General Tech Jeep/Dodge's ZF 8HP 8 speed automatic transmission

Greg

Wanderlusting
Admin
The ZF 8HP is the new transmission coming in the JL, JT and Dodge Ram 1/2 ton trucks and is really one of the biggest upgrades to the new Wrangler, IMO. The ZF 8HP has been used in many other very different vehicles, starting with a BMW 760Li fitted with the V12 engine, as well as vehicles from Aston Martin, Fiat Chrysler, Jaguar Land Rover, and Volkswagen too.

The ZF 8HP is rated up to 1000 ft/lbs of torque in some variations that demand that much power and it's built so that the torque converter can be replaced with an electric motor, for a mild hybrid drive. The efficient, low-mass triple-line torque converter’s lower inertia helps during shifting and starting, while its twin torsional damper system allows fast engagement with little “slip.” Other efficiency and shift-improvement features include a hydrodynamically cooled clutch, low-viscosity transmission fluid, and chain-driven axial parallel vane cell pump.

The transmission uses four planetary gearsets and five gear shift elements (two brakes, three clutches); there are two opened shift elements per gear, minimizing drag losses. Only two shift elements are open in each gear, cutting parasitic losses; and it can make extreme transmission shifts, such as eight-to-second kickdown, in one step.

The gear ratio spread of 7.0 ensures that the engine is always in its optimum operating range and close to peak torque. -

Gear12345678RSpread
Ratio4.713.142.101.671.291.000.840.672.657.03


I had a chance to drive a new Dodge Ram 1500 with a 5.7 Hemi and the 8HP transmission. The Ram has transmission shift buttons on the steering wheel and allows manual shifting without placing the transmission in 'manual' mode like other vehicles. The shifts are tight and smooth, making it easy to upshift or downshift as needed. The factory display claimed 18-19 MPG over the last 400 miles, with much of that being in the Colorado mountains! The gear ratio spread was awesome, it was obvious that the engine was kept at it's peak powerband at all times with normal driving.

Personally, I think the ZF 8HP is an amazing transmission and really makes the JL & JT even that much better.... from the high MPG and great gear spread, I think it's a winner. It will be interesting to see if the Rubicon's 4 to 1 will be too deep with a Jeep in 1st gear, low range. It makes me wonder if a non-Rubicon will have a pretty good crawl ratio with that super deep 1st and 2nd gear. Coupled with the EcoDiesel, the torque and a non-Rubicon should be pretty capable offroad if shifted in 1st or 2nd gear.
 

Hickey

Rusty Girdle
Supporting Member
It's also been behind all motors in the Grand Cherokee since 2014. It's a fantastic transmission. It holds up to the Hellcat and the Demon motors just fine.
 

DAA

Premium Member
Supporting Member
Have had one in my Ram 1500 for going on six years now. Love that transmission. I think it must be part of why I get such surprisingly good MPG with a 5.7, 3.92 axle gears and 34" tires. Always run within 1- 2 MPG of the EcoBoosts on the same trips. Wife has one in her JL now too and I think it has a lot to do with how drivable and fun that little 2.0 four cylinder is.

- DAA
 

anderson750

I'm working on it Rose
Location
Price, Utah
This is the transmission in my wife's Durrango R/T. We consistently knock down 22 mpg on the highway and it always seems to be in the right gear.
 
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UNSTUCK

But stuck more often.
Location
Magna
It does have shift buttons on the steering wheel, but it’s not really a manual shift mode. All it does is lock out the gears higher than what you have it set at.
I have one in my ecodiesel 1500. Love it for the most part. Never misses a beat when towing my 8600 pound boat.
 

Anchor_Mtn

Work Less, Travel More
Supporting Vendor
Location
Fruita, CO
It's already being done! Not sure who though and what it takes, but I think the idea to swap the 8 speed into a JK is AMAZING.
I have heard its being working on. I really want a 5.3 LS and the 8 speed in the JK.
 

TRD270

Web Wheeler
Location
SaSa Sandy
Ford needs to take note, been meaning to post something in this thread the last few days as I drive around and fester about this pile of crap 10speed. Then today this happened to a 2016 Expedition. Reminded me to post. Ford needs to burn the plans and recycle the molds for the 10 speed and work out a deal for the ZF8HP. As it is superior
 

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Greg

Wanderlusting
Admin
Thought this would be an interesting comparison... the previous Jeep JK's ('12-17) NAG1 5 speed automatic has a 3.58 1st gear ratio. Combined with 2.72 t-case of the non-Rubicon and say axle 4.10 gears, you get a crawl ratio of 40 to 1. With a Rubicon running the same axle ratio, you end up at 58 to 1.

Now the 8HP's deeper 1st gearing brings a lot to the table.... 4.7 in 1st gear, 2.72 in the t-case and 4.10 gears a non-Rubicon has a 52 to 1 crawl ratio! The Rubicon comes in at a incredible 77 to 1 crawl ratio!

So the non-Rubicon JL with the 8HP has a crawl ratio in 1st gear that is ALMOST as low as the Rubicon JK! That right there is pretty interesting information.
 

Omgbecki

Well-Known Member
Location
Ogden
I just drove a sport pickup with this trans. Oh my. I'm sure the numbers are different but it felt as quick if not quicker than the EcoBoost and I'm not going to lie I really like those. After driving that sport I'm seriously looking into getting one when I get in the market.
 

pELYgroso

'Merica
Location
LEHI, UT
I was in Moab this weekend and a friend rented a jeep from Twisted Jeeps down there. I asked how they liked the 8 speed trannies and the tech said that he hates them. For freeway driving, yes. For Moab trails, no. he said they are constantly hunting for the right gear in 4-Lo which makes them Lurchy unless you're constantly using the manual mode. The trail guides all prefer the JKU's because they can focus on just driving/leading rather than fiddling with the touchy tranny. I though of this thread when I was talking to this guy. Has anybody here wheeled a JL enough to weigh-in on this? The jeep my friend rented was a JK so we didn't get to see if this is true or not.
 

Greg

Wanderlusting
Admin
I was in Moab this weekend and a friend rented a jeep from Twisted Jeeps down there. I asked how they liked the 8 speed trannies and the tech said that he hates them. For freeway driving, yes. For Moab trails, no. he said they are constantly hunting for the right gear in 4-Lo which makes them Lurchy unless you're constantly using the manual mode. The trail guides all prefer the JKU's because they can focus on just driving/leading rather than fiddling with the touchy tranny. I though of this thread when I was talking to this guy. Has anybody here wheeled a JL enough to weigh-in on this? The jeep my friend rented was a JK so we didn't get to see if this is true or not.
That's interesting and a good point, in 4 low I could see the 8 speed trans being unsure about what gear is best and jumping around. Wonder how much difference it is for the JL Rubicon versus a non-Rubicon, due to the t-case gearing.
 

pELYgroso

'Merica
Location
LEHI, UT
That's interesting and a good point, in 4 low I could see the 8 speed trans being unsure about what gear is best and jumping around. Wonder how much difference it is for the JL Rubicon versus a non-Rubicon, due to the t-case gearing.
Not sure, theirs were the Rubicons and they weren't really happy with them. He said he will be buying new JL's to slowly phase out the JK's just because people are starting to ask for them and he doesn't want to lose business. But he'd rather use JK's due to the tranny.
 

Caleb

Super Moderator
Super Moderator
Supporting Vendor
Location
Riverton
Ford needs to take note, been meaning to post something in this thread the last few days as I drive around and fester about this pile of crap 10speed. Then today this happened to a 2016 Expedition. Reminded me to post. Ford needs to burn the plans and recycle the molds for the 10 speed and work out a deal for the ZF8HP. As it is superior
I’m glad to see I’m not alone on here in my hate for the garbage Ford 10 speed.

I’m super excited for our JL to come in and I can get rid of my Raptor.
 

UNSTUCK

But stuck more often.
Location
Magna
There are a couple tuners out for the transmission. I haven't heard anything thing about how the tuning works in 4 low though. Highway driving is a huge improvement though as it holds gears longer before a downshift.
 
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