Brake Failure

Brake Failure

If you've read my previous blog called "BMW Brake lines", you would undoubtedly remember that I had a problem with a seized front brake calipers and a ruptured brake-hose. Since BMW / Motorad is closed for business on a Saturday or for that matter the entire weekend, I couldn't get the requisite break-hose in time, so that I could remedy the problem. So this morning, I telephone their spares department and requested a price for the  two brake hoses for my BMW R1100RS. Namely the two 29cm long hoses with a banjo fitting at either of its end, that sits between each front caliper and the fluid distribution T junction that's bolted to the root of the fork.  



After a sort while, the spare parts sales person  returned to the phone, and gave me two distinctly different prices for the each of them. The left  hose was  R1859.00 and the right side R630.00. I was gobsmacked, my question to him was, "How can two hoses identical in length that can be used interchangeably, have different price tags". Turns out, he was a bit confused and gave me prices for the R1100R break hoses. He then performed another computer search —including JHB— and the quote per brake-hose was R1142.00. However, it appeared that they have never had them in stock nor had a reason to order them. So I was told ex-Germany ... six weeks wait, alternatively get an aftermarket part.

After spending several hours hose-hunting, visiting several motor spares and motorcycle shops, non of them had anything remotely close to what I needed, so I decided to have them made up. Fortunately I found several business that manufacture custom  hydraulic brake hoses, using SAE J1401 1/8" specification,  Department of Transportation approved (DoT) hose. Meanwhile, I was still in the process of servicing the calipers and since I had no other way of extruding the pistons, I connected the master cylinder supply hose directly to the caliper to pump out the pistons. I managed to completely service one caliper when the main supply break-hose also ruptured. However, before it sprung a leak, I managed to video the hose ballooning every time I squeezed the break lever. See below! Instead of the brake fluid pushing the pistons out, the brake fluid pressure just make the hoses puff-up.

I found that the loose PVC sleeve that covers the nitrile rubber hose —on the original BMW hoses— somewhat prevents the brake-hoses from ballooning but it ruptures in the areas not constrained the PVC covering. Also that the hose tends to rupture within the last 3cm od the hose, closes to the crimped-on fitting. 

The faulty main supply brake hose that sits between the master cylinder and
the fluid distribution T junction.

In my opinion, the brake-fluid seeps in between the layers of the nitrile rubber pipe at the cut where it butts with the crimped-on fitting, (see image below).  The reason why I think this, is because the above hose is still fairly solid throughout and cannot be compressed between the fore fingers and the thumb. When I bent it, it forms a good curve and is difficult to kink, but along the area where it ruptured, it is quite floppy and can easily be compressed between the thumb and fore finger. The SAE J1401 brake hose specification rules that the inner layer of the hose should be made of Eethylene Propylene Diene Monomer (EPDM), a type of synthetic rubber, covered by two layers of reinforced red and one layer white rayon, alternatively a layer of  Poly Vinyl alcohol (PVA), with the outer layer also made of  EPDM. Most importantly that it should be able to withstand pressure of 34.5 Mpa (500psi) before it bursts.

Two types of SAE1401 brake hose, the top ones are double reinforced
whereas the bottom hoses are not. I think this is where the brake fluid
enters and destroys the EPDM over a few years,

BMW specifies that brake-hoses should be replaced every 4 years. However my 1998 BMW 1100RS probably never had a brake hose replacement in 20 years because the date stamp on the hose appears to be from 10 '95. I compared manufacturer's identification against the brake hoses I had made up, which just reinforces the idea that it was never changed. I've had the BMW in question for 17 months and the day I bought her, the previous owner said that he had it for 10 years and had it serviced at BMW Motorad throughout his ownership. Based on that, if the hoses where ever replaced, I would have expected to find a date stamp somewhere between 2005 and 2010,  but that's certainly not the case.

The date stamp is on the ruptured brake hose is - 10 '95

The date stamp is on the ruptured brake hose is - 12 04 16 (12th April 2016)

Understandably, manufacturers of hydraulic hoses using SAE J1401 have to buy a roll of the stuff and may not sell all of it in the same year of purchase. So I'm ok with the fact that its 2 years old because it wasn't exposed to brake fluid during this time.  From what I've seen, the brake hoses perishwa because the brake fluid ages, looses its viscosity of the fluid 

The new brake-hoses I bought is really hard and fairly stiff compared to those that came off the bike, As can be seen below, the old brake hoses have a tight fitting PVC over their length except for the last 8 mm close to the banjo fitting. 

The out two hoses with the shiny banjo fittings are the ones I had made-up. 

This is exactly the point where the brake-hose will perish and eventually rupture.  I've lifted the  tight fitting PVC sleeve to expose the perished segment of nitrile rubber on the image below, to highlight the weak area.  This area had fine cracks in it from continuous ballooning. The video beneath the image below, gives a good idea of how dangerous a burst brake hose could be when traveling at high speed and there's a need to stop on a penny.

I've lifted the  tight fitting PVC sleeve to expose
the perished segment of nitrile rubber 

Having read the above and watched the video, its all too easy to imagine the consequences of a brake hose that's been in service for longer  than it was designed to be. I therefore beg every motorcycle rider, not to delay checking those hoses, especially if you bought your bike recently. The seller will tell you what you want to hear but don't take his or her word for it. Do you own checks and if it needs fixing, do it yourself, if not, send it to a reputable mechanic or the BMW service agents. You only have one life, so don't skimp on getting those brake hoses replaced. Also don't buy cheap break fluid. Get the DOT 3 or DOT 4 brake fluid recommended by the bike manufacturer.

The caliper hanging from the  supply brake hose

The main thee socket needed to remove brake calipers, floating disk
screws and split the calipers to get access to the pistons.

As can be seen the mudguard needs to be removed to get
access to the fluid distribution T junction

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