Interested to see that this inquest / accident investigation conclusion was that the ...brake failed as the pad had been "completely destroyed by excessive heating" due to the "poor condition of the hydraulic retarder".
I've never heard of such a thing as a 'hydraulic retarder' on a bus, the only 'retarders' I'm familiar with being Telma electrical retarders and Jake brakes. Anyone know about hydraulic retarders used on buses / coaches?
Link to article: http://www.bbc.co.uk/news/uk-england-tyne-42083779 (http://www.bbc.co.uk/news/uk-england-tyne-42083779)
Jeremy
All buses here if equipped will be a hydraulic retarder built into the Allison transmission ,Allison has the used hydraulic retarder since the 70's.ZF auto transmissions also have it as a option
Being they mention "pad" they could be talking an air over hydraulic disc system, with an antilock as the retarder or controller. Just my $.02
Floyd
Quote from: brmax on November 22, 2017, 02:15:50 PM
Being they mention "pad" they could be talking an air over hydraulic disc system, with an antilock as the retarder or controller. Just my $.02
Floyd
I took it to mean that the service brake pads overheated because the separate retarder system wasn't contributing enough to the overall braking effect. Surprising to me though that this could apparently happen without the driver being aware of it and only realising there was a problem when the brakes suddenly failed completely.
And it hadn't occurred to me that the retarder could actually be inside the gearbox - makes sense. I imagine it being something like a torque converter in reverse
Jeremy
An experienced and careful driver would have noticed that the retarder wasn't as effective and adjusted his driving accordingly...
JC
That's one reason to have a brake application force pressure gauge. If you notice you're needing progressively more braking air pressure to hold the same speed down a constant gradient, it means that your brakes are fading because the drums are expanding from overheating. I bought a Mack dual-needle gauge that matches all my other gauges, and if I ever have a leak in the front or rear air system it would also help me narrow down where the problem is.
John
What is really needed is a trained driver.
Whether it is a Jake, a retarder or no supplemental braking it is the driver that has to understand and respect his equipment.
Don't discount poor maintenance by company, a different driver on this trip, previous driver's abusing brakes and not reporting lack of retard, and first leg of trip may have been climbing to resort, so didn't show up.
Jeremy: I agree and after taking a proper look at the link, your spot on. Cheers 🍻
I understand that Europe uses a lot of disc brake systems in their equivalent class 8 vehicles. Im not familar with these newer systems. The new disc systems look to be real interesting and unlike some older construction equipment im a bit more familiar with, as air over hyd disc.
The new description on Bendix systems looks to be total air as I briefly look around the net. In any event I found a good piece of info online and from another great coach group, Wonderlodge. This Alison information I found particulary interesting on page 22 for the retarder applications available. This is a pretty decent bit of info. Although I really havent a clue what the coach in the link had for brand of trans system, so this is just for conversation here.
http://www.wanderlodgeownersgroup.com/downloads/PT-42%20Files/GPS%20&%20ENGINE%20MONITOR/http___www.allisontransmission.com_servlet_DownloadFile_Dir=publications_pubs&FileToGet=OM2157EN.pdf (http://www.wanderlodgeownersgroup.com/downloads/PT-42%20Files/GPS%20&%20ENGINE%20MONITOR/http___www.allisontransmission.com_servlet_DownloadFile_Dir=publications_pubs&FileToGet=OM2157EN.pdf)
Happy Thanksgiving
Its a great day for a harvest feasting enjoy the day everyone.
Floyd
Early HT740 Allison transmissions had an input hydraulic retarder that mounted between the torque converter and the transmission. Was very effective since it operated with the engine input speed. Later Allison offered the output shaft hydraulic retarder that is available also on 3000 and 4000 series. Some of the output retarders had multi plate wet brakes built in that could actually stop the vehicle with only the retarder. When buses have retarders that are automatically operated through the brake pedal, 500,000mi between brake replace is not unheard of. Good luck, TomC
Quote from: TomCWhen buses have retarders that are automatically operated through the brake pedal, 500,000mi between brake replace is not unheard of. Good luck, TomC
Yeah but the transmissions suffer a great deal of abuse and rarely last near as long as a HP 740 used to!
A B3000R or B4000R hardly ever last over 200-300, 000 miles verses millions one many 740's!
Been there done that with both transmissions and can tell you that the 740's are nearly bullet, bomb AND ALMOST IDIOT PROOF! (not so with the newer ones! and as a friend who used to order his DL3's w/60 series engines backed by 740's used to say
"For $25-30,000 dollars I can buy a lot of fuel vs rebuilding a trans every couple hundred thousand miles!"
;D BK ;D
Quote from: chessie4905 on November 23, 2017, 04:30:42 AM
Don't discount poor maintenance by company, a different driver on this trip, previous driver's abusing brakes and not reporting lack of retard, and first leg of trip may have been climbing to resort, so didn't show up.
While I cannot disagree maintenance or lack of it may have been the ultimate cause a skilled driver will know pretty quick when something is not operating up to snuff. It is not like one day everything is perfect then the next it is worn out. Too many steering wheel holders on the road today.
Quote from: chessie4905 on November 23, 2017, 04:30:42 AM
Don't discount poor maintenance by company, a different driver on this trip, previous driver's abusing brakes and not reporting lack of retard, and first leg of trip may have been climbing to resort, so didn't show up.
supposed to know that before you need it.
the plaintiff's attorney gonna love this answer...
I wonder if checking operation of a hydraulic retarder in pre trip is soa or if drivers know little about them. I thought normal brakes are required to do the job of stopping, irregardless of supplementary braking assist systems. Maybe driver was inexperienced and was just driving too fast for conditions. Maybe we'll get more detailed info down the road.
Quote from: chessie4905 on November 23, 2017, 03:58:27 PM
I wonder if checking operation of a hydraulic retarder in pre trip is soa or if drivers know little about them. I thought normal brakes are required to do the job of stopping, irregardless of supplementary braking assist systems. Maybe driver was inexperienced and was just driving too fast for conditions. Maybe we'll get more detailed info down the road.
I tell the Jake Brake lovers all the time learn to stop without the Jake because someday when you flip the Jake switch and they are not going to be there
Quote from: chessie4905 on November 23, 2017, 03:58:27 PM
I wonder if checking operation of a hydraulic retarder in pre trip is soa or if drivers know little about them. I thought normal brakes are required to do the job of stopping, irregardless of supplementary braking assist systems. Maybe driver was inexperienced and was just driving too fast for conditions. Maybe we'll get more detailed info down the road.
The lawyer that hears this on the stand will have a field day...
They will have a field day regardless of the situation particulars. Death and injuries are enough to spread the blame to driver, company and their insurance company. Be interested in testimony of passengers.
English bus drivers (I hate to say) are probably less experienced than their continental counterparts at descending long steep Alpine roads, simply because there are no roads like that anywhere in Britain. When I watch the Tour de France mountain stages such as the climb to Alpe d'Huez (where this accident was), I'm always amazed how narrow and steep those roads are, with gradients sometimes exceeding 10% and with dozens of very tight switchback corners. I would NOT want to take a 12-meter bus up or down roads like that. Many years ago I took a daytrip by bus up the Gross Glockner Pass in Austria, and that narrow steep road and its vertiginous drop-offs are still fresh in my memory - even in a Mercedes O-302 with an experienced local driver it was very scary.
I'm curious if the hydraulic retarder that failed was an add-on like a Telma, or something built into a transmission, or what? Automatic transmissions in long-distance buses are not common outside USA and Canada, so what did this British-owned bus have? And how could a hydraulic retarder fail - did the oil overheat and catch fire (which could explain why the bus then caught fire), or what happened? Maybe the fuel tank broke free and started the fire?
Very sobering.
John
I was also curious why it should so quickly turn into a complete inferno (to quote the article) after the crash - yes the overheated brake pads would cause a fire, but the speed and ferocity of it suggests something very combustible ignited very quickly - perhaps that was indeed overheated hydraulic fluid from the retarder as Iceni John suggests
I wouldn't presume to comment on the competence of the driver or anything like that but I'd also agree that navigating this type of road with a fully laden coach (and trailer) is an experience that probably very few British coach drivers ever have, and probably not many Italian, French or Swiss drivers either
I notice that the website of the coach operator no longer exists, and perhaps the company doesn't either. Plenty of photos of their vehicles on the web though, and they all look like very modern and high-spec models
Here are a few more photos of the crash site itself
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi.dailymail.co.uk%2Fi%2Fpix%2F2013%2F04%2F16%2Farticle-2309922-1953C901000005DC-28_634x423.jpg&hash=c4df1883e0537b6f186a460f4deabb236a813c8f)
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi.dailymail.co.uk%2Fi%2Fpix%2F2013%2F04%2F17%2Farticle-2310339-1953F580000005DC-396_634x688.jpg&hash=37f4cc20e12f36a3d341edbd58f1fc75c947613c)
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi.dailymail.co.uk%2Fi%2Fpix%2F2013%2F04%2F16%2Farticle-2309922-1953ACD0000005DC-155_634x422.jpg&hash=86e3a490ec00b955d3793806cf4b093a410d278d)
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi.dailymail.co.uk%2Fi%2Fpix%2F2013%2F04%2F16%2Farticle-2309922-1953AE03000005DC-366_634x422.jpg&hash=00236d5e1bc2e77ce8f7200d6407f1770b84ecfe)
That last photo in particular make me wonder whether the steel frame deformed like that during the accident itself, or whether it sagged afterwards because the steel was softened during the fire. It also makes me wonder whether steel stretch panels (as my bus has) would have contributed anything useful to the strength and stiffness of the frame - clearly fibreglass panels on this bus contributed nothing at all
Jeremy
Looking at the side it looks to be started from a brake fire and those babies burn hot in a hurry
We were trained by Brewster Transport in the '70s how to drive steep mountain roads. Descending steep grades doesn't bother me, but I have, over the years, met some professional drivers who drive down steep mountain roads in high gear, just using the brakes. Just recently, at the truck terminal (no mentioning names) in Lewiston ID, this trucker pulls in, pale faced and quite exited, brakes still smoking, telling everybody how scary the hill into town is... Appalling! I have met some bus drivers in the Rockies that come in from far away in the summer with charters with the same blessed clueless ignorance. They're only as good as you train them.
JC
A lot of bashing of S&S goes on here but I'm not sure it matters much in a situation like this. OK, so the shell did not fully turn into ash and the metal structure survived. Not sure that is much to crow about but rather humble us all to stay vigilant and aware while moving down the road. I have two extinguishers but adding on the to do list is adding a couple more.