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Author Topic: Exhaust brake terminology  (Read 10576 times)

Smoky

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Exhaust brake terminology
« on: April 02, 2005, 01:56:35 PM »
I enjoyed reading the messages here about exhaust brakes, jake brakes pac brakes, etc.  But now I need a terminology primer. What is the difference, if any, between these terms?

Also I noticed that on every test drive, the dealer recommended that the brake be turned on and left on all the time.  somehow this does not make sense to me.  If the dealers are correct, then why the on off button?

Smoky
Smoky S  Ham radio - W3PY

The magic of a campfire
where the fish get bigger
the mountains get higher
the hike was uphill both ways
and new friends become old friends

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On our way to the Poudre River in Colorado for the summer!

Ron

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Re: Exhaust brake terminology
« Reply #1 on: April 02, 2005, 03:36:43 PM »
Smoky,

First to explain the reason for having for an engine brake or exhaust brake on a larger diesel engine vehicle.

Unlike gas engines the same amount of air is drawn into the engine cyclinders on each stroke and the fuel injected is metered to adjust power.  You might say there in no restriction to the air flow through a diesel engine thus with out a exhaust brake or jake brake there is very little back pressure felt from the engine when you lift your foot off the acceletator. It is almost the same as puting the transmission in neutral.  Not much to help you slow down.

In a gas engine, including fuel injected, the air flow iin to the engine is regulated by the butterfly valve in the intake, inaddition to the fuel flow being regulated.  When you take your foot off the accelerator the air inlet is restricted by the butterfly valve being closed and you feel the engine being restricted becuase the iit is pulling so to speak against the restricction in the air inlet.

Some folks will leave the exhaust brake on all the time they are driving.  We normally have it off when traveling on the highway over relatively level roads. We always have it on when going down long hills or any hills that requires braking as well as when driving in traffic like in town.

The pac brake is an Exhaust brake .  They operate by closing a butterfly valve in the exhaust system restricting the flow of exhaust causing a back pressure the engine has to push against,  Thus producing braking action.  A jake brake is a systen which changes the valve timing causing the the engine to act as a compressor of sorts thus producing braking action.  The jake brake is actually a better brake system over the exhaust brake but is more comonly only available on engines over 350HP.  I am amazed that there are some diesel powered motorhomes that are sold without an exhaust brake or a engine brake.  Our 93 Bounder as well as other make coaches with the Cummins 190/230 HP engines did not have any type of engine or exhaust brake.  We added the exaust brake after we got the MH.




« Last Edit: April 02, 2005, 03:41:59 PM by Ron »
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Tom

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Re: Exhaust brake terminology
« Reply #2 on: April 02, 2005, 03:49:45 PM »
Smoky

Pac brake is an exhaust retard system attached to the turbo. When activated, a flap restricts the flow of exhaust gases, causing an increase in back pressure. Activation of the Pac brake also downshifts the transmission from 6th to 2nd on my coach.

Jake brake opens/closes exhaust valves using solenoids mounted on the head. I'll let someone else describe the operation.
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blueblood

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Re: Exhaust brake terminology
« Reply #3 on: April 02, 2005, 06:06:10 PM »
Brakes come in two flavors - exhaust and engine. Engine brakes supply retarding HP and require strengthened engine components for the higher levels. Exhust brakes simply block off free flow of exhaust gases. It's counter to names but engine brakes are the type banned by communities because of the loud noise introduced. Occassionally some town gets it wrong and puts up a sign banning exhaust brakes. Saw one not too long ago in WA. As for leaving the brake on all the time, :o that is a statement sure to get one into trouble. Brakes should never be on when road conditions can be slippery from ice, water or whatever.

Cummins has a new engine brake called InteBrake (meaning brake built into engine) that uses special lobes on a second cam shaft to provide major retarding HP on its big on hwy engine(ISM). Their other engines use the std Jake E-brake (made by Jacobs)  in smallest engine (ISB) and their own design C-Brake (made by Jacobs) in mid range where the engine has a strenghtened block and roller followers.
« Last Edit: April 02, 2005, 06:12:24 PM by blueblood »
Leo

Ron

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Re: Exhaust brake terminology
« Reply #4 on: April 02, 2005, 06:10:53 PM »
Brakes should never be on when road conditions can be slippery from ice, water or whatever.

Good point Leo.  We try to avoid being anywhere it is cold enough for ice or snow but Sam makes sure its off if road conditions warrant it. ;D
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Karl

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Re: Exhaust brake terminology
« Reply #5 on: April 02, 2005, 06:52:48 PM »
Tom,
Not being diesel savvy, when you say it downshifts from 6th to 2nd, is that in one jump or incrementally? I'm thinking it is the latter.
Karl (Cheesehead) Kolbus   Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting "...holy cow ...what a ride!"

Ron

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Re: Exhaust brake terminology
« Reply #6 on: April 02, 2005, 06:59:00 PM »
Karl,

On our coach the transmission selects 4th as the target gear.  It does not shift until the coach is slow enough to allow it to start shifting down.  Some coachs are set up so it will target 2nd but again it only shifts down to the gear approprite for the speed traveling. IOW going 60MPH it wont shift until you are slow enough for the trans to shift to 5th, then on down as speed decreases.  Transmission will protect from over reving the engine.
Ron & Sam-home is where we park it. Currently located   HERE

Ned

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Re: Exhaust brake terminology
« Reply #7 on: April 02, 2005, 07:01:09 PM »
The transmission will downshift as the computer allows.  It won't let you overspeed the engine and it will shift down one gear at a time.  The preselect only determines how far down it will shift.  I could never understand why anyone would want to have the preset to 4th gear instead of 2nd, but some have had that done.
-- Ned -- Fulltimer 1997-2013
1997 Holiday Rambler Endeavor LE
2007 GMC Canyon

Ron

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Re: Exhaust brake terminology
« Reply #8 on: April 02, 2005, 07:06:01 PM »
Our coach came with it set to preselect 4th.  A couple coaches we drove had it set to preselect 2nd and we didn't really carone way or the other.  There has only been a few times when we manually preselected 3rd and I don't recall ever preselecting 2nd.
DSFDF ;D ;D
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Karl

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Re: Exhaust brake terminology
« Reply #9 on: April 02, 2005, 07:08:42 PM »
Thanks all,
That clarifies that point but brings up another question. If the Pac brake is activated, can you still override the gear selection to pick an even lower gear? I realize that you may break the motor or tranny by doing that, but in an extreme emergency, I wouldn't hesitate tossing an anchor out the window!
Karl (Cheesehead) Kolbus   Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting "...holy cow ...what a ride!"

Tom

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Re: Exhaust brake terminology
« Reply #10 on: April 02, 2005, 07:42:00 PM »
Karl

Ned described it the way I should have. Don't know the answer to your second question, and I probably wouldn't want to experiment  :)
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Ron

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Re: Exhaust brake terminology
« Reply #11 on: April 02, 2005, 08:07:41 PM »
Thanks all,
That clarifies that point but brings up another question. If the Pac brake is activated, can you still override the gear selection to pick an even lower gear? I realize that you may break the motor or tranny by doing that, but in an extreme emergency, I wouldn't hesitate tossing an anchor out the window!

The transmission controller will only let the transmission downshift to a lower gear when it is safe to do so without over reving the engine.  One of the transmissions responsibilities is to protect the engine from an overspeed condition. 
Ron & Sam-home is where we park it. Currently located   HERE

Ned

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Re: Exhaust brake terminology
« Reply #12 on: April 02, 2005, 08:19:50 PM »
Karl,

In a word, NO.  You can tell the transmission anything you want, but if would cause the engine to overspeed, it won't do it.  If you get in that situation, you need to stand on the service brakes, but you shouldn't have gotten there in the first place :)
-- Ned -- Fulltimer 1997-2013
1997 Holiday Rambler Endeavor LE
2007 GMC Canyon

Ron

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Re: Exhaust brake terminology
« Reply #13 on: April 02, 2005, 08:23:56 PM »
Karl,

In a word, NO.  You can tell the transmission anything you want, but if would cause the engine to overspeed, it won't do it.  If you get in that situation, you need to stand on the service brakes, but you shouldn't have gotten there in the first place :)

Called anticipate driving conditions. ;D
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BernieD

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Re: Exhaust brake terminology
« Reply #14 on: April 03, 2005, 09:21:07 AM »
Thanks all,
That clarifies that point but brings up another question. If the Pac brake is activated, can you still override the gear selection to pick an even lower gear? I realize that you may break the motor or tranny by doing that, but in an extreme emergency, I wouldn't hesitate tossing an anchor out the window!

Karl

Actually you can. When your tranny is "seeking" say 4th gear and you want it to continue braking, you can push the gear selection button down to 3rd or 2nd. The engine won't downshift right away, just wait until the engine speed is low enough for the next gear. The Allison is a very smart transmission, it is very hard to do anything that will hurt it :)

As to the preselection of gear when the brake come on, that seems to work with the size of the engine. My UltraSport had an exhaust brake (PacBrake) and it preselected 2nd. The TS has an engine brake and much more hp and it preselects 4th. I thought I would miss the 2nd gear preselection when we got the TS but it turns out 4th works fine for the engine
Bernie & Marlene Dobrin
Home is Goodyear, AZ
Missing our Travel Supreme

Gary RV_Wizard

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Re: Exhaust brake terminology
« Reply #15 on: April 03, 2005, 11:39:19 AM »
There is another class of extra braking system not yet mentioned - the transmission retarder.  These are neither exhaust or engine driven; instead they work by impeding (slowing) the revolution of the driveshaft  A few retarders may  use straight-forward friction, essentially a drum brake on the drive shaft, but the most popular type (the Telma Retarder)  is electro-magnetic and slows the shaft via magnetic field action.  Allison also offers a retarder integrated into some of their transmissions. I don't know if it can be retrofitted after the factory or not.

See Telma Retarder
Gary
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Home: Ocala National Forest, FL

Ron

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Re: Exhaust brake terminology
« Reply #16 on: April 03, 2005, 12:39:08 PM »
I think one of the forum members maybe John Wilson had a Telma retarder.  However I have only seen one in Erics display booth at QZ.  Do you have any idea what the cost is for the Telma.  Might be good information for some.  For us the Exhaust brake does fine.
Ron & Sam-home is where we park it. Currently located   HERE

Karl

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Re: Exhaust brake terminology
« Reply #17 on: April 03, 2005, 05:18:58 PM »
I did a little research and found that the Telma retarder uses 12V power to create, in effect , a locked rotor motor. The frame is mounted to the chassis and the rotor is mounted on the driveshaft. Heat generated is dissipated by the frame, and it can be moved to a different vehicle. Not sure how it's controlled, but suspect a mechanical hook-up to the braking system or maybe a pressure sensor on the hydraulic or pneumatic brake line. There is another kind of retarder also - a type of torque convertor which is either integral to the transmission (I believe Allison uses this arrangement), or one mounted externally between the output shaft and the final driveshaft with the stator afttached to the frame. Either electrically or hydraulically operated and modulated, it uses (probably) ATF fluid or something similar and requires external cooling like a tranny cooler in front of the radiator and, thru hydraulic bypassing, it acheives a variable stall speed.   
Karl (Cheesehead) Kolbus   Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting "...holy cow ...what a ride!"

blueblood

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Re: Exhaust brake terminology
« Reply #18 on: April 03, 2005, 05:59:19 PM »
We had these on our commuter buses going to/from Denver airport from Breckenridge. Used them coming down from Eisenhower tunnel into Frisco especially when road conditions were marginal. Initiated from a lever on the steering column as I recall. 
Leo

Gary RV_Wizard

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Re: Exhaust brake terminology
« Reply #19 on: April 04, 2005, 10:24:53 AM »
Industrial Automatic (Telma dealer in my link above) says $5500-$6500, depending on the specific motorhome.  More expensive than a PAC Brake or similar turbo-exhaust-type brake, which is probably why we don't see many of them.  Competitive with Jake or other engine brake, though.
Gary
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Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Ron

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Re: Exhaust brake terminology
« Reply #20 on: April 04, 2005, 01:19:07 PM »
Industrial Automatic (Telma dealer in my link above) says $5500-$6500, depending on the specific motorhome.  More expensive than a PAC Brake or similar turbo-exhaust-type brake, which is probably why we don't see many of them.  Competitive with Jake or other engine brake, though.
Sounds kinda priicey but probably not as expensive as upgrading to a Jake brake.
Ron & Sam-home is where we park it. Currently located   HERE

Ron

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Re: Exhaust brake terminology
« Reply #21 on: April 05, 2005, 10:38:08 AM »
The Pacbrake website has a lot of information on Pacbrake maintnence, service letters etc. click HERE

For lube instructions click HERE

Ron & Sam-home is where we park it. Currently located   HERE

Smoky

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Re: Exhaust brake terminology
« Reply #22 on: April 06, 2005, 06:19:54 AM »
Any one know what kind of brakes are on the pusher I ordered?  Newmar Kountry Star KS3910 with 330 turbo Cummins.

The Beaver I looked at clearly labeled the switch PAC brake.  I think the KS is labeled exhaust brake, but cant remember.

On all the MHs I testy drove, the exhaust braking seemed rather subtle.  Is that actually the case?  It did not seem as noticeable as when I downshift a gasoline vehicle.

Smoky S  Ham radio - W3PY

The magic of a campfire
where the fish get bigger
the mountains get higher
the hike was uphill both ways
and new friends become old friends

2005 KSDP3910 Newmar Kountry Star
Toad - Taurus wagon w/ axle lock
On our way to the Poudre River in Colorado for the summer!

BernieD

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Re: Exhaust brake terminology
« Reply #23 on: April 06, 2005, 09:21:39 AM »
Smoky

The 330hp Cummins is only available with the exhaust brake, compression brake isn't offered on that series engine. PacBrake is a brand name for a particular company's exhaust brake model.

The effect of the exhaust brake is 2 staged; first is the transmission downshift (speed permitting) then the effect of the exhaust backup. A lot depends on the speed at which you are traveling when the brake is actuated. If you are at a good speed and both stages occur at the same time, you can get a significant effect.
Bernie & Marlene Dobrin
Home is Goodyear, AZ
Missing our Travel Supreme

Ron

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Re: Exhaust brake terminology
« Reply #24 on: April 06, 2005, 09:35:34 AM »
Smoky,

The exhaust break efficiency is dependent on engine RPMs at lower RPMs it provide much breaking.  That is why the transmissions are programed to preselect  4th or even 2nd. Then the transimission will shift down as engine speed allows.  At 65 MPH the transmission will not shift down even though 4th or 2nd is preselected until a down shift will not over speed the engine.  As speed allows allows the transmission will continue to down shit to the preselected gear 4th or 2nd.
« Last Edit: April 06, 2005, 11:03:17 AM by Ron »
Ron & Sam-home is where we park it. Currently located   HERE

Karl

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Re: Exhaust brake terminology
« Reply #25 on: April 06, 2005, 10:29:29 AM »
Ron,
Watch your language; this is a framily forum ;D ;D ;D
Karl (Cheesehead) Kolbus   Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting "...holy cow ...what a ride!"

Karl

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Re: Exhaust brake terminology
« Reply #26 on: April 06, 2005, 10:30:12 AM »
BTW, Thanks for a good chuckle!
Karl (Cheesehead) Kolbus   Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting "...holy cow ...what a ride!"

Ron

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Re: Exhaust brake terminology
« Reply #27 on: April 06, 2005, 11:05:14 AM »
Ron,
Watch your language; this is a framily forum ;D ;D ;D

oops, didn't catch that computer error. ;D  Thanks I fixed it.  Could be me so must have been a computer glitch. ;D ;D
Ron & Sam-home is where we park it. Currently located   HERE

Smoky

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Re: Exhaust brake terminology
« Reply #28 on: April 06, 2005, 04:50:38 PM »
Fixed what?  It still is recommending shitting.
Smoky S  Ham radio - W3PY

The magic of a campfire
where the fish get bigger
the mountains get higher
the hike was uphill both ways
and new friends become old friends

2005 KSDP3910 Newmar Kountry Star
Toad - Taurus wagon w/ axle lock
On our way to the Poudre River in Colorado for the summer!

jscuzz

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Re: Exhaust brake terminology
« Reply #29 on: April 06, 2005, 05:43:18 PM »
Quote
Fixed what?  It still is recommending shitting.

Smokey:

That's why Allison says they designed the trans to prevent us dummies from hurting it or the engine. ::) ::)

 

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