Brake Line Failure

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03 Feb 2021 06:30 #1 by John and Bronwyn
John and Bronwyn created the topic: Brake Line Failure
Had an interesting and rather troubling problem with 191 a couple of months ago - total brake failure. Definitely not what you want on the road, luckily it was only about 100 metres from home and on a gentle slope at very low speed. Everything went my way! (for once).
Initial fault: One of the brake lines failed (blew out) where the lines run on top of the chassis crossmember, from the right to the left side of the chassis. The probable cause: external corrosion of the line. The lines are not visible in this location and are very difficult to access, but are prone to mud and gunk buildup.
But - there was complete loss of brakes. The dual circuit didn't work, and the fault emptied both sections of the brake fluid reservoir. Hence - no brakes. There was no 'brake fail' alarm. (I can be confident of this because 191 has an alarm buzzer as well as the warning light. There was no alarm.)
Hence there had to be a cross-connection between the brake circuits, which turned out to be a faulty brake fail switch assembly.
Replacement of the lines was not practicable in their original location (without taking the body off) so the lines were re-routed and replaced with hydraulic hose and fittings. All lines were replaced including the existing flexibles.
The final fault was that the rear pressure limiting valve was seized. On 191 (a bus) this is not load sensitive, it is just a pressure limiter.
So: this was a very nasty combination of faults which could have contributed to disaster.
'Heads up' to check your brake lines are OK and that the 'fail' switch is OK. These are probably both age-related faults and so could strike other vehicles.

John
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03 Feb 2021 07:01 #2 by Peter_n_Margaret
Peter_n_Margaret replied the topic: Brake Line Failure
Nasty.
By pure coincidence, I recently removed the curved 3mm thick bit of steel at the front that covers the brake lines as part of my weight reduction efforts on #077. It weighed 5kg and seems to serve no purpose.
The brake lines were very corroded externally.
Cheers,
Peter

Cheers, Peter.
OKA196 tinyurl.com/OKA196xtMotorhome
Mob.0428171214
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03 Feb 2021 19:32 #3 by Alister McBride
Alister McBride replied the topic: Brake Line Failure
I removed the same plate on #57 as it seemed to serve no purpose other than to stop a flailing winch rope from connecting with brake lines. My brake lines were rotted out too so were replaced. Glad you're ok considering the circumstances!

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04 Feb 2021 06:21 #4 by John and Bronwyn
John and Bronwyn replied the topic: Brake Line Failure
Thanks Alister
Sounds like (as I feared) the corrosion could be a common problem. It's bad enough if a brake line blows out, but if the dual circuit system isn't working as well.....
It also sounds like (from your & Peter's descriptions) that mine might be in a different location, mine are on top of the crossmember just in front of the radiator.

Cheers, John

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04 Feb 2021 07:02 #5 by Alister McBride
Alister McBride replied the topic: Brake Line Failure
Hi John, i'm no expert but that location sounds nonstandard, but the same issue we had anyway... Did both lines blow out or just one?

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04 Feb 2021 15:57 #6 by Paul Scherek
Paul Scherek replied the topic: Brake Line Failure
Quick word of warning not to do something really stupid like I did. Up in Vic high country, brake line sprung a leak and all fluid gone before I noticed. No chance of recovery assistance, on our own, so went down gently in low range first... but dickhead, I forgot to lock the front hubs! Back wheels lost traction on first steep bit, I was mighty lucky to find a spot to point uphill for a moment. So don't forget to lock your hubs in that situation.

Down at the bottom, a quick call to Paul Knott and a new hose arrived almost before I asked!

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04 Feb 2021 18:59 #7 by John and Bronwyn
John and Bronwyn replied the topic: Brake Line Failure
Hi Alister
So far as I know, only one blew out. The BIG mystery then was - why did both brake circuits fail? Must admit I'm still not totally sure but the alarm switch assembly is a strong suspect. I can't think of anywhere else the two circuits come together. I didn't end up with the faulty switch, it is feasible the seals in it had failed. If I had the switch ass'y I would investigate further, but I don't.
Where my lines were (on top of the x-member in front of the radiator) they were extremely hard to get at without a lot of dismantling, so we (the repairer and I) decided to run the new lines across the front using bulkhead fittings every time they had to go through a panel (ie each side of the radiator air inlet tunnel). It all came out pretty good in the end.

Paul - sounds like you also had total brake failure from only one blown line. Interesting, and worrying. But glad the 'adventure' had a happy ending!

Cheers, John

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05 Feb 2021 05:52 #8 by Paul Scherek
Paul Scherek replied the topic: Brake Line Failure
Thanks John, my pedal didn't go all the way to the floor, but there was no braking at all. I suspect the rear brake apportioning valve had seized in the OFF position, blocking all flow to the rear brakes.

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07 Feb 2021 10:40 #9 by John and Bronwyn
John and Bronwyn replied the topic: Brake Line Failure
Hi Paul
Could be a jammed proportioning valve. On mine the pedal went to the floor and both fluid reservoirs emptied. The rear proportioning valve on mine was also seized but in a position to still allow rear axle braking.
I was just starting to get worried that there could be a deeper fault (apart from the brake lines) that the dual circuit doesn't work due to some as-yet undiscovered problem. Hopefully mine was a unique combination of circumstances rather than something lurking in wait in other vehicles.
When I get the chance I want to crack open one system and check I still have brakes on the other system, and that the alarm works.

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07 Feb 2021 19:31 #10 by Peter_n_Margaret
Peter_n_Margaret replied the topic: Brake Line Failure
By coincidence, yesterday I removed the rear proportioning valve (that was jammed, like they all are) from 077 as part of my weight saving work. It will be replaced with a manual proportioning valve in the line up near the master cylinder.
1.5kg weight saving and makes space for an under floor storage box (if I need it).
Cheers,
Peter

Cheers, Peter.
OKA196 tinyurl.com/OKA196xtMotorhome
Mob.0428171214

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