Engine brakes

gpg58, Oct 1, 6:52pm
Bought a 1989 hino bus on here, and notice the the exhaust makes a very loud hissing noise constantly when sitting running, but goes away when i turn engine brake off. Checked vacuum hose connection at actuator, and it was loose, but that did not fix it, so think noise is brake is actuated although stationary in neutral, without touching brake pedal.

Thinking about it, (but not a truck driver so don't shoot me), the vacuum brake light in dash stays on constantly if system is turned on(lever on steering column), is that normal? i would have thought light would only come on when they actuate, ie when you use brake pedal, am i thinking right? (suspecting stuffed brake pedal and/or accelerator pedal switch's, or someone's stuffed round with wiring).
Have seen a circuit diagram, and it seems to indicate i could be right, but would like some advise on usual operation before ripping into it.
oscars.emporium, Oct 1, 8:10pm
In my experience, when the system is live, the engine brake is activated by the accelerator pedal, not the brake. The engine brake should activate when you lift of the accelerator and stop when you start to press down again.
strobo, Oct 1, 8:12pm
Exhaust brakes v engine brakes ?They both interact so guess it doesn't matter .Anyway leaking air within the vacuum pot . the rubber diaphragm has sPlit .I had years ago repaired my own with bango patches ! But if cof people are aware of brake alterations they will fail it. I do suggest a whole new unit incl /butterfly if it is worn will leak exhaust fumes as it's all part of the brake system if you find these parts worn out or faulty.
Use a prybar at lower butterfly cam linkage at lower vacuum pot against the spring and check it freely moves all the way up and down .Check the mechanical side first.
gpg58, Oct 1, 8:19pm
Ok, thanks, that's interesting, so it would be on when stopped with feet off in neutral. Will test if accelerator switch is working, before looking for a fault that may not actually be there.
However, Here's the diagram i found, Which indicates light would be on when accelerator and brake switch's are closed.(light "never goes off" if system is on, so do not think pedal switch's are normally closed ones.)
https://trademe.tmcdn.co.nz/photoserver/full/1411016820.jpg

Think it is operating ok, (just never listened to one up close before) as hiss goes away when off, and does sound like its inside exhaust, not at actuator itself(its mounted immediately in front of muffler). Hard to check whats up on my own, will get someone to operate brakes, accelerator etc while i watch, when i can.
strobo, Oct 1, 8:33pm
Correct but usually only when in motion or engine running above 2000rpm you can't replicate that test but down the road . Some may have a master brake switch on the panel and a secondary switch at the steering column (combo switch unit) to be aware of .Most now just activate at the combo.The other switch is at the clutch pedal ! Isuzu use a very similar type of system!
bigfatmat1, Oct 2, 8:03am
Exhaust brake should operate when in gear only via neutral switch. There is a clutch switch and a accelerator switch. It should disengage in neutral, foot on clutch or when accelerator is pushed. The light should operate when the exhaust brake switch is switched on. They do not have a low rev cut as stated above that is Jake's brake different system. Also if you have the engine warm up switch switched on it will use the exhaust brake actuator to warm engine up quicker while idling.
gpg58, Oct 2, 9:56am
Thank you, i see i missed that diagram is clutch not brake pedal, opps.
Vehicle owners handbook says warmup switch should increase revs, but it does nothing at all(that i can see or hear), except turn light on(book also warns against driving with it on)but will check if it operating actuator now, thanks. Strange that diagram does not show neutral switch in circuit, but do recall seeing one on another diagram, will have another look thru them all. cheers
kingfisher21, Oct 2, 12:50pm
As above, not always true, some exhaust brakes will still operate when in neutral, my Hino motorhome does, as does a lot of other light truck, buses I've driven, some when doing this idling in neutral make a hissing sound has the exhaust is restricted. So going by what you describe in your original post everything is normal light and all, exactly the same as my 1989 Hino.
gpg58, Oct 2, 1:17pm
Excellent, mines a motorhome/house bus as well.
Can now confirm clutch and accelerator switches are working(was easy as engine revs change when disconnected).

Question though, my exhaust brake light operates regardless if key is on or not (ie with only dc isolator on).

Also does your ones revs increase with warmup switch on? cheers.

I also think engine temp my be in the exhaust brake circuit in some way, as when first started just now, it was not actuating, but 2 minutes later it was(perhaps it was vacuum not yet built up though).
gpg58, Nov 12, 5:55am
Additional question, my front heater(engine water one) is/was gutless.
Have traced pipework, and see 2 further ones, (one mid bus and one at rear) have been removed, and pipes joined together (supply inlet and outlet) with a loop of hose. Also i see a water pump in circuit, which never runs (think rear ones turned it on originally). However there is a shut off tap by pump, which is in water circuit for rear heaters, which i have now closed, and heat is a lot better, even though pump not running (water supply is simply being pushed thru it).
So wondering if others also have this heater water pump, and if it runs (with only a front heater).
Thinking of ripping all this excess pipework out, and perhaps pump as well, as most of it is fairly rusty anyway, and thinking will get better flow still, with pump gone.(unsure if making it run would be safe, without other circuits taking some of flow/pressure)

Also going to rip out all the unused air conditioning pipework and compressor, thinking may put a second alternator in compressors place (may put a 12v one to charge house batteries).