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Old 03-18-2013, 11:02 AM   #29
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I have a 1T diesel PU. I had an exhaust brake (BD) installed when I only had 50 miles on it. I wasn't impressed with Pac Brake's design. They put a hole in the butterfly to reduce excess pressure so it requires higher RPM to be more effective. Some others use a spring to release excess pressure. Mine works almost down to a stop. A friend got his PU (which was same year & model as mine). He replaced the brakes on one axle (don't remember which) at 40K and replaced both at 80K plus burned up the shoes on his 3 axle trailor. I had tried to get him to get an exhaust brake for years. Along with new brakes he got a Jacobs exhaust brake (also a Jake brake). I have about 90K on my PU and stilll have about 50% brake lining and the exhaust brake is on if I am moving. I haven't replaced any trailor brakes either. I wouldn't be with out it.
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Old 03-18-2013, 11:23 AM   #30
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Lost mine comming down the Sierras and fried my brakes. $12.00 part with a $700.00 labor charge.

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Old 03-18-2013, 01:02 PM   #31
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We didn't have one at first (Tundra towing a 27' TT). Then got one (Dodge 3500 towing a 36' fifth wheel).

What a world of difference. Wouldn't even consider driving the western mountain states with one...

If you are staying in flat states, it's probably not so important.
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Old 03-18-2013, 01:22 PM   #32
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Originally Posted by RustyJC View Post
Since an exhaust brake only engages when the accelerator pedal is fully released, no fueling is taking place; therefore, there's nothing going on to build heat up ahead of the brake. If one has an EGT gauge, they can verify this for themselves; just look at the temperature when the exhaust brake is in operation. Typically, a thermocouple in the exhaust manifold ahead of the turbo will read only about 450-500 degreesF when the exhaust brake is in operation, much lower than the 1150-1250 degreesF or even higher that might be seen at full throttle operation. Therefore, the turbo components aren't being exposed to temperatures even approaching what they're designed to handle.

The exhaust brake works by building up PRESSURE ahead of the brake's closed butterfly valve, not HEAT.

Rusty
Rusty,

I hope you understand that I'm just presenting someone else's argument. Comments that I have read either on this forum or others over the years.

With that said... the temps you present above. Did those come from your own personal observation? I assume yes.

Next, some people support the notion that any restriction downstream of the turbo will cause additional heat. Even an OPEN butterfly valve. Just thinking about it (visualizing it in my head), the exhaust comes out of a turbo spinning at speeds up to 120,000rpm (have read some turbo can reach as high as 200,000rpm). The exhaust comes screaming off the impeller in a spiral, only to almost immediately hit an open butterfly valve that stops the spiralling, and generates additional back pressure. This additional back preasure causes additional heat at the turbo. Again, the butterfly valve is open, but just by being in the exhaust stream it has caused additional back pressure that a non-exhaust brake engine doesn't experience.

So maybe comparing EGT of "on-throttle"/"off-throttle" of the same engine is not really what we need to be looking at. Instead maybe what we need to be looking at is EGT's of engines with exhaust brakes installed vs no exhaust brake installed. Assuming everything else is equal (same engine, same RPMs, etc).

Again... this is not my argument, just something I read somewhere and thought it fit the discussion. ... and is certainly worth discussing.
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Old 03-18-2013, 01:29 PM   #33
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...

If you are staying in flat states, it's probably not so important.
I live in a pretty flat state (Texas) so maybe that's how I've managed to get along without it.
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Old 03-18-2013, 01:40 PM   #34
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Yes, the temperatures I cited were from personal experience on an ISB with a Jacobs exhaust brake that installs directly on the turbo outlet (it replaces the stock cast elbow) of the Holset HX35W turbocharger.

Although the butterfly valve might create a bit of back pressure, look at the modern diesel. My current truck has a NOx adsorber, a diesel oxidation catalyst, a diesel particulate filter and an exhaust silencer all creating backpressure. In addition, the turbocharger itself incorporates a variable geometry nozzle sleeve that moves as directed by the ECM to improve spoolup without providing excessive restriction at full boost - this VGT nozzle sleeve also serves as an exhaust brake by moving to minimum flow position when exhaust braking is called for.

As far as damaging the engine, I'll just point out that Cummins approves the Jacobs exhaust brake and even sells and installs them at Cummins service centers, as does Dodge on the pre-VGT Ram trucks as a Mopar over-the-counter accessory. The one on my 2002 was fully warranted as it was installed by the dealer on my factory-ordered truck before I took delivery. That doesn't sound like Cummins or Dodge are too worried about engine or turbocharger damage, does it?

Cummins - Jacobs Exhaust Brake

Rusty
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Old 03-18-2013, 02:41 PM   #35
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Rusty,

Next, some people support the notion that any restriction downstream of the turbo will cause additional heat. Even an OPEN butterfly valve. Just thinking about it (visualizing it in my head), the exhaust comes out of a turbo spinning at speeds up to 120,000rpm (have read some turbo can reach as high as 200,000rpm). The exhaust comes screaming off the impeller in a spiral, only to almost immediately hit an open butterfly valve that stops the spiralling, and generates additional back pressure. This additional back preasure causes additional heat at the turbo. Again, the butterfly valve is open, but just by being in the exhaust stream it has caused additional back pressure that a non-exhaust brake engine doesn't experience.
vtwinwilly,
Reading through you comment, it seems that your research has lead to the idea that a turbo gets realy hot if using an exhaust brake. In your comment you state the exhaust come screaming off the impeller, causing back pressure and of course heat. However, an engine is nothing more than an air pump; air in = air out. So, would it make sense if the butterflies in the throttle are closed, then not much exhaust is being generated? And with the back pressure in the exhaust created by the brake, there would be very little flow across the impeller preventing excessive RPM's and high pressures on the turbo.
I agree the back pressure of the exhaust brake would generate a higher exhaust temp then none at all, but only a fraction of what the turbo was designed to handle. You want to generating heat in a turbo, pull a steep grade. Some of these turbos will glow red hot for the same reason you stated ealier about the exhaust come screaming off the impeller. There are definatly ways to shorten the life of a turbo, but and exhaust brake would be at the bottom of the list. Hope I haven't "muddied" the waters here. Just trying to provide a clearer picture.
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Old 03-18-2013, 05:06 PM   #36
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As far as damaging the engine, I'll just point out that Cummins approves the Jacobs exhaust brake and even sells and installs them at Cummins service centers, as does Dodge on the pre-VGT Ram trucks as a Mopar over-the-counter accessory. The one on my 2002 was fully warranted as it was installed by the dealer on my factory-ordered truck before I took delivery. That doesn't sound like Cummins or Dodge are too worried about engine or turbocharger damage, does it?

Cummins - Jacobs Exhaust Brake

Rusty
Rusty,

That pretty much says it all doesn't it. Especially if they are willing to back it with a warranty.

BTW thanks for the link. When I do finally decide to pull the trigger and add an exhaust brake, I think the Cummins E Brake would be the way to go.

Of course at the rate I'm going I'll have a new coach with an exhaust brake before I add one to my existing coach. I'm still reluctant to add this to my old C8.3. It's working as is, not sure I want to upset the balance. You know it's kind of like working on the plumbing in an old house, once you start into it, you never really know where it's going to stop as you fix one leak another starts.. then another... and another.. etc.
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Old 03-18-2013, 05:20 PM   #37
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vtwinwilly,
Reading through you comment, it seems that your research has lead to the idea that a turbo gets realy hot if using an exhaust brake. In your comment you state the exhaust come screaming off the impeller, causing back pressure and of course heat. However, an engine is nothing more than an air pump; air in = air out. So, would it make sense if the butterflies in the throttle are closed, then not much exhaust is being generated? And with the back pressure in the exhaust created by the brake, there would be very little flow across the impeller preventing excessive RPM's and high pressures on the turbo.
I agree the back pressure of the exhaust brake would generate a higher exhaust temp then none at all, but only a fraction of what the turbo was designed to handle. You want to generating heat in a turbo, pull a steep grade. Some of these turbos will glow red hot for the same reason you stated ealier about the exhaust come screaming off the impeller. There are definatly ways to shorten the life of a turbo, but and exhaust brake would be at the bottom of the list. Hope I haven't "muddied" the waters here. Just trying to provide a clearer picture.
Just a quick update. I did do a quick google search (not very scientific) and the only reference I could find to an exhaust brake causing turbo failure was one where the butterfly got stuck in the closed position. I suppose that's a risk if you don't maintain the exhaust brake correctly.

BTW... thanks to all for the discussion.

Do we now want to talk about how exhaust/engine braking might effect your rearend, drive shaft and transmission? The braking force puts loads on these components in the opposite direction from which they were originally designed.
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Old 03-18-2013, 06:27 PM   #38
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One thing that has been muddled in this thread is that compression brakes (Jake Brakes) and exhaust brakes (some of which are also made by Jacobs) are totally different in design and implementation. As was previously stated an exhaust brake is essentially nothing more than an exhaust flow restriction.

A compression release engine brake uses an extra lobe on the camshaft to open a second exhaust valve at the top of the compression stroke. The stem of this valve telescopes during normal operation so the valve remains closed, but is locked at full length by a solenoid when the engine brake is engaged so that the valve opens as directed by the cam. When a compression release engine brake is active, this extra valve releases the pressure from the cylinder before the piston starts back down, so the slowing effect is present on the up stroke, but no accelerating effect is present on the down stroke and the net effect is the vehicle slows down.

With a compression brake in operation engine horsepower is essentially being used to slow the vehicle down. With my C-12, at engine rpms close to redline, roughly 300 hp is directed into braking. It's very reassuring coming down a long steep grade to feel that I might actually have to gently give it a little fuel to keep our speed up because we are slowing down so much. I agree that vehicles can safely be driven without an engine brake, but I sure wouldn't want to own a DP that didn't have one.
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Old 03-18-2013, 06:57 PM   #39
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How important is an exhaust/jake brake?

My coach weighs 24,000 lbs, has hydraulic disc brakes, a workingPacBrake, 130,00 miles and brake pads that are worn less than 50%.
Try to accomplish that without an exhausts brake!
Mel
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Old 03-18-2013, 10:35 PM   #40
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Old 03-18-2013, 10:46 PM   #41
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You know, I've never paid any attention to the EGT's when using the exhaust brake to see if it raises or lowers the temps. My EGT is mounted in the exhaust manifold before the turbo as per Banks instructions. Since the fuel is completely shut off I can't see where there would be much, if any raise, in the EGT's when it's in use.
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Old 03-19-2013, 09:24 AM   #42
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Quote:
and the only reference I could find to an exhaust brake causing turbo failure was one where the butterfly got stuck in the closed position.
Had to drive a bus home that had the butterfly stuck almost closed. 10mph maximum with huge clouds of black smoke billowing out the exhaust pipe. Not sure how that condition could cause turbo failure.

My MCI weights 17 tons and has a 4-speed manual crash box and drum brakes all-round and no auxiliary braking.

Get too fast and it is impossible to change down a gear because you can't match the revs, so if you let things get out of hand, all you have is some pretty crappy braking and that doesn't last long.
No alternative but to make a judgement at the top of the hill and get in the right gear right at the start. 15mph all the way down in first gear is a bit of a drag, but since I have just come up the other side at 15mph, I'm used to it.
All the fancy gear like auxiliary braking, auto or synchromesh gearboxes certainly make for easier driving by drivers who don't realise what the limitations are, but I still shudder when I see a tag axle big rig with a big trailer on the back wheeling down a steep grade in the fast lane at 75mph without a care in the world.
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