Volvo B12BLEA Brake Blending Problem

I don't think you'll find much info on that here, this is the first I've seen someone post regarding buses or trucks, most of us here drive cars.

Crossposting is very much frowned upon, there's separate newsgroups for a reason.

Such as what?

Every one I've driven, including one that had over 1.1 million km on, have worked fine. (Tractor units..FM10/12, FH10/12 both 4x2 and 6x2 with ABS and EBD) As an agency driver, that's a fair few units. Must be at least 20 different ones in the last couple of years.

1.1 million miles? Christ, where was that delivery? Mars?

Me gurgled happily, sounding much like they were saying:

No, 1.1m km. About 700,000 miles.

Indeed. However it was only 6 years old and although it ran 7 days a week, it wasn't double shifted.

Conor gurgled happily, sounding much like they were saying:

So just over 300 miles per day average.

Yeah..sounds about right. Got used less as it was older as they rotated the work amongst the fleet when it was quiet.

Hypermobility?

No, not 1.1 million miles - 1.1 million kilometres, 687,500 miles :-)

Depends if you want to eat or not.

Yes but do you really need to do that mileage with the truck, could you not cycle or use horse & cart or even handcarts?

Oh, just the moon then ;-)

I suppose so but we'd have to bring over a few hundred boatloads of "those nego folk" to do the work cos the locals won't want to.

;p

I know of a bloke with a bike & cart who might help.

I doubt it..he'll claim the methane output he generates would contribute towards GW.

Just to return to the OP`s original request. I notice its a B12BLEA...Is this an artic ?

Suffice to say that there are indeed "issues" surrounding Volvo`s "brake blending" setup on it`s later B7 and even the newer B9 chassis.

To my knowldege this has presented as a most disconcerting "Snatch" at just about the worst possible point in a Bus journey.....just as the Bus is approaching a Bus-Stop of in Low-Speed Traffic.

The speeds involved are all in the sub 10 Kph bracket and result in much discomfort for passengers and allegations of poor driving being flung at the Busdriver !

Essentially it appears as if the Retarder cuts OUT at too high a speed which requires the Busdriver to compensate by last minute rapid application of the service brake accompanied by a certain coarse graduation of the delivery pressure from the footvalve.

Again,AFAIAA Volvo are aware of these issues and have in some cases referred to a "Software Modification" to addres them.

In my experience this modification IS successful,but it raises serious questions as to whether such a critical component as Braking/Rertarding should be the subject of research and development whilst actually in revenue service.

Do they not have Test Tracks for this type of safety-critical issue ?

I get a version of this on a 2002 B12B automatic coach, when the gearbox goes into neutral (Volvo call it Bus Stop Neutral or summat, & it's a pollution control thing they blame on the EU) under ECU control at just below walking pace. Drive stops, but the brakes are still on hard countering the drive, so there's a jerk at about 5kph. It's a deliberate design feature, & there's no way to turn it off easily.

The one that *really* annoys me is on the Scanias, when the automatic retarder cuts out at about 20kph, & half your brake force disappears just when you're committed to stop in a certain distance, say, the distance to a bus stop or stop line.

IUt would have disappeared anyway as it relies on high engine speeds to work. Any engine speed below 1500RPM isn't going to supply much retardation. On my lorry when I use it, the autobox drops a gear or two and takes it up to within 500RPM of the redline.

It disappears gradually with reducing input shaft speed, yes, much as the effectiveness of an exhaust brake does. I can live with that, on our Volvo autoboxes. On the Scanias, it's still quite noticeable in low gears down to about 750rpm. That isn't too bad, but suddenly losing

*all* gearbox retardation from quite a high value isn't funny,it feels to the passengers as if the vehicle is lurching forward just as things are getting critical. Because of this, I disable the transmission retarder function in town for more predictable braking. The normal brakes run hotter & work harder, but the passengers get a much smoother ride.