72 K20 6.0 4l80e swap questions

[chev-obsession]

Hey Guys, I recently bought a 72 K20 350/350 and thinking of doing a 6.0, 4l80/205 swap. The truck is stock height and want to keep that way. I know the 4l80e is a pretty long trans plus the length of the adapter and t case. I didn’t know if that causes bad driveline angles? I’d also like the t case shifter to be somewhat close to the factory location. Can the motor be moved forward with a dirty dingo or pacific fab X-member?

I didn’t find much about this exact combination when I did a search. Any tips or advice?

Thank you
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[LS short box]

I would contact either Advance Adapters I believe is in CA. Also Novak Adapt in Logan UT.
I used Novak parts on my 98 Wrangler LS6/4L60E and they have worked great for over 14 years.

[chev-obsession]

Originally Posted by LS short box

I would contact either Advance Adapters I believe is in CA. Also Novak Adapt in Logan UT.
I used Novak parts on my 98 Wrangler LS6/4L60E and they have worked great for over 14 years.

I’m not so worried about the adapter, I’m more wanting to know if the combined length of the engine, trans, adapter and t-case is too long for a 72 k20. Will the driveline angles be too steep? And can the t-case be mounted in the factory location? Looking for advice from anyone who has done this exact setup.

[LS short box]

I would search 350 turbo bell housing face to trans mount dimension. Do the same for the 4L80E. That will give you an idea if you want to keep the stock trans cross member In the stock location and how much you might have to move the engine forward.
On many hot rod sites they describe the the 4L80E as a longer 400 turbo due to the extra gear.
On my Wrangler LS swap I had to run a rear CV drive shaft due to the angle. It has worked well. I believe the trans to transfer case adapter is about 4-5 inches long? On my Wrangler I kept the 4WD shifter in the stock location and modified the linkage going to the TC.

[Accelo]

The THM 350 has an length of 21 5/8 in. to where the tail shaft attaches.
The 4L60E has an length of 23 3/8 in. to where the tail shaft attaches.
The 4L60E 1998 and later has an length of 23 3/16 in. to where the tail shaft attaches.

I failed to find the total length of the transmission / transfer combination. Since you have both post the total lengths of each.

With a nominal 2" greater transmission length, you should be fine, but without transfer-case length I can't tell for sure.
Using your current driveshaft length I could calculate the difference in angle. I can't do the maximum angle unless I know the current angle.

Don't forget the new transfer-cases swing both ways and one is a give away price the other expensive. But you likely know that already.

The speedometer going to be analog or digital?
The rear reluctor ring is not always installed in the 4L80e transmission. The basic rule of thumb is 4WD transmissions up to 1996 should have a rear reluctor ring in the main transmission case. The 1997 & newer 4WD 4L80E transmissions had a sensor provision; however, the reluctor ring in the transmission was left out.

[kwmech]

Since you are remaining stock height I wouldn't worry about it. Even if you were going to put a 4'' lift on it you should still be golden. It's a long bed truck---you've got a lot of room to work with. As far as the placement and shifter. I don't think there is too much room to play with as far as engine placement with the Ls platform.....it pretty much sits in the same place. T-case is going to be moved backwards a few inches so you will/may have to fab something up for the t-case like longer brackets and linkage so it pops up through the floor where you want it. Cross members are going to moved and re-drilled anyways.

[chev-obsession]

Originally Posted by Accelo

The THM 350 has an length of 21 5/8 in. to where the tail shaft attaches.
The 4L60E has an length of 23 3/8 in. to where the tail shaft attaches.
The 4L60E 1998 and later has an length of 23 3/16 in. to where the tail shaft attaches.

I failed to find the total length of the transmission / transfer combination. Since you have both post the total lengths of each.

With a nominal 2" greater transmission length, you should be fine, but without transfer-case length I can't tell for sure.
Using your current driveshaft length I could calculate the difference in angle. I can't do the maximum angle unless I know the current angle.

Don't forget the new transfer-cases swing both ways and one is a give away price the other expensive. But you likely know that already.

The speedometer going to be analog or digital?
The rear reluctor ring is not always installed in the 4L80e transmission. The basic rule of thumb is 4WD transmissions up to 1996 should have a rear reluctor ring in the main transmission case. The 1997 & newer 4WD 4L80E transmissions had a sensor provision; however, the reluctor ring in the transmission was left out.

Thanks for the info, I measured my driveshaft… from the center of the yoke on both ends, I get 61”. I forgot to grab my angle finder and the truck isn’t level at the moment.

Speedometer will be analog which if I’m not mistaken I can use the speedometer port on the t-case to drive the 72 speedometer and the vss port to talk to the pcm. My plan was to use the advance adapters 2wd 4l80e to figure 8 205 t case adapter. Seems like that is the way to go. I would be getting the 4l80 and 205 rebuilt. So if I have to swap parts or machine stuff it’s not a big deal to me. The 4l80 I have is the LS version. So I don’t see too many hiccups there.

At this point I am mostly concerned about placement of the engine, trans and t case and what I should expect, that way I can start accumulating parts. If I can keep the t case in the factory location that would be best for me since I could keep the driveshafts the same and not have to modify the t case shift linkage. I know that is not always possible.

[ls1nova71]

I don't know why you couldn't put the transfercase in the original location and just move the engine forward a bot to fit. I just did an L83/6l80 swap on a '72 4x4 Blazer and that's what I did. Worked out pretty good, puts the engine in roughly the 2wd location in the frame.

[chev-obsession]

Originally Posted by ls1nova71

I don't know why you couldn't put the transfercase in the original location and just move the engine forward a bot to fit. I just did an L83/6l80 swap on a '72 4x4 Blazer and that's what I did. Worked out pretty good, puts the engine in roughly the 2wd location in the frame.

What did you do for an engine crossmember? Did you use a 2wd or 4wd trans?

[ls1nova71]

Originally Posted by chev-obsession

What did you do for an engine crossmember? Did you use a 2wd or 4wd trans?

Used a Dirty Dingo crossmember, which I honestly wasn't too impressed with. It worked, but seems like there could be a better alternative to bolting together a thousand parts... Also used a 4x4 transmission with an Advanced Adapters adapter to mount it to the np205 transfercase. The downside to that was there was no place for the shifter to bolt to like a GM adapter, so I had to fabricate a bracket for that.

[LS short box]

On my Wrangler swap the Novak trans/tc adapter has a tapped port so you can screw in a magnetic pickup. And the replacement tail shaft from Novak has toothed gear on the shaft so the ECM will get VSS signal. Per Novak the VSS signal must come from the tail shaft of the trans so it shifts properly in high and low range.

[Richard]

Originally Posted by LS short box

On my Wrangler swap the Novak trans/tc adapter has a tapped port so you can screw in a magnetic pickup. And the replacement tail shaft from Novak has toothed gear on the shaft so the ECM will get VSS signal. Per Novak the VSS signal must come from the tail shaft of the trans so it shifts properly in high and low range.

No way trans will shift properly in low range with rear vss in trans. Something I have been looking for a solution. Only option without vss after t-case is to use my trans in manual shift mode when in low range.

[ls1nova71]

Originally Posted by Richard

No way trans will shift properly in low range with rear vss in trans. Something I have been looking for a solution. Only option without vss after t-case is to use my trans in manual shift mode when in low range.

I used an adapter that went on the rear output yoke of the transfercase that took a GM speed sensor. Worked great, but was a little spendy... Can't seem to remember the name of the company right now though.

[Richard]

Originally Posted by ls1nova71

I used an adapter that went on the rear output yoke of the transfercase that took a GM speed sensor. Worked great, but was a little spendy... Can't seem to remember the name of the company right now though.

Think I remember seeing a post about it. Probably by you. Billet piece that replaced the rear seal/bearing retainer. ORD can modify rear housing as well to accept a VSS sensor. As you most likely know the 6L80/90 use a front and rear VSS to control shifting. The reluctor wheel included in both of those kits has significantly less teeth than the rear reluctor in my 6L90. Assuming the wheel generates pulses, I made the assumption that those options would not solve the problem and probably create more. Still do not have enough information to know if anything can be changed in programming to change the value of pulses at rear VSS.

[Richard]

Put an LSA and 6l90 in my K10 SWB. You can check out the build thread for some details.