Community Forums

palehorse89 · 12-09-2011, 03:45 AM

[QUOTE=dons2346;1028966]

Quote:

Originally Posted by palehorse89

All I can say is you don't "have your buddy" do anything to your transmission/engine system unless he is a Cummins or Allison tech. If anything goes wrong, it is not "your buddy" that will be picking up the tab.

INFO FOR PERRY WHITE: AS REFERED TO AS "MY BUDDY" HE IS A CUMMINS TECH. I EXPLAINED TO WHAT WAS GOING ON WITH THE HIGH RPM'S WHEN DOWNSHIFTING INTO 4TH AND WHAT I WOULD LIKE AND HE SAID NO PROBLEM. HE HAS DONE THEM BEFORE BUT AT THAT POINT ON THE PHONE HE JUST DID NOT TAKE THE TIME TO EXPLAIN IT ALL TO ME AT THAT TIME.........

THE BIGGEST REASON FOR LOOKING INTO THIS IS IN MOST OF MY DRIVING WHEN I NEED MY EXHAUST BRAKE I DON'T NEED THE HARSH AND HIGH RPM'S OF 4TH GEAR. I JUST WANT IT TO COME ON IN 6TH AND IF NEED BE I'LL SHIFT IT INTO 5TH IF NEED BE. I DROVE TRUCK AND LOGED QUITE A FEW MILES AND I UNDERSTAND EXHAUST BRAKES AND ENGINE BRAKES AND THE EFFECTS THE ENGINE RPM'S HAVE ON THE BOTH OF THEM. THANKS FOR YOUR CONCERN THOUGH.

336muffin · 12-09-2011, 04:33 AM

In my honest opinion, I think I can trust the engineers at Cummins,Catapillar and Allison. I don't think one would do something as to void a warranty of another company that they rely on to distribute their products in a market as big as RV manufactures. I have never heard of a engine brake damaging a engine or a transmission. I'm sure somewhere there is someone that "blames" one or another repair to a exhaust brake or a real Jake Brake. I use mine all the time and have in the last 4 coaches with out a problem.

Dr4Film · 12-09-2011, 05:19 AM

For those reading this thread, there is a BIG difference in how a diesel engine operates that is equipped with a PacBrake versus a Jake Brake.

I can only speak for a PacBrake as that is what my Cummins ISC 350HP came with. I upgraded to the PRXB PacBrake last year and really love the improvement.

I drive with the PacBrake switch activated ALL of the time. I also drive with the cruise control when needed and my ECM's have been reprogrammed to allow them to work together.

I want the PacBrake to activate whenever my foot leaves the accelerator pedal COMPLETELY and if the cruise control is NOT active.

To coast, I simply leave my foot slightly touching the accelerator but with no pressure and that prevents the PacBrake from activating.

Anyone that has a Jake Brake, I am sure that the operation and function is completely different.

Only my opinion.

Dr4Film ----- Richard

Navy Flier · 12-09-2011, 12:03 PM

As a final note to this thread I talked to a Cummins rep on their customer service line today and he said that my engine has a 2200 rpm limit on acceleration and a 2400 rpm limit on deceleration.

powerboatr · 12-09-2011, 01:38 PM

my epa 07 cummins uses the variable van turbo for the exhuast brake or restriction
it does not have the retarding hp the jake brake does
i think it is only 250hp of retarding power compared to higher numbers a jake brake develops

i can have cruise on and the exhuast brake selected to come on if i hit the brakes

also i found on last trip i left it on at highway speeds ( i usually shut it of at highway speeds) i had cruise on and started down a long grade coming into Austin. The cruise mph was set at 65ish and when i sped up due to down hilling it the engine/exhaust brake came on and cruise shut off/dis-engaged

that being said
mine will select 4 or 3 then as speed drops it will down shift to 2.
i will say...loaded and heading down a hill the exhaust brake will NOT slow you down to the point the speed does not increase, without occasional application of the service brakes to pull her back

2200 -2400 is pretty routine for the engine rpm during the exhaust brake event
i use it everytime we are in traffic. it keeps the tranny and engine pretty cool, plus saves the brakes

bdaball · 12-09-2011, 08:50 PM

Just curious. For all who have offered advise and or direction on this post, How many have been to Camp Freightliner and is your input based on knowledge gained there or otherwise?

336muffin · 12-09-2011, 10:00 PM

Professional driver with over 5 million paid safe miles in 48 states and Canada.

Perry White · 12-10-2011, 09:02 AM

Engine brake needs the high revs to work Think about it. If your engine brake is on and you stay in high gear the engine is just above idle speed. No exhaust to back up against. The trans should show a "2" when engine brake comes on. That means it will automatically down shift all the way to second gear if needed. If it is just downshifting to 4th gear that is 1 to 1 in a six speed. You might have it programed only to use the top two gears. If your going down a hill and the weight is pushing you,your engine should be up reving about 2200-2300 RPMS.

Also you want to make sure your fan is enabled with the exhaust brake. While your at it make sure you have exhaust brake discrete lites enabled.

RickO · 12-10-2011, 02:25 PM

Quote:

Originally Posted by bdaball

Just curious. For all who have offered advise and or direction on this post, How many have been to Camp Freightliner and is your input based on knowledge gained there or otherwise?

I haven't been to Camp Freightliner yet. My info came from Cummins/FL techs.

Rick

Crabby Mike · 12-10-2011, 05:34 PM

Quote:

Originally Posted by bdaball

Just curious. For all who have offered advise and or direction on this post, How many have been to Camp Freightliner and is your input based on knowledge gained there or otherwise?

I've been to Camp Freightliner, and as such read this thread without much concern. I don't want to misquote Mike Cody, but as I recall, when the subject of over-revving your engine came up, he said something to the effect of "don't worry about it, the engine and transmission are programmed to work together, and they won't let anything bad happen." I think he went so far as to assure a student that even if you try to downshift far enough to cause an engine overspeed condition, the computer will ignore you, and keep the revs in a safe range.

For what it's worth, I use my engine brake wherever and whenever I feel it helps me, and never worry about the RPMs.

Navy Flier · 12-14-2011, 12:37 PM

Just to make sure everyone is on the same page, the Cummins engine brake does not work like a Pac Brake. When selected, the engine brake system is a hydraulic circuit that opens the exhaust valves (3 in low, 6 in high) near the end of the compression stroke. Therefore, it uses the engine compression for vehicle retardation rather than blocking the exhaust. Also, in my particular system the transmission has never upshifted during a slowdown event. It just keeps working its way to 2nd gear as I slow down. I get gradual retardation through 6th and 5th gear and hard retardation at 4th gear. I believe that is because 5th and 6th are overdrive gears and 4th is the first non-overdrive gear. In any case this has been an interesting conversation. I hope everyone learned something.

Perry White · 12-14-2011, 06:47 PM

While he's in there adjusting what ever you want adjusted, ask him to check your DROOP speeds. He'll know what they are.

Also, do you have a high and low switch on your eng brake?

Old Trucker · 12-16-2011, 02:38 PM

Quote:

Originally Posted by palehorse89

i am just getting ready to address this issue, i am going to have a buddy of mine (w/ laptop and proper software) reprogram my ecm so it does not down shift with the engine brake. i just want to use my engine brake in any gear and down shift as i need to. most of the time at interstate speeds a long down hill grade justs needs the engine brake (pac brake) and not the transmission to downshift to 4th also. at this point i am not sure what options i will have but i will soon see.

Palehorse; I am a retired cross country trucker. I know more about trucks than RV's,. The engine needs to have higher RPM's to create enough back pressure to make the pac brake proform properly. I agree with you, many times just the brake without the trans downshift, is all that is necessary. As an old trucker, we use the exhaust brake on a seperate switch without the benefit of the automatic shift on the tranny. I do not know if you can make these changes you talk about with a lap top, but I would be interested to know. I would be happy with a manuel toggle switch, but I am old school. Good Luck from the Old Trucker.

palehorse89 · 12-17-2011, 06:25 AM

Quote:

Originally Posted by Old Trucker

Palehorse; I am a retired cross country trucker. I know more about trucks than RV's,. The engine needs to have higher RPM's to create enough back pressure to make the pac brake proform properly. I agree with you, many times just the brake without the trans downshift, is all that is necessary. As an old trucker, we use the exhaust brake on a seperate switch without the benefit of the automatic shift on the tranny. I do not know if you can make these changes you talk about with a lap top, but I would be interested to know. I would be happy with a manuel toggle switch, but I am old school. Good Luck from the Old Trucker.

Thank you for your post,you came from the same school that i attended. when higher rpm's were needed for stopping with the engine brake you downshifted to get higher rpm, that is just what i want to do. i don't use my brake a lot of the time just due to the downshift to 4th gear. due to the winter here in penna. i most likely will not be able to test drive it after the adjustments. i will come back and add to the post and let you know what we were able to do with it and what the options were. the guy that is coming over is a cummin's tech and he has the laptop w/ the cummin's software to enter the engines ecm. a lot of reading on the internet on changes to cat engines but not to much on cummins, so we will see. thanks again and have a nice holiday....