6spd v 8spd trans??

[ppine]

After driving a Ford diesel with a 4 speed, the newer Ram 6 speeds are big step forward.

 

[jaflowers]

One of the biggest deals/problems was the 66RFE was geared like the 68RFE......for a diesel. Big problem when the hemi makes it's power at higher RPM's. That's why you read about so many 2500 owners regearing the diff's to get better power delivery. The new 8 speed solved that.

 

[TONY4X4NC]

My 16 2500 6.4 has 296k on original trans but is geared with 4.56 and regular drain and fills plus filter changes every 30-50k. I also have the bypass on it, if not abused these transmissions are fine. I rent a new 2500 from hertz with the 8 speed if I feel the need to be in a "newer,nicer" truck for the weekend or for a family trip. Drive it, enjoy the truck.

 

[Gary Fields]

Got a 2020 5.7 1500 with the 8 speed ZF trans. It feels great and is always in the right gear. It inspires confidence almost as good as a Turbo 350 from the early 70's.

 

[man n black]

I believe that part of the reason is that they had to change transmissions completely to deal with the torque.

The 8 speed transmission in the 2025 Cummins version 2500 / 3500 is supposed to be much stronger to deal with the ~ 1 000 ft lbs.

I dont think this was the issue.

Even mildly tuned 6.7s put out around 1000 ftlb torque. I've been on my 68rfe for many thousands of miles towing all kinds of stuff all over the country and Canada with no issues.

However, ZF does build fantastic mid duty and heavy duty OTR truck transmissions, particularly used in Europe. Makes sense that Stellantis choose a reliable partner with a company in thier home region.

Ch

 

[Sherman Bird]

For a 2500, the 8 speed starting in '19 has a much lower first gear and tighter split in ratios in the first 5 gears. Basically, on the 6 speed you have first gear through direct drive (1:1) is 4 gears, while on the 8 speed first through direct drive (1:1) is 6 gears. On the 8 speed, 2nd gear is about the same as 1st gear on the 6 speed. The combination of the lower 1st gear and tighter splits makes the truck feel peppier/faster on take off. However the highway cruising gears are almost identical. This means the top 3 gears on both trans, which are the gears you will be in when cruising down the road at highway speeds. On a 6 speed that would be 4th, 5th, and 6th which are almost identical ratios to 6th, 7th, 8th on an 8 speed. With an empty truck it's unlikely you would shift down more than that unless maybe climbing a mountain pass.
I was shopping for a new truck when the 19's with the 8 speed became available and test drove several. I did wind up buying a '16 with a 6-speed because it only had 24k on the odometer and was $20k cheaper. Yes, the 8 speed made the newer models feel stronger during acceleration from a stop (exact same engine and gear ratio) but I'm cheap and decided the 8 speed wasn't worth $20k. Does the 8 speed shift better....from test driving I can't say it was noticeably better. Maybe if I drove one more now I will say that. Some people claim it tows a lot better. From a stop it should feel better, but on paper there isn't any real reason it would feel stronger at highway speeds because the top 3 gear ratios are the same. But have obviously never towed with an 8 speed truck.
More reliable? I mean, we will see. Maybe they are? Everybody claims that but keep in mind that the 8 speed 2500 trucks are "only" 5 years old meaning there is simply not a lot of older high mileage trucks running around. The national average annual mileage on a pickup is under 12,000 miles. This means the average '19 2500 only has 60,000 miles on it. On the other hand I think the 66RFE was introduced around 2013 in the 2500 truck? So you are talking 11 years at an average 132,000 miles, or over the double the mileage. Of course you would see more failures reported on an older truck! My last comment is that failures or issues are blown way out of proportion on the internet. That is because anybody with an issue will jump on every Ram related forum they can find and complain their transmission failed. However nobody just randomly makes a post saying "hey, just wanted to let you know my trans has not failed....". Again, maybe the 6 speed failure rate is higher than typical but you can't confirm that based on browsing the internet. Let's say 1/2% of Ram 2500 6 speed trucks have a trans failure. Ram sells almost 500,000 Ram 2500's annually (not sure exactly how many are 66RFE trucks), but let's say 200,000 of them are. Even though only 1/2% have problems, that is still 1,000 trucks with issues. Now each person makes 3-4 different posts on different forums and Facebook groups and seems like a LOT of trucks have issues....even though it's only 1/2% of the total. Then on top of that, anytime somebody asks the question about the 66RFE you get 20 people reply back that they are junk and will explode and kill a bus full of nuns. Not because they personally have had a trans failure, but simply because they read a post 3 months ago about a guy who did have a trans failure.

GM/Ford 8-speeds have NO direct ratio of 1:1. I wonder if the units in RAMS are any different?

 

[HEMIMANN]

When I looked up the RFE's and found the two upper gears were BOTH overdrives, I was shocked. They split the typical single OD gear ratio into a mild OD and heavier OD, undoubtedly for EPA miniscule fuel savings, at the expense of lugging the transmission and engine like so many other stupid things they did for miniscule fuel savings.

When I found this out, I always pull (I have the 66RFE) limited to 4th gear ratio, which is 1:1. Even then, they engage one of the OD gearsets to make this ratio. And use the tow shifting program, of course. I decided just to leave the MDS on with my tuner to lube the lifter bores better during light loads - going downhill, etc.

If I were rich I would have swapped to a billet aftermarket RFE. Or the 8 speed. Oh, well. Change oil with Red Line C+ATF frequently and have the thermostat bypass. Maybe it will live.

 

[SouthernBornRebel]

2016 is better truck than 2019, 8sp better than 6sp........ so...............

 

[tron67j]

When I looked up the RFE's and found the two upper gears were BOTH overdrives, I was shocked. They split the typical single OD gear ratio into a mild OD and heavier OD, undoubtedly for EPA miniscule fuel savings, at the expense of lugging the transmission and engine like so many other stupid things they did for miniscule fuel savings.

When I found this out, I always pull (I have the 66RFE) limited to 4th gear ratio, which is 1:1. Even then, they engage one of the OD gearsets to make this ratio. And use the tow shifting program, of course. I decided just to leave the MDS on with my tuner to lube the lifter bores better during light loads - going downhill, etc.

If I were rich I would have swapped to a billet aftermarket RFE. Or the 8 speed. Oh, well. Change oil with Red Line C+ATF frequently and have the thermostat bypass. Maybe it will live.

I have been searching for the bypass valve for my 2018 2500 6.4 with a 6 speed, but the only ones I find indicates for diesel applications. How hard was the install? I haven't messed with transmissions in many years, with the install is there a bleeding requirement like doing brakes? Like I said, last work was a mid-80s standard that I replaced the clutch and before that an automatic in a Chevy.

 

[HEMIMANN]

I have been searching for the bypass valve for my 2018 2500 6.4 with a 6 speed, but the only ones I find indicates for diesel applications. How hard was the install? I haven't messed with transmissions in many years, with the install is there a bleeding requirement like doing brakes? Like I said, last work was a mid-80s standard that I replaced the clutch and before that an automatic in a Chevy.

RFE's are straight forward. They're all the same. The bypass is nothing but an aluminum block with thru passages and connector ends.

There are tips and tricks, though. I wrote up my experience somewhere. The block is in the oil lines to and from the oil cooler radiator - it's not in the transmission.

 

[N0NAMETOGIVE]

I have the 1500 5.7 8speed for work and I find it too aggressive, as compared to my 2500 6.4L 3.73 6 speed. It is easy to break traction when turning, and also in rain.

 

[mtofell]

if not abused these transmissions are fine

Maybe..... a statistical study of one unit is irrelevant.... as is my statistical study of saying these trannies are total garbage since mine failed 2X before 100K miles. All that being said I will go out on a limb and say the 66rfe is pretty far below average in terms of reliably based on what I read here.

 

[2018Hemi]

I pull a 34’ fifth wheel 12000lbs with no issues. 6.4 with 3.73 gears. 6 speed

 

[Dusty]

So ask yourself why it took so long to make it in the 2500. Not that the rfe is a great transmission because it isn't, but if you ask me this is a lateral move at best with a real commitment if you want to service it.

The ZF design came into being because at the time Chrysler was forced into purchasing A5W580s from Mercedes at an exorbitant cost <>$4100 versus $2900 from ZF. Chrysler was cash strapped in 2008-2012 and although Marchione had committed to the ZF as early as 2007, ZF production was initially limited to Germany. Chrysler built a new plant for US production in Kokomo, IN, 2010, and slowly ramped up fitting both cars and LD pickups. For a period of time there was overlap between 8HPs and RFEs.

The incorporation of ZF to heavy duties was delayed by necessary adoption upfitting and constrained production, plus software development for new shift algorism.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 125115 miles.

 

[Dusty]

Maybe..... a statistical study of one unit is irrelevant.... as is my statistical study of saying these trannies are total garbage since mine failed 2X before 100K miles. All that being said I will go out on a limb and say the 66rfe is pretty far below average in terms of reliably based on what I read here.

And based on what you read here is going to be 10x + in complaints and reports of issues compared to those that have experienced no problems. There is no way to properly, faithfully, and statistically categorize how these transmissions have been used and maintenanced in actual service.

However, based on personal experience, the engines in front of a 66RFE is an engine that should never receive a tune.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 125115 miles.

 

[Burla]

The ZF design came into being because at the time Chrysler was forced into purchasing A5W580s from Mercedes at an exorbitant cost <>$4100 versus $2900 from ZF. Chrysler was cash strapped in 2008-2012 and although Marchione had committed to the ZF as early as 2007, ZF production was initially limited to Germany. Chrysler built a new plant for US production in Kokomo, IN, 2010, and slowly ramped up fitting both cars and LD pickups. For a period of time there was overlap between 8HPs and RFEs.

The incorporation of ZF to heavy duties was delayed by necessary adoption upfitting and constrained production, plus software development for new shift algorism.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 125115 miles.

That is not what I have been reading to the why it took 12 years to make the 8 speed a viable option to put in HD rams. Which most of the paper out there from the people who know that said the zf8 simply could not handle the torque, especially when you pair it with the Cummins. Since they are brand new to HD trucks nobody knows how it will work out, time will tell that story. It is an unknown if the zf powerline will be an upgrade, or a downgrade, or a wash when compared to the 68 in HD rams. 12 years is a pretty long time to drag your feet on updating your HD ram transmission. I wonder how long it will take for 2500 to get hurricane engines. Seams like fitting a round peg in a square hole takes some real engineers and time.

 

[HEMIMANN]

They went bankrupt trying to come back from the Daimler-Benz takeover from hell, remember?

Then Fiat, and now Peugeot "saved" them to the point where they're damn near out of business today.

 

[Dusty]

That is not what I have been reading to the why it took 12 years to make the 8 speed a viable option to put in HD rams. Which most of the paper out there from the people who know that said the zf8 simply could not handle the torque, especially when you pair it with the Cummins. Since they are brand new to HD trucks nobody knows how it will work out, time will tell that story. It is an unknown if the zf powerline will be an upgrade, or a downgrade, or a wash when compared to the 68 in HD rams. 12 years is a pretty long time to drag your feet on updating your HD ram transmission. I wonder how long it will take for 2500 to get hurricane engines. Seams like fitting a round peg in a square hole takes some real engineers and time.

Okay, twelve years is a long time. But the corporation didn't have the financial bandwidth to bring it to market any sooner. In engineering and product development, Ram heavy duties had to compete for dollars with everyone else under the umbrella, and under past management it wasn't as high of a priority.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 125115 miles.

 

[62Blazer]

When I looked up the RFE's and found the two upper gears were BOTH overdrives, I was shocked. They split the typical single OD gear ratio into a mild OD and heavier OD, undoubtedly for EPA miniscule fuel savings, at the expense of lugging the transmission and engine like so many other stupid things they did for miniscule fuel savings.

When I found this out, I always pull (I have the 66RFE) limited to 4th gear ratio, which is 1:1. Even then, they engage one of the OD gearsets to make this ratio. And use the tow shifting program, of course. I decided just to leave the MDS on with my tuner to lube the lifter bores better during light loads - going downhill, etc.

If I were rich I would have swapped to a billet aftermarket RFE. Or the 8 speed. Oh, well. Change oil with Red Line C+ATF frequently and have the thermostat bypass. Maybe it will live.

Typical that transmissions have multiple "overdrives" now. Overdrive meaning a ratio that is higher (lower numerically) than 1.00:1, so like 0.84:1, 0.63:1 etc... So definitely nothing unique to the RFE transmissions. I have a car with an 8 speed automatic and it technically has 4 overdrives. I think the 10 speed in the Ford F-250 has 3 overdrives. You can't compare an "overdrive" gear on today's transmissions to when overdrive gears first started coming out 30-40 years ago.

 

[RickyJ108]

I have a 2014 Mega Cab 6.4 6speed I bought it used with 155000 on the clock. My truck threw a tranny code 4 days after driving it. When it was diagnosed it was determined that I could drive it till it stops or replace it. The warranty company was willing to pay for a factory tranny. I plan on doing quite a bit of towing a 7,500 camper up and down the eastern seaboard especially through PA (all up hill both ways) lol. The warranty company paid $4,700.00 towards the new tranny I paid $5,800.00 for upgrades so for just over 10 grand I have a truck that pulls great shifts smooth. It's all about personal preference when it comes to which tranny you want. I was told the 6 speed has small clutches and overheats quickly. I could not change the size of the clutches but my tranny cooling system is taken care of.