Besides the T56 currently in the car, I've also got a complete TH350 built for 800 hp by Century and a brand new Vigilante 3800 stall. It also has an LT1 specific flexplate for the TH350, a large B&M transmission cooler w/stainless B&M prostick shifter. The TH350 has a B&M dipstick for the 4th Gen Fbody. I have a BMR torque arm relocation cross member for the M6 and a A4 cross member modified for the TH350.

Questions:

• What of the TH350 stuff can I still use in a swap to a 4L80E?
• If I opt for a fully manual valve body in the 4L80E, do I still need some special pigtail to make it operational? I assume a VSS at a minimum?
• If I don't opt for a fully manual valve body setup, what will I need to make the transmission fully operational?

Thanks,
Dave

 

I've been looking for similar answers Dave. I want to swap a T56 into my automatic. I decided the best way to do it was to buy an M6 car and swap transmissions between the two. I've tried selling a 4L60 by itself and had a hard time a few years ago, and the prices I have been seeing for the T56 swap parts add up really fast! I bought a donor car this week and am going to begin work today on the swap.

I'm going to leave the computer and wiring harness in each car, because the wiring harness from the donor car is pretty rough! I found all the pin numbers from the ECM connector plug that goes to the transmission plug. My thinking is to add the pins to the ECM and run new wires down to the transmission plug. The VSS connector looks the same for both cars, so I don't think any modifications need to be done there. I copied wiring diagrams from the factory service manual. If you would like, I can bring them home from my shop and upload them for you. I'm concerned about the fitment of the automatic shifter assembly due to the hole cut out of the M6 car. Aside from that, I think putting the auto in the M6 car is going to be easier than the M6 into my car.

If you find any info out there about this, let me know. I haven't had any luck finding a write-up from someone who has been down this road yet. I'm hoping it goes quick for me, because I want t sell the donor car ASAP to get my money back out of it!

 

I did get some info on the 4L80E swap. Several guys have done it but it does require some special handling.

• There is a generously sized plug for the command of the 4L80E on the drivers side. Most people pull out that most prized of tools, their Snap-On BFH, Nascar edition, and beat the floor pan till it complies. Others, a very professional effort BTW, have cut out the pan in the affected area, fashioned a shell of sorts out of sheet metal that fits the necessary contours of the plug + some and the shape of the cutout and then welded it back onto the floorpan.
• The torque converter is unique to the 4L80E so I'm outta luck as far as using my TH350. The trans crossmember seems to be different than the manual or auto x-members I already have <drat>
• There's some trickery on the VSS hookup and cooling lines too.

 

Well, that sounds like a big PITA, but it'll be worth it from what I've heard. Does the VSS operate differnetly than from the 4L60? I pulled the wiring harness for the 4L60 from my car by un-pinning each wire at the computer plugs. It was a lot easier than i thought it would be! The VSS for the 4L60 plugs into the ECM in the same spot on the both cars, the only difference is the plug style at the tranny. Do you have to get a stand-alone computer to run the 4L80?

 

I'll look thru my notes regarding the VSS, I may have misspoken. PCM4Less has a plug n' play harness for the swap and with that (and possibly with your repinning?) Bryan can program the stock LT1 PCM (OBDII only?) to command the 4L80E.

 

Here's a knowledge loaded cut n paste from an Impala SS forum. Of course some of this info is B-Body(Impala) specific and others just not applicable, but in the main, I think it covers quite a few bases...
Since there have been several interested people on this I’ll go ahead and outline what we did to change over a ’95 Impala to a 4l80E.

While the reasons to stay with the 4L60E can be argued until everyone is blue in the face, the fact is that we felt the 4L80E was better a long-term solution for our application. It is important to clarify that it is _not_ necessary to use an aftermarket transmission controller, the LT1 PCM _can_ control the 4L80E. As far as the weight/rotating mass argument goes – well, first of all we weren’t that concerned as this isn’t a drag car, and secondly, the same was said when the Syclone and Typhoon guys started changing over from the 700R4’s to the 4L80E’s. But what was found was they generally ran the same or up to 2 tenths quicker, something they attribute to the quicker shift event times and/or reduced RPM drop on the 1-2 shift. This is only an explanation of what we did, not necessarily an argument for/against the changeover.

Mechanicals:

We purchased a used 4L80E locally from a 2500 Chevy Express van, something like a 2003 or so, just before they were switched to the LS engines. The converter is supposed to be the loosest one that the factory offered (look for 2000 - up small block applications) so it has a stall speed not too far from a factory SS converter. Dropping $800.00 - $1000.00 for a decent lockup converter wasn’t in the cards at this time, so we tried to get as close as we could and upgrade later, if necessary. To mount it into the Impala, we obtained a 4L80E crossmember from Dan @ CIA.

Since the 4L80’s use the large ring gear, and there isn’t room to readily adapt it to the smaller 153 tooth Impala flexplate, we bolted it up using a 168 tooth flexplate (from a 350 powered ¾ ton pickup) found on eBay. As the LT1 blocks are already double drilled for both starter configurations, we then selected a 454 gear reduction starter (as used on the ‘96 – up Vortec 454's) and that went in by just rerouting the starter cable. By going to the larger ring gear flexplate, we were able to reuse the converter that came with the transmission. Note that iIf you were to obtain an aftermarket converter this step would be unnecessary, as most are available in the smaller - 153 tooth - bolt pattern.

The trans went in as is, without having to slice the converter dust shield mounting ears as we had expected we might need to. As the car is equipped with FLP headers, they may have helped this time. In this instance, the starter to header clearance actually improved, but you may not be so lucky with your particular configuration. There was no floorpan massaging necessary to fit, though it is a bit tight in a couple areas. Since our 4L80E was a post-1997 model, it was necessary to lengthen the cooler return line to reach the rearmost fitting, easily handled with a section of brake tubing, a compression union, and some careful bending.

The shift cable was too short by about 5 inches – we ended up going to the wrecking yard and selecting several that looked like they might work. Not sure what we eventually ended up with, but a Blazer unit might be a good place to start. The floor shift conversion was performed while the car - again this was on a ’95 SS - was still running the 4L60E. At that time the column linkage was retained to actuate the reverse lights, etc. That had to go clearance reasons - it is necessary to tie into the combination switch on the 4L80 range selector shaft - similar to the setup used in the '96 Impalas – to get the safety interlocks and reverse lights back up and operational.

Everything we could find showed that the 4L80E is 5/8" longer than the 4L60E. Since the car had already been fitted with the extended rear control arms, we were thinking of reinstalling a factory shaft with a conversion U joint to fit the larger yoke, but as it turned out we couldn’t locate a nice unit quickly and ended up having the existing aftermarket shaft cut down 1 inch by a local shop. It was their opinion that the conversion joint was not the best solution in terms of future availability and recommended that we proceed welding in the proper end, so we followed their advice.

Electricals: You will want to tie into the combination switch as mentioned above. It may have been necessary to re-pin the VSS connector to fit the 4L80E housing. That would be a function of year, as the ’94 & ’95 cars use a different connector than the 96’s. Using the ’95 FSM and 4L80E SRTA manual, the car’s transmission connector was repopulated to match what the transmission expected. To accommodate the inverted logic of the ‘Shift B’ solenoid, the output line from the PCM was split and a tied into a standard Bosch relay at Pin 30, with the transmission side tied to the normally closed – 87A – contacts. The coil contacts - 85 & 86 - are supplied by an ignition-switched source. See http://www.teamrocs.com/technical/pa...lay_basics.htm if you need a better explanation.

That is pretty much it except for the PCM programming, there are a number of people that can better speak to the table values that should be modified to account for the various transmission differences better than I can, so I’ll defer to them for that.

Once out on the road, we did find that the shifting was softer that we had expected, that may be due to the OEM van application our transmission was sourced from, so a TransGo kit was installed and then the car brought back to do the final adjustments on the shift firmness.

This is pretty much what was needed to put a 4L80E where the 4L60E was. Hopefully this will give everyone an idea of what to expect if they are contemplating doing the same.



Here's the PCM4less harness info and some that relates to what Bryan Herter said in a reply to me about programming the LT1 PCM...

Hi,
The LT1 PCM did not have the capability to control the 4L80E, but our shop in NC has a special harness that can make the 4L80E work with the 4L60E commands and plugs right into it's harness. I have to shut off a couple codes in the LT1 PCM, but other than that it is pretty straightforward.
Thanks,
Bryan


He had CC'd his sales dept and they sent this...
Hello, yes we do have a harness for that. Here is a link,

Performance Parts

The part number is P-120018. It is plug and play except for Bryan disabling a couple codes for you!

 

I just picked up an 80e and will be doing this swap over the winter. AFAIK you only need to swap a few wires around in original harness and the VSS plugs right in, no need for ISS. The stock PCM controls it just like the 60e.

 

Cool. Let us know how it goes as you make progress.
Thanks,
Dave
Newest mod: Upgrading from TC76 to PT76GTS w/billet wheel .96 A/R