Faulty Brake Booster??

[romaniac85]

Hi Lads,

Car: 2004 Pajero NP Diesel Manual
The final conclusion of the rear brake issue is upon me.
End result = "Rear brake jamming on and staying because the ABS module is faulty".
Apparently I have the module that includes the master cylinder and other bits n bobs (MR569728). Course I do. Checked the lines, the caliper and rear distribution module (I actually don't have one), all fine.
So, I've read online that a new complete unit is $3275 from MM stealership but second hand parts range from $500-$850.

What to do in this situation?
1) Am I able to replace just the bottom part of the unit - is that even a thing? According to this forum page: https://www2.pajeroclub.com.au/forum...ad.php?t=46516
2) Does anyone rebuild these things? If so, where and how much?
3) Has anyone on here come across this problem and how did y'all fix this issue?

TIA

[rykiel575]

Is it the HBB motor that is shot?
If so all your answers are in that thread.

[romaniac85]

Unsure if it is the motor. How would one go about finding out if the problem lies within the motor?

[benckj]

If the motor is faulty it won’t pump up enough pressure for brakes to operate. There should be a multitude of alarms activated for low pressure warning. This does not seem to be your issue. Accumulators do fail as does the pump itself. Parts can be found off shore but best to find issue first. Have you scanned computer?

[rykiel575]

If your issue is rear brake jamming on i doubt it is the motor.
Usuallly the symptoms of motor failing is loss of brake pressure.

There is a test you can do but it wears out the motor faster. It is basically pumping pedal multiple times (about 40 times) with engine off to loose all brake pressure and then turn on acc and count how many secs for hbb to pressurize. Full procedure is on here somewhere

[romaniac85]

Thank you for the reply.
I definitely have all the brake pressure and no warning lights on the dash. My symptoms aren’t like some of the stories I’m reading on the forum.
I’ve had everything replaced at the wheel. The line from the calliper to the mid section of the car is running smooth but the clutch “specialist” didn’t test it from the ABS unit to the mid section.
What else could cause this in your opinion?

[rykiel575]

So the mechanical aspect is okay?

im not sure if you have disks or drums but if it were disks, it isnt a sticking caliper, or the bolt hasnt seized up, etc?

Do you have any check engine lights, abs lights, traction control, or stability lights on the dash?

[romaniac85]

Heya Rykiel,

I have no messages or codes come up on the dash. The brakes feel as if nothing has been zip tied at the back. The mechanic(s) have checked the calliper (replaced), disks (replaced), bearing (replaced), pads (replaced). The line going from the calliper to the MIDDLE of the undercarriage is performing normally but the mechanic didn’t check the line from the ABS UNIT to the middle (if that makes sense). I don’t have a distribution module apparently. Is there anything I can check?