Brake Accumulator

[nrp22101]

I need confirmation that my symptoms are brake bomb related.
1. I get a recurring noise from the engine bay near the pentosin reservoir every 7 seconds when stepping on brake. I checked to make sure no air in the system by checking for bubbles in the reservoir when pumping the brake.
2. Brake is soft but no issues with stopping.
3. I know I am missing one of the rubber seals that sandwich the filter (the top one)...not sure if that could cause the repetitive sounds.
4. Groaning when turning steering wheel.

Thanks in advance for ur advice.

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[8eights]

When you slam on the brakes and it stops today, The Accumulator is fine! It will be stiff hard stopping with a delay when it go's south from my experience, If the pentosin level and filter is ok, There is a post on adding a small cut in the top of the reservoir to relieve some air pressure and the winding noise has left in several cases.

[peake]

Too low pentosin level?!

[nrp22101]

When you slam on the brakes and it stops today, The Accumulator is fine! It will be stiff hard stopping with a delay when it go's south from my experience, If the pentosin level and filter is ok, There is a post on adding a small cut in the top of the reservoir to relieve some air pressure and the winding noise has left in several cases.

I read the post suggesting notching to allow air in but my symptoms are different than what they were describing. I'll review again tho.

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[nrp22101]

Too low pentosin level?!

Naw, that was the first thing I thought too.

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[peake]

My brakes were soft but braked like you described although the ABS never activated. The reason was I had never ever changed brake fluid. Not too much air in the system but water in the fluid. After changing ABS worked and brakes were stiff/hard and did their job much better.

[nrp22101]

My brakes were soft but braked like you described although the ABS never activated. The reason was I had never ever changed braked fluid. Not too much air in the system but water in the fluid. After changing ABS worked and brakes were stiff/hard and did their job much better.

That'll be good to do regardless but don't think that would address the rhythmic Brrrt noise every 7 seconds. Anyone else have any thoughts on this?

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[Timm]

Could the noise be the pre-charge pump running? Removing the relay would test this (and probably be rather dangerous) - K94:

http://www.meeknet.co.uk/e31/Timms_B...lay_Finder.htm

[Gary Knox]

If the booster 'bomb' is original, it is - at a minimum - 20 years old!! That rubber diaphragm does not last forever. Mercedes has used these accumulators for self leveling and to augment the hydraulic suspension in cars for quite a long time. Ten to fifteen years is considered a reasonable lifetime in that community. I always replaced mine at around 12-15 years on the Benzes.

I replaced this pressure accumulator on the e31 a few weeks ago. I've noticed improved braking and less hydraulic fluid/pump noise. Working slowly (on a lift), probably took about 2 hours for the job.

Gary

[nrp22101]

Could the noise be the pre-charge pump running? Removing the relay would test this (and probably be rather dangerous) - K49:

http://www.meeknet.co.uk/e31/Timms_B...lay_Finder.htm

Thanks Timm, did you maybe mean K19...I don't see 49 on your diagram? Thanks.

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[nrp22101]

If the booster 'bomb' is original, it is - at a minimum - 20 years old!! That rubber diaphragm does not last forever. Mercedes has used these accumulators for self leveling and to augment the hydraulic suspension in cars for quite a long time. Ten to fifteen years is considered a reasonable lifetime in that community. I always replaced mine at around 12-15 years on the Benzes.

I replaced this pressure accumulator on the e31 a few weeks ago. I've noticed improved braking and less hydraulic fluid/pump noise. Working slowly (on a lift), probably took about 2 hours for the job.

Gary

I hear ya Gary. Im all for preventative measures and will likely do this soon regardless.
Thanks.

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[Timm]

No, I meant K94.....

[peake]

The K94 is present in the 840 but is it also present the the older 850?

[Timm]

If you have slip control 5 then you have K94 - otherwise the relay is part of the hydraulic unit Y1

[nrp22101]

If you have slip control 5 then you have K94 - otherwise the relay is part of the hydraulic unit Y1

will give it a go when it warms up. Hard to motivate with sub freezing temps! Thanks.

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