Downshifting bad?

[Adam]

The other day I came running up to the skeet range at a decent pace and when I started to slow down, I dropped from 5th to 4th with a little throttle bump to ease the shift before I slowed to turn into my parking spot. The range manager is a good friend of mine, and he commented that downshifting a turbo diesel is really hard on the engine bearings and especially hard on the turbo bearings. He's fairly knowledgeable when it comes to heavy diesel equipment, and had a military license to drive just about everything the Air Force used to inventory, so I'm sure he believes what he's saying, but I'm trying to see how it could be a problem. Should I not try to match engine speed to transmission speed during downshifts? Should I just not downshift while slowing down at all? Or am I even hurting anything?



Thanks all,

-Adam

 

[Diesel Freak]

I think your Range Manager is smoking a little too much herb while out picking up spent shell casings.

 

[illflem]

Article by South Bend Clutch in the recent tdr mag says improper downshifting will damage your clutch, brakes are cheaper than clutches to replace, avoid downshifts.

Highly doubt it will cause engine damage unless you do a 5th to 1st shift at 80 mph and run the rpms up to 10k.

 

[A Johnson]

I don't see how it would be any harder on the engine than turning a Pac-Brake on. Don't do it to the point where you overspeed the engine.



A Johnson

 

[pkennedy]

Adam lets sit back and look at this logically, #1 does a diesel engine produce more pressure on the bearings (con rod, crankshaft) when decelerating with no fuel being injected for combustion or when pulling a hill at maximum boost pressure and maximum combustion in the cylinders. Mr. Fleming, Peter and I had this discussion the other day as per the article and at another site and like Adam said with proper rpm management there should be no clutch or transmission damage when performed correctly. Peter showed pictures of damaged clutches and explained why, all pertained to improper equipment use. Adam as for the turbo problem the most rpm it will see while being fed oil in a running decelerating engine would be about 30000rpm/400 degrees F. Under load at 26psi it could run at 100,000+ rpm/1200-1400 degrees for minutes to hours depending what and when the pulling conditions are. You will be far more likely to kill your turbo by shutting off the truck to soon after driving with a hot turbo and coking the oil on the impeller shaft. To dispell any rumors the Cummins B series engine IS a medium duty industrial engine rated for commercial truck use which when trained to be driven properly should be downshifted to maintain control of the vehicle. If you feel the need to read up on this subject it is described in the driver qualification and training requirement section of the national safety codes in the transportation. Basically short version says that any vehicle decelerating while travelling down a hill or preparing to negotiate another maneuver shall remain in gear to maintain control. One can demonstrate this to themselves with a little experimenting. Adam I do not suggest confronting a superior for the sake of argument but with due respect he is not a truck driving instructor. PK

 

[monkfarm]

I agree with diesel freak and Mr. Kennedy. It sounds like you did the shift perfectly (revving it up to match the lower shift rrrs) and I don't see how it would damage the clutch or engine. Some people are just hyper -critical.

 

[HBarlow]

Downshifting NV-5600

In addition to the preceeding comments, which I agree with, at the summer TDR rally in Columbus, IN I asked the New Venture Gear engineer who claimed he designed the NV-5600 transmission if continual use of the Jacobs e-brake and downshifting would reduce the service life of the transmission.



The engineer told me the transmission was designed to handle the same amount of torque and the same loads when decelerating as it handles when accelerating a truck loaded to full rated GCWR.



I don't doubt that downshifting places a little additional wear on the clutch unless the driver is very skilled and can perfectly match engine and transmission rpm when downshifting.



Harvey

 

[RKohn]

What's wrong with this picture?

He was in the Air Force but only driving the stuff on the ground...



Yup, that's my kinda expert... :--)

 

[GeneralMachine]

Down Shifting

Engine's were designed to pull your truck down the road, the brake's were put on there to slow down and to stop, every Manuel driver uses the engine to help slow down but too much will cause accelerated were to the top ring land on the piston's. every comp, in the engine was designed to do the pulling not the stopping. My 97 is stock 155k now on the same engine & drive train and I use the engine to pull and the brake's to stop, work's for me. Harv

 

[Wirenut]

What about engines equipped with engine or exhaust brakes? Those engines are designed to slow you down just as much as they were designed to pull.

 

[Doc Tinker]

Let's hear from some Million Milers. If they downshift to slow down, then I'll keep doing it.



Doc

 

[GeneralMachine]

PackBrake

Originally posted by Wirenut

What about engines equipped with engine or exhaust brakes? Those engines are designed to slow you down just as much as they were designed to pull.

These Engine's didn't come out with Jake's or PackBrake's from the factory, but the brake setups keep pressure on the cylinder's seems the engine has to work as if it is pulling, instead of trying to unwind like a loaded spring. that's just my opinion lot's of driver's down shift and get away with it. Harv

 

[pkennedy]

Mr White is a flatlander and is entitled to his opinion but not a professional driver otherwise he would have understood my post. I also believe he has never had to put out a brake fire for a fellow driver or clean the seat after BBQing his own brakes. I surely would like for him to show me how to navigate down say the grade into Ontario Ca or equivalent with even a light trailer (4000lbs) without cooking the brakes. Of course he is welcome any time to come trucking and demonstrate his theories in action, however as I have gotten older my nerves ain't what they used to be. I really hate bailing from a perfectly good truck because all that experience went MIA temporarily to disprove logic and prescribed practice. Adam keep practicing on the flats it may save a life some day including yours, know your vehicle it is one of the key parts to good defensive driving. PK

 

[HC]

Originally posted by Doc Tinker

Let's hear from some Million Milers. If they downshift to slow down, then I'll keep doing it.

Doc,

What are you talking about? I don't think the Million Milers ever slow down, except maybe once per day to refill the fuel tank.

 

[Adam]

Professsional drivers and the cost of brakes

Thanks everyone. Some other things I'd like to point out. My brother IS a professional truck driver, been doing it since he left the service in 1986. He prefers to downshift while slowing a load, but says most of the companies don't want their drivers to do it, claiming brakes are cheaper than fuel. Also bear in mind he runs the majority of his loads in Wisconsin and Minnesota, but sometimes wanders over the passes in the Rockies. He has also been known to row a box without touching the clutch. He doesn't do that in his 3500 CTD though, and it's not something I'm willing to do. Done it numerous times in sports cars and such, but never in a truck weighing 7000lbs empty. As for driver awareness, my job requires me to drive anywhere from 25-500 miles a night, at speeds ranging from 15mph to as fast as the car can go without killing me. It all depends on the number of incidents we have happen in the local area, or the events scheduled for the night. Of course an '02 Impala police package handles a bit different than my CTD, but I'm also a firm believer that any time behind the wheel is experience gained. Having attended several driver's training courses (military and otherwise) I have a pretty good grasp on what's going on around me, and agree with Mr. Kennedy that thoroughly knowing your vehicle is the best available tool to not only get you out of a jam, but probably keep you from getting into one to start with.



RKohn, I don't know what your perceptions of the Air Force are, but only 15% of the service get to fly the little planes. The rest make the planes work by providing basic stuff like telephones, food, fire suppression, radio support, life support, etc. You kinda see where I'm going with this. And for what it's worth, I'm quite certain I could gain more experience pertaining to the question at hand from driving stuff on the ground than being an overpaid, glorified airline pilot spelling the girlfriend-of-the-week's name in the sky. How exactly do you downshift an F-16?



Sorry everyone else, had to get that off my chest.



Thanks for the replies, Happy Holidays,



-Adam

 

[GeneralMachine]

Originally posted by pkennedy

Mr White is a flatlander and is entitled to his opinion but not a professional driver otherwise he would have understood my post. I also believe he has never had to put out a brake fire for a fellow driver or clean the seat after BBQing his own brakes. I surely would like for him to show me how to navigate down say the grade into Ontario Ca or equivalent with even a light trailer (4000lbs) without cooking the brakes. Of course he is welcome any time to come trucking and demonstrate his theories in action, however as I have gotten older my nerves ain't what they used to be. I really hate bailing from a perfectly good truck because all that experience went MIA temporarily to disprove logic and prescribed practice. Adam keep practicing on the flats it may save a life some day including yours, know your vehicle it is one of the key parts to good defensive driving. PK

PK You are right there might be time's you need to down shift, or have too but a professional wouldn't let himself get in a spot as to where he would get his brake's afire or bbq them either! I have pulled my 11000 tt all over them thar hills and not burnt up the brakes or had to abuse my ctd each to there own,im hunting the 400,000 over haul.

 

[HBarlow]

Downshifting/Exhaust Braking

To perk up the discussion about use of the Dodge Ram transmission for slowing the truck here are several quotes from Dodge and Cummins Engine Company literature:



From the 2001 Dodge Ram Towing Guide pg. 9:



"Exhaust brake or Jake Brake requirement"



"An exhaust brake or "Jake Brake" is required for Dodge 3500 Pickup and Chassis Cab models pulling a trailer weight of 10,000 pounds or more. "



From the 2001 Dodge Ram brochure pg. 33"



"Jacobs Exhaust brake. For Cummins-powered Rams with a manual transmission, it increases driver control in both downhill situations and level surfaces, especially when towing or carrying a heavy payload. "



From the Jacobs Exhaust Brake For Dodge Ram Trucks Driving Instructions pg. 2:



"Driving with the Jacobs Exhaust Brake"



"To obtain the optimum braking performance from the Jacobs Exhaust Brake, it is necessary to keep the engine RPM as high as possible, but NOT TO EXCEED 3100 RPM. "



"Select a gear that will cause the engine to operate as near to 3100 RPM (but not over that speed) as driving conditions permit. "



I think most would agree that the above quotes from official Dodge and Cummins (Jacobs E-Brake) literature advocate use of the engine and transmission for slowing the truck, particularly when loaded.



Harvey

 

[pkennedy]

Mr. White in posting that there is never a time to downshift in your first post you now admit there may be times where it could be used to your advantage. Adam was asking the question with no experience and looking for information to better understand the positives and negatives, in your first post you left him no alternatives. Your goal to achieve 400k without rebuild is reasonable, to recommend bad driving technique without explantion is irresponsable. You may have travelled loaded with your trailer down some hills and made it safely however you did not explain your method to substantiate your claim. The law enforcement agenies are full of files with substantiated reports of "wrecks" where people were killed or injured because of inadequate driving skills or training especially with unfamiliar vehicles and loads. Again you are right professionals should know most of this but experience is what makes one a professional while adhering to the training one of which says a vehicle must be in gear in order to maintain control. We have gone over this issue with arguments based on opinion continously while others have made an effort to bring facts into the forums. SBC has stated there should be NO adverse effects on the clutch downshifting if done properly. New Venture has also stated downshifting was considered when engineering its products, Cummins uses this product (4B,6B) in all kinds of applications which include decelerations at variable RPM's. Guess what "nobody" with the exception of 1 post has shown any reasonable reason not to drive in a manner using compression assisted deceleration as proper driving technique. Personal goals and interests should never take precedence over safety. I would project that the majority buying diesel trucks will use them for the purpose of towing/hauling. For the few that play race car or use them as daily drivers the service brakes will work fine. When presented with the facts in general vehicles with automatics require more brake maintenance than manual as most people do downshift them to a degree. I have driven logging truck and lowbed in the mountains and had brake problems this is not a good feeling or safe, encountering this condition without knowledge and experience is deadly. Adam obviously realizes that abuse can harm his truck as stated by the question. I have noticed that there are a bunch of junior Billy Big Riggers out here driving CTD's, PSD's and Chevy's that have cranked up the juice so they can truck like the big boys. Thats okay but if you are out of control on the road inexperienced and uneducated with more power and loaded heavier than what you are used to everyday you are Dangerous. These forums as stated before contain valuable information and lots of it but I also see lots of misinterpretation and people who dont read the forums completely. PK

 

[GeneralMachine]

Down Shifting

PK Don't get me wrong I agree that we are all on this forum for the knowlage, Here we are not trying to lead anyone astray, if you will read my first reply all i said was to much was not good and my opinion was it was not good, hbarlow shows what cummins say's, but that is with a ex brake or with a pac installed, as i said with some kind of brake on the engine the engine will work like as loaded. I have seen the results of down shifting and overspeeding engines, too much and your gona hurt the engine, and I think that Adam needed to just keep that in mind. Harv

 

[pkennedy]

Mr White I had reread what you had written before answering back and the way it was stated gave us all a misunderstanding of your meaning. The ring wear issue seems to be false as when ever the engine is rotating under load or not there is a certain amount of wear amongst the components. At times there have been certain issues of excessive wear until the problem was rectified as in the 380HP/3406 Cat where the rings were to narrow and were breaking while jakes were being used. Despite what DC or Cummins says there are also thousands of these engines that run under various conditions (deceleration, high idle, continous high load) that fall outside the "manufacturers" recommended operating procedures. There has not been any published factual documents that Cummins B engines failed continously in these varied conditions any more than if they were run exactly as prescribed. I have witnessed far more B series failures among Dodge pickup owners than industrial. Some of these were product defects but a large number were due to diesel owner inexperience. I dont do anything to my pickup that I haven't done with the other trucks. Equipment owners in the southern portion of the continent do not deal with the conditions that we do continously for weeks or months. The second myth comes from like Adam said trucking companies that recommend free wheeling to save fuel. This type of suggestion comes from pencil pushers not understanding that the same amount of fuel travels through the injection system at idle or higher rpms coasting. On dry roads freewheel stops may not present the same lack of control hazards as adverse but driving schools have always preached " in gear is in control". Thanks to Harvey for those publicized quotes as they are specific and straight forward. Adam take what your training ingrains into you and use it always, this stuff is taught to you for a reason whether on the job or not. I am sorry if anybody was offended by Flatlanders but as a driver trainer it takes 1 misinterpreted comment on an issue like this to screw up 6 months of training because somebody seen it written on the internet. There was one year ago a coach driver that while coming down an 8% grade to a T intersection "listened" to what her friend said kicked it out of gear and "just use the brakes". Fortunately although the light was red no one was hurt but $20k damage to the pickup she hit and $15k to the coach. PK