Bad new Master cylinder?

I put on a new Master cylinder and a ford 8.8 disk rear. Currently running a gutted proportioning valve which I will address later. I bleed them 3 times with a quart of fluid. 35" tires on alloy wheels. During normal breaking it seems just ok. But that last bit of total stopping or panic stopping the pedal is squishy and goes way down. It wont jerk your head if you really mash it going from 5 to zero. It's a 1998 so it should be the better xj Master cylinder and booster and is non ABS. You can kinda of hear a squishy noise in the master cylinder as the pedal goes down and it is never solid feeling. Do you think I got a bad rebuilt master cylinder? I know I should not have great breaks with this setup but I have all new pads,hoses and master cylinder all bleed well but they just feel like crap. The booster holds vac. This is the first time out with this setup and I can't judge how it should feel.

When I had "unanswerable to all local shops" questions with my braking I called Van at VancoPBS. He knew exactly what was wrong right away, was very helpful. Give him a try

323 563 1588
He is also on JU as Vanco or VancoPBS

Did the master cylinder get bench bled? If not, there's a part of your problem. A good way to tell is to completely block off the outlet ports of the m/c and check the pedal with motor off. Should be hard as a rock and high pedal. Then you can move plugs around to various downstream locations in the sys to see where the sponginess is coming from.

Switching to rear discs calls for a master cylinder with a larger bore, and one preferably intended for 4-wheel discs. The stock XJ cylinder is 15/16, or 1", depending on year. You probably need a 1.125 bore cylinder. Since it's a '98, you'll need a MC that will fit your double diaphragm booster. I beleive, but am not positive, that a '99 Dodge Durango will work. I've seen more than one wright-up that states "they" installed one on a 99 TJ, and a 98 ZJ. Worth a look. If you go that direction, let us know how it works.
http://napaonline.com/masterpages/N...967&Description=Brake+Master+Cylinder+-+Remfd

If you can make it to Loveland, I will vacuum bleed those brakes for you. This is a common problem. Getting a good bleed is easy with the electric bleeder. That is most likely your problem. I have fixed multiple rigs with similar problems.

I was specifically told by advanced auto parts not to bench bleed a rebuilt master cylinder. So I bench bled it any way and they say that is my problem. So I asked for a "new" master cylinder and they can't get one. So I got a refund today and now I have my freshly built rig with no master cylinder. I just did a search and ran into my post first but will go back and research an up-grade like the Durango. Thanks and let me know if anybody knows of a good upgrade for the newer XJ's. I have so much invested I'll drop the cash for a real upgrade or will buy a brand new MC.

What would you charge to vacuum bleed my brakes I am having the same problem. I just got done convering my front brakes to Wj brake system. I also have a 8.8 with drum brakes.

Thanks