About two years ago I had a brake pedal that was soft and wouldn’t stop vehicle if I put it in D at start up. Giving it about 30 seconds and worked proper pedal was soft until pressure built up. Never would have issues throughout the day.
I replaced the accumulator and all was grand. Now the same issue is back again. I’m assuming it’s an accumulator fault again, BUT could it be something else? The accumulator would be the cheap and first fix I suppose?
Thoughts……
Soft pedal is usually air in the system, a lack of fluid pressure gives a rock hard pedal with very little stopping power. Once up to pressure, air in the system will cause a very slight delay between you hitting the pedal and the brakes coming on (as you are having to compress the air before anything moves). It is so slight that you tend to not notice it until the bleed the brakes and it goes away. Bleeding the brakes, following the steps in RAVE to the letter, would be the first call and even cheaper than a new accumulator.
TY… Just to confirm, if I start the vehicle the pedal is soft until I “pump” the brake a few times and it then feels normal. In addition if I start it in the morning and let it sit at idle for 30 seconds the brake pedal will also operate “normally” ….. are both of these symptoms of air in system?
And on the subject, what would have caused air to get in the system? She’s never been low on brake fluid….
Accumulators are just cannisters with nitrogen on one side and brake fluid on another with a butyl seal in between the two.
Over time the nitrogen leaks out and the pump has to run more often to top up the pressure, a sure fire sign you have a dead accumulator is the pump has to run every time you press the pedal.
Having the pedal sink to the floor upon cold start is another sign it is past it.
Mine has started doing it.
Thanks StrangeRover…..
Took it out today and every time I press the pedal the accumulator pump motor kicks on for 3 seconds or so.
Ordering a new accumulator now and will advise….
Other vehicles don't have a powered system though so air in the hydraulics has a different affect. Until pressure has built up you should have a very hard pedal that gives very little braking effort.
@Gilbertd, are you suggesting with the symptoms that I mentioned in post #5 that my issue could still be air in the system? Asking cos I’m genuinely not sure. As mentioned, the air compressor for accumulator kicks on every time I press the brake pedal.
Well, I am not sure because if you say in #3 pedal is "soft" at first start I would be tempted to consider an "air in the system" problem (like I have, I have read and re-read the RAVE procedure but I can't get it right, alone is nearly impossible it seems), but the pump running at each press it could be a separate problem.
As StrangeRover has said, it is an expected matter if life of the canister goes out.
You should make sure as Richard said, you got no air in the system at all.
Air in the brake system can come from the ... air :-) but it could be also not just air: brake fluid is hygroscopic and it does attract moisture and water molecules in the air (there is a membrane in the reservoir to equalize pressure), water/moisture content which besides lowering boiling point of the fluid and diminish brake performance, plays havoc with caliper pistons and seals "from inside". Considering caliper pistons have already a rough time from crud "from the outside" which can get past the caliper seals, once they get rusted you can expect more trouble, and more expensive as well :-)
Pump running on every pedal press could point to a failing accumulator but equally can be caused by air in the system. It stores a specific amount of fluid under pressure and with a failing accumulator, that quantity is lower so is used up sooner so needs to be replenished. However, if there is air in the system, more fluid is needed when you press the brake pedal as some of it is used in compressing the air before the remainder is used to operate the brakes.
Ordinarily, when you press the brake pedal all you are doing is opening a valve to allow some of the high pressure fluid through to operate the brakes. As a safety feature, there is also a conventional hydraulic circuit which is what you are using when you have no stored pressure. That will only allow the pedal to go to the floor if it has air in it, otherwise it will feel like a conventional brake pedal where the servo isn't working. All I know is from experience when my pump failed. That meant there was no pressure stored at all so I was relying on the conventional circuit, the pedal was rock hard and I needed both feet on it to get the car to stop.
Great link for brake bleed….