2 more exhaust brake questions

[Rick Vyncke]

Does the 2004 Marquis have a Jake Brake or a PAC Brake?  I ask because (as I understand it) the PAC Brake is external and therefore needs maintenance in the form of periodic lubrication whereas the Jake Brake is internal and therefore lubricated by engine oil. Ultimately trying to determine if I need to lubricate something or not.

Second question.... I know my exhaust brake works because it downshifts into 4th and slows the coach.  With that said, I can feel little difference between high and low other than high illuminates 2 lights on the dash whereas low illuminates 1.  They both shift into 4th.  Are the differences supposed to be subtle or should there be a more obvious difference. 

Thanks!!!

[David T. Richelderfer]

Rick -  Our coach is a 2004 with a Cat C12, 505 hp engine and it has a Jake Brake.  I leave our Jake Brake on the high setting almost all the time.  If I take my foot off the acelerator or drop the cruise control, then I want the coach slowing down immediately.  I had our transmission reprogrammed to stop it from dropping from 5th or 6th gear down to 4th when the Jake Brake engages.  If you do a search on this automatic downshifting, then you will find a substantial number of posts with most opinions not liking the downshifting because it forces a near over-revving of the engine RPMs.  As I understand it, Jake Brakes have three braking settings but our coach allows for two settings on a three-position toggle switch - high, low, and off are the three settings.  I find a great difference between the high and low settings when engaged.  Interestingly, on the Silverleaf screen there are three colors representing the Jake Brake when engaged.  The colors are red for the high setting, yellow for the middle setting, and green for the low setting.  So, even though the toggle switch allows for two settings of engagement, the Silverleaf shows it passing through all three settings while slowing when the cruise control is engaged.

[Rick Vyncke]

Thanks Dave!   Assuming we too have the Jake brake... our coaches are quite similar. 

I don’t mind the downshifting.... although I have learned that the Jake brake does not slow the coach sufficiently on steep grades.  Went over Wolf Creek pass last week (9 miles of 7% grade) and I had to downshift to 3rd along with the Jake brake to keep from increasing speed.  Good news that’s a once a year trip.

Thanks again for the feedback.  And just to confirm.... there is no needed maintenance on the Jake brake - is that right???

Rick

[David T. Richelderfer]

Rick -  I do not expect my Jake Brake to completely hold back nearly 25 tons from increasing speed down a several percentage point grade.  I remember going down the east side of Lookout Pass on I-90 east of Wallace, ID several years ago.  I do not remember the grade percentage but I am thinking it's about 6%.  As I crossed the summit heading east, I had the cruise control off and was going 55 mph with the Jake Brake on the high setting.  I would let the coach's speed increase to near 60 mph, then touch the brakes to slow to under 55 mph.  I had to touch the brakes every 10 to 15 seconds.  Using the brakes is okay; the idea is to not heat the brakes such that the pads glaze.  A glazed brake pad is slick and offers little braking due to loss of friction.

We travel over Cabbage Hill and Hilgard on I-84, and over the Tonopah, NV grades, for example, going to and returning from our winter residence in Yuma, AZ.  In all cases, the Big Jake, as I call it, will not hold the coach's speed from increasing on those steep downhills.  Due to the tighter corners on Cabbage Hill, I get the coach down to under 45 mph before the viewpoint turnoff because right after the viewpoint there is a 45 mph corner.  On the Hilgard side, I do the under 55 mph to over 55 mph speed control similar to the Lookout Pass grade.  On the Hilgard grade, there is a 60 mph corner at the bottom!  In all these cases, I need to touch the brakes every 10 to 15 seconds to manage the coach's speed.

In one day short of eight years of ownership of this coach, I have not done any Jake Brake repairs or maintenance - lots of other expensive repairs though!  We purchased this coach on August 24, 2012 from RV Sales of Oregon in Eugene, OR as a consignment sale.

[Stan Simpson]

We did a 14% grade (we have a Pac brake) from Torrey, UT just outside of Capital Reef National Park, to Escalante, UT. Utah Hwy 12. Our Pac brake downshifts us to 2nd gear. It was a distance of 64 miles, took us 3-1/2 hours. Only touched the brake a few times. NO guardrails on the curb side! 800+foot drops right next to the edge on a narrow road.

[Bill Lampkin]

Jake brake is adjusted as part of "Overhead Service"; i.e. valve adjustment.

[Dave Atherton]

Gentlemen, this is a very good talk about experience descending steep grades . What I can see
With several post we are talking about two types of braking systems. Yes the compression brake on
sleeve engines will hold back excess pressures where a exhaust brake will only hold back engine
exhaust exiting the engine . The term Jake brake which is commonly used with engines with
exhaust brake or PAC brake but does respond like the compression brake which the term Jake
Brake comes from. The compression brake adjustment is required anytime the engine overhead
is worked on. Dave Atherton Retired Cat Mechanic

[Joel Ashley]

Rick, I think the guys pretty well answered your questions.  My simple take is that smaller engines like a C9 just aren’t built for a compression brake, but do well with the exhaust (external) type.  So anything larger than a C9 can have a compression (internal) type.  Whether the Jake Brake is standard or optional on C12’s and C15’s is for others here to say.

So you won’t need to worry about lubing yours, but take Bill’s and Dave’s service advice.

Joel