I'm pretty certain I have a leaking brake booster.

Here's how it was diagnosed;
- engine idling
- pump brakes up and hold the pedal
- engine idle is low and rough
- disconnect booster line, plug manifold
- engine idling
- pump brakes up and hold the pedal
- engine idle is unchanged

The line to the booster passed a visual inspection.

So, now I want to know what sort of work I'm looking at to have the booster replaced with a fresh unit.

Anybody done this before?

Interested in this too.

Stupid local Mitsubishi dealer overfilled mine a few weeks ago at a service and it leaked down and ripped all the black paint off the brake booster.

Idiots.

Interested in this too.

Stupid local Mitsubishi dealer overfilled mine a few weeks ago at a service and it leaked down and ripped all the black paint off the brake booster.

Idiots.

Flyboy, just curious did they happen to put in new brake pads at the same time?

Why I ask is that apparently when a vehicle has worn brake pads and the caliper piston is further out (to hold the thinner pads) more of the brake fluid is stored at the caliper (thus making the brake fluid level appear lower in the reservoir). If the mechanic topped up the fluid in the reservoir thinking it was low, then compressed the caliper piston back for the new pads, it would force the brake fluid back up into the now freshly topped up reservoir causing it to overflow.

I'm just curious to hear if that was what may have happened.

I'm pretty certain I have a leaking brake booster.

Here's how it was diagnosed;
- engine idling
- pump brakes up and hold the pedal
- engine idle is low and rough
- disconnect booster line, plug manifold
- engine idling
- pump brakes up and hold the pedal
- engine idle is unchanged

The line to the booster passed a visual inspection.

So, now I want to know what sort of work I'm looking at to have the booster replaced with a fresh unit.

Anybody done this before?

Skapper, this video is for a Honda, but I think you'll get the picture...


http://youtu.be/trotrlIG2sk

Flyboy, just curious did they happen to put in new brake pads at the same time?

No, they didn't. Just incompetent, that's all.

Flyboy, can you not just clean it and get a rattle gun to spray it while taping the surrounding areas?

It's almost impossible to remove all the brake fluid, and there's no way to get access to paint it without taking it out.

I agree with your diagnostics - it does seem the Booster may have a leak allowing air into the manifold, causing the rough idle.
Booster failure is very uncommon in my experience, and I think it either will or won't work. Can you feel the booster giving assistance when you brake?

There is a plastic valve on the Booster Body that connects the Vacuum Hose to the Booster.
It is a one way check valve - should allow air from the Booster to be sucked into the engine, but not the other way.
Check that valve is working before ripping the Booster out.

Good Luck

Simple process of removing some fluid prior to pad change prior to pushing back pistons does wonders.......

As for booster, IF you have pumped pedal with motor off to check the system and then you start and do the same it is perfectly normal for a change in idle. if however after some operation this still occurs and is excessive then there may be issues. Remember that any time you use the pedal and activate the booster you are supplying additional unmetered air to motor and you will find with repeated pumps your idle may change and in some cases if excessive pumps are done the idle will then deteriorate

I will second what Mal has said!

"Simple process of removing some fluid prior to pad change prior to pushing back pistons does wonders......."

Mal is 100% correct here. Brake fluid is hygroscopic ie absorbs water. The moisture comes from the air and gets into the brake fluid either at the wheel cylinders or more likely at the master cylinder as it breathes when you apply the brakes. Moisture in the fluid drastically lowers the boiling point of the fluid and when you really stomp on the brakes, the heat buildup can go through to the fluid and start to boil it. Result - brake pedal goes to the floor. Not nice....

Brake fluid is cheap. As Mal says, suck some fluid out of the master cylinder before you replace pads. Also, crack open the bleed nipple on the wheel cylinder and then retract the pads. Then close off the nipple of course. Then refill the whole system with new fluid and you have minimised the risk of brake failure. Another benefit of this is that you minimise the risk of corrosion of the master and wheel cylinders.

Just going back to the original question - from memory (distant) I don't think they were too difficult to do.
Remove the nuts that hold the master cylinder on. Hopefully the pipes will bend a little to be able to get the booster out. I think there are 4 nuts on near the break pedal and the pin in the break pedal.
If you need to remove the master cylinder then you will have to bleed the system.
Good luck.

Okay. So I tested the booster according to the manual today. Seems it may have been a false alarm.

My reaaon for investigating the brakes was the difference in feel, at the pedal, compared to my old Magna. The old Magna (non ABS) had a firm, solid pedal. Not much pedal movement and it had a progressive rate about it. I like that.

The AWD, and my old GTVI, seem to have more pedal movement and without that firmness.

I tried Ziek's Magna and it seems no different to my AWD. So... I'm just not going to mess with anything now.

"Simple process of removing some fluid prior to pad change prior to pushing back pistons does wonders......."


I don't know if this was aimed at the OP or me, but assume it was at me because I had the overflow of brake fluid which had ripped all the paint off my booster.

Like I said in my earlier post, pads weren't (and never have been) changed. Wasn't caused by retracting the pistons. Brakes were just bled IAW the 24 month service interval, and the reservoir was overfilled.

So sounds like it might not be as hard as expected to remove the booster. Might give it a go this weekend.