Lowering shift points for 545RFE

Ripple · **Posted:** Fri Oct 30, 2009 3:49 pm

I drive roughly 40 miles a day at 60mph (speedo readout) for my daily commute. at this speed the 545RFE is tuned to be in 4th gear (.75:1 overdrive) this puts the car at 1900RPM for as long. i found that if i speed up to 65mph and slow back down to 60 it will stay in 5th gear (.67:1 overdrive) and about 1700 RPM, 200 RPM less. this is a pretty well known thing, but its right where i run the car.

I think that dropping 200 rpm and increasing the load to make the same power will give the engine about 2% more thermal efficiency, and this should translate to ~1.3 MPG more. classic down-speeding MPG increase.

my question is: is there any economical way to change the shift point on the '06 CRD? i know there are some tune-it-yourself chips coming out that may allow me to tune the shift to my driving style, but they are at a price point that makes it an irrational buy for the money. i would like to pull the 5th gear low-load shift point to 55mph, down from 65mph and the 4th gear low-load shift point to 45mph down from 55mph. i would want the medium load shift points to be left alone, in case i find myself needing to tow anything.

I also looked at the effect of installing 3.55:1 axle gears, and the amounted to only a .5 MPG increase. the gear swap would cost between $1000 for new gears, to as little as the work to swap diff's with a 3.7L gasser who would want the 3.73:1 ratio the CRD has already. given all that trouble, running a more favorable shift point looks like the easiest way to lower cruise RPMs.

CRDMiller · **Posted:** Fri Oct 30, 2009 5:49 pm

1. Your speedo may be wrong, matter of fact i can almost guarantee it.
2. What size rubber do you have. go to the mfg website and find your size.

3. We can easily change shift points by modifying the revs/mile setting in the computer. This will make your odo way off, and could cause undesirable low speed shifts (that you could always get out of by giving it some power (f37 will jump out of a low gear real fast)

The computer goes from what i believe was 600 revs a mile to 800 revs a mile.

My shoes are 650 revs a mile at 32 inches (straight up 32 inches) I had that programmed into the jeep at a local dealer (30 miniute job, takes 3 minutes, took them 2 hours)

When it was set up stock (29.2?) (712 revs/mile) with taller rubber (32), before i got it re programmed, i was grabbing top gear at 70+ (real) mph.

SO if we tell the computer we have BIG (35+) rubber, when we have smaller shoes, we get sooner shifts, and a useless speedo.

AFAIK there is no other way to change shift points, and i've emailed every tuner on the planet, even guys that have hardware/software that changes 545rfe shift points to whatever you want, on a hemi, they say it wont work with the liberty.

I would love 4th at 40 mph and fifth at 55 or 60 depending on input. (like 15% vs >=50%)

edit, check out superchips flashpaq, that thing can reprogram the shift points in 545rfe's in hemi's. I would love to try to swap tcm's with a hemi and flash it, and swap them back.

Joe Romas · **Posted:** Fri Oct 30, 2009 7:15 pm

Ripple.

Your speeds and shifts points are the same as mine (maybe 64 instead of 65) are after F37. Before I could get into 5th at about 59 mph as I recall (It was "F-37ed" two weeks after I bought it)

MrMopar has indicated, ok hinted, that there "might" be a transmission tune forth coming. Think GDE :lol:

Miller.

Hemi's have a combined ECM/TCM and we have seperate units :wink:

Ripple · **Posted:** Fri Oct 30, 2009 8:11 pm

i also am positive my speedo is off, have verified with GPS and radar its ~4-5% low. so 60MPH on the speedo is really exactly 56 mph. i thought it would be more clear to talk in terms anyone can relate too. the tires are stock goodyear ST's with 86K on them, maybe .050" of tread left on them @ 45 PSI.

good info so far thanks for the replys!

I'm a little worried if GDE does make a tune that includes shift pattern changes, they appear to only be interested in performance, and anything "performance" orientated can command a price greater than its true worth to the users. so I don't see them making a gas-saving tune, that would include a revised shift pattern, for a price that would make sense. it would have to be less than $200 to have a fuel savings payoff in close to 2 years, and all their tunes are over $500. plus any additional work and development on their part would only add to the cost....here is to hoping.

CRDMiller · **Posted:** Fri Oct 30, 2009 8:49 pm

You may never break even from buying a crd for mpg, over your old vehicle.

So have some fun and a little better economy. I have a IM II and scored 41.2 mpg on a 200 miles day trip last week, i was amazed. I changed out my diff fluids from 75-140 to 75-90 and went from 36 to 41.2 This is at 65 mph (62 indicated) 1750 rpm (1705? cant remember)

But i've done a lot to it, however this is the best i've ever gotten.

I usualy get around 28 combined, in a hilly area, 50/50 with a ton of traffic (east San Diego County)

Diggerfreek · **Posted:** Fri Oct 30, 2009 9:20 pm

First, as far as I know, didn't the crd's come stock with the 4.10 gear set?

Also, B&G, http://www.bgperformancepcm.com/ might be able to help you with the TCM reflash. I don't know how much that know/have ever done on the CRD, but it may be a second option to GDE

geordi · **Posted:** Fri Oct 30, 2009 9:42 pm

CRDMiller wrote:

You may never break even from buying a crd for mpg, over your old vehicle.

So have some fun and a little better economy. I have a IM II and scored 41.2 mpg on a 200 miles day trip last week, i was amazed. I changed out my diff fluids from 75-140 to 75-90 and went from 36 to 41.2 This is at 65 mph (62 indicated) 1750 rpm (1705? cant remember)

But i've done a lot to it, however this is the best i've ever gotten.

I usualy get around 28 combined, in a hilly area, 50/50 with a ton of traffic (east San Diego County)

Hmm.... That is a BIG jump for just changing the differential oil. I've never done it, how hard is it? How often should it be changed?

over 200k miles on my 97 ZJ, and that was never changed either... Until it ate an axle end bearing on the rear passenger. Sounded fun while it was going tho.

Diggerfreek · **Posted:** Fri Oct 30, 2009 9:46 pm

geordi wrote:

CRDMiller wrote:

You may never break even from buying a crd for mpg, over your old vehicle.

So have some fun and a little better economy. I have a IM II and scored 41.2 mpg on a 200 miles day trip last week, i was amazed. I changed out my diff fluids from 75-140 to 75-90 and went from 36 to 41.2 This is at 65 mph (62 indicated) 1750 rpm (1705? cant remember)

But i've done a lot to it, however this is the best i've ever gotten.

I usualy get around 28 combined, in a hilly area, 50/50 with a ton of traffic (east San Diego County)

Hmm.... That is a BIG jump for just changing the differential oil. I've never done it, how hard is it? How often should it be changed?

over 200k miles on my 97 ZJ, and that was never changed either... Until it ate an axle end bearing on the rear passenger. Sounded fun while it was going tho.

Easy to do and should be done every 30K

Ripple · **Posted:** Sat Oct 31, 2009 10:54 pm

Diggerfreek wrote:

First, as far as I know, didn't the crd's come stock with the 4.10 gear set?

Also, B&G, http://www.bgperformancepcm.com/ might be able to help you with the TCM reflash. I don't know how much that know/have ever done on the CRD, but it may be a second option to GDE

thanks for the link, this is exactly the technology I was looking for! unfortunately they want $1000 per TCM tune, plus custom modifications. would almost be cheaper to put in a manual gear box or new diff gears.

this is sort of a catch 22 for the CRD, we have a very unique PCM/TCM configuration, and overall this is an fuel economy oriented vehicle (ie an excursion diesel can do everything the CRD can plus more at 15 MPG, instead of 28mpg+). but all the possible mods are uneconomical. sigh.

danoid · **Posted:** Sat Oct 31, 2009 11:16 pm

CRDMiller wrote:

You may never break even from buying a crd for mpg, over your old vehicle.

Compared to my 2002 3.7L KJ I broke even at 42k miles. Comparing it to the Hemi Durango I drove in the middle is a joke. The CRD gets the same mileage towing my 27' 5600# travel trailer as the Hemi did unloaded.

I wouldn't be holding my breath on the trans reflash. I talked to the Mopar aftermarket transmission guy and told him I could hand him the changes needed on a silver platter with a small market eager for it. They're not interested. It's locked and proprietary software so it's going to be real tough for anyone else.

Wish I could report a happier picture.

Joe Romas · **Posted:** Sun Nov 01, 2009 8:22 am

danoid wrote:

I wouldn't be holding my breath on the trans reflash. I talked to the Mopar aftermarket transmission guy and told him I could hand him the changes needed on a silver platter with a small market eager for it. They're not interested. It's locked and proprietary software so it's going to be real tough for anyone else.

Wish I could report a happier picture.

And that's another reason why the once "big three" is now a "also ran" :roll:

Ripple · **Posted:** Sun Nov 01, 2009 10:37 am

not looking good for putting in a lower gear at tranny rebuild time either. basically jeep put the deepest overdrive ratio they have in the CRD, no other transmission over the entire DCX line has better than a .65:1 OD, so when it is time for a rebuild it could not get any better.

also looked at really deep axle gears, they make 2.71:1 gears for the 8.25", but the D30a is super limited in available ratios, I'm not even sure if anything other then OEM sets are even available. tomorrow i'll run the MPG numbers on 2.71:1 gears with the .75:1 "4th" gear and see if it would be worth it. it would be a massive 520RPM reduction in cruise engine RPM, 55mph (60 speedo) would be at 1360 RPM, and that same speed in 5th gear would be 1130 RPM, a 750 RPM drop! as long as there is more than ~20 PSI it should cause damage from lugging the engine, its a diesel anyway. specified minimum pressure is 10 PSI at idle and 29 PSI at 3800, the oil relief opens at 94 PSI. just to be sure, can anyone post warm oil pressures in the 1000-1900 RPM range?

other than this, the only way to get marginally better down-speed would be slightly taller tires, like CRDmmiller suggested. only problem with messing with tires is that I have found with only one or two exceptions aftermarket tires weight LOTS more than the lean, 29 lb OEM goodyears. looks like a 32" tire would knock down the RPMs by 115 RPM and a 31" tire by 60 RPMs. not alot.

flman · **Posted:** Sun Nov 01, 2009 11:04 am

Tight fit, but I wonder if we could squeeze a Gear Vendors OD unit under the Jeep?

kdlewis1975 · **Posted:** Sun Nov 01, 2009 11:36 am

Ripple wrote:

not looking good for putting in a lower gear at tranny rebuild time either. basically jeep put the deepest overdrive ratio they have in the CRD, no other transmission over the entire DCX line has better than a .65:1 OD, so when it is time for a rebuild it could not get any better.

also looked at really deep axle gears, they make 2.71:1 gears for the 8.25", but the D30a is super limited in available ratios, I'm not even sure if anything other then OEM sets are even available. tomorrow i'll run the MPG numbers on 2.71:1 gears with the .75:1 "4th" gear and see if it would be worth it. it would be a massive 520RPM reduction in cruise engine RPM, 55mph (60 speedo) would be at 1360 RPM, and that same speed in 5th gear would be 1130 RPM, a 750 RPM drop! as long as there is more than ~20 PSI it should cause damage from lugging the engine, its a diesel anyway. specified minimum pressure is 10 PSI at idle and 29 PSI at 3800, the oil relief opens at 94 PSI. just to be sure, can anyone post warm oil pressures in the 1000-1900 RPM range?

other than this, the only way to get marginally better down-speed would be slightly taller tires, like CRDmmiller suggested. only problem with messing with tires is that I have found with only one or two exceptions aftermarket tires weight LOTS more than the lean, 29 lb OEM goodyears. looks like a 32" tire would knock down the RPMs by 115 RPM and a 31" tire by 60 RPMs. not alot.

The 2008 KK's equipped with manual transmissions apparently came with 3.21's in the axles. From what I can tell, they also have a Dana 30A front axle, so this may be the only possibility for going lower. While not as significant as above, these would still lower the RPMs by a good chunk and may not be as drastic in terms of lugging the engine. I also looked and places like Mopar Parts America does sell them.

geordi · **Posted:** Sun Nov 01, 2009 12:13 pm

If a gearset was available, that would have to be cheaper than trying to stuff a Gear Vendors under there... How hard to change them out tho? Can the slightly-better-than-average grease monkey handle it?

Ripple · **Posted:** Sun Nov 01, 2009 1:17 pm

kdlewis1975 wrote:

The 2008 KK's equipped with manual transmissions apparently came with 3.21's in the axles. From what I can tell, they also have a Dana 30A front axle, so this may be the only possibility for going lower. While not as significant as above, these would still lower the RPMs by a good chunk and may not be as drastic in terms of lugging the engine. I also looked and places like Mopar Parts America does sell them.

this is an excellent piece of info! Thanks for posting. looks like for around $350 of parts, plus ~ $200 supplies, this approach might work. (minus $50-100 resale on the old 3.73 gears) the nice thing about gears compared to a shift pattern change is that the downspeed benefit is at all speeds. and in a jeep so-called highway gears are not going to hurt any of the capability, it has a deep first gear and there is always low range. FYI 3.21:1 gears will give about 260 RPM drop compared to 3.73:1, will crunch the MPG increase tomorrow. plus i have been wanting to put in a trac-loc in my 06, and this would be a great time.

however, depending on the MPG increase it may be less of a deal than the GDE tune, which also is 550. they indicate that they can get 2-3 MPG more with their ecotune. so optimistically that's $185/MPG increase for GDE.

thanks for the link to mopar parts america, great deals!! however i found the best price on a 3.21:1 rear 8.25" gear on ebay

the next question is how does one change the speedo so that it reads out correctly? is there a chip/tuner or does the dealer alone do this. Thanks!

kdlewis1975 · **Posted:** Sun Nov 01, 2009 11:09 pm

The gear set for the 30A is the only one that has to be bought from a Mopar source. There are lots of sources for the 8.25 gears. I have been researching this for a while. Unfortunately, I'm not a position yet to take the plunge. Once I get the Jeep paid off, I'll be able to do mods.

I've read many times, and see this for myself, that we get the best fuel mileage when we keep the tach under 2000 rpm. The thing is that I don't understand what the greatest contribution is...the lower rpm or the lower aero drag (which is a squared relationship relative to speed mathematically).

It would be interesting to see what a GDE tune plus a set of 3.21 ratio gears would do economy-wise. With the extra power, there would be less concern for lugging the engine.

For the speedo thing, it will probably depend on the year. I have a 2006 and from what I've read, it just uses the ABS sensors to determine the speed. So, for a 2006, it seems that one wouldn't have to do anything. I seem to recall the 2005's having a sensor that goes to the differential housing, and if it's looking for something on the diff, this could be an issue. One of our more knowledgeable colleagues would need to confirm and/or conjecture.

I also wonder if changing the gearing would affect the electronic stability program adversely. Would the shift points change substantially? Putting this together from different posts...it seems that our shifts are triggered based on the combination of throttle position and speed.

In terms of pay off, some of this is hard to justify. Some people just get gratification (me being one of them) from getting that higher mpg number and sticking it to OPEC in a small way...and use the mathematical payoff thing to justify stuff to the wife. But I intend to keep the vehicle for a long time, so over its lifetime, there is a potential for it to pay off...especially if diesel prices go back to $5.00/gallon again.

Ripple · **Posted:** Mon Nov 02, 2009 11:59 am

here is the break down for the different gearing scenarios. the 3.21 gears would get about 1.5 MPG more than the 3.73's at 55 MPH (60 speedo)

danoid · **Posted:** Mon Nov 02, 2009 4:00 pm

System wide, the vehicle runs into problems at low lockup speeds. This is why the production setup didn't lock up until 1600 engine rpm in any gear. The combination of high torque / low number of cylinders / low rpm sets up a resonance that is most unpleasant (ask a manual trans driver from over either pond about lugging the engine too much).

Changing the final drive gearing will increase your road speeds per engine rpm. This will increase the speed at which you can achieve torque converter lockup (about 37 mph in third) and potentially decrease your fuel economy in city / slow urban type driving. Also lower (numerical) final drive gearing will decrease torque converter efficiency because it will take more torque at the transmission input to deliver the same torque at the wheels.

Steady state highway driving can improve with a lower set of axle gears, but there are trade offs.

Diggerfreek · **Posted:** Mon Nov 02, 2009 4:08 pm

The front of the KK is a D30M not a D30A. Now I'm not sure if the 3.21's will fit in the A model. It should. now I do know that the inside case space must be different on the M's since they can handle the 4.88's gear set because it is modeled off of the JK wrangler front end...

Lowering shift points for 545RFE

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