Details: Rebuilt 4R100 with 4000 miles. Fluid level good. 1999 F250 Super Duty.
Going down hill 6-8% grade shifted from 2nd to low and low did not engage.
At the bottom of the hill, stopped. Let brakes cool.
Level ground put transmission into low gear and transmission was in low gear as the truck moved forward. Continuing on,
started up a hill in drive then shifted to 2nd, transmission engaged, then shifted to low and transmission engaged.
Down another hill, shifted from 2nd to low and the transmission did not engage.

Input anyone?
Thanks in advance.

 

If you're going too fast for the gear when you pull the shifter down, I do not think it will downshift.

 

How fast were you going? The previous poster is correct. The calibration allows a 2-1 manual downshift only below a certain speed.

 

Let me see if I understand you correctly. With the lever in 1 and your foot ON the throttle, you get high RPM and the truck goes just fine in first gear. With the lever in 1 and your foot OFF the throttle while coasting downhill, the RPM is low and you get no engine braking. Right?

You don't say if your truck is 4x4, but a really good way to rule out going too fast as Walleye and cleatus mentioned is to find a really steep dirt road downslope and put it in 4 Low and first gear and see if it stays at a nice slow crawl. If you have to ride the brakes something isn't right.

My truck is doing the exact same thing, no engine braking in 1, and unfortunately nobody--including the Ford transmission engineer here on FTE--seems to know anything about it. Can you run ForScan? Mine says "Yes fault" when I monitor the shift solenoids SSAF and SSBF. https://www.ford-trucks.com/forums/1...-coasting.html. I would be interested to know if yours does the same.

 

There is a Ford transmission engineer here? Who is it? I used to be one, but not anymore. There is a difference.

When the problem occurs, can you check if there is engine braking in reverse? There should always be engine braking in reverse, but if there isn't, and there isn't engine braking in M1, the problem is the low/reverse clutch isn't working. This clutch is actuated by the manual lever, not by any solenoid. So if it doesn't work it means there is a mechanical problem with the clutch.

 

Thanks for all the input thus far. The truck is a 4x4. The transmission is an upgraded 4R100 rebuild with upgraded shift solenoids, valve body, flexplate and torque converter. It's an IDP Stage Two transmission. It's rebuilt for hauling and towing. I spoke with the company that rebuilt the transmission and describe the concern I have after I posted the query. I'm not a transmission mechanic so my understanding/knowledge is limited. My take away from our conversation was that the transmission has low range and it is the upgraded torque converter (stall speed) that keeps the transmission from downshifting from 2nd to low when moving at more than 25mph going downhill. If I would have shifted directly to low as I crested the hill, low range would have applied and then have low range going down hill. In the end it was advised to install a PacBrake system to help with downhill speeds.

Just want to mention the old transmission had 406,000 on it before the rebuild. It was the flexplate that failed when the truck stopped moving forward. I had a photo of the flexplate but unable to find it at the moment. The center of the flexplate where the mounting holes mount to the crankshaft cracked all the way around separating from the rest of the flexplate. I never seen or hear of this happen before. The Flexplate was 9 years in service. Along with the rebuilt transmission I had the new bellowed up pipes installed and they are worth the money. What a difference. A new rear main seal was installed. At 411,000 miles the truck and engine are still running strong. Thanks Again,
Jeff

 

Sorry I didn't specify "former." No offense was intended.

Mine has engine braking in reverse. In 4 Low and R, revving it up above 2000 then suddenly releasing the throttle feels almost like slamming on the brakes. In 4 Low and 1, not so much.

I hope the OP comes back. I'd like to compare notes with him.

 

The type of flexplate failure you described is likely the more common type of failure found in flexplates, but still, we would love to see the photo of your carnage, as they are always instructive, especially when it matches our application here.

My guess is that the flex plate flexes, and arguably the area of greatest stress is the junction between where the flexplate is constrained (by the circle of bolts into the crank flange in the center) to where the flexplate suddenly unconstrained (free to flex). The bolt circle diameter where the flexplate bolts to the torque converter is larger than the bolt circle diameter where the flex plate bolts to the crank. The larger bolt circle diameter has some inherent advantages over the smaller bolt circle diameter in distribution of stress. Compounding this is that the torque is delivered from the crank, straining the plate to over come the inertial resistance of the rest of the drivetrain down to the contact patch of the tires, so the sudden transition between constrained and unconstrained at the crank bolt circle diameter is challenged by both axial and radial forces and resistance, which the flexplate resolves by flexing. Until it cracks.











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Yes, Sir....That's what the old flexplate looked like.

 

Was the plate/washer/doohickey with the curled edge that goes between the bolt heads and the flexplate missing?