Help with brake booster - intermittent hissing noise - is this normal? (1 Viewer)

[Jaysway10]

Long time lurker, finally bought my first Landcruiser a few months ago; "Dirt tub" a river rock green 100 with 275000 on the clock I am now slowly trying to work through all the little quirks. Cosmetically she has a few minor issues that I am working on but mechanically she seems to be in great shape, she has the factory rear locker, and almost zero rust. My concern now though is the brakes/booster/master cylinder. Every time I start the truck what I assume is the brake booster makes a hissing (pumping?) sort of noise for about 20 seconds, but usually goes away. The noise will happen intermittently as I drive as well but I can usually get it to stop if I pump the brakes a little. Also, when I make a stop, the first press of the peddle is pretty soft, but if I pump the brake again the peddle becomes much firmer and more responsive. I understand from my searching that the brake system is subject to random failure, something I would like to avoid, so I wanted to get MUD's advice.

I've googled and searched on here without much luck but I want to know if the sound is normal or if I'm quickly headed toward needing to replace the master cylinder. I am aware there is a relatively inexpensive repair kit (about $70 from what I can find) but not sure if that is worthwhile and if I should just save my time and money and prepare for the cost of the whole brake booster/master cylinder.

As a note, pads look to be in good shape with no visible leaks from the calipers or elsewhere, front or rear.

 

[nckwltn]

It's normal at first start of the day for the brake booster motor to run for 20-30 seconds to build up pressure in accumulator.

a couple of things to perhaps test/try:

With truck off, pump the pedal 20 times, you should notice a significant change in the pedal feel over the presses. This will remove all of the pressure from the accumulator and will also cause the master cylinder reservoir to fill fuller with brake fluid. Check the level, it should be near the "max" line. Then turn the key to the on position (don't start the truck). This should activate the accumulator motor and pressure should start to build. This will also take brake fluid from the reservoir. Time how long the motor runs, shouldn't be more than 30 or 40 seconds.

This will also let you hear the specific sounds that might be made.

The $70 fix replaces the plunger that is depressed when you press the brake pedal. My brake booster was squealing quite loudly and the plunger fix didn't work for me.

The most common failure is the motor itself (used to build pressure in the accumulator), the brushes wear away the copper commutator bars and the motor will no longer turn. If you have the original booster, it's likely that your motor is fairly well worn. This video is from an '03 Montero that uses the same or VERY similar brake booster as the 100s. The video shows the worn commutator bars:

Motors can be sent away to be rebuilt. You'll have to find other posts where rebuilders are recommended.

You might also want to check out this long thread with quite a bit of discussion on the brake booster: Master Cylinder Rebuild - DIY - https://forum.ih8mud.com/threads/master-cylinder-rebuild-diy.406533/