Brake Master Leak

[MARHD]

Hi everyone,

 

I have a leak on my brake Master cylinder, where one of the reservoir pipes fits into the grommet, as well as a smaller leak in the same area on my clutch Master.

 

I have recently had both of these refurbished with a local brake shop. I've tried replacing the grommet (although not genuine bmw) as well as replacing the little washers that fit below the grommet.

 

So I'm not sure if they were refurbished poorly, of the grommets are not seated properly (or are not good enough quality), or if the plastic fitting that connects the feed pipe to the grommet has a small crack.

 

I did take a video of the area with the grommet removed and myself pressing the brake pedal. When pressed the master sucks in brake fluid as expected, but once released it seems to fill back up. Is this expected behaviour (video attached)?

 

 

 

 

Edited December 17, 2022 by MARHD

[tzei]

BMC looks like it’s leaking from the hose, not grommet.

CMC. Bit hard to see but might be that grommet is not fully home. Could be hose too. Is hose used 100% b/fluid compactible?

 

Wipe all super clean and observe where it starts to get moist so you’ll know what to fix.

[dlacey]

Agree it look like the hose is leaking...there's no pressure there other than gravity acting on the reservoir...has the hose split??. Is that proper brake hose? Look like fuel hose (I could be wrong).

In my experience, to get the grommets seated properly, it's best to fit the elbow to the grommet and then push that grommet assembly into the master cyl.

[dlacey]

W&N have the grommets listed for 5 series:

Plug 17/8 for 518, 520/4, 520i only LHD-models, all years of manufacturing, you need 2 for 1 car

WWW.WALLOTHNESCH.COM

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Plug 17/8 for 518, 520/4, 520i only LHD-models, all years of manufacturing, you need 2 for 1 car

 

[MARHD]

17 minutes ago, dlacey said:

Agree it look like the hose is leaking...there's no pressure there other than gravity acting on the reservoir...has the hose split??. Is that proper brake hose? Look like fuel hose (I could be wrong).

In my experience, to get the grommets seated properly, it's best to fit the elbow to the grommet and then push that grommet assembly into the master cyl.

 

The hose was replaced at the same place that refurbed the BMC and CMC, so I do believe it is brake hose. It may be that the plastic fitting cracked when they moved it to the new hose. I'll try to get a replacement.

 

Thanks for the tip on installation of the grommet, I have been pushing the grommet in first then the elbow, so could be in there a bit skew as well.

 

I'll see how far I get 👍

[jimk]

8 hours ago, MARHD said:

When pressed the master sucks in brake fluid as expected, but once released it seems to fill back up. Is this expected behaviour (video attached)?

Yes, the fluid that is pushed back from the wheel cylinders/disc calipers has to go somewhere.

[ray_]

That brake hose still looks weird to me. I wonder if it's the proper ID, among other things...

 

Cheers,

['76mintgrün'02]

The size is written on the hose.  7.5 x 14.  I looked up the part number for the hose to get the size and it's 7.5 x 13, so the ID matches, which is what matters.  I also learned that BMW no longer offers cloth covered hoses.

 

EDIT- I initially searched for '76 hose and then wondered if the early cars used the same size and found this, which appears to confirm that they did/do.

 

BMW 21521163714

Hose

1967-2020 BMW 21-52-1-163-714

Edited December 17, 2022 by '76mintgrün'02

[Mikesmalaga72]

I would spray some brake cleaner solvent(drying agent) on there and try to observe where the fluid comes out.  

Edited December 18, 2022 by Mikesmalaga72

[MARHD]

I do believe the hose is correct. I did a bit of a hack job and put a hose clamp on it and sprayed some brake clean. I guess we shall see if it continues to leak.

 

I also took the clutch grommet out, it seems to fit in there a bit more easily than the BMC grommet, even though it seems they have the same part number.

 

[Mike Self]

Coupla thoughts:

• Many years ago I had one of the little plastic elbows crack and cause a leak.  The crack can be down inside the grommet and still leak...
• I recall the last time I replaced the hoses, the cloth-covered hose was blue, specifically to distinguish it from the black cloth-covered fuel line. 

Both of those hoses can develop cracks in the rubber that's hidden by the cloth covering, and ooze brake fluid/gas (depending on the fluid carried) without revealing the location.  Both gas and brake hoses seem to be susceptible to this.  

 

When installing the elbow into the grommet and the grommet into the master cylinder, a (very) little silicone grease does wonders.

 

mike

[MARHD]

I do believe you were all correct, it does seem the leak was coming from the pipe end. After adding a sketchy hose clamp and spraying brake clean on the area it seems a lot drier. While the clutch master area still seems wet as I did not add a hose clamp to it.

 

So I will order some new fittings from BMW, possibly some new hose and I will probably get the nicer style hose clamps that don't cut into the hose just for peace of mind, even if it isn't necessary.

 

Thanks for the help, all I would like to think this is solved but I suppose I will only know once everything is in.

 

BMC

 

CMC

 

[Mikesmalaga72]

The master cylinder feed lines are gravity feed lines they do not require hose clamps at either end of the feed lines to and from the brake fluid reservoir they are friction fit. The act of tightening the hose clamp could fracture the plastic elbow. 

 

https://www.realoem.com/bmw/enUS/showparts?id=ST12-USA-04-1972-114-BMW-2002&diagId=34_0808

 

[tech71]

That hose whatever it is, is funky.

Too fat, too rigid (dont start guys)

wrong application, replace it

BMW E10 E28 E30 E36 Brake Fluid Hose Reservoir to Master Cylinder 7.5x13 1 meter

WWW.EBAY.COM

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MADE IN GERMANY.This is made by Continental/contitech which is an OEM producer of this hose. We will work with you to resolve any problems.

 

Edited December 18, 2022 by tech71

[larry_in_socal]

I'm also getting ready to do some work on my brakes, I almost have everything I need.. Let's wait to see what Santa Brings...

 

I purchased some items when I.E. had their open house in summer.

 

I purchased some brake fluid hose from the reservoir to the MC.

 

FYI... the hose has the following printed on it: "Conti - Brake - L3L-2.1 - 7,5 x 3 > EPDM/EPDM< 25/21/21".

 

Here is what the label on the hose that I purchased in-case anyone needs the info.

 

 

Once I have everything I'll start putting it all together... In about a month, when time permits.