dont understand?

LOL, yeah, but its still math,

[shackwrrr]

LOL, yeah, but its still math,

Meh, easy stuff. Just like sprockets and chain, but liquid and pistons.