ECODIESEL DIFF RE-GEARING

[drick]

That's what I would go with. I'm at 45k miles with 4.56's. I would do it again in a heartbeat. We live at altitude in Colorado and tow an off-road trailer quit frequently.

thanks for confirming

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[Ratbert]

maybe this is another one of those things where i've just been lucky?
i don't seem to have experienced any such aberrant behavior (yet!).

How does yours behave when climbing / cresting hills?

 

[zouch]

it pulls uphill at whatever speed i set, and rolls out of the pull as the load decreases; whatever it needs to do to maintain speed. nothing unusual; just what it's supposed to do. (i don't remember my Quattro being much different.)

How does yours behave when climbing / cresting hills?

 

[Ratbert]

it pulls uphill at whatever speed i set, and rolls out of the pull as the load decreases; whatever it needs to do to maintain speed. nothing unusual; just what it's supposed to do. (i don't remember my Quattro being much different.)

Interesting. I noticed it a lot more when driving home last night loaded down with people. Definitely had to cut it off at the crest of hills to keep it from "launching".

 

[drick]

Interesting. I noticed it a lot more when driving home last night loaded down with people. Definitely had to cut it off at the crest of hills to keep it from "launching".

FWIW - this happens to me all the time, not just when loaded

 

[ALeeL]

cruise control for me is fine on the flats, on hills it bangs all over through the gears and significantly over revs the engine vs. what is needed.

this behavior coupled with the overheating problems is a recipe for disaster

Same here. Without cruise control, I can go up just about anything in 8th. The exact same hills and speed on cruise control will cause it to slow down one to two mph going up the hill, then downshift a gear or two to compensate for the cruise control letting the Jeep loose speed. This happens even with my 50hp/100 lb-ft tune, and has nothing to do with power, but rather how the CC was programed.

Most Jeep diesel owners I spoke with about this, who have never had diesels, generally don't notice since they are used to this with gas engines and don't see an issue. However, most that have owned diesels before and are used to their diesels not having to downshift on such a low grade are the ones that are very annoyed by it.

I just put in manual mode in 8th gear while on cruise control past 55 mph. Last trip to Moab, it took every mountain like this aside from a very long and steep one that required downshifting to 7th at 2,100 rpm. That same mountain had my buddy, who was following me in his 3.6L 8-speed, downshift to 4th screaming at 4,600 rpm.

 

[zouch]

interesting indeed!
looks like we all 4 have similar build dates, so that should eliminate some amount of variable. (mine is Oct '20.)
i think John and i are running similar tire/gear setups. i think Drick hasn't regeared yet, so that's a little off, and Anthonys re-tune definitely throws in a wild card.

i know my old XJ had a box where we could adjust the rate of attack and how hard it would accelerate when in Cruise; i wonder if there's an equivalent function of that same sort of thing in our JLs,..? (probably somewhere in software, knowing the way these things are these days.)

our Mercedes turbodiesel was pretty good on cruise too, even with significantly less torque available. i always just thought this JL thing did such a nice job on Cruise because it was also a turbodiesel.

i don't fret about it downshifting; it's got 8 gears to use to keep it at whatever it thinks its 'optimum' is as opposed to the 3 and 4 speeds we grew up with, and is likely to split those loads into smaller slices.
the 8HP75 does such a nice job moving through gears it's a non-issue.

Interesting. I noticed it a lot more when driving home last night loaded down with people. Definitely had to cut it off at the crest of hills to keep it from "launching".

FWIW - this happens to me all the time, not just when loaded

Same here. Without cruise control, I can go up just about anything in 8th. The exact same hills and speed on cruise control will cause it to slow down one to two mph going up the hill, then downshift a gear or two to compensate for the cruise control letting the Jeep loose speed. This happens even with my 50hp/100 lb-ft tune, and has nothing to do with power, but rather how the CC was programed.

Most Jeep diesel owners I spoke with about this, who have never had diesels, generally don't notice since they are used to this with gas engines and don't see an issue. However, most that have owned diesels before and are used to their diesels not having to downshift on such a low grade are the ones that are very annoyed by it.

I just put in manual mode in 8th gear while on cruise control past 55 mph. Last trip to Moab, it took every mountain like this aside from a very long and steep one that required downshifting to 7th at 2,100 rpm. That same mountain had my buddy, who was following me in his 3.6L 8-speed, downshift to 4th screaming at 4,600 rpm.

 

[ALeeL]

My BMW diesel has the same ZF 8-speed except it is an 8HP55 instead of a 8HP75. The shifting on that thing is significantly better than my Jeep, even when not in cruise control. I think that if I never had my BMW, then I would not complain about the Jeeps 8-speed as much. I have just never felt like I am in the wrong gear at times like I have with the Jeep.

In cruise control, it does not wait to load up the engine until you are two mph below your set speed like the Jeep does. Using my Torque app on both to see commanded engine load and actual engine load, the BMW starts commanding engine load the second the speed drops from your set speed to keep you within that speed and hardly ever requires a downshift. The Jeep waits until you dropped two mph, then loads up the engine causing the torque converter to slip, forcing an unneeded downshift with often too much power shooting you over your set speed. This is especially frustrating in the Texas hill country where you are going up and down hills and it is constantly shifting when it does not need to.

The other way the BMW 8HP is programmed better is that it has sport/tow haul mode as well as regular auto and manual mode. With the Jeep, moving the shifter to the left puts it in manual mode. With the BMW, moving the shifter to the left puts it in sports/tow haul mode which still shifts automatically, but holds gears longer to keep you in slightly higher rpms than stock for more power. Moving the shifter up or down while in sport/tow haul mode will then put it in manual mode where you can shift manually if you wanted. I was shocked that it did not do this when I got my Jeep since it can clearly be done.

Most of the time, I manually shift my Jeep because I prefer manuals and the Jeep shift points are horrible for a diesel. It feels like Jeep just slapped the same shift programming on the diesels as what was used on the gasers and called it a day. Like I said, I probably would not complain as much about if I did not have my BMW to feel what the 8HP is really capable of, even in their heavy SUV variants.

 

[zouch]

since you mention it, the 8HP45 6HP in our E93 did a very nice job, even with the gas engine and no turbo.

cruise worked fine there too.

EDIT:
corrected typo in transmission spec

My BMW diesel has the same ZF 8-speed except it is an 8HP55 instead of a 8HP75. The shifting on that thing is significantly better than my Jeep, even when not in cruise control. I think that if I never had my BMW, then I would not complain about the Jeeps 8-speed as much. I have just never felt like I am in the wrong gear at times like I have with the Jeep.

In cruise control, it does not wait to load up the engine until you are two mph below your set speed like the Jeep does. Using my Torque app on both to see commanded engine load and actual engine load, the BMW starts commanding engine load the second the speed drops from your set speed to keep you within that speed and hardly ever requires a downshift. The Jeep waits until you dropped two mph, then loads up the engine causing the torque converter to slip, forcing an unneeded downshift with often too much power shooting you over your set speed. This is especially frustrating in the Texas hill country where you are going up and down hills and it is constantly shifting when it does not need to.

The other way the BMW 8HP is programmed better is that it has sport/tow haul mode as well as regular auto and manual mode. With the Jeep, moving the shifter to the left puts it in manual mode. With the BMW, moving the shifter to the left puts it in sports/tow haul mode which still shifts automatically, but holds gears longer to keep you in slightly higher rpms than stock for more power. Moving the shifter up or down while in sport/tow haul mode will then put it in manual mode where you can shift manually if you wanted. I was shocked that it did not do this when I got my Jeep since it can clearly be done.

Most of the time, I manually shift my Jeep because I prefer manuals and the Jeep shift points are horrible for a diesel. It feels like Jeep just slapped the same shift programming on the diesels as what was used on the gasers and called it a day. Like I said, I probably would not complain as much about if I did not have my BMW to feel what the 8HP is really capable of, even in their heavy SUV variants.

 

[ALeeL]

The years of the BMW E-chassis like my old E90 335d diesel did not have an 8-speed 8HP transmission. They had the 6-speed transmissions that was either a ZF 6HP or a transmission made by General Motors.

 

[zouch]

you're right; typo on my part. our E93 was indeed a 6-speed transmission.

The years of the BMW E-chassis like my old E90 335d diesel did not have an 8-speed 8HP transmission. They had the 6-speed transmissions that was either a ZF 6HP or a transmission made by General Motors.

 

[BAKNBLK]

My A6 TDI had the ZF 8HP55A and shifted fine, my JTD shifts fine also no complaints at all.

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