Short shifting the 8 speed

[JTGuy]

I have 37s and 4.88s. When getting on the freeway it does just fine but does rev to 4500 or more so I shift it in manual mode before it hits 4000 and I like that better. By 6th I am doing about 70 and it gets there quickly. Is there anything wrong with doing that?

Sponsored

 

[JeepOfTheseus]

I assume you’ve used a programmer to account for the tire size and gearing changes?

 

[JTGuy]

Tire sizes and gears have been adjusted with a Tazer Mini. It goes and shifts fine I just shift it manual when getting on the freeway for personal preference . But don't want to be hurting the trans.

 

[WILDHOBO]

I have 37s and 4.88s. When getting on the freeway it does just fine but does rev to 4500 or more so I shift it in manual mode before it hits 4000 and I like that better. By 6th I am doing about 70 and it gets there quickly. Is there anything wrong with doing that?

In my opinion, yes. These engines are designed to run at high rpms before shifting. You’re likely doing nothing bad to the tranny, but are running the engine at lower rpm’s than it’s designed. I’ve had several engines that require high rpm’s in my life. I’ve seen people with identical engines have more issues when attempting to stay under a certain rpm. Think of having a turbo engine and staying too low so you never use the turbo. The turbo will likely fail prematurely.

 

[ShadowsPapa]

I have 37s and 4.88s. When getting on the freeway it does just fine but does rev to 4500 or more so I shift it in manual mode before it hits 4000 and I like that better. By 6th I am doing about 70 and it gets there quickly. Is there anything wrong with doing that?

Mine routinely gets into the 4,000s
It's not uncommon to get into the 3,000s
In fact, when I get onto what we call "the bypass" (65/69) south of Pleasant Hill going north to Altoona or I80, mine is in those areas for 2 or 3 miles and never sees over 6th gear at times.
Thinking back to my 2011 Silverado LS days - that's not much different from what that Chevy did. It had to wind up to 5,000 RPM at times to make hills under a load. The Chevy guys all said "let it".

Below about 3,000 RPM you are in the economy mode of the engine - lower valve lift, etc. for better mpg. Above that, it's running for peak performance, more breathing.

Tire sizes and gears have been adjusted with a Tazer Mini. It goes and shifts fine I just shift it manual when getting on the freeway for personal preference . But don't want to be hurting the trans.

Query - have you "checked your work" as far as the right tire size numbers by comparing your trip odo to a GPS app on a phone or a real GPS? Rolling circumference can be different from what you think it is by measuring.

You won't hurt the transmission unless you somehow get it HOT - forcing a high gear when it should be in a lower gear.
The top gears are overdrives anyway.

 

[MattK]

Query - have you "checked your work" as far as the right tire size numbers by comparing your trip odo to a GPS app on a phone or a real GPS? Rolling circumference can be different from what you think it is by measuring.

This is worth double-checking. I have 37" BFG KO2s but under the truck they are actually closer to 35.5" input into the system based on GPS and those construction zone radar signs on the freeway around me matching up. I run at 35psi cold. I just ran a few passes on the freeway at night past 3 of them while I had a GPS speedometer app running, (while not connected to Apple CarPlay mind you - it will read the Jeep's speedometer if it's connected), and just kept adjusting tire size and then making the pass again until the app/radar matched up with the speedometer in the Jeep.

 

[ShadowsPapa]

This is worth double-checking. I have 37" BFG KO2s but under the truck they are actually closer to 35.5" input into the system based on GPS and those construction zone radar signs on the freeway around me matching up. I just ran a few passes on the freeway at night past 3 of them while I had a GPS speedometer app running, (while not connected to Apple CarPlay mind you - it will read the Jeep's speedometer if it's connected), and just kept adjusting tire size and then making the pass again until the app/radar matched up with the speedometer in the Jeep.

Took two tries with mine - then nailed it perfectly 2nd try. sometimes, rarely, but sometimes, luck is with me......

 

[JTGuy]

I have checked it with my Garmin GPS and the speedo is perfect. I tend to overthink and double check everything. The trans will probably be just fine as I don't beat it.

 

[PuddleJumper]

I have 37s and 4.88s. When getting on the freeway it does just fine but does rev to 4500 or more so I shift it in manual mode before it hits 4000 and I like that better. By 6th I am doing about 70 and it gets there quickly. Is there anything wrong with doing that?

As far as I can tell the 3.6 is a high rev designed engine. It does have excellent tuning to have consistent torque throughout its band albeit barely respectable amount by my standard. But, i digress. The transmission of a vehicle normally would see extra wear from excessive engine speed under acceleration as usually it will remain in a state of slip until it touches higher gears that it can hold. Jeeps don't really have this problem as there are 8 long gears that it can fully lock into as it goes through the paces. Considering this is the same transmission in Supras and M3s, it'll handle a lot of power quite safely. The only reason to go to the beefier 8HP75 if you get a deisel or hemi is that we weigh quite a bit more than an M3 so having 400 plus ftlbs of torque would eventually find a component to prematurely chew up inside the stock trans. I let my gladiator eat, till we need to turn or are at the speed limit. I let her have the full pedal. Jeep tuning is obviously not gonna let the engine have all the beans tho. It will still open the throttle body very conservatively imo; and not even open all the way. long story short, its fine dude. just change the fluid regularly cus its not true lifetime fluid and you'll be fine.

 

[Lunentucker]

Someone on here a few months ago was replacing a transmission because, according to them, they were doing a lot of manual overriding and caused damage.

 

[JTGuy]

If they were overloading they were loaded and possibly pulling a trailer. I only do it when getting on the freeway on an onramp that causes the trans not to upshift. With 4.88s the torque is multiplied nicely.

 

[ShadowsPapa]

The transmission of a vehicle normally would see extra wear from excessive engine speed under acceleration as usually it will remain in a state of slip until it touches higher gears that it can hold.

Not sure where that comes from - but not in my experience with automatic transmissions. Once that clutch pack is applied, it's applied and doesn't slip. The torque converter takes care of anything otherwise - that's what "slips", and it's made to.
The clutch packs lock up solid. The only slip is while they are engaging.

Someone on here a few months ago was replacing a transmission because, according to them, they were doing a lot of manual overriding and caused damage.

And that ended up being debunked.............
the torque converter can be unlocked if there's any slippage needed. (or, it will force an upshift or downshift, even in M)
"Hunting" causes more damage than shifting manually and holding gears manually, hunting leads to heat as constant shifting is damaging - the clutch packs and bands naturally must slip until locked - it's an extremely brief moment, but still - try to catch a spinning disk. until you grasp it firmly, it spins in your fingers. Hunting is catching, releasing, catching, releasing... manual shifting reduces the amount of hunting if used for that purpose.
There's a few of us who have shifted our automatic cars manually for decades - and some of us have put in manual valve bodies - making it more like a clutchless stick.

 

[PuddleJumper]

Not sure where that comes from - but not in my experience with automatic transmissions. Once that clutch pack is applied, it's applied and doesn't slip. The torque converter takes care of anything otherwise - that's what "slips", and it's made to.
The clutch packs lock up solid. The only slip is while they are engaging.



your right. When I mean slippage, I mean when the vehicle is in a state in which it is trying to lock up the clutch but can't. so it searches for a gear, which keeps the clutch in a constant state slip even when the solenoid tries to engage it for lock up. As this produces a insane amount of heat, this will burn fluid. And eventually smoke the clutch. under the appropriate conditions a 'wet' clutch should last a really long time. but things like, towing over capacity, crawling in 4hi, running a heavy or well oversized tire, etc. all introduces suboptimal conditions for operation. the 8 speed is a lot more forgiving tho then say compared to the old school 4 and 5 speed transmissions. as the "cliff" between gears is much greater. specifying load instead of RPM would've made more sense though for sure.

 

[ShadowsPapa]

When I mean slippage, I mean when the vehicle is in a state in which it is trying to lock up the clutch but can't. so it searches for a gear, which keeps the clutch in a constant state slip even when the solenoid tries to engage it for lock up.

But that's not how these work. none of that takes place. There's no searching for a gear because it can't lock a clutch. The pressure is applied and it's locked and the torque converter absorbs and shock or speed variation.
There's no searching for a gear because it can't lock up anything. That doesn't happen - especially with modern vehicles, but it never did before the ZF 8 speeds, either.
There's no constant state of slip, just doesn't happen (unless grossly over-loaded then it's more torque than the clutch or band can handle and that's a totally different unrelated topic)

If you are getting it hot, you are trying to force the transmission to handle too much torque, and breaking the clutch pack grip causing slippage, or it's hunting gears - and going to M as outlined in the owners manual handles that.

The reason towing an over-heavy load, or sending too much torque through a given transmission is bad is because the torque overcomes the clamping force on the clutch pack or band.
the 75 vs 50 transmission will have the larger disks and bands to handle the increased torque.

Maybe time to bring out the TSMs and transmission books ?

 

[PuddleJumper]

But that's not how these work. none of that takes place. There's no searching for a gear because it can't lock a clutch. The pressure is applied and it's locked and the torque converter absorbs and shock or speed variation.
There's no searching for a gear because it can't lock up anything. That doesn't happen - especially with modern vehicles, but it never did before the ZF 8 speeds, either.
There's no constant state of slip, just doesn't happen (unless grossly over-loaded then it's more torque than the clutch or band can handle and that's a totally different unrelated topic)

I feel like thats what i said. but hey you've been using the english language longer than me so maybe thats the disconnect.

Sponsored