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5,187 Posts
Discussion Starter · #1 · (Edited)
So you have your new Gen III motor and want to run a early auto transmission with it.

There is lots of confusion on this! I need this spacer or that flexplate or this converter.

Really all you need is the right Stock GM flex plate and spacer.

The Gen III/IV has a different crank offset vs the Gen I SBC.

Basically its .400 in. from the were the SBC crank flange location.

So to use the 4l60 with the Gen III GM changed the torque converter by adding a longer nub on the center hub that contacts the crank to support the TC. As well as going with a metric TC spacing.

Gen III converter with long hub

(need a better picture as this is not mine)

SBC converter note smaller shorter hub

Gen III engines with a stock 4l60/65/70 GM uses a dished flex plate. Note its the one on the right with the shorter crank bolts. The flat flex plate is on the left note the longer bolts.

On Gen III engines using the 4l80 trans which uses a convter with the Gen I style center hub GM used a Flat flex plate and a spacer mounted between the crank and flex plate. This mounts the TC flush with the center hub and it slides into the spacer to support it.

The flat flex plate has the spacer on the fwd side facing the crank.

Dished 5.3L flex plate mated to a SBC Gen I converter. Note the hub is un supported

Flat 6.0L flex plate and spacer on a SBC converter. Note hub is supported by the spacer.

So you want to bolt your 700r4/TH350/TH400 to a Gen III motor.

Well your in luck!

You have two options using stock GM parts.
1)Use a the dished flex plate and add the spacer after the flex plate. The spacer serves to just support the center of the SBC TC only.

Spacer from GM parts direct or local dealer
GM PART # 12563532
CATEGORY: Engine Flywheel
GM LIST: $52.86
OUR PRICE: $31.34

GM PART # 12563533
GM LIST: $6.86
OUR PRICE: $4.06

Another option for a spacer is the bushing spacer it doesn't need longer bolts and just sits in the end of the crank. So its a lot cheaper option $20 vs buy the GM spacer and bolts.

PRW1800346-LS Engine to Old Style GM Trans Crank Spacer

2) Use a 6.0L flat flex plate with the spacer between the flex plate and crank. Note:the spacer is part of the flex plate ie its installed onit and should come off with it.

The spacing of the two flex plates when attached to the crank are the same IE the teeth of the both flex plates are in almost the same location. The dish of the 5.3L flex plate makes up for the spacer. So any Gen III starter should work.

Now you will still have to elongate the flex plate to TC holes as the spacing for the Gen III TC is metric. Not much will be need, test fit it first on the TC.

And from what I have seen you just can't use a Gen III 4l60 TC in an earlier trans.

There is a couple of kickers. Some early 99-2000 4.8L and 6.0L had a longer crank flange to make up for the .400 inches. If your motor happens to be one of these all you need is the flat flex plate and remove the spacer.

And you really have no way of running a DBW TB with a TV cable. Unless you mount the TV cable to the DBW pedal itself. Its easier just to use a Gen III trans.

1,901 Posts
Thanks for posting this!! It's damn sure hard to sort out all this information and you've done a great job. It would be nice if we could have a subforum called FAQ's so this could be stickied there.

465 Posts
Heck yeah, that's some really good info. I know TCI makes an adapter for running a TH-400 or something (been quite a few years since I looked).
But much better if you can get away with using "regular" parts that are readily available.

1,190 Posts
took me an hour of reading a while back when I was trying to mate my 4L80E to my 6.0L. Got the flat flex plate the spacer on order eventually, but that was 4 years ago. There's way more info on this stuff now. I'll take note of this if I go to another tranny but love the 4L80E.

5,187 Posts
Discussion Starter · #11 ·
What about running a manual like a NV4500 with one of the newer Gen III/IV engines? Do the cranks have a hole for a pilot bushing?
The 6.0L came with the NV4500 till around 05 or so. And the 4.8L had the NV3500 as well. So have provisions for the pilot bearings.

5,187 Posts
Discussion Starter · #14 ·
Great thanks, I wonder if only those years have them.
The all have provisons for them, all the Gen III/IV's. So you can use the flywheel and bushings out of the NV4500 motors. The part numbers are listed on here as well.

Heres info on a early model manual swap. Be aware of the crank spacing difference Gen I vs Gen III/IV as well.

cardinal fang said:
Flywheel and clutch solution.


Thanks to 'Logic2" off of Ih8mud. He tracked down the part number for the flyhweel he got from Summit that fits the LS cranks and has both SAE and metric bolt holes. So old school clutches will fit the flywheel.

The fly wheel is a RAM 1550, Summit's #1550. Jeg's has it also for the same price. Ebay too, $259 - all have handleing charge, $13

It fits my 2000 Sierra 5.3 crank perfect. See pics below. I used the bolts from the chevy dealer to attach it to the crank. The bolts take a 15mm head socket. With the flyhwheel attached, the bolt holes in the crank are 1.245" deep. The torque for the bolts, per the Sierra manual I got, is are 15-37-74

I wrote up the costs of various ways to get a flywheel on a 5.3 vortec. This may help someone trying to figure out wich way to go.

Manual transmission 5.3 vortec
AA setup
This custom clutch kit is designed to adapt the Gen III / LS series to a GM manual transmission (SM420, SM465, NV4500) into a Land Cruiser FJ40. The kit includes:
A custom flywheel, with the correct 0.40 offset
11mm flywheel bolts,
11” Centerforce pressure plate & disc,
pilot bushing spacer,
throw-out bearing,
10mm bellhousing bolts,
10mm lock washers,
XRP dowel bolts
~Total: $621 + Tax + shipping ~$700

Do it yourself option
Stock OEM flywheel # 12561680, ~ $428, internet $300
Uses GenIII clutch assymb, ~$250, only fits the OEM flywheel, 1” taller than old school
OEM 0.400 spacer #, 12563532, ~$52, internet $40
Throwout bearing, SM465, ~$20
Pilot bearing, must use the extended one like the Mcleod, $36
~Total: $600 + tax – shipping?

Shipwreck’s solution
McLeod set, per Car Craft’s Article
McLeod Conversion Flywheel #460535 ~$400
McLeod extended pilot bushing #8617 ~$36
Luk 12" clutch kit for sm420 #04-064 ~$130 ??
~Total: $550 + tax – shipping

My solution
Logic2’s find on Summit for a flywheel, “Ram-1550”, $270, free shipping,
Luk 04-049 clutch kit, pressure plate, bearing, pilot bearing(can’t use), clutch disk, $130, Autozone
Special pilot bearing to fit the vortec crank, GM 12557583, ~$20
Flywheel bolts, ~$36-45
~Total: $500

1,326 Posts
Like the Pirate "search" feature..... thanks for the useful info...... HOWEVER.... I am currently running a 02 4.3 with a dished flexplate and am swapping to an 03 (DBC) 6.0 with a dished flexplate...... to a 700r4........ looks like a simple swap based on your tech here.....thanks again

5,187 Posts
Discussion Starter · #20 ·
Great write up!

Just a little confused I have same setup as your scout 6.0 (lq4), 4l65e, 241c did you have to change the flexplate for a dished one?


Yes I had a 5.3L dished flex plate. The one pictured, and it bolts right up. But you will need shorter crank bolts as the dished one is thinner.
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