8th gear - highway speed?

[pizzatots]

New truck. 6.4 with 3.73s. Noticing at 65mph the truck stays in 7th gear. If I bump up to 70 it will fall down to 8th gear. What speed does this truck like to go in to 8th? Anyone notice?

 

[Rockcrawlindude]

stock size tires?

 

[snocam]

So I seem to catch 8th gear just above 60 anywhere flat or just slightly uphill. I'm on 37s though. As soon as the grade gets steeper it's back down to 7th, or 6th, depending on condition. I've also caught 8th below 60 by feathering the throttle, although it makes no difference in mileage. The truck likes cruising at just over 1500rpm no matter what gear.

 

[pizzatots]

stock size tires?

Stock tires.

 

[ppine]

Your transmission has several overdrive gears. It is not that important which one you are in as long as your tach shows your engine in the right rpm range.

 

[pizzatots]

Your transmission has several overdrive gears. It is not that important which one you are in as long as your tach shows your engine in the right rpm range.

Good call. I noticed 7th and 8th are overdrive. I’m coming from a 1500 with 3.92s and stock tires. That truck would shift to 8th as soon as it could. Sometimes too fast. Just learning the differences in the two setups.

 

[Dave01]

Mine is into 8th much earlier than you are describing. In fact just yesterday I was fiddling with gears and noting that these modern trannies use all the gears they can. Even around town I'm into 7th pretty soon, on the highway if I let off the gas I'm into 8th certainly by 60.

 

[pizzatots]

Mine is into 8th much earlier than you are describing. In fact just yesterday I was fiddling with gears and noting that these modern trannies use all the gears they can. Even around town I'm into 7th pretty soon, on the highway if I let off the gas I'm into 8th certainly by 60.

What rear end do you have? Seems like the 4.10s might shift sooner from a map I saw online.

Or this is my tranny still learning.

 

[Dave01]

4.10.

 

[snocam]

Funny, 4.30 was always the sought after lower ratio in ford super duty trucks, my 2012 6.2 F350 mason dump has them, but my Ram still has a lower final drive in 1st because of the 8sp, even though it's 3.73 axle gears. I'm really thrilled with the overall drive ability of the Ram.

 

[Dave01]

In some cases we (people) will pine away for the good old days ... not in the case of transmissions. The improvement of the "modern" 6, 8, and 10 speed transmissions over our old 4 speeds is night and day. I left 6 in there because they are still pretty good behind the diesels, but truly they need to move to 8 speed as well IMO.

 

[pizzatots]

I've been playing with the speeds and the transmission shifts and seems like 68-69mph is when the 3.73 8speed likes to move to 8th. Will see if this changes as I put more miles on the truck..

 

[ClawSS]

I would say the same with the 8...but I have no base since never owned a prior gen. I will say that the learning aspect of the TCU has a love/hate relationship with me. Example, this morning it was absolutely flawless. Easy, smooth downshifts and upshifts for over an hour of commute time. 3 days ago it lost its freakin' mind and decided on the same drive that it needed to do a few downshift thumps coming to a stop at stoplights and a few strange 2nd-3rd gear shift weirdness. JUst my .02.

 

[Dave01]

Last night I was able to do a bit of experimenting and here's what I saw. On ramp, gentle acceleration, was in 7th by 54 and 8th by 60. Then I slowed down and then let it speed up on level ground, barely accelerating, and was in 7th in high 40's and 8th by 54. So if barely on the gas or coasting mine will drop into 8th in the low 50's.

The difference in 3.73 and 4.10's is actually pretty minor, a few hundred rpm, so I'm surprised you have to get to high 60's to get it into 8th. Say you are in 7th at 60, if you just coast does it not drop into 8th then?

 

[jetrinka]

I've never actually paid attention to when it grabs 8th. I do remember watching the gear shift indicator and thinking "why is it still in 7th"? My PW has the 4.10's. Stock tire size.

I'll try and pay attention later.

I think somebody else said it but 7th and 8th on the ZF are both overdrives.

 

[Poolmonkey]

I’m just glad that mine still shifts gears at all and that there are no pending recalls at the moment.

 

[pizzatots]

Someone posted this to another forum for the ZF, and it really jives with what I'm seeing. Shift to 8th with the 3.73s comes around 68-69mph, since that is around 2k RPM in 7th gear.

 

[dieselscout80]

Someone posted this to another forum for the ZF, and it really jives with what I'm seeing. Shift to 8th with the 3.73s comes around 68-69mph, since that is around 2k RPM in 7th gear.

View attachment 53738

The 4.10 numbers track with what I have observed.

 

[OldJeepsNewTrucks]

[me with my Cummins] : wait, you guys get 8 gears!?

 

[Dave01]

[me with my Cummins] : wait, you guys get 8 gears!?

Mine is a 9-speed, it was a special order. And my radio volume goes all the way to 11.