Adding Jake Brake to ISC8.3

[Brian63nova]

Originally Posted by bizzerbiz

Yes. Nice layout of your work. I purchased a 2002 Monaco Windsor a few months back and it has the 350ISC 1050 torque motor with the Pac brake 2 stage and bringing it back to Washington I was amazed how the brakes held coming down Mt Ashland in Oregon. Very impressed. Safe travels and Enjoy!

So then you understand my desire for this upgrade very well. I live 20 minutes from the Siskiyou Pass that you’re referencing; highest point on I-5 and I believe the steepest grade as well, but don’t quote me on the grade for certain.
Yes, our old motorhome, with a small 5.9 and true exhaust brake provided much more effective auxiliary braking than the VGT “brake” on this motorhome. Yes it was lighter too of course, but not enough to account for the drastic difference in capability.

[Brian63nova]

Well I finished the rest of the install last of my install. I did discover what I assume is one other difference. The large diameter breather tube coming off the valve cover mounted breather must be longer on the engine brake equipped engines with the taller valve cover. The rubber elbow is too short to reach the breather tube coming up and connecting to the diaphragm looking device at the back of the breather. I am going to get some fuel/oil rated hose and use it in place of the factory rubber elbow. Luckily my suspicions were right and the standard Cummins engine harness had provisions for equipping an engine brake. I found the capped connector zip tied to some breather tubes just above the starter. Cut the zip ties, removed cap and the engine side engine brake harness plugged right in!
Other than that it is ready to go to Cummins for the ECM reflash shortly and i can report back on drivability improvements around town, but no mountain treks until next week.

[Brian63nova]

Originally Posted by mackwrench

Great write up! Looks like a awesome upgrade as well

I can say the valve clearance adjustment is critical on these engines, I set them on the "tight" side of the adjustment... Meaning it takes a fair amount of effort to slide the feeler gauge across the rocker. I've seen them where the cross bridge falls out from a loose setting, makes instant engine miss and lots of raw fuel white smoke.

Just curious..... what it all cost?

On another note, can you explain the wizardry of how three stage engine braking is accomplished on these using a signal to two ECM pins, a single wire to each brake head, two heads mounted over 3 cylinders each????
Also, if you know how my existing on/off switch will integrate with a new multi-position switch. I mean if I’m making wishes that would be great LOL. I know that my existing switch will power the new switch AND my current switch currently signals OEM pin 36, so I can move that wire over to the new multi switch. Then I have to also signal PIN 30, but again how two wires integrate with other sets of two and provide three levels… Have not had anyone able to answer that or reach someone who could.

[shootist]

You have a 2 stage I think. That is all Monaco used on the 400s I've been told.

[Brian63nova]

Originally Posted by shootist

You have a 2 stage I think. That is all Monaco used on the 400s I've been told.

Make no mistake, every mechanical and electrical bone in my body says that is all it can be. BUT, the literature from Jacob’s on this specific brake head says 3 levels of engine braking. I have a request into Jacob’s technical support just to stop my brain cycling over that topic.

I did get back to my wiring harness currently connected to the prior VGT exhaust brake switch. Interestingly it has an unused wire on the chassis side, not connected to the current switch. So, one can only assume this does to the second ECM pin necessary to engage both braking heads.

[Brian63nova]

Well first drive report is in and now I can say it actively decelerates the way a coach like this should! And, I only have one brake head active currently until I add my level switch. On that note, I poked around at my wiring under the dash and made a potentially nice discovery. My harness is labeled engine brake. Interestingly it has 4 wires on the chassis side, 12v hot, black ground, a brown and pink lead. Pink currently does not connect to any wire on the switch side. So, it seems only natural to assume that wire leads to the second ECM pin (30) I need to energize to activate the other braking head. I’m still stumped by the Jacob’s literature reporting 3 level of engine braking and I have a technical request into them. But, even if I end up with 3 cylinders or 6 cylinders as my options, I know I am going to be more than satisfied. We are headed camping next week and should encounter some decent terrain to put it to the test!

[Max Headroom]

Originally Posted by shootist

You have a 2 stage I think. That is all Monaco used on the 400s I've been told.

That's what I'm thinking. Hi/Low 3 or 6 cyl. I have the 450hp M11 and my Jake is a two position. Even though my coach is older (97), I'm guessing they didn't make any big changes to the wire harness unless necessary, and had long thought 2 settings were sufficient for a coach.
I'm assuming that pac brakes are only on/off, so a Hi/Low Jake would seem like a big improvement for most folks.

Really interesting to see someone add a Jake to an existing motor!

I recommend setting it up with the foot switch, rather than the various auto activation methods. My coach is set up like that, and it's so much better than auto activation on service brake application, or worse, activating on every throttle lift.

[mackwrench]

Originally Posted by Brian63nova

On another note, can you explain the wizardry of how three stage engine braking is accomplished on these using a signal to two ECM pins, a single wire to each brake head, two heads mounted over 3 cylinders each????

Also, if you know how my existing on/off switch will integrate with a new multi-position switch. I mean if I’m making wishes that would be great LOL. I know that my existing switch will power the new switch AND my current switch currently signals OEM pin 36, so I can move that wire over to the new multi switch. Then I have to also signal PIN 30, but again how two wires integrate with other sets of two and provide three levels… Have not had anyone able to answer that or reach someone who could.

As others have posted, I don't think you'll have 3 stage engine braking....
While I've only seen a few ISC/ISL with Jacobs, I'm pretty sure they are 2 stage, switch in dash was off/high/low

[Toribk]

Brian63nova:

Glad to see you are happy with your results thus far and are confident going forward.

However, I am still inclined to think your VGT was not functioning properly when you purchased the coach.

Over the years, we have had several Discovery owners have issues with supplemental braking with the Pac-Brake on the older CAT models and the Cummins VGT and most times it resulted in a lack of routine maintenance (Pac-Brake) or in the cases of the Cummins VGT....a mechanical issue or programing errors with the ECM/Allison TCM.

I can honestly say that my VGT has provided me with all the supplemental braking I've ever asked and expected for it to deliver and admittedly, towing a Jeep Trailhawk without a supplemental braking system over mountain ranges in Colorado and Wyoming.

(Before everyone starts with the "its against the law to tow over 3000 lbs without one", I do have one now)

Anyhow, it would have been interesting to see the measurable difference between the two knowing both products were operating at optimal efficiency before your upgrade.

Anyway, check out www.discoveryowners.com and you can search this topic of discussion. There are several threads about supplemental braking.

Thanks for sharing your thoughts and skills with us here.

[Brian63nova]

Originally Posted by Max Headroom

That's what I'm thinking. Hi/Low 3 or 6 cyl. I have the 450hp M11 and my Jake is a two position. Even though my coach is older (97), I'm guessing they didn't make any big changes to the wire harness unless necessary, and had long thought 2 settings were sufficient for a coach.
I'm assuming that pac brakes are only on/off, so a Hi/Low Jake would seem like a big improvement for most folks.

Really interesting to see someone add a Jake to an existing motor!

I recommend setting it up with the foot switch, rather than the various auto activation methods. My coach is set up like that, and it's so much better than auto activation on service brake application, or worse, activating on every throttle lift.

Yes, my “old” system utilizing the VGT was simply and on/off. That’s how my current engine brake is operating until I swap switches, so only signaling one wire on the ECM versus two. I am in touch with Jacob’s and Cummins, with a TSB number finally that is supposed to layout the 3 level engine braking. The literature on the Model 490A, exactly what I installed, specifically identifies 3 stage braking AND I can say our ISL9’s with 3 level braking in my fire engine at work does in fact have 3 discernible levels.

I’m comfortable with and accustomed to the auto-apply engine braking. I’ve learned a driving style over the years to be able to “float” the accelerator pedal so you aren’t actually accelerating but it causes the engine brake to disengage. Then simply lift a little more and get engine brake engagement.

[Brian63nova]

Originally Posted by mackwrench

As others have posted, I don't think you'll have 3 stage engine braking....
While I've only seen a few ISC/ISL with Jacobs, I'm pretty sure they are 2 stage, switch in dash was off/high/low

If it’s easier to accomplish two stage, ultimately it will be worlds better than before. But, Jacob’s does specifically identify the Model 490A as three stage capable; middle of the features and benefits section of the picture. But I’ll admit, wizardry seems like the only explanation as to how this is possible! Lol

[shootist]

The second pin from the ecm is coming from the same wire inside the ecm on mine. You can run both heads from one wire if yours is the same.

[Brian63nova]

Originally Posted by Toribk

Brian63nova:

Glad to see you are happy with your results thus far and are confident going forward.

However, I am still inclined to think your VGT was not functioning properly when you purchased the coach.

Over the years, we have had several Discovery owners have issues with supplemental braking with the Pac-Brake on the older CAT models and the Cummins VGT and most times it resulted in a lack of routine maintenance (Pac-Brake) or in the cases of the Cummins VGT....a mechanical issue or programing errors with the ECM/Allison TCM.

I can honestly say that my VGT has provided me with all the supplemental braking I've ever asked and expected for it to deliver and admittedly, towing a Jeep Trailhawk without a supplemental braking system over mountain ranges in Colorado and Wyoming.

(Before everyone starts with the "its against the law to tow over 3000 lbs without one", I do have one now)

Anyhow, it would have been interesting to see the measurable difference between the two knowing both products were operating at optimal efficiency before your upgrade.

Anyway, check out www.discoveryowners.com and you can search this topic of discussion. There are several threads about supplemental braking.

Thanks for sharing your thoughts and skills with us here.

I completely respect and understand what you are saying. And, obviously at this point I have no way to definitely say one way or the other. However I can say that I didn’t notice any other performance related issues (under power) that would seem indicative of the VGT not functioning appropriately.
But, we can look at the Cummins rating for their “EBrake” - VGT brake and see the differences offered by the Jacob’s.
At 2200 rpm the EBrake offers 151 braking horsepower, versus 274 via the Jacob’s at slightly lower 2100 rpm. At 2400/2300 rpm it’s 178 versus just over 300.

I’m glad yours has performed well for you. Maybe mine wasn’t in fact, we’ll never know at this point I suppose, and maybe my specific driving experience and style with the engine brakes in similar size and weight vehicles just predisposed me to being unhappy with the VGT performance.

I’ll give that link a look. Always happy to hear and learn more. As shown here, I’m the guy wrenching when it comes to our vehicles, so any knowledge is good knowledge!

[n2zon]

Nicely researched, and a bargain basement priced BIG upgrade. Awesome job! (We love the 2-stage jake on our ISL.)