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Street Race Truck More... The Toolbox

LS Flexplates for TH350, TH400, or 700R4

6/22/2021

In this video, Pat from the Tech Team talks to you about LS flex plates for everyone out there doing LS swaps to old-school turbo 350, 400, or 700r4 transmissions.

Reason to Keep 350, 400, or 700r4 transmission.

Not everybody wants to use the 4L60E or 4L80e that came behind the motors because if you're like me you're a little cheap and you just want to use the transmission that's already in the car. Let's say you just went out and bought your junkyard LS for an 8, 5.3, or 6-liter truck motor and it already has a flex plate. That's awesome, we're halfway there to mate in those two up. However, f you want to run that old-school TH350, TH400, or 700R4 behind an LS motor, you will need a couple of parts to make it work. If you have a junkyard 4.8, 5.3, or 6.0L LS, take a look and see what style of flexplate you have.

Adapter for Concave 5.3L Flexplate
Torque Converter Adapter Sleeve

Most of the 5.3's came with a concave style flexplate. You can tell because the center of the plate will protrude towards the motor. If you have this plate, all you need is P/N 57518346. This sleeve slides onto the nose of the torque converter and helps align the unit into the flexplate.

Adapters for Flat 6.0L Flexplate
Flat Flexplate

If you have a 6.0 LS, the flexplate will be completely flat. It's gonna be similar to the one pictured on the left. If you have one like this you’ll need an adapter that fits on the crank side, or the engine side so you'll need to pick up the following items: P/N 12563533 and P/N 57518346.

Replacement Flexplate Kits

Now if you like me you bought a motor the flex plate was way out of balance when you try to run it, it was off, is cracked, or you just want something new, Speedway Motors carries a kit from TCI that has everything for you; P/N 282399753. This kit gets you the 6.0L style flexplate, the sleeve, and the flexplate to crankshaft bolts. This flexplate is built .35” thicker and so you do not need an adapter plate. The adapter is built right in!

Spacer and Hardware Included with TCI Kit

If you want a new 5.3L style plate you will want to order P/N 57534610 and the adapter sleeve, P/N 57518346. It's a great plate, it's SFI rated and then all you need is the sleeve to make it work. Using these 2 items will get your transmission bolted up to the motor.

Using these combinations of parts from Speedway Motors will hopefully help you make that LS install a lot easier.

Products Featured in this Article

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