Another Break Question

Just installed SS break line, and replaced the master cylinder as it was bypassing. I get the new lines installed and master cylinder. Bleed the system till there is no air. Now the break petal feels good for the first 2 inches of travel but if you real push fast on the petal after the “good” 2 inches its rock hard and no i'm not bottoming out the petal. Not to mention the breaks don’t work very well anyways. I’ve run a search and couldn’t find anybody with the same problem i’m having. I’ve have an 89’ XJ d30 up front d35 in the rear with factory lsd. Break shoes and pads have a good a mount of meat left on them. Any help would be great.

generally when your break pedal feels hard, that just means the pad is contacting the rotor... maybe your old ones were just really mushy and you didn't notice until the new lines?????

Did the brakes not work well before or after the new master cylinder? Is your vacuum line hooked up to the master cylinder booster? Good vacuum, no leaks? I would check those first. Did you get the right master cylinder, with the right bore size?

the breaks always worked, But with the old master cylinder if i was at a stop some times the petal would go down almost to the floor. This is after ive already been stoped with holding down the break petal.
Everything is connected, good vacum and no leaks. I do have the right master cylinder.
When i say the petal gets hard. Im talking rock hard. The first 2" of good petal feel. feels just like a break petal should. then when you need to give it more brake to slow down faster you get this really hard petal, and you almost have to stand on the petal for the breaks it work any more.

Sounds like a problem with the booster. Does the idle change (get kinda rough) when you stand on the pedal (obviously not moving)? If it does you might have a leak in the diaphragm.........Hans

I know it does not have a leak as i can turn off the car and take out the rod to adjust it from the break booster and you can hear the air getting sucked in.

I can't take it anymore!!!

It's B-R-A-K-E !!!

Haleyes said:

I can't take it anymore!!!

It's B-R-A-K-E !!!

Click to expand...

HA HA (x2)

But really... I know you would hate to think it... but it might be a bad Master Cyl. If ou got it from Auto Zone, Advance, or O'Reily's it could be bad straight out of the box. I recently went through my whole system because I knew i had a leaky Prop Valve. (This was in my CJ). When everything was fnished, my brakes were still crap. A mechanic friend of mine told me that about 1 in 5 of the Mater Cyls. you get at the typical parts stores don't work very well straight out of the box.

Did you bench bleed the master Cyl?
How's your prop valve?

Something else to check... jack up all 4 wheels on stands. Put it in drive to get the wheels spinning at a pretty good speed then hit your brakes. Does either the front or rear not want to stop at all?

I haven't messed with it much on my XJ, but on other rigs, if you have a leak in your front or rear system that is bad enough... or if you screw up while bleeding the brakes, your prop valve will shut off that system. When the prop valve shut off the rear half of the brakes in my CJ, it felt like what you are describing.

Is your dash indicator "brake" light on all the time?

Anyway... just some ideas for you. Maybe one of them might be the issue.

Thanks everyone for the input. And yes I did get the master cylinder at AutoZone. I also did bench bleed it. I don’t have the break light on in the cab. But from what I could read on other threads and what it looks like here it might be the proportioning valve. I’m taking it to a mechanics house today so ill let everyone know what it turns out to be if we find the problem

Well we took the Proportioning valve apart and the whole insdie was corroded to the point hardly any fluid could get to the rear breaks. so we are 99% sure that is the problem. don't know why with the new master cylinder made the petal feel the way it did, but once i put the new valve ill let you guys know.

this info might help

http://www.mpbrakes.com/troubleshooting.htm