braking sytem noises

[footman]

Hi all, Just joined up...couldn't sleep because I keep hearing this noise in my head. Have a 2000 NM pajero (196 000km) and it had the same problem years ago and was fixed under a factory recall. At that time I think they (MM) called it the COLLIMATOR. It is part of the ABS system and I think it also gets called an ACCUMULATOR. Is it the cricket ball size pressure vessel near the brake fluid reservoir? It makes a noise akin to throttling a chook repeatedly every time you apply the brakes.

How do you get this thing off? It says it is under high pressure...but does this dissipate when the engine is off?

Many thanks for any help...

[john_char]

I really don't know too much about the MMA accumulator, but most accumulators are the same.

Some of the pressure does dissipate when you turn off, but, all accumulators have a pre-charge. In the accumulator, you will have a separating piston, one side has the hyd oil, or in this case, brake fluid and the other side has the pre-charge air, usually nitrogen. The whole idea, is that when the system is turned on, the oil pressure builds up to equalise the air pressure on the other side of the pistion, this allows a little back-up pressure. So when the system pressure drops, then the accumulator will provide that back-up pressure to equalise the system pressure, also, when the system pressure rises too much, then the accumulator will absorb that surge. So when the abs system needs to apply the brakes, then it will use this accumulator pressure to do this, not your foot pressure, this works the same with the tractioon control.

One of the official definitions is, it eliminate the peaks and troughs of the system pressure.

so, in answer to our question, do not remove the accumulator without dissipating the pre-charge.

The problem you may have is the pre-charge may be low or the separator may be seized.

Hope this helps.

John

[footman]

Thank you John,

Your description of the mechanics/physics of the accumulator was very helpful.

Do you have any tips on how to dissipate the pressure prior to removal or should I fork out some cash and get a brake guy to do it?

Thanks again

[john_char]

Mate,

There is a huge risk when playing with the brake system. I do a lot of stuff myself, but when it comes to the brake system I pucker just changing the pads. If I were you, I really would go to MMA or similar and get it fixed there. For starters, if you do manage to dissipate the accumulator pressure and sort it all out, then how are you going to replenish it? There are no charging valves for the air side of the cylinder. I can think of a few things that you can do, but I really can't post them and keep a clear conscience.

IMHO, leave this one to the experts. Last thing you want is for the accumulator to spring a leak and have no brakes doing 110.

But this is just my advice.

Lets us know what happens.

John

[footman]

Mate,

There is a huge risk when playing with the brake system. I do a lot of stuff myself, but when it comes to the brake system I pucker just changing the pads. If I were you, I really would go to MMA or similar and get it fixed there. For starters, if you do manage to dissipate the accumulator pressure and sort it all out, then how are you going to replenish it? There are no charging valves for the air side of the cylinder. I can think of a few things that you can do, but I really can't post them and keep a clear conscience.

IMHO, leave this one to the experts. Last thing you want is for the accumulator to spring a leak and have no brakes doing 110.

But this is just my advice.

Lets us know what happens.

John

Hi John, Soory took a while to get back with a response.

Purchased a new accumulator from MMA ($332.75) and as per your advice will be getting the MMA boys here at Redcliffe to do the change over. They reckon about 30-45 minutes and are very familiar with this as the accumulator on this model was part of a national recall in its early days.

So I will let you know next week how it went and if their time estimate was on par.

Many thanks for your advice.

Footman

[footman]

braking system noises - follow up

Hi John,

Thanks for the excellent advice. Bought the genuine part as mentioned previously and had it fitted at MMA Dealer at Redcliffe. Thoroughly recommend them, service was great and they told me that my vehicle had missed a couple of 'recall' checks due to a few changes of address etc..

Anyway it took them 30 minutes a bit of DOT4 to fill her up and of I went only $83.00 lighter.

Very happy not to have the choking duck in my brake system.

Oh well, off to Fraser Island for a couple of weeks......might have to do a spot of fishing and sleeping and imbibimg of the Bundy!!

Again, many thanks.

[john_char]

No worries mate. Good to see you got it all done and sefely.

Take care

John