SquareRoot
Full Access Member
- Joined
- Mar 18, 2017
- Posts
- 4,230
- Reaction score
- 8,124
- Location
- Arizona
- First Name
- Mike
- Truck Year
- 85
- Truck Model
- K20
- Engine Size
- 350
Short back story:
Swapped in a 14FF with a Detroit Locker and 4:56 gears (CUCV) donor into my 85 K20 about a year back. At the time, I had a Turbo 400 automatic, aka "slushbox". I have always hated auto transmissions, but that's another story. Anyway, all was good except for the engine screaming at 55 mph. So, the logical choice was to kill two birds with one stone and toss the th400 and replace it with a NV4500! Ahhh, life was great......except...that obnoxious, ratcheting, clicking, banging, surging, jerking thing that happens at low speed when taking off, slowing down and especially turning. What the hells going on with that?! Just the nature of a manual transmission in an older truck I told myself. I checked and double checked and checked every part of the drivetrain once more for any slop, misalignment, out of round, worn out, defective part that would cause the issue. Nope, everything new or good as new.
Conclusion; well more of a hypothesis at the moment. The locker does NOT play well with manual transmissions on a street driven daily driver! My logic is the constant locking/unlocking, ratcheting in the locker translates directly thru the mechanical connection of the drivetrain right into the transmission. Never noticed it with the "fluid coupling" that a torque convertor provides. Ahhh, maybe that's where the "slushbox" moniker came from? Anyway, I digress.
Fortunately, I still have the SF 14bolt that came in the K20 with the OEM open differential laying around. I figured the easiest way to test my theory would be to swap the rear end and see if that solved the issue. If so, that locker is NOT going back in. It will either get replaced with an ARB or I'm looking at the Eaton Detroit TrueTrac. I'm not keen on the price of the ARB ($1100+ a compressor) for something that's not a hardcore off-road rig. I think the Limited Slip diff is more appropriate for my use and far more affordable.
I welcome opinions on that choice if anyone has experience with it.
The swap is done, except for the E-brake cable hookup and quick brake line bleeding process. Should have it back on the road Friday when I get some time. I am very curious to drive it for a few days and see how she feels. I also need to pull that front shaft before I pull a stupid and put it in 4 WD. They say 4:10 gears in back don't play well with 4:56 gears in the front? lol
Swapped in a 14FF with a Detroit Locker and 4:56 gears (CUCV) donor into my 85 K20 about a year back. At the time, I had a Turbo 400 automatic, aka "slushbox". I have always hated auto transmissions, but that's another story. Anyway, all was good except for the engine screaming at 55 mph. So, the logical choice was to kill two birds with one stone and toss the th400 and replace it with a NV4500! Ahhh, life was great......except...that obnoxious, ratcheting, clicking, banging, surging, jerking thing that happens at low speed when taking off, slowing down and especially turning. What the hells going on with that?! Just the nature of a manual transmission in an older truck I told myself. I checked and double checked and checked every part of the drivetrain once more for any slop, misalignment, out of round, worn out, defective part that would cause the issue. Nope, everything new or good as new.
Conclusion; well more of a hypothesis at the moment. The locker does NOT play well with manual transmissions on a street driven daily driver! My logic is the constant locking/unlocking, ratcheting in the locker translates directly thru the mechanical connection of the drivetrain right into the transmission. Never noticed it with the "fluid coupling" that a torque convertor provides. Ahhh, maybe that's where the "slushbox" moniker came from? Anyway, I digress.
Fortunately, I still have the SF 14bolt that came in the K20 with the OEM open differential laying around. I figured the easiest way to test my theory would be to swap the rear end and see if that solved the issue. If so, that locker is NOT going back in. It will either get replaced with an ARB or I'm looking at the Eaton Detroit TrueTrac. I'm not keen on the price of the ARB ($1100+ a compressor) for something that's not a hardcore off-road rig. I think the Limited Slip diff is more appropriate for my use and far more affordable.
I welcome opinions on that choice if anyone has experience with it.
The swap is done, except for the E-brake cable hookup and quick brake line bleeding process. Should have it back on the road Friday when I get some time. I am very curious to drive it for a few days and see how she feels. I also need to pull that front shaft before I pull a stupid and put it in 4 WD. They say 4:10 gears in back don't play well with 4:56 gears in the front? lol
