Compression Vs. Exhaust Brake

[npfd801]

Thanks for the heads up. Between looking through my quoting software, on the net to try and make sense of what's out there, I really screwed this up...

Sorry.

[chiefengineer11]

Joel, recheck your terminology here, correct me if I'm wrong. Jakes (and C-brakes), unless I've been in outer space for some years, are the compression brakes. They work on changing the valve timing in order to make the engine into a big air compressor. Exhaust retarders, (Pacbrake and the like) work by partially blocking the exhaust so as to create resistance in the cylinders.

Stay safe out there, everyone goes home!

[npfd801]

I don't think anyone here will argue that a true Jake brake will perform better than a compression brake. And like Sam said, you won't see a true Jake on the smaller diesel motors many of us are forced to use for our engine choices.

Keep in mind, if your rig exceeds a GVWR of 36,000 pounds, the thing must have some sort of auxillary braking system per our friends with the NFPA, so you will have to have something if you exceed that weight. I don't think you're debating about having some sort of additional braking capability at this point, but I thought I'd throw that out there.

We have three engines all with exhaust brakes, and they all work well for our application. No doubt we'd try to have true Jake's if the motors were large enough, but the exhaust brakes are a lot better than nothing.

For those who read my original reply, I've been without sleep too long...let me fix this. Sorry guys and gals.

[chiefengineer11]

Telma retarders

I don't have any personal experience with Telmas, but from fleets and what I've been able to learn by studying them for possible use on our engine, this is my understanding. Like anything else, there are applications where they're great, and others where they're not.

Telma retarders normally go into the driveline. That is, the driveshaft is cut and the Telma is placed in between, sort of like a pump transfer case. So, first, you have to have space for it. The retarder unit has to be supported and placement of it for driveline angle purposes is critical. There is another version of it that was developed with Rockwell (now Meritor) that bolts to and becomes integral with the rear. That eliminates or reduces the placement/angle problem. I don't know, but I think that's the version that FDNY uses. One of their people or FWDbuff could probably shed more light on that point

Unlike all of the other retarders, the effectiveness of the Telma is not dependent on engine speed. They are extremely powerful and are capable of bringing the vehicle nearly to a stop without using the service brakes. They can be modulated more than the others. But they are very heavy, require large amounts of electrical current, and generate lots of heat when they are in use.

I remember being at an ATA truck show in Chicago in the early '70s and hearing of an electric retarder that did not require any power input. It actually generated power as it functioned. How and where it dissipated the power is something I never learned or have long since forgotten.

Like others have said here, exhaust retarders are generally not as effective as compression brakes. But on the smaller engines (C9 Cats, ISC Cummins, 40 Series Detroits and the like), compression brakes aren't usually available.

Hope this helps you make your choice.

Stay safe out there, everyone goes home!

[firepiper1]

We have been using Telma Brake Retarders for over 20 years, without a problem. Look at that as an option.

http://www.industrialautomatic.com/html/telma1.htm

[MG3610]

If I had a choice, I would spec. my fire apparatus with a Telma brake retarder... FDNY has used them for years on their fleet of apparatus with little to no problem.

We have them, they suck

[NozzleNutz]

If I had a choice, I would spec. my fire apparatus with a Telma brake retarder... FDNY has used them for years on their fleet of apparatus with little to no problem.

[VanIsleEVT]

Not to steer you in one direction or the other but the C-9 is now available with a compression brake for 2007.

[rpierce]

I would do some checking on the cat c-9 engine. We just spec'd a new pumper. I went to our local heavy truck garage and talked to the service manager and he told us to stay away from Cat. Local town highway departments have been having big trouble with them. Dropping turbos, loose oil pumps and so on. They recomended we go with Cummins. Also when I was at SeaGrave Canada they told us same, stay away from Cat.
We have a Rescue truck with a Volvo chassis with a Volvo engine \ exhaust brake, very impressive when you let off. Tranny is programed to go into second gear.

If I had a choice I would go with a Jake Brake.

[lvwrench]

Look at the overall unit size, weight, etc and the territory you are running in to see if the engine brake is really needed. My personal feelings are from a safety standpoint as well as brake life; so then the numbers of runs could be a factor. I fully understand budget restraints but then again way safety and all the rest of the factors in before cutting yours and the crews and citizens throats by not getting something to save money that might wind up saving lives.

[MG3610]

Thank you for the info so far. The dilemma here is on a new engine we are specing we are trying to incorporate verbage into our section about the motor that allows more than one manufacturer of motor to be eligible. We have looked at Cat and Cummins (the meduim duty engines). The cummins ISL and Cat C-9 are our two possibilities. I just discovered that the C-9 is only offered with an exhaust brake. I wonder why? I don't know alot about engines, so thats why I come here to ask. We had said no exhaust brakes in the beginning, but the engine is a big ticket item. We can save about 7 grand going from an ISL to a C-9 but that limits us to an exhaust brake.....kinda in a dilemma, we are up against a very very tight budget and 7 grand means alot. What do we do???

[SSHANK42]

I would agree that the "Jake Brake" is the way to go. One thing to be mindfull of is how it is programmed. They can be programmed to call for downshifts at different points. The faster they downshift the higher the rpms and the more braking effect it has. Fire0099881 is correct that they can be much quieter now than in the past, but to me the only thing that sounds better is the sound of an old 4barrel carb. sucking the hood down.

[fire0099881]

I have used both, the compression brakes seem to slow you down quicker without using the brakes as much, especially on long grades. although they are quite loud, they are doing many things to try to muffle them now these days, the exhaust brake does an ok job, it will tend to hold you at a desired speed on a small downhill grade, but if you ask me I would go with the compression brake aka "Jake brake"

[lvwrench]

Rather than try the full explanation here go to www.pacbrake.com or http://en.wikipedia.org/wiki/Jake_brake and you will get the explanations there. Or post at www.evta/forums.com for more from the mechanic side.

[MG3610]

I would like to know some details from some of you mechanics and engine gurus about the upsides and downsides of both types of engine brakes. Thanks.