Exhaust brake.....Any comments?
31 Oct 2012 20:36 #1
by dandjcr
David and Janet Ribbans - Oka 148
Oka148 profile here.
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dandjcr created the topic: Exhaust brake.....Any comments?
Forum Home > OKA Maintenance > Exhaust brake.....Any comments?
Peter_n_Margaret
Member
Posts: 198
Getting a quote to fit an exhaust brake with simple floor operated 'press to operate'.
Any comment on how the Perkins will like it?
--
Cheers Peter, OKA196 Motorhome. www.oka4wd.com/xt196.htm
November 8, 2011 at 5:44 AM Flag Quote & Reply
Peter & Sandra James Oka 374
Member
Posts: 412
How ya going over there Peter?
If anyone can find out if it is ok to run an exhaust brake on the Perkins you will be the one.
374 has an exhaust brake fitted by the RAAF, sits in the exhaust nearly right alongside the RHS spring hanger. Oka deny ever fitting exhaust brakes to any Oka which is interesting. Allan couldn't (or wouldn't) elaborate on why not.
It seems to be a kit fitted by I think " Exhaust brakes Australia" or similar, there was a sticker on it which had the name and phone number but it has disappeared. It is operated by compressed air from an ARB air compressor and has interlocks (microswitches) on clutch, brake and accelerator. It is operated by a two switches on the dash, one turns the compressor on and the second one operates an air solenoid which makes the brake work if all microswitches are closed.
It wasn't working when we bought 374 but with a bit of fiddling I've got the system operational.
BUT when we first bought the Oka several people told me not to use it as the Perkins has weak valve springs which can be kept open by the exhaust back pressure caused by the brake and leading to engine damage (valves kissing pistons). I've asked everyone I can think of, Perkins dealers, diesel mechanics (old ones
) and no one can give me a definative answer as to whether to use the exhaust brake or not.
Interestingly looking back through the RAAF records at about 40k k's the head was removed to repair oil leaks and "something else" which was never elaborated on but cost several $K and had a new head fitted. From then on there were several references to "inoperative exhaust brake" in drivers reports at the end of exercises and all the mechanics wrote was "exhaust brake Not Servicable". Reading between the lines it does appear that the exhaust brake may have caused valves to kiss pistons, especially as when I started chasing why it wasn't working it had been rendered inoperative in a very crafty way in two places, one electrical and one in the air circuit. Both would not have been found easily in the field and both required parts to repair, the electrical one had a tag, "DO NOT REPAIR" .
I have tried it out at low speed and it did not seem to work very well, actually not much retardation at all, have not been game to try it on a big hill in a situation where you would use it for fear of causing valves to kiss pistons as it seems there may be something in that line of thought.
Peter
--
Oka 374 LT Van
November 8, 2011 at 7:19 AM Flag Quote & Reply
Tony Lee
Member
Posts: 539
Come over the top of a hill at 100 and lift the foot and very little seems to happen that can be attributed to the exhaust brake.
Need to brake manually and drop it back a gear so the revs are at maximum and the retardation starts being felt and it will make the difference between using brakes rarely and applying them every few seconds.
At lower revs the brake does very little.
On automatics like in the Airstream - say with a six-speed allison, when you lift the foot, the transmission preselcts second gear and the system drops the gears down when it can without over-revving the engine. However, unless you brake manually at the beginning so it can drop down to 5th and then 4th at least, you will still get a runaway situation because the transmission stays in 6th.
If revs rise to the maximum, the transmission shifts up automatically to keep the engine revs down - so if you do the wrong thing on the way down, the electronics just saves the system, not the occupants.
--
Tony
picasaweb.google.com/114611728110254134379
November 8, 2011 at 8:28 AM Flag Quote & Reply
Peter_n_Margaret
Member
Posts: 198
Peter...getting warm and sticky here...
Your report puts a different light on the matter. I will need to find others with direct experience. Don't want to bugger up the Perkins.
Ta Tony. Not expecting miracles, but I reckon any help would be useful.
--
Cheers Peter, OKA196 Motorhome. www.oka4wd.com/xt196.htm
November 8, 2011 at 6:52 PM Flag Quote & Reply
Tony Lee
Member
Posts: 539
Used properly, they will achieve miracles in terms of driving enjoyment and safety. Getting down some very steep long mountain roads in the US with hardly a touch of the brakes gives you the peace of mind of knowing that at all times, you have 100% of your brakes available.
Mind you, at the speed the OKA goes up the hills it would be a real pity to spoil the few chances of getting a decent speed up by going down hills too sedately.
--
Tony
picasaweb.google.com/114611728110254134379
November 8, 2011 at 8:37 PM Flag Quote & Reply
Peter & Sandra James Oka 374
Member
Posts: 412
Ha ha I like that Tony, I've found though that the Oka slows down pretty well on compression when you lift your foot off the accelerator, just an occasional dab of the brakes on most hills, must have something to do with the Rockwell banging and clanging underneath.
Mind you once the auto is in I might find the brakes get a lot more use))
--
Oka 374 LT Van
November 9, 2011 at 6:59 AM
Peter_n_Margaret
Member
Posts: 198
Getting a quote to fit an exhaust brake with simple floor operated 'press to operate'.
Any comment on how the Perkins will like it?
--
Cheers Peter, OKA196 Motorhome. www.oka4wd.com/xt196.htm
November 8, 2011 at 5:44 AM Flag Quote & Reply
Peter & Sandra James Oka 374
Member
Posts: 412
How ya going over there Peter?
If anyone can find out if it is ok to run an exhaust brake on the Perkins you will be the one.
374 has an exhaust brake fitted by the RAAF, sits in the exhaust nearly right alongside the RHS spring hanger. Oka deny ever fitting exhaust brakes to any Oka which is interesting. Allan couldn't (or wouldn't) elaborate on why not.
It seems to be a kit fitted by I think " Exhaust brakes Australia" or similar, there was a sticker on it which had the name and phone number but it has disappeared. It is operated by compressed air from an ARB air compressor and has interlocks (microswitches) on clutch, brake and accelerator. It is operated by a two switches on the dash, one turns the compressor on and the second one operates an air solenoid which makes the brake work if all microswitches are closed.
It wasn't working when we bought 374 but with a bit of fiddling I've got the system operational.
BUT when we first bought the Oka several people told me not to use it as the Perkins has weak valve springs which can be kept open by the exhaust back pressure caused by the brake and leading to engine damage (valves kissing pistons). I've asked everyone I can think of, Perkins dealers, diesel mechanics (old ones
) and no one can give me a definative answer as to whether to use the exhaust brake or not.Interestingly looking back through the RAAF records at about 40k k's the head was removed to repair oil leaks and "something else" which was never elaborated on but cost several $K and had a new head fitted. From then on there were several references to "inoperative exhaust brake" in drivers reports at the end of exercises and all the mechanics wrote was "exhaust brake Not Servicable". Reading between the lines it does appear that the exhaust brake may have caused valves to kiss pistons, especially as when I started chasing why it wasn't working it had been rendered inoperative in a very crafty way in two places, one electrical and one in the air circuit. Both would not have been found easily in the field and both required parts to repair, the electrical one had a tag, "DO NOT REPAIR" .
I have tried it out at low speed and it did not seem to work very well, actually not much retardation at all, have not been game to try it on a big hill in a situation where you would use it for fear of causing valves to kiss pistons as it seems there may be something in that line of thought.
Peter
--
Oka 374 LT Van
November 8, 2011 at 7:19 AM Flag Quote & Reply
Tony Lee
Member
Posts: 539
Come over the top of a hill at 100 and lift the foot and very little seems to happen that can be attributed to the exhaust brake.
Need to brake manually and drop it back a gear so the revs are at maximum and the retardation starts being felt and it will make the difference between using brakes rarely and applying them every few seconds.
At lower revs the brake does very little.
On automatics like in the Airstream - say with a six-speed allison, when you lift the foot, the transmission preselcts second gear and the system drops the gears down when it can without over-revving the engine. However, unless you brake manually at the beginning so it can drop down to 5th and then 4th at least, you will still get a runaway situation because the transmission stays in 6th.
If revs rise to the maximum, the transmission shifts up automatically to keep the engine revs down - so if you do the wrong thing on the way down, the electronics just saves the system, not the occupants.
--
Tony
picasaweb.google.com/114611728110254134379
November 8, 2011 at 8:28 AM Flag Quote & Reply
Peter_n_Margaret
Member
Posts: 198
Peter...getting warm and sticky here...
Your report puts a different light on the matter. I will need to find others with direct experience. Don't want to bugger up the Perkins.
Ta Tony. Not expecting miracles, but I reckon any help would be useful.
--
Cheers Peter, OKA196 Motorhome. www.oka4wd.com/xt196.htm
November 8, 2011 at 6:52 PM Flag Quote & Reply
Tony Lee
Member
Posts: 539
Used properly, they will achieve miracles in terms of driving enjoyment and safety. Getting down some very steep long mountain roads in the US with hardly a touch of the brakes gives you the peace of mind of knowing that at all times, you have 100% of your brakes available.
Mind you, at the speed the OKA goes up the hills it would be a real pity to spoil the few chances of getting a decent speed up by going down hills too sedately.
--
Tony
picasaweb.google.com/114611728110254134379
November 8, 2011 at 8:37 PM Flag Quote & Reply
Peter & Sandra James Oka 374
Member
Posts: 412
Ha ha I like that Tony, I've found though that the Oka slows down pretty well on compression when you lift your foot off the accelerator, just an occasional dab of the brakes on most hills, must have something to do with the Rockwell banging and clanging underneath.
Mind you once the auto is in I might find the brakes get a lot more use
))--
Oka 374 LT Van
November 9, 2011 at 6:59 AM
David and Janet Ribbans - Oka 148
Oka148 profile here.
Visit our technical and travel blogs: here.
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