Exhaust break

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Reece
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Re: Exhaust break

Postby Reece » Tue May 15, 2018 7:12 pm

it would be interesting to see the practical result of trying to roll down a hill in a low gear with the engine off.


Is that not what an exhaust brake normally does? Cut fuel, prevent combustion and absorb energy by turning the engine into an air compressor? I'm sure I read in a truck engineering book recently that turning off the fuel supply was an essential part of an exhaust brake. Will dig it out...

crinklystarfish
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Re: Exhaust break

Postby crinklystarfish » Wed May 16, 2018 7:53 am

Done a little bit more web-trawling.

Retro-fitting exhaust brakes to pickups in N America seems popular and cutting fuel doesn't seem to be a prerequisite:

https://youtu.be/Tqegu2YKeKY (if you can bear to watch)

There are some vague references to cutting fuel on Neil's engine on the following thread but most mogs that share the engine seem (reading between the lines) to have the system Neil described - ie a twin air-ram style setup to 1) operate the exhaust butterfly and 2) lock the throttle pedal up. Reference to warming the engine whilst operating the exhaust brake strongly suggests fuel is not cut:

http://www.benzworld.org/forums/unimog/ ... om352.html
Last edited by crinklystarfish on Wed May 16, 2018 1:52 pm, edited 2 times in total.

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NeilandPat
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Re: Exhaust break

Postby NeilandPat » Wed May 16, 2018 11:49 am

Interesting link to the EN thread Steve.

I am now not sure if the fiel is completely shut off. I think it is but will happily stand to be corrected.

All I can say is that when activated the throttle pedal is rammed up to the closed position.

When in nuetral pushing the heel button is the only way to stop the engine which it does immediately.

Howeve when releasing the retarder after a long down hill there is no sensation of the engine re firing up again it is seamlessly smooth.

Who knows. I am doing some work on the engine in the next few days so i will have a close look at all the push rods and linkages.

On a different note I am currently following a a thead in the MB section of Expedition Portals Forum. Its about tortion free subframes. Its between an american, canadian, brit and an australian and they all have your book and make several references to it. Its become the must have guide.

Your an international writer now and no coffee table would be complete without it.

Neil

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Re: Exhaust break

Postby crinklystarfish » Wed May 16, 2018 2:29 pm

Thanks for the info, Neil. Nice to know.

It will be good to eventually get to the bottom of whether the fuel's cut or not on your engine. I'm finding the whole thing intriguing to the point of realisation that I'm sat behind a keyboard pondering stuff I don't really need to ponder instead of being out there living my life. :roll:

Looking forward to seeing what you find.

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NeilandPat
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Re: Exhaust break

Postby NeilandPat » Mon May 21, 2018 12:31 pm

Ok folks

I have had a really good look at how mine works and the simple answer is I don't know.

As previously described my throttle linkage is by pushed and at the mid section of these roads it is attached to an arm that pushes the rod in its closed direction when the heel button on the exhaust brakes pressed.

There is only one for that connects the throttle to the pump and no electrics that I can see.

My assumption is that when I take my foot of the throttle the rods return to an idle position letting a small amount of fuel through to allow the idle.

However when the button is depressed it moves the rod that bit further and cuts the fuel off.

The fuel is definitely cut off when the button is pressed as this is the only way to stop the engine other than stall it. And it kills it instantly.

I am pretty confident that this is how it operates.

Neil

Ivan C
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Re: Exhaust break

Postby Ivan C » Mon May 21, 2018 1:17 pm

Sounds sensible and logical to me
Ivan C

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NeilandPat
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Re: Exhaust break

Postby NeilandPat » Tue May 22, 2018 4:24 pm

Another great advantage of the exhaust brake shutting off the fuel is that after an oil change you can turn the engine over with your heel on the button to build up oil pressure and pump the new oil around before you fire it up

Neil

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Re: Exhaust break

Postby Toby3 » Sun May 27, 2018 5:42 pm

Hi Neil,

Have the same set up I think in the Merc 1124 fire engine. Certainly have the same heel kill button on the floor, just hadn't realised it was also an exhaust break. Its currently in the garage getting a load of work done on the cab so can't go out and play.

Can I check on yours, will it only stall it in neutral or any gear when stationary. Trying to work out when it works as an exhaust break rather than kill switch. Do you have to be moving or is simply having it in gear enough (that might sound odd, think yours is a manual, mines an auto so can be in gear and engaged without moving.

Thanks for this, I was following debate thinking about retro fitting so its a bonus to find might already have it.

Cheers Tobias

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Re: Exhaust break

Postby bromleyxphil » Sun May 27, 2018 8:29 pm

I promise I will get back on this thread when I know a bit more.......could be a long time.

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NeilandPat
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Re: Exhaust break

Postby NeilandPat » Mon May 28, 2018 12:57 am

Hi Toby

Welcome to the group.

Yes if in neutral it kills the engine but when moving and in gear it regards the engine. Howevef, it doesn't put the brake lights on so be aware of that.

It can be used in any gear but the lower the gear the more regarding. I don't know if there is time limit but I have had mine on for stints well over 10 minutes at a time with now proboems.

Thought you would have finished your build by now

Neil


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