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Old 02-03-2014, 10:53 PM
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8 speed vs 9 speed transmissions

I've wondered now that i have a Cherokee with the 9 speed, why jeep didn't just use the reliable 8 speed which is used in many vehicles across the Chrysler line up. I've had the opportunity to drive a 14 srt grand Cherokee and i gotta say, the shifts are alot smother and it actually gets to the 8th gear without driving at ridiculous speeds, compared to the Cherokees hard shifts and the fact that i have yet to see one actually hit 9th gear. Also, the cost i would imagine would be alot less since they wouldn't have had to design a all new tranny, not to mention that it would've been released 5 months sooner due to software issues in the 9 speed. Someone mind sharing some incite here to this besides the fact that they wanted to be the first car maker with a 9 speed?
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Old 02-04-2014, 12:00 AM
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Re: 8 speed vs 9 speed transmissions

Quote:
Originally Posted by CherokeeTy View Post
I've wondered now that i have a Cherokee with the 9 speed, why jeep didn't just use the reliable 8 speed which is used in many vehicles across the Chrysler line up. I've had the opportunity to drive a 14 srt grand Cherokee and i gotta say, the shifts are alot smother and it actually gets to the 8th gear without driving at ridiculous speeds, compared to the Cherokees hard shifts and the fact that i have yet to see one actually hit 9th gear. Also, the cost i would imagine would be alot less since they wouldn't have had to design a all new tranny, not to mention that it would've been released 5 months sooner due to software issues in the 9 speed. Someone mind sharing some incite here to this besides the fact that they wanted to be the first car maker with a 9 speed?
You answered your own question I believe in the last line. The 8 speed had plenty of issues too that had to be ironed out.
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Old 02-04-2014, 12:04 AM
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Here is my guess....The Cherokee is now a FWD transmission design with rear driven wheels for AWD/4WD operation. The 8 speeds are RWD designs with transfer cases for front drive. Also, the Cherokee uses a higher rpm, lower torque powerplant and won't lug itself around like a v8. I suspect 9th gear is used for 65mph+ flat ground economy cruising. Any power demand will likely cause a downshift.

Honestly, my 8 speed EcoDiesel GC could use a 9th gear at 75 and higher on flat ground. Lower rpms might yield a slight increase in economy. It feels like 1700 rpm would easily pull it at 80mph. As is, it runs 2100 rpm. There is no 9 speed in a RWD tranny that I know of. Jeep engineers know what they are doing.
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Old 02-04-2014, 05:59 PM
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I hope in the future, they could possibly program these transmissions to shift into 9th at lower speeds. That would help with fuel economy. As it sits, 9th gear is kind of a waste. I own the V6 model, so I can't imagine the 4 cylinder holding 9th gear at any time.
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Old 02-13-2014, 03:58 PM
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Re: 8 speed vs 9 speed transmissions

From what I've read, it's a new transmission because the engine is mounted transversely (sideways). They are not compatible with the 8 speed Jeep currently uses.
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Old 02-13-2014, 04:28 PM
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There are 2 different models of the 8 speed, 1 for the 3.6L and the other for 3.0/SRT. The SRT seemed to be better in the beginning with less issues. The 9 speed has been talked about for over a yr now for the Cherokee.
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Old 02-13-2014, 04:36 PM
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Quote:
Originally Posted by SnoFire View Post
There are 2 different models of the 8 speed, 1 for the 3.6L and the other for 3.0/SRT. The SRT seemed to be better in the beginning with less issues. The 9 speed has been talked about for over a yr now for the Cherokee.
The 3.6L has the 845RFE 8-speed transmission which is a Chrysler-modified ZF 8HP45 produced by Chrysler under license.

The 5.7L, 6.4L, and 3.0L diesel have the ZF 8HP70 8-speed transmission built by ZF.

The 9-speed is also a ZF design but is an entirely different setup designed for transverse-mount (Front-wheel drive) arrangements.
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