Community Forums

EngineerMike · 08-12-2011, 05:43 PM

Coupla clarifications, since I've been waist deep in this:
1) Cummins installs & services its "CBRAKE by Jacobs" on ISL's and above, a device which mounts in a spacer under the standard rocker cover and works w/the engine valves to provide braking. ISC's and ISB's use (when installed) an exhaust brake, basically a butterfly valve in line w/the exhaust pipe to put back pressure on the engine slowing the crankshaft & therefore the vehicle.
2) CBRAKE operates by opening the exhaust valves at the top of the compression stroke to exhaust compressed air, then closing so the piston is blowing off the compressed air energy instead of allowing it to push the piston down. Basically the engine uses energy compressing air on the upstroke, then releases that energy, via the Jake, which would otherwise push the piston down on the down stroke. W/out the Jake operating, energy burned on upstroke is mostly compensated for in the down, so engine doesn't provide a lot of resistance.
3) Engine has a rev limiter which is controlled via the transmission shift and fuel/air table, so engine won't blow itself up. However, in gear 6, running down a sufficient hill, the rig can run away and there is no relief for that other than service brake, since there is no further braking the engine can apply and its just gravity till you step on service brakes.
4) the downshift "seek" can be set in the Allison programming. Some come programmed seeking 5th, others 4th, etc. The seek, however, won't override the rev limiter, so in 6th it has to first seek 5th (i.e. rev down in 6th to a level that will not over-rev 5th), then seek 4th, etc.

OF- on mine either Hi or Lo work in CC (even tho my Hi Jake function is busted). My 06 it came w/Jake programmed Off in case of CC, so if Cruising I had to tap brakes disabling CC to allow activation of Jake. I like the Jake-enabled-in-CC better for the reasons you state.

I'm hopeful Cummins West will get my Hi function fixed next week. Wish I were confident as well.

Renipladlo · 08-12-2011, 06:27 PM

OF & EM - hmmm, Is their some way to test if the CC and EB are enabled to work together (choice of words might be wrong).

Should I then set CC and see if when it backs off on setting the jake comes on? Don't want to take it someplace and have it tested, like allison or cummins since they would want money most likely.

Don't think I want to have 5th gear as a option either since it does not have a lot of hold back, guess I will leave it the way it is, since I understand it's function now, and would have to re-learn it all over again. Someone said they were/have had it reprogramed, but no results were posted.

bcbowers · 08-13-2011, 05:05 PM

FWIW - My engine brake does NOT activate with either "Low" or "high" selected when CC (Cruise Control?) is active. The CC simply backs off when traveling downhill but the engine brake does NOT engage. I have to tap on the brake pedal or press the CC "Cancel" button in the Smartwheel to cause the engine brake to activate (assuming my speed is low enough to allow the engagement).

EM - I don't know what's absolutely correct but you might ask your Cummins dealer when you have it fixed.

EngineerMike · 08-13-2011, 07:13 PM

BC- you can have the engine brake programmed one of two ways- work under CC or don't. Yours is programmed don't. It can be switched if you want.

Mine comes on under cruise to control speed as set for cruise, plus works after taping brakes releasing CC. I prefer that setting greatly. My 06 was like yours, no Brake under CC.

ORV'r- Yes, and Yes. Set CC and then observe on downhill if it engages brake to hold speed. Could go either way; don't know when they switched programming option.

OldForester · 08-13-2011, 10:04 PM

ORV'r -- on my 06 the auto cruise enable minimum speed over set in cruise control is 6-7 mph. Mine didn't come set for it and so that's why I had Cummins Yakima set it, but they couldn't set it any lower than 6-7 mph -limited by software. So if it's working, and CC is set for 60, it will have to reach 66-67 before it engages. That's why if I'm in hilly terrain with a lot of ups and downs -- such as I-5 in Southern Oregon, I set the cruise for 58 so it won't go over 65 as it starts going downhill. When the jake comes on at 65 it will reduce the speed almost immediately, and go back to 58 before it releases, then wait for it to climb to 65 before it engages again.

That's why I wanted a lower overrun speed above CC, but it's just limited to 6 to 7 mph. Still, I like it a lot and use it all the time.

Make sure you have CC set on high when you try this and give it the 7 mph or so to see if engages.

If you have a recent printout of your ECM settings, there's a section on cruise enable and you can see whether it's set for on or not.

EM-Sounds like you have about as much hope on fixing our hi setting in Jake Brake as I do high idle adjust. Haven't got the nerve up to disconnect the ECM connector and see if I can get a ground signal on pin #45 with high idle set, as I've learned has to be there for high idle to work. Something about being under the coach with the engine running and the ECM disconnected that I'm not quite ready to do myself. In the meantime, I now have a new and improved high idle stick that allows me to adjust the tension on the throttle with the power seat adjustor. A few more tweaks and I may have to apply for a patent.

takepride · 08-14-2011, 02:07 PM

Quote:

Originally Posted by EngineerMike

Mine comes on under cruise to control speed as set for cruise, plus works after taping brakes releasing CC. I prefer that setting greatly. My 06 was like yours, no Brake under CC.

eMike:

Is there a reason you prefer the Jake not to engage on CC? I've always thought that it'd be way more convenient for speed control in CC to use the Jake.

Renipladlo · 08-14-2011, 03:36 PM

All - again, it might be nice (will have to test it as OF suggests) to see if EB engages after CC reaches it's set point going downhill. But, since the cummins person I talked to did not seem to know if I could overrev the engine going downhill I will keep doing as I learned in CDL driving Class, which is, don't go down any faster than you went up the hill. Now I know we don't have nearly the weight of the big rigs, but, with our hydraulic braking system, and numerious failures to that system for a variety of reasons, I wont push it mugh higher than 50 and even then over some downhill roads, that is even too high a speed. I will see if the CC and EB are set to work in harmony, but wont' leave it that way. Real worried about overrev situation, especially after getting a non type answer from cummins. Suggest at the Jan QZ rally we see if we can get a Cummins Tech to give us some information in person backed up with documentation. OF do you have good contact in the Yakima Store to suggest this?

takepride · 08-14-2011, 06:57 PM

Quote:

Originally Posted by Renipladlo

Now I know we don't have nearly the weight of the big rigs, but, with our hydraulic braking system, and numerious failures to that system for a variety of reasons, I wont push it mugh higher than 50 and even then over some downhill roads, that is even too high a speed.

Am I missing something? I've never heard of numerous failures with the hydraulic braking system with the Meritor calipers, which were installed on coaches after 2001 (maybe as late as May 2002, mine are the new style).

I've always felt the hydraulic braking system is a superior design (that whole air vs. hydraulic thing), but numerous failures??????? I'm not sure brake failures are any more common on our systems than others. Calipers hanging, etc. are usually traced back to poor maintenance, not design.

That aside, I agree with the downhill speed matching the uphill, given the same grade. I'm also heading out to lube my calipers....

Renipladlo · 08-14-2011, 08:33 PM

You are maybe missing something, but my guess no, just maintenance. In fact one of the attendees to the Anacortes rally had brake failure coming over the Mt Hood Highway into Sandy, OR. He had not had his brakes fluid flushed like he should have and the water in the system turned to steam, and he had no brakes coming down the mountain into Sandy. He was going slowly, and by pumping the pedal “like a madman – his words, and downshifting he was able to stop, he said it was his third brake failure since he had owned the coach.

So problems with the brakes are something that can happen with this system, Engineer Mikes Recommendation to have the brake fluid flushed at every other year interval should be followed, too many owners don't even know of this maintenance requirement, especially folks who have purchased an alpine, and have not owned one prior to now. And dealers won’t do it because they most likely don't have enough profit into the sale of a coach from a company out of business. So they don't inform the buyer, I have never read the words about it in the owner’s manual, and the only reason I am aware of it, is I have done my cars myself because it's something I know you need to do on them.

Hydraulic braking systems are one of two designs for large medium to heavy duty systems; the other is air based systems. Superior?, I won't say, but it needs regular maintenance just like air based systems do. Regular maintenance needs to include power flushing the brake fluid system and the 30K hydraulic reservoirs filter and fluid change requirement. Alpine did not do a good job of making sure owners are aware of this maintenance item. I don't have the owner’s manual in front of me to see exactly what their words are concerning it, but, it's something that needs to be done, and remember, the rear wheels need to come off the coach to get to the upper bleed screw/valve unit.

Do the calipers need to be lubed on all model/year coaches? If so, the next gearhead session, we need a primer on it. Again, if the rear wheels need to come off, I don’t have the equipment to do that.

Route 66 · 08-15-2011, 06:02 AM

Folks, we're getting

with brake discussion.

Let's get back to the Jake Brake discussion.

EngineerMike · 08-15-2011, 05:03 PM

Take- I wasn't clear; the 08 has Jake function set to come on to control speed during CC if the Jake is On in either Hi or Lo. That's the program option I think works best for me.

When going thru the rolling flats of I-5 in CA, I run in CC w/Jake off. No sense in not taking advantage of the fuel savings from the rig using gravity on shallow downhills. On big hill sections I just shut CC off, and run w/Jake On. With just Jake-Lo function that still works fine up to maybe 7% downhill. Around 8% I have to use service brakes a fair amount and that's where I start to need the more vigorous Jake-Hi which I hope to have restored some time this week.

takepride · 08-15-2011, 11:25 PM

eMike:

Thanks. I am thinking that arrangement would be best for me, too. I'll see in Cummins Cal Pacific can program that. (They seem unable to program anything else, though.)

Dirk needs to read our forum more often. If he thinks THIS thread is off topic........

bcbowers · 08-16-2011, 01:26 PM

EM - On a related note based upon your previous post, does using the EB affect fuel economy? I would have assumed that not pressing the accelerator stops adding fuel to the engine even when using the EB and therefor can't affect the fuel economy. Perhaps this is the reason why ny fuel ecomony dropped by atleast 1 - MPG on my last trip after getting a new turbo charger and fixing the "High" EB (which I use almost exclusively).

EngineerMike · 08-17-2011, 12:18 PM

BC- My theory on fuel economy and running w/jake or not is probably unimportant as a function of fuel cost, and certainly so as a function of motorhome ownership cost. The retarding to my preferred running speed of 60 on a weak downhill keeps the coach from running up to maybe 63 on a downhill to start the next uphill or to coast a bit going onto a flat w/the added inertia. Over a lifetime (and probably w/in any one week of driving) I'm confident the savings rounds to $0.00.

Your issue may be different. There were some improperly programmed ISL engines in model year 2004 that I know of (2003 builds), and so might also be in late 03 M.Y. rigs, that the EPA forced Cummins to reprogram when next they entered the system. Those reprogrammed engines saw a significant drop in fuel mileage with the new compliant programming. iRV2 has a Cummins forum w/threads on this subject. There were some Alpine'rs reporting 13mpg who dropped to 9-ish IIRC. This is a by law reprogramming and Cummins cannot reverse it w/out facing further fines (they paid a fine when the non-compliance was discovered). Also, I had a recalibration on my ECU which dropped reported mileage by about 15%; I knew the original mileage reports were bunk, and the recalibration came out w/in a small margin of my tank/pump calculation of mileage both before & after the recal.

Alternative theory- if your recent trip was short, or atypical for volume of hills, you may have had a high fuel use trip. Averaging 1,000 miles when I do a fuel usage check should get you to a usable average, but its good to know what hill country will do to that average over a short (say 3-400 mile) run.