1996 xj brake problems.... master cylnder or brake booster

[dragon0310]

I have a 96 xj 4.0

I have replaced everything except the master cylinder and the brake power boost. If i pump the brakes with the car off it builds up complete pressure within 3 or 4 pumps, if i keep pressure on the pedal and turn the car on it drops staright to the floor. then it never buils up complete pressure again. There is fluid leaking form the area of the master cylnder, power boost area.. but i dont know wich one needs to be replaced or if bolth do... i appreciate all the help i can get.... Thank you

[XgeekstarX]

replace the master/booster as an assembly and it makes life easier

[motroutmo]

You will not see fluid leaking from a bad power booster. Start with a new Master Cylinder. Replacing the Booster is a pain and they are a little pricy for what they are.

Good Luck !

[Matthew Currie]

Master cylinder for sure, but be prepared for the possibility fluid in the booster will damage it as well. I'd try just the MC first, but don't be surprised if the booster dies too.

Just as a general rule, a bad booster will cause a hard brake pedal and ineffective braking, but if the pedal sinks it's the master cylinder.

[dragon0310]

Thank you for the help everyone.... will have to do it over the weekend

[Shadetree]

I have a similar problem on my 88 but I'm not losing any fluid. Can it still be the MC?

[Matthew Currie]

I have a similar problem on my 88 but I'm not losing any fluid. Can it still be the MC?Yes, it's a common way for a master cylinder to fail. If the seal isn't worn out, it will not leak fluid out, but it will still allow fluid to leak past the piston cups, allowing the pedal to drop.

[Jeepm@n]

Be aware that a 95-96 Booster and master cylinder are the only ones that work on a 96. It is sought after due to being an upgrade for 87-94 XJ's with the single diaphram style booster.