ZF 6 locked up but not.
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6th Gear
Joined: Nov 2025
Posts: 6
Likes: 4
ZF 6 locked up but not.
Hi, I have a ZF6 transmission i received when I bought my 2003 f250 v10 4x4. I was told the transmission was locked up and got no explaination as to what happened but i came to the conconclusion it was run low on fluid due to the rotted leaking cooler llines.
Any ways, The transmission will not spin in any gear except reverse. When put into neutral it will spin over but the output will spin also and you cannot keep the output from spinning when turning the input.
The weird thing to me is when I took off the tail housing all the gear change and roller over just fine it seems.
I experimented with taking the idler gear out and put the tail housing back and which resulted in the gears all spinning over.
Now, the back story on the idler gear is when I initially took off the tail housing I found the needle bearings had let go for the idler gear. I replaced them and it did not changed any symptoms of the lock up.
I feel I am missing something in plain sight and hoping someone can shed some light. Thank you in advance!
Any ways, The transmission will not spin in any gear except reverse. When put into neutral it will spin over but the output will spin also and you cannot keep the output from spinning when turning the input.
The weird thing to me is when I took off the tail housing all the gear change and roller over just fine it seems.
I experimented with taking the idler gear out and put the tail housing back and which resulted in the gears all spinning over.
Now, the back story on the idler gear is when I initially took off the tail housing I found the needle bearings had let go for the idler gear. I replaced them and it did not changed any symptoms of the lock up.
I feel I am missing something in plain sight and hoping someone can shed some light. Thank you in advance!
More Turbo
Joined: Jun 2008
Posts: 564
Likes: 93
Is the reverse shift sleeve moving to the correct position when shifting out of reverse? When you have the transmission in neutral, is the output shaft turning the same direction as the input shaft, or is it turning the opposite direction? It seems like there may be an issue with the reverse shift mechanism that is leaving reverse engaged, so when you engage another gear, you have both a forward gear and reverse engaged at the same time, resulting in lockup.
Last edited by Super Duty DJ; Today at 11:03 AM.
Thread Starter
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6th Gear
Joined: Nov 2025
Posts: 6
Likes: 4
Turning the opposite direction
Is the reverse shift sleeve moving to the correct position when shifting out of reverse? When you have the transmission in neutral, is the output shaft turning the same direction as the input shaft, or is it turning the opposite direction? It seems like there may be an issue with the reverse shift mechanism that is leaving reverse engaged, so when you engage another gear, you have both a forward gear and reverse engaged at the same time, resulting in lockup.
More Turbo
Joined: Jun 2008
Posts: 564
Likes: 93
That indicates that reverse is not disengaging when you have shifted to neutral, so any time you shift into another gear you are engaged in both reverse and a forward gear at the same time, resulting in lockup. You probably have to get into the main case enough to see if the low/reverse shift fork broke, or disconnected from the shift rail or something while the shift collar is engaged in reverse. I suspect that you may find that the shift fork is broken or disconnected because there are other interlock mechanisms to prevent the shift rails from allowing multiple gears to be selected at the same time and those are almost always geometric constraints that physically lock the "inactive" shift rails in the neutral position when the "active" shift rail moves out of the neutral position.
Thread Starter
|
6th Gear
Joined: Nov 2025
Posts: 6
Likes: 4
That indicates that reverse is not disengaging when you have shifted to neutral, so any time you shift into another gear you are engaged in both reverse and a forward gear at the same time, resulting in lockup. You probably have to get into the main case enough to see if the low/reverse shift fork broke, or disconnected from the shift rail or something while the shift collar is engaged in reverse. I suspect that you may find that the shift fork is broken or disconnected because there are other interlock mechanisms to prevent the shift rails from allowing multiple gears to be selected at the same time and those are almost always geometric constraints that physically lock the "inactive" shift rails in the neutral position when the "active" shift rail moves out of the neutral position.
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