Bus crash investigation findings - hydraulic retarder

Jeremy · November 22, 2017, 01:47:45 PM

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

Jeremy

luvrbus · November 22, 2017, 02:04:57 PM

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

brmax · 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

Jeremy · November 22, 2017, 02:52:03 PM

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

lostagain · November 22, 2017, 02:56:41 PM

An experienced and careful driver would have noticed that the retarder wasn't as effective and adjusted his driving accordingly...

JC

Iceni John · November 22, 2017, 07:31:43 PM

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

Jon · November 23, 2017, 04:06:26 AM

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.

chessie4905 · 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.

brmax · November 23, 2017, 06:26:57 AM

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

Happy Thanksgiving
Its a great day for a harvest feasting enjoy the day everyone.

Floyd

TomC · November 23, 2017, 07:07:56 AM

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

B_K · November 23, 2017, 08:37:37 AM

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!"

BK

Jon · November 23, 2017, 08:42:58 AM

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.

eagle19952 · November 23, 2017, 01:10:58 PM

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...

chessie4905 · 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.

luvrbus · November 23, 2017, 05:18:53 PM

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