Exhaust Brake ?

[mechmagcn]

I have a R-Model, with an EM6 300, that only pulls a 16K 5th wheel trailer. I was wondering if Mack ever used an exhaust brake? What would be the downside of using one on my truck? Some of the exhaust brake manufacturers are using a 4" brake assy. in the exhaust that just clamps in a flange like the turbo to exhaust pipe connection. This would be easier and cheaper for me to fit than to retrofit to a Dynatard or Jake.

Jeff

[Packer]

Paul Vanscott has done a bunch in this area.

Look up his thread and check it out.

Packer

[vanscottbuilders]

Jeff,

There are several exhaust brake manufacturers, all with basically the same idea.

The units simply provide a controlled obstruction in the exhaust system to pressurize the

exhaust back through the cylinders, to provide resistance to the piston coming back up on the

exhaust stroke.

It's a very simple principle, and a very effective way of getting engine braking from a diesel.

However, it is not without risk.

First - the higher rpm diesels are more efficient at exhaust braking. Mack engines, with redlines of 2,100 or so,

are slow turning, and thus, not as good at exhaust braking as the new "pick-up" diesels, which wind up to about 3,500 rpm.

Second, and most important, pressurizing the exhaust system also provides resistance to the valve train by making the

valve spring work harder to close the exhaust valve. Therein lies the rub - particularly with older engines. The valve springs

need to be beefed up to stiffer units, if you are going to use an exhaust brake with substantial back pressure. (ie.: more than 25psi)

The unknown piece of this puzzle is "how strong does the spring need to be?" Too strong, and you will be doing damage

to the valve train and camshaft, and, if not strong enough, the valve will float, and potentially contact the piston.

That's not typically a desired result!

Other diesel manufacturers (Cummins, Caterpillar, and Detroit) have all offered exhaust brakes as options in the past.

The Williams exhaust brake was the pioneer in the field. As Jacobs engine brakes became more popular, exhaust brakes

fell out of favor, for the above mentioned problems.

Today, they seem to making a comeback with the advent of diesel motorhomes and pick-ups.

Mack, as near as I can tell, never offered a factory approved exhaust brake. There were a lot of units installed by the dealers.

Probably made for some interesting warranty conversations, when the engines failed.

From my research, I have found that the Mack 673 and 711 series diesels were designed for 35psi backpressure, as new.

Age and hours weaken the valve springs, so it stands to reason that a used engine will not stand that pressure.

With a healthy valve train, I would not be afraid of a 30psi brake unit. Again, however, you only have about 2,100 rpm

to work with. As the revs wind down, so does the braking effectiveness. In the end, I am not certain the effort is worth it.

Keep us posted.

Paul Van Scott

[mechmagcn]

Thanks Paul. Looks like you have done the research. I would be adding an exhaust brake for little reason seeing as to how my engine is a EM6-300R. This engine is governed at 1800 RPM, so the brake effect would be almost non-existant.

I would guess my next question would be: How much does the engine brake cost for this engine? I probably wouldn't ever need it.... but would like to have it when we travel through the mountains.

Thanks again, Jeff

[MACKS]

A jake brake kit would cost you around 15 hundred or a little more, you might be able to find a used one for a lot less, in my opion a dynatard is not the way to go I have one on my truck and it's pretty much useless, I also have a truck with a jake and the differernce is like night and day.

[vanscottbuilders]

A jake brake kit would cost you around 15 hundred or a little more, you might be able to find a used one for a lot less, in my opion a dynatard is not the way to go I have one on my truck and it's pretty much useless, I also have a truck with a jake and the differernce is like night and day.

Jeff,

I suggest that you talk to Barry at Watts Mack - they have a TEC engine brake kit for all two valve diesel

Mack engines. TEC is a good replacement for a Jacobs brake. Jacobs apparently does not offer the two

valve engine brake for the Mack engines any longer.

Paul VS

[fjh]

>Mack, as near as I can tell, never offered a factory approved exhaust brake. <

This option was offered for several years late ninteys it was called (Stealth Brake)!It was A jake brake exhast brake combo!The valve springs had to be changed in order to install with the jake!Not sure if you would have to change them with an exhast brake alone!ON a CH it was fitted under the passenger side floor board just before the flex pipe!

[mudslut28]

I have seen a bunch of them..just not sure what kind they were. Never owned a truck with one either. I remember some RD800's having them in the mid and late 90's but I really dont think they helped that much.

[vanscottbuilders]

I have seen a bunch of them..just not sure what kind they were. Never owned a truck with one either. I remember some RD800's having them in the mid and late 90's but I really dont think they helped that much.

You guys are way too new for me. My experience and knowledge of Mack stops in the early 70's.

Sorry if I have given out any bad information.

It would be my guess that the reason for the exhaust valve spring beef-up for the optional combo engine brake was for

the pressurizing of the engine, as I said earlier here. That is the primary stress point of the exhaust brake.

Paul Van Scott

[mudslut28]

No didnt mean to come across that way at all Paul...I was talking about the exhaust brake that worked with the engine brake..I think Mack called it the Stealth Combo when it was out? I think even those required a longer pushrod and a stiffer exhaust valve spring so your info was corect as well. Just talking slightly different things I believe. Im sure your knowledge trumps mine anyways so dont ever think Im tryin to step on any toes. I have learned a ton reading this board even after messin with them all these years.

[vanscottbuilders]

I appreciate that, Thanks.

But I meant what I said about my old knowledge -

you guys who know about the newer trucks have a leg up on me.

And you're right - this is a great forum for the exchange of info, and don't ever be afraid to correct anybody here.

Thanks again,

Paul Van Scott