zildjian4life218

I was reading that in order to put a 5.3L LS motor to a GEN I trans (TH350, TH400, 700R4 etc) that I need to buy the converter hub, longer bolts, and then elongate the holes on the flexplate to match the bolt pattern. I took a spare flexplate I had from an '01 and lined it up to the 700 r4 converter and the factory holes did not line up (which I expected). I then noticed another set of holes on the flexplate and after lining everything up it lined up perfect. I checked this on a flexpalte from an 03' 5.3L I had and it did not have the extra bolt holes.

Any one else run into this? Since the motor with the 03' flexplate was going to be backed up by a GEN I trans I took the flexplate and bolted them together using the existing LS trans bolt holes and then marked the additional 3 holes and using the 01' flexplate as a template drilled out the holes. Everything lined up perfect.

I have some pics below of the flexplates.

mrvedit

There are people here who know 1000x more about flexplates than me, but IIRC there is a GM dual-pattern flexplate with holes for both older and newer style converters. Some aftermarket flexplates are dual-pattern too.

Circle-D

iTrader: (21)

The earlier LS flexplates had the dual bolt pattern, LS and LT(TH350). So you are good to go there. Downside is the earlier flexplates do crack easy. Upgrading to a SFI version might be a good idea. You will also need a pilot extender, pic attached.

Chris

zildjian4life218

Great! Glad to know I wasn't going off the wrong track. I bought this to extended the converter hub http://www.summitracing.com/parts/nal-12563532

This is just a 5.3 with an LS2 cam and ls6 intake. No crazy go fast parts. Hopefully it doesn't crack the flexplate.

Is the flex plate cracking a common issue? I have never heard of that but this is only my second LS engine that I have worked on or modified.

Circle-D

iTrader: (21)

You can use that extender from Summit, but it will need to go on the transmission side of the flexplate. That adapter is actually for the 4L80 OE setup, but you can use it as an extender in your case. You will need longer crank bolts, summit should sell those as well.

And typically when they crack they just make noise. Sometimes they do come apart and destroy lots of stuff, but you are probably ok.

Chris

ZONES89RS

iTrader: (25)

I find it best to just get a 4L80 flex plate and spacer. Works every time. Otherwise a 99 up 4.8/5.3 flex plate with a 4L80 spacer between the bolts and flex plate have never failed me either.

ezstriper

they used a few different flywheels for sure, I run the beveled stock one from a 6.0 and worked fine with a PG, other car doing a 400 swap right now, using another 6.0 one that is flat but has the spacer already on it and the pattern matches the TCI converter we are going to use, now I do need to come up with the correct crank bolts now...

mrvedit

The longer crank bolts for use with a spacer are:
GM 19257940 bolts (need 6 bolts). About $5.95 each at Summit or Jegs.