T18 interchange question
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Mountain Pass
Joined: Mar 2003
Posts: 124
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From: Up state NY
T18 interchange question
I've got an 83 F350 with a bad T18 (fixed yoke , two piece driveshaft). It jumps out of reverse and has alot of bearing noise. I also have an 82 F250 with a good T18 (tail housing, slip yoke and one piece driveshaft). Is it a big deal to convert the good T18 to a fixed yoke? Can I just simply swap the rear casting or is it more involved? Or do I just move everything from the 250 to the 350 (slip yoke transmission and one piece driveshaft)?
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Mountain Pass
Joined: Mar 2003
Posts: 124
Likes: 0
From: Up state NY
Same wheelbase , different axle though. The 350 has a 10.25 and the 250 has a semi floater. I'd imagine worst case I'd have to change the U-joint
FTE Legend
Joined: Nov 2015
Posts: 30,915
Likes: 4,123
From: Angier, NC
If the T18 is anything like auto transmissions the out put shaft would need to be swapped between the 2 trans and IIRC that is a tear down of both trans.
Also some of the gears are on the out put shaft so if the shaft you need has bad gears then you are right back where you started.
You said 2 different rear axles. Yes a Ujoint change may work but you need to measure from the wheels axle center line to the pinion ujoint seat.
The pinions maybe longer between the 2 axles.
In that case a new drive shaft would fix it.
Now a FYI for an option: I pulled a T18 out of my 81 F100 because it was worst then yours and came across a NP435, also a granny first, that was a bolt in as long as I had the same drive shaft hook up, mine was a slip joint.
So a NP435 with a bolt up drive shaft like the 350 should bolt right in.
Dave ----
Also some of the gears are on the out put shaft so if the shaft you need has bad gears then you are right back where you started.
You said 2 different rear axles. Yes a Ujoint change may work but you need to measure from the wheels axle center line to the pinion ujoint seat.
The pinions maybe longer between the 2 axles.
In that case a new drive shaft would fix it.
Now a FYI for an option: I pulled a T18 out of my 81 F100 because it was worst then yours and came across a NP435, also a granny first, that was a bolt in as long as I had the same drive shaft hook up, mine was a slip joint.
So a NP435 with a bolt up drive shaft like the 350 should bolt right in.
Dave ----
Mountain Pass
Joined: Aug 2018
Posts: 127
Likes: 31
From: Livermore, CO
Why not swap out the rear axle also. If you haul heavy loads, use it for towing, or have a slide in camper the full floater axle is an upgrade. GVW for a semi-floater is around 7700# and the full floater is around 8600# or more.
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Mountain Pass
Joined: Mar 2003
Posts: 124
Likes: 0
From: Up state NY
You've confused the two trucks. The one that's ultimately be repaired is an 83 F350 which has already been updated to an 87+ 10.25 Sterling. It's just got a bad T18 in front of it. I'm going to take the long tail T18 and one piece driveshaft out of the 250 and install it in the 350.
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