What's the deal with the crank spacer on early 6.0s?
On most LS engines the crank flange sits farther forward than an old small block's, so bolting up a TH350/400/700R4 uses a dished flexplate plus a torque-converter sleeve/spacer in the crank. The exception is the 1999–2000 LQ4 6.0, which has a "long" crank flange and uses a flat flexplate with no dish or spacer. Confirm which crank you have before ordering adapter parts.
Last updated
The 1999 and early-2000 6.0s used a crank spacer tied to 4L80E fitment, so check transmission compatibility whenever you mix an early engine with a later transmission or the reverse. Behind a 4L60E or T56 you don't need the spacer, so take it off; an LT1-style 4L60E has been reported to need it. Those early LQ4s also had iron heads, and the LQ9 didn't exist yet, so any 'LQ9' 1999/2000 engine is mislabeled.
Check this first:
- Check the block date code to confirm the engine's year
- Confirm which transmission you're mating it to and whether it needs the spacer
Based on what we've seen work across our own builds, our friends' builds and the wider LS community, reviewed by our lead shop tuner (over 20 years of LS and LT tuning experience). Every combination is different, so use at your own risk.
Go deeper
Check this first
- Measure the crank flange before ordering anything (1.25 vs 0.857)
Try this, then this
- Measure the flange, then order the matching spacer/flexplate — the 0.4 in difference must be compensated exactly. Worked if: converter fully seats in the pump
How you know it's fixed
- Spacer/flexplate installed, converter seated, endplay correct
Still not fixed?
- Wrong spacer stack = converter not seated = pump failure; measure twice
Key numbers
| What | Value |
|---|---|
| Long crank flange | 1.25 in (99-00) |
| Standard crank flange | 0.857 in (01+) |
| Long crank + 4L60E solution | spacer and modified flexplate documented |
Every option we know of
| Maker / product | Part # | Fits | Price | Where | Status / notes |
|---|---|---|---|---|---|
| Advance Adapters crank spacer | 716155A | LS to early transmissions | varies | advanceadapters.com | In production must pair with correct flexplate |
| Novak crank spacer kit | n/a | long-crank 6.0 | varies | novak-adapt.com | In production verify stack height |
Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.
Time and cost: A day with the trans out
Related questions
- Are LS swaps legal in California?
- What sensor and wiring differences are there when swapping an LS2 in place of an LS1?
- What does California's smog referee require for an LS or Hemi engine swap in a Jeep, and can it pass the sniffer anyway?
- Lifters ticking - fix it or sell the truck?
- Should I LS-swap my SBC 400 squarebody or keep the 400?