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Old 04-01-2013, 10:31 AM   #1
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Exhaust brake, what should I feel when activated?

I am new to exhaust brakes and was wondering a couple things.... (By the way this is an older exhaust brake, mechanic suggested I get it changes to a newer version. For now I am going to try my older one.

1st what should I feel when I switch it on while driving down a grade and let up off the accelerator?

When I switch it on and off I do not feel much of a difference. Although my mechanic did go through the system to make sure it was working.

2nd when parked, with the switch on, I hear lots of air escaping in the rear of the coach, when I switch it off the air stops. Is that normal?

3rd, now that the exhaust brake is connected the air system is depleting. When the engine is not running It takes a couple hours but empties completely. The braking pressure on my gauges stay in the same place and never goes down unless i hit the brakes. It might be a coincidence but I am thinking since that is the only thing that changed on the air system it is probably causing the issue.
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Old 04-01-2013, 10:40 AM   #2
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I have no experience with older exhaust brakes but with my engine brake, it feels like I've thrown a large anchor out behind my coach when I engage it. There's no doubt that it is on.

Be aware that I believe you need to completely back off of the accelerator for the brake to engage. Just letting up on the pedal a bit won't do it.

I'm having a tough time making a link between the exhaust brake and your air system depleting... but I'm over my head technically on that so I'm sure some of our experts will chime in.

At any rate, having functional engine braking on a large DP is worth its weight in gold IMHO.

Best of luck.

Rick
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Old 04-01-2013, 10:47 AM   #3
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Quote:
Originally Posted by bobioknight View Post
I am new to exhaust brakes and was wondering a couple things.... (By the way this is an older exhaust brake, mechanic suggested I get it changes to a newer version. For now I am going to try my older one.

1st what should I feel when I switch it on while driving down a grade and let up off the accelerator?

When I switch it on and off I do not feel much of a difference. Although my mechanic did go through the system to make sure it was working.

2nd when parked, with the switch on, I hear lots of air escaping in the rear of the coach, when I switch it off the air stops. Is that normal?

3rd, now that the exhaust brake is connected the air system is depleting. When the engine is not running It takes a couple hours but empties completely. The braking pressure on my gauges stay in the same place and never goes down unless i hit the brakes. It might be a coincidence but I am thinking since that is the only thing that changed on the air system it is probably causing the issue.
1. When the exhaust brake engages, you should feel a retarding force similar to driving into deep mud.

2. If the exhaust brake is set up to be closed at idle, you're hearing the engine exhaust rushing around the closed butterfly valve in the exhaust stream. This "whoosing" or "hissing" sound is normal.

3. Unless your exhaust brake is pneumatically actuated and has a leak in the air supply line to the solenoid, I don't see how the exhaust brake could bleed down the air tanks of your MH.

Rusty
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Old 04-01-2013, 11:47 AM   #4
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2nd when parked, with the switch on, I hear lots of air escaping in the rear of the coach, when I switch it off the air stops. Is that normal?
No, this is not normal. An exhaust brake should never be operating at idle.

Find a mechanic who has a slight clue about how an exhaust brake should work. Failing that, find a DP owner that knows a bit about his rig's operation.
Or open up the engine bay and find out where all that air is coming from.

As for what you should feel - given that an exhaust brake only develops about 60% of an engine's rated power as braking force, then when you apply it at 60mph in top gear, any thoughts of it being like driving into an arrestor bed are quite fanciful. If the speed is such that the transmission can't drop down to a lower gear, the best it can do is retard you at 60% of whatever you could accelerate at that speed and in that gear.
If you are driving slow enough that the transmission can slam straight down into second gear and the revs rise to 2500 straight away and the exhaust valve closes, then the results can be very obvious - but a fair bit of that happens anyway even if the exhaust brake is switched off and you manually select second. They are an auxiliary brake and have limitations that make them nowhere near as effective as the proper brakes.
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Old 04-01-2013, 11:52 AM   #5
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No, this is not normal. An exhaust brake should never be operating at idle.

Find a mechanic who has a slight clue about how an exhaust brake should work. Failing that, find a DP owner that knows a bit about his rig's operation.
Or open up the engine bay and find out where all that air is coming from.
Ahem, the Mopar/Jacobs exhaust brake on my 2002 Ram Cummins 5.9 HO was programmed to be closed at idle when the exhaust brake switch was turned on - it was a dealer installed option and was controlled from a dedicated pin on the ECU. I repeat, this was a normal condition. The feature was used to hold EGT at around 500 degF during extended idling to prevent "cold-stacking" and lacquering and resultant sticking of exhaust valve stems as well as to speed warmup from a cold start.

Rusty
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Old 04-01-2013, 11:59 AM   #6
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Some , early , Pack Brake , on Cummins 12 valve engines , would allow the exhaust brake on at idle; to speed up engine warm up.
Once Cummins went to 24 valve, electronic injector pump, I never saw this feature again on the Pack Brake installs I did.
Sorry I see Rusty got in while I was typing.
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Old 04-01-2013, 12:32 PM   #7
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The following is from the Pacbrake installation instructions for a 5.9L Cummins:

Quote:
Turn the ignition to ON and the Pacbrake switch ON. Do not start the vehicle yet. The compressor should start pumping air for approximately 2 minutes (this will fill the air tank from empty). Once maximum pressure is achieved, the compressor should shut off. Wait 2 minutes, listening for the compressor to start up. If the compressor cycles then an air leak is present and must be repaired.

Start the vehicle and allow to idle with the Pacbrake applied. Lightly depress the accelerator pedal and the exhaust brake should release. If not, adjust the throttle switch so the exhaust brake is disabled with light throttle pressure. To check for exhaust leaks, idle the vehicle with the exhaust brake applied and before the engine gets hot, feel around all the exhaust connections for leaks. Repair as necessary.


Road test the vehicle attaining high engine RPM and apply the exhaust brake several times to ensure that it applies and releases quickly. Please note that the exhaust brake will activate whenever the Pacbrake switch is ON and the engine is at idle. This feature can be used to aid in shortening the warm-up time by half.
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Old 04-01-2013, 12:44 PM   #8
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It's interesting to me that the 7.3 liter Ford Powerstrokes came with a warm-up valve that partially closes the exhaust system when the engine is cold. This allows faster warm-ups, just as the Pacbrake instructions say their exhaust brake does at idle.

What's ironic about this is that Ford never used this fast warm-up valve as an exhaust brake. However, many enterprising owners caught on to this and wired a $10 switch to allow them to close the valve when needed as an exhaust brake.

It works quite well, as I have found out.
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Old 04-01-2013, 10:47 PM   #9
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I do not see any air hoses going to the brake so the sound must be exhaust escaping through the valve/brake. This older switch does not automatically downshift. When traveling down a grade should I take my foot off the gas pedal then flip the switch, should I have to downshift to feel the anchor effect? At this point when I am in 5th gear and the switch on and gas released, I really do not feel much of any change.

The air leaks are unrelated, I found a quick disconnect fitting with a leak using a soapy mixture and a spray bottle. I will keep hitting all the joints to be sure they are sealed.
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Old 04-02-2013, 09:39 AM   #10
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Turns out I have a Williams exhaust brake which is air controlled. When activated, the air system pushes a plunger and blade down, blocking the exhaust. I am thinking since I hear lots of air escaping and the brake does not really slow me down, the escaping air is probably either the hose is disconnected, or the plunger is worn out letting the air just escape without pushing the blade into position.
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Old 04-02-2013, 10:00 AM   #11
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It appears the Williams exhaust brake is now marketed as a Blue Ox exhaust brake and is manufactured and marketed by Brake Systems Inc. You might want to contact them regarding parts or replacement units if you stay with the Williams design. Brochure with application and contact information HERE.

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Old 04-02-2013, 12:16 PM   #12
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Quote:
Originally Posted by bobioknight View Post
Turns out I have a Williams exhaust brake which is air controlled. When activated, the air system pushes a plunger and blade down, blocking the exhaust. I am thinking since I hear lots of air escaping and the brake does not really slow me down, the escaping air is probably either the hose is disconnected, or the plunger is worn out letting the air just escape without pushing the blade into position.
The blade in the exhaust is a restriction, not a complete shut off; the engine would stall; so your exhaust sound is going to sound like a leak.
You do have to downshift , if your set up won't do it automaticly.
Exhaust brakes do best with engine RPM over 2000, so you will need to downshift to keep your engine in this range. Later systems do the downshifting, mine drops a gear every time RPM drops below 2000, all the way down to second gear.
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Old 04-20-2013, 11:22 AM   #13
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High RPM's? finally on the road testing the exhaust brake. Headed down a long grade picking up lots of speed, I flipped the switch and feel a little resistance, I down shift and feel much more resistance. Leaving the lower gear and flip the switch off... Speed picking up again... So the brake is working.

The question is the RPM's, I understand the brake works best at 2000 RPM's, but it goes up into the yellow zone marked on the tachometer, nearly reaching the red. Is that dangerous hitting the red without the fuel peddle being used. I kept hitting the peddle brake to keep from reaching the redline, downshifting further just increases RPM's.
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Old 04-20-2013, 11:45 AM   #14
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You have to decide on a control speed for your down hill speed.
Control speed , is the speed at which you feel confident that you could quickly come to a complete stop should the need occour. Depending on the grade that could be 40 to 50 MPH in my coach. I set up at the top of the grade at the control speed and as I go down hill ; watching the tach and speedo; keep the tach between 2000 & 2400 by using the brakes.
When the tach gets above 2500,I use the service brake until down to 2000 then coast again with the exhaust brake , allowing the service brakes to cool. The cooler the brakes the better they will work when you need them.
If you find your having to apply the brakes very often , then you are going too fast and need to slow down to the point where you can gear down the trans and continue in the next lower gear.
The auto gear down feature of the newer systems will not allow engine over reving, trans will shift up when limit is reached. Not the thing you need to have happen , part way down a steep grade.
As I read in another post, you can come down a hill too slowly as often as you like , you can come down too fast only once!
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