G'day folks, I am getting an occasional (though increasingly frequent) 'brake pad' noise from one or more of the rear brakes on my NHW11. Initially it would only manifest for half a minute or so per trip (and would disappear after some braking) but it is now more or less constant. It is a light 'rubbing' noise which you would expect from worn brake pads. I inspected the brake pads and they are not worn down at all, and nor is the disc surface oxidised or otherwise weird looking. I think then that the brake cylinder is perhaps 'sticking' and not retracting completely when it should, therefore applying a very light braking pressure. I guess this means I should replace the brake fluid, but I have two questions: 1) Does this diagnosis sound correct for what I have described? 2) Can anyone direct me to some pointers or tips on doing a brake fluid change on the NHW11? I can't seem to access the 'prius technical stuff' yahoo group. Thanks and kindest regards, Jeremy
I followed your first two paragraphs with no problem, and then you lost me. What were the steps between 'cylinder perhaps sticking' and 'should replace the brake fluid'? One thing I would try before anything else is just to find a nice open stretch of street, build up some momentum, shift to neutral, and firmly brake to a stop. Repeat a few times. This is a thing most Priuses need from time to time, simply because the regenerative braking means that the friction brakes don't usually get used enough to stay clean. Shifting to neutral takes the regenerative system out of the picture, so that you can firmly apply the real brakes. Often that will quiet any strange noises you've been getting from the brakes. If that doesn't, I would next take the brake drums off and inspect the whole mechanism at the wheel hub. Do the joints in the parking brake linkage move freely? How about the threads and ratchet pawl on the adjuster? How are the springs? A little fresh brake grease on the contact points where the shoes touch the backing plate? With the shoes removed, do the wheel cylinder pistons move smoothly? (Generally you can push them smoothly - push one inward, the other moves out and vice versa - don't push so far you pop one out. You could back off the adjuster a couple of notches, and then readjust once you've reassembled. Perhaps you will find something mechanically binding. Could be the exposed linkage, could be the cylinder pistons. If it's the pistons, changing the brake fluid won't fix it; replacing or rebuilding the cylinder will. The only way the brake fluid could contribute would be if it is very old and has absorbed a lot of water, it could corrode the cylinders/pistons to the point where they bind. The only way changing the fluid can help that is if you change it before that happens. Otherwise the damage is done and needs repair. Anyway, my bet is that either your problem will be resolved with a few firm stops in neutral, or you'll eaily fix it by attending to the mechanical linkage and springs. -Chap
Hey Chap Thanks for the reply. OK, it was a fairly large jump to make - I am guessing that the cylinders (the displacement of which would push the pads/calipers closed) had somehow become stuck in the extended position, and wasn't returning to its normal position, therefore the brakes were being ever so gently applied all the time. I guessed that the cause of the stickiness was old fluid and/or sediment buildup, or something. I don't know if this is a reasonable theory. I had forgotten the tip about putting in neutral and braking hard. I will try that. When I inspected the discs I did note that they were very clean and shiny though. Thanks! Jeremy
If it comes from the front (which is more likely) or if your brake disc is totally different looking in the inside: Problem is way more likely caliber sliding pins or even brake pads themselves jamming. Just disassemble, clean, inspect, and lubricate stuff CORRECTLY. If it comes from the back: It’s almost impossible that its brake cylinder fault unless it leaks which is very easy to tell when drum is removed. Just disassemble, clean, inspect, and lubricate stuff CORRECTLY. Drum brakes can be hard to assembly. Changing brake fluid is good idea if it hasn’t been changed for the long time but it’s mostly just to prevent brake fading and corrosion and normally doesn’t fix pre-existing problems.
