- First Name
- Jason
- Joined
- Sep 2, 2021
- Threads
- 3
- Messages
- 260
- Reaction score
- 277
- Location
- California, US
- Vehicle(s)
- 2021 Bronco Sport
- Thread starter
- #1
Looking at the gear ratios plotted vs. RPM for the 8F35 (8-speed automatic, FWD, 350 Nm design range*), and from seat-of-the-pants analysis, I'd noticed that the spacing between 1-2, 2-3, and 3-4 seemed... "odd". Between first and second gear is a "normal" ratio delta. Same for third and fourth. BUT... second to third? Not so much.
( * 350 Nm ~= 258 lb-ft)
When you're manually shifting (Badlands / First Edition with SelectShift Manual mode) and you don't go directly from first-to-third, or second-to-fourth, this ends up feeling like the equivalent of a missed-shift on a manual transmission … or reaching for 6th on a 5-speed motorcycle. ;-)
Initially I thought it might perhaps have been a solution for providing additional options in reducing roll-away torque in snow/mud/ice conditions, by starting the vehicle off from a standstill in up to third gear vs. just second gear or first gear.
I'd been hunting around for the answer, finally found at least one other interpretation of it:
A few other articles for background on the transmission:
Related, the stop-start accommodations on the 6F35, similar (line pressure maintenance) in the 8F35:
( * 350 Nm ~= 258 lb-ft)
When you're manually shifting (Badlands / First Edition with SelectShift Manual mode) and you don't go directly from first-to-third, or second-to-fourth, this ends up feeling like the equivalent of a missed-shift on a manual transmission … or reaching for 6th on a 5-speed motorcycle. ;-)
Initially I thought it might perhaps have been a solution for providing additional options in reducing roll-away torque in snow/mud/ice conditions, by starting the vehicle off from a standstill in up to third gear vs. just second gear or first gear.
I'd been hunting around for the answer, finally found at least one other interpretation of it:
The 8F35
Ford decided that there was no real advantage to having 9 speeds [[as inherited from the GM 9T / GF9 it is based-on]], and the extra gear added weight and cost that didn’t improve fuel economy. Essentially, Ford decided to remove the 4th gear, among other adjustments. These changes made the 2-3 shift step very small, and the transmission acts as a 7-speed under most driving conditions.
Ford also decided that they would use several design features they had used in the 10-speed platform. Borrowing the 10R torque converter saves space and weight but is a more complicated unit to control because it applies the torque converter clutch towards the impeller assembly rather than towards the cover. Ford also redesigned the valve bodies and the oil pump assembly to use the same software platform used by the 10-speed unit. This saved weight and reduced the number of valves needed in the system. It also borrowed parts already in inventory for the 10R transmission.
A few other articles for background on the transmission:
https://gearsmagazine.com/magazine/fords-new-8-speed/ (tidbits on the internals)
In the initial design phase, Ford and GM parted ways as to how many gears they would have in their platform. GM opted to use nine gears in the GF9 front wheel drive platform to allow for smoother gear ratio transitions. When Ford tested the design for the 8-speed, they ended up with a large ratio step between the 2-3 and 3-4. This is a result of reusing the 6F50 series planetary designs. Although this was a 0.45 ratio change, it didn’t affect the fuel economy or durability of the unit in testing. Functionally, 2nd gear is often skipped and sees use mainly in manual mode.
In the end, Ford only allowed this large ratio change in the 8F35 and 8F57.
…
In the end, Ford had design decisions to make when working with GM on this joint venture unit. By going with eight speeds instead of nine, Ford eliminated the C4 clutch. It reduced weight, loss of efficiency and overall cost. By doing so, Ford had to make shift ratio and timing decisions that made a useable 4th gear unavailable. It also meant that the 2-3 step is quite small, and the transmission will often run as a 7-speed unit instead of an 8-speed platform.
https://gearsmagazine.com/magazine/diagnosing-the-erratic-shifting-fords-8f35-57/ (covers some bits about shift-points / shift-schedule)
Related, the stop-start accommodations on the 6F35, similar (line pressure maintenance) in the 8F35:
Sponsored
Last edited:
