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brake pedal feel/ brake accumulator issue?
PostPosted: Sun Jul 12, 2009 12:07 am Reply with quote
jmitro
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brake pedal on my 87 635Csi is soft initially but when stepping on it, it sinks to a lower level and then firms up. Sounds like a bad accumulator or "brake bomb." Or is it the brake pressure regulator? That part is quite a bit more expensive.

I'm not sure what exactly this all means. Has anybody else had these problems? What did you replace? Is it possible to eliminate the "brake bomb" or accumulator from the system? RealOEM photo below:


http://www.realoem.com/bmw/showparts.do?model=5384&mospid=47205&btnr=34_0296&hg=34&fg=25


PostPosted: Sun Jul 12, 2009 2:19 am Reply with quote
Chris Wright
Senior Member
Joined: 12 Jul 2005
Posts: 5576
Location: Columbus, IN (INDY 500 area)




It may not be the Accumulator, but testing it is easy.

The "Brake Bomb" is a hydraulic accumulator and fails when it loses it's gas charge. It is just a chamber split by a rubber diaphragm with a gas charge on one side and is charged with power steering fluid (ATF) on the other. This system was used on most BMW's throughout the '80's, the 5, 6, 7 and 8 series all used this system. The accumulator is only $80 and is fairly easy to replace. It's purpose it to ensure that there is no delay in brake response.

To check the accumulator, remove the top on the hydraulic reservoir and pump the brakes 15/20 times with the engine off and watch for the ATF level to stop rising** as the accumulator is discharged back into the reservoir. Start the engine and the level will drop below the screen as the accumulator is recharged. If the level does not rise and fall as described (discharge and recharge), the accumulator is bad.

(**The reservoir is full when it is 10mm (3/8") from the top. Only fill it after pumping the brakes or you will over fill it.


Flushing the Hydraulic system and changing the hydraulic filter: http://bigcoupe.com/phpBB2/viewtopic.php?t=2314&highlight=accumulator




Last edited by Chris Wright on Wed Feb 17, 2010 7:48 pm; edited 1 time in total

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PostPosted: Sun Jul 12, 2009 2:56 am Reply with quote
jmitro
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Thanks for the help. Very Happy I just checked and indeed my accumulator is bad. No significant rise/fall with pumping.

I'll get one of those and look into what all is involved in changing it.


PostPosted: Sun Jul 12, 2009 3:43 am Reply with quote
Chris Wright
Senior Member
Joined: 12 Jul 2005
Posts: 5576
Location: Columbus, IN (INDY 500 area)




It is a relative common, cheap, simple repair. Pump the brakes to discharge the system first, then loosen the 4 hydraulic lines and remove Regulator to the bench and unscrew the accumulator from the bottom with a strap wrench and replace it. They come pre-charged. Make sure you have the right size wrenches before starting, and make sure you have a new O-ring for the accumulator.

I'd flush the Hydraulic system and change the hydraulic filter also: http://bigcoupe.com/phpBB2/viewtopic.php?t=2314&highlight=accumulator

$78 - AutoHausAz.com - Free shipping



It takes approximately a 4 in. dia strap wrench or filter wrench to remove the accumulator.


For parts, the lowest prices I've found on the net: check all 3 when looking for parts (they also make good references):

http://www.AutoHausAZ.com

http://www.Pelicanparts.com

http://www.BavAuto.com (Great Catalog, order it, it's free)


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PostPosted: Sun Jul 12, 2009 4:56 am Reply with quote
jmitro
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great, thanks a lot for the help!

PostPosted: Tue Dec 01, 2009 12:41 am Reply with quote
j-carlton
Guest




FYI:
I just ordered an accumulator from Pelican Parts for $71 with free shipping (with orders over $75). The order went through online, but I got a phone call a few hours later saying they couldn't ship it, as it's considered hazardous. It is a will-call only item, although the site listing didn't mention this.

I cancelled that order, went to AutohausAZ and ordered an accumulator there for $74 plus free shipping - hoping it arrives in a few days.

Have others had this part shipped without issue??

I'm having the "panic stop" stiff pedal issue on my '85 CSi Euro, though normal operation seems fine. My reservoir fluid level rises some after pumping with the engine off, maybe the pressure is enough to discharge some fluid, but not operate in a panic stop situation? Also, I have no brake assist after shutting off the engine and applying brakes while coasting. It is actually shocking how poorly the brakes work without pressure assist!


PostPosted: Tue Dec 01, 2009 12:47 am Reply with quote
j-carlton
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duplicate post deleted


Last edited by j-carlton on Tue Dec 08, 2009 5:53 pm; edited 1 time in total

Shipping
PostPosted: Wed Dec 02, 2009 3:52 am Reply with quote
bsccp
Bigcoupe supporter
Joined: 17 Nov 2008
Posts: 116
Location: Lubbock, TX




Ordered the same part from Autohausaz a few months ago with no problems. Came UPS ground as all the stuff I have ordered from Autohausaz.

I had the same issues on my plain 85 c manual. I was able to remove the "bomb" from the distribution piece reaching in from the top. Some of the hard lines are a bit tricky to reattach but if you are patient it is not too bad. Absolutely must have metric flare wrenches otherwise you will round off the fittings. Harbor Freight, etc less than $8.

Tremendous improvement in braking! Well worth the the money and time.

bill

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PostPosted: Wed Dec 02, 2009 3:12 pm Reply with quote
Chris Wright
Senior Member
Joined: 12 Jul 2005
Posts: 5576
Location: Columbus, IN (INDY 500 area)




j-carlton wrote:
FYI: ........ but I got a phone call a few hours later saying they couldn't ship it, as it's considered hazardous.

Have others had this part shipped without issue??


It is pressurized, so it might be considered "hazardous" for Air Freight. Does Pelican ship FedEx? Like bsccp, I've had several shipped ground with no problems.


Quote:
I'm having the "panic stop" stiff pedal issue, though normal operation seems fine. My reservoir fluid level rises some after pumping with the engine off, maybe the pressure is enough to discharge some fluid, but not operate in a panic stop situation? Also, I have no brake assist after shutting off the engine and applying brakes while coasting. It is actually shocking how poorly the brakes work without pressure assist!


The bomb doesn't have to be fully discharged to be bad, check out this thread:

http://bigcoupe.com/phpBB2/viewtopic.php?t=6770&


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PostPosted: Tue Dec 08, 2009 6:06 pm Reply with quote
j-carlton
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Chris Wright wrote:
The bomb doesn't have to be fully discharged to be bad, check out this thread:

Thanks Chris, that sounds exactly like what's been happening to me.

I initially ordered the bomb through Pelican with UPS Ground shipping. The clerk who called just said it was a pick-up only item,they cannot ship it. We took it off my order and I suggested they list the no-shipping info on their site. I have ordered MANY a Porsche part through Pelican over the years and have been happy with their service.

I received the Lemforder bomb yesterday via UPS/AutohausAZ. I don't know why they will ship UPS ground and Pelican won't?

I was expecting it to come with a new O-ring since nobody listed one separately, but there is no o-ring. I can't find a listing or part number anywhere, does anybody have a number or a size? Should the bomb have come with a new O-ring? I obviously do not want to use the old one.

Edit - Through further search, I found an O-ring at autoanything.com for $1.95.

I think it is poor/sloppy service on the part of AutohausAZ to not list a separate o-ring and/or note that the part does/does not include one. This in addition to the Pelican confusion above has delayed my repair. Let's hope I don't rear end someone in the meantime!

Guess it all goes with the wonderful world of DIY. Still better than dealing with know nothing mechanics though.


PostPosted: Thu Dec 10, 2009 5:19 pm Reply with quote
Chris Wright
Senior Member
Joined: 12 Jul 2005
Posts: 5576
Location: Columbus, IN (INDY 500 area)




j-carlton wrote:
I initially ordered the bomb through Pelican with UPS Ground shipping. The clerk who called just said it was a pick-up only item,they cannot ship it. We took it off my order and I suggested they list the no-shipping info on their site.


That is strange that they won't ship it?? Did you click on the "More Info" link at Pelican? It states that it is considered HazMat and won't ship, so either you missed it or they are quick at updating there data base!

Quote:

I was expecting it to come with a new O-ring since nobody listed one separately, but there is no o-ring. I can't find a listing or part number anywhere, does anybody have a number or a size? Should the bomb have come with a new O-ring?

I think it is poor/sloppy service on the part of AutohausAZ to not list a separate o-ring and/or note that the part does/does not include one. This in addition to the Pelican confusion above has delayed my repair.



Seems like few of the German parts come with the proper self-locking nut, O-ring or crush washer that is supposed to be replaced, I've come to assume that they don't come with and ask.

It's hard to fault only AutoHaus when Pelican doesn't state it either, but I agree it is aggravating. I was looking at some of my old invoices and I noticed that the part numbers shipped where different from the BMW part number or the numbers listed on some of the parts sites:

Brake Bomb O-ring
BMW part No. - 34 33 1 119 868 (Old 34 33 1 157 560) = 15.3 x 2.4mm - $1.90 from the dealer.

If, however, you enter the BMW part number into the parts search at AutoHaus, you get this substitute:
"W0133-1663821 - Brake Accumulator ORing NLA 12;08" - $1.98 (If "12;08" is 12.08mm, it seems a little small)

Pelican has to special order the BMW O-ring (34 33 1 119 868) - $2.25

Neither solution seems very good, but Steve H. sent this substitute with his bomb: 64 11 1 468 435 = 14mm ( 13.98 ) - $1.50. Which when entered in an AutoHaus or Pelican part number search returns this: "O-Ring/Gasket/Seal; Heater Core to Heater Pipe; 13.98mm Diameter" - $0.48/$0.50. All in all, this seems the way to go and is available at both stores, cheap and without waiting.



Last edited by Chris Wright on Wed Feb 17, 2010 7:44 pm; edited 1 time in total

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PostPosted: Wed Dec 16, 2009 2:50 pm Reply with quote
TN_M6
Bigcoupe supporter
Joined: 21 Apr 2008
Posts: 248




j-carlton wrote:
I initially ordered the bomb through Pelican with UPS Ground shipping. The clerk who called just said it was a pick-up only item,they cannot ship it. We took it off my order and I suggested they list the no-shipping info on their site. I have ordered MANY a Porsche part through Pelican over the years and have been happy with their service.


Did you ask them how the parts get to them? Are they shipped or do they make a trip overseas to pick them up? Crazy California probably lets anything come in under any condition but gets goofey about what they let ship out. 49 other states haven't come to this thankfully.

Hope you got your brakes fixed up by now!

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PostPosted: Sun Dec 20, 2009 6:21 pm Reply with quote
j-carlton
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TN_M6 wrote:
Did you ask them how the parts get to them?


Great question! Wish I had thought to ask it!
I have since been told that some organizations are "certified" to ship components like this, and others do not want to go through the hassle of certification.

The bomb is in, and it IS the bomb -- makes a huge difference in quick brake actuation, was definitely my issue. The steering feels slightly more fluid and smooth, is that possible? Perhaps it's all in my head.

The job was what I expected based on the info I have read here. I removed the lines and switching unit to undo the accumulator sphere on a table vise. As I was fully emptying the sphere out, there was black gooey stuff dripping out with the red ATF. I'm guessing it's a disintegrated membrane from age??


PostPosted: Sat Jun 19, 2010 2:16 pm Reply with quote
okidok
Guest




Chris Wright wrote:
It is a relative common, cheap, simple repair. Pump the brakes to discharge the system first, then loosen the 4 hydraulic lines and remove Regulator to the bench and unscrew the accumulator from the bottom with a strap wrench and replace it. They come pre-charged. Make sure you have the right size wrenches before starting, and make sure you have a new O-ring for the accumulator.

I'd flush the Hydraulic system and change the hydraulic filter also: http://bigcoupe.com/phpBB2/viewtopic.php?t=2314&highlight=accumulator

$78 - AutoHausAz.com - Free shipping



It takes approximately a 4 in. dia strap wrench or filter wrench to remove the accumulator.


For parts, the lowest prices I've found on the net: check all 3 when looking for parts (they also make good references):

http://www.AutoHausAZ.com

http://www.Pelicanparts.com

http://www.BavAuto.com (Great Catalog, order it, it's free)


Hi,

I need to change my accumulator (BMW 735i e23 from 1982).
Can I unscrew it directly from within the car or do I have to dismantle the regulator and then unscrew the booster?

I'd rather not dismantle the regulator id I don't have to.

Thanks


PostPosted: Sat Jun 19, 2010 3:35 pm Reply with quote
Chris Wright
Senior Member
Joined: 12 Jul 2005
Posts: 5576
Location: Columbus, IN (INDY 500 area)




You may, .... but I don't know if you can? Mr. Green

Is there enough room to get on it and loosen it in the car (I've not done a 735)?

Give it a shot if you think you can get to it, but be prepared to pull the regulator if the last accumulator was installed by a gorilla!! The last one I did, I had to put a monster "C" clamp on it with a bit of a cheater bar to loosen it! But having said that, it is only supposed to be torqued to 35 Ft/Lbs, so give it a shot, maybe it was put on right and it will come right off.[/list]


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brake pedal feel/ brake accumulator issue?
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