81 cutlass 455 swap.

[olds307 and 403]

The 7.5" stock rear will also be a time bomb. Exploding spider gears first followed by everything else, depending on the power level. I broke a Power Trax No Slip and then the stock spider gears behind a mild Olds 403. The TKX is great trans but big dollars. I just picked up a used 4L80E, also not cheap these days. As said for the TH400, a slightly shorter driveshaft, possible frame extensions, depending on the year and an electric kick down switch. You also probably don't want the stock converter, even with a mid 70's smog 455. You will need a drop base air cleaner and short filter due to the taller deck height. Good luck.

 

[Jarhead85]

The 7.5" stock rear will also be a time bomb. Exploding spider gears first followed by everything else, depending on the power level. I broke a Power Trax No Slip and then the stock spider gears behind a mild Olds 403. The TKX is great trans but big dollars. I just picked up a used 4L80E, also not cheap these days. As said for the TH400, a slightly shorter driveshaft, possible frame extensions, depending on the year and an electric kick down switch. You also probably don't want the stock converter, even with a mid 70's smog 455. You will need a drop base air cleaner and short filter due to the taller deck height. Good luck.

Probably going 9 inch ford rearend.

 

[Jarhead85]

With the TH400 you might have to tweak the crossmember a little to pick up the rear mount tab. You might also have to swap out your existing prop shaft for one slightly shorter; I'll leave that possibility to someone else to comment on. Other things to consider would include whatever tweaks to the shifter linkages that would need to be performed. The 400 ought to possess a vacuum modulator valve for shifting so the tubing and plumbing that ought to be already resident should work for that. If not, it can be fabricated from brake line and short lengths of vacuum rate rubber hose. Other things to consider: does the 400 converter need a specific flexplate to mate it to the 455? Starter? Brackets and bits to attach the kickdown cable to the carb? Cruise Control, it is there??

With the TKX, you may need to think complete new crossmember that has the adaptability to work with various transmission mounting points. After that, there is the small matter of the third pedal. The Factory version of the clutch pedal mount can be had as a repro from Original Parts or salvaged from a 4 speed car if you can find one. With that in hand you then have two basic options and a lot variations on them.

The first is go OEM mechanical with respect to the clutch linkage. Meaning the OEM Z Bar and the upper and lower rods along with the engine and frame mounted pivot points. This is a lot of work to assemble, ( And I am not the only one on this board to have done it) and it only gives you the equivalent of what the stock assembly would have offered when it came from the factory. You can upgrade the rods for strength and ease of installation using a rod kit; supplier name escapes me but i just picked mine up a few weeks back so still the bag but out in the shop--there is a link attached to a thread on this forum site, probably about ten or more pages back by now, or run a search, or someone will repost it. With the factory assembly you will also have to identify exactly where on the firewall the upper rod is supposed to come through, which can be something of a chore as the firewalls were all the same and supposed to have witness marks punched into the metal to identify that location. Never did really work for me all that accurately.

The second option is to go totally hydraulic and set your clutch pedal and linkage up accordingly. This option come with more work attached to it because you have to deal with both a master cylinder and the slave or actuator cylinder; one located on the firewall and the other down on the bellhousing or in immediate proximity.

For both options there are a lot of videos on You Tube that can be reviewed to get some idea of what has to occur. Take the videos with a box of salt, not just a grain. They can be precise and accurate or just as easily be ridiculously vague and senseless; too much talk and too little show how.

And, as always, someone can usually be found hereabouts who has the experience and knowledge to attempt to talk you through the agony and the angst of it all.

If all else fails, hit the local pool supply store and score a couple of dozen foam rubber bricks!?!? They are a lot easier to throw than wrenches, don't damage what they hit, and don't need to be tracked down and retrieved because you still need the tool for what you are doing.

I have everything to convert it to a manual but I have been a professional welder and fabricator for 35 years.

Don

 

[CopperNick]

700-R4 (4L60) Performance Transmission Build Guide

700-R4 (4L60) Performance TransmissionIntroduced in 1982, the 4-speed Overdrive GM 700-R4 transmission — also known as the 4L60 — remains a popular option for s

www.sonnax.com

Link above will take you to the Sonnax transmission site. Interesting articles on the 700R4 vs the 4L60, and yes they are mostly the same unit, just a designator change as has been mentioned. Sonnax comments that the "as-is" configuration of them is sturdy enough to handle 700 Hp or slightly higher.

Overview of the 700R4 Transmission - Gearstar Performance

We've outlined an overview of the 700R4 transmission, its upgrades, problems, and what made it one of the best automatic transmissions in its time.

gearstar.com

In its preface to the 4L60/E GearStar Transmissions notes that GM renamed the 700R4 to 4L60 (4-speed Longitudinal 6,000 lb GVWR) in 1990, even though it was the same transmission without any significant changes. However, there was an enhancement to the 4L60 in 1993 where it was electronically controlled instead of hydraulically with a TV cable.

Here, electronic controls replaced its hydraulic shifting system, and the transmission was called the 4L60E. It is also worth noting that the 4L60E cannot be easily swapped for the 4L60 since the 4L60E shifts using a powertrain control module (PCM).



Motor Trend Magazine, also, suggests the 4L60E, commenting at one point, "Why 4L60E Is the Best for Your Swap Project. For a few reasons, the 4L60E is one of the most common transmissions for LS swap. It is known to be a strong and reliable transmission. It is also what originated to be the original automatic transmission giving backing to the majority of LS engines.Feb 20, 2022."

Due, as you say, to your engine being an LM-7 from 2004, which essentially is GM designation for their truck Vortec which is actually an LS by another name, sourcing the 4L60E might prove to be your easiest and cheapest option. Just be aware that the "E" means electronic. The engine doesn't control the transmission, it has its own personal dedicated CPU and to make it work properly you may have to add sensors of some kind so that the engine can "tell" the transmission controller what is going on.

The other thing is shear physical size here. That 4L60E may prove to be the largest unit you can get into the tunnel of your ride without major surgery to the tunnel.

So I guess at this point, which way you go depends entirely on what you think will have to be done and how much you can afford to get to that goal.




Nick

 

[olds307 and 403]

I would not trust a 700R4/4L60,65,70E behind a 455. If he can stomach the cost of a TKX, it is a great option with better gear options than a 700R4.