Gearbox Upgrade

[Tony302]

There are computer "kits" for the more popular transmission retrofit swaps. Usually from $500-750 for a standalone module, wiring harness, and various bits to make it work. Once again, the 4L80E kit for this application runs about $500.

Though Rolls and even a couple of mid-1990's Jaguars used 4L80E's, this doesn't mean one will bolt to the back of your engine. They don't have swappable bellhousings. The bellhousing part that bolts to the engine is the actual case. I know they made a few different cases for them. Now whether they made some specially for the RR and Jaguar applications or they were a standard Chevy configuration I frankly do not know. Not so many of those cars over here. Ideally you'd want one from behind a 5.7 Chevy/GMC truck or van.

I've not seen one in a Ford. You could do that but it involves cutting the bellhousing part off the case and machining bolts holes to attach a custom bellhousing. Such bellhousings run $500 each. No idea what the case machining would cost.

You have a Mustang II? Best fit for adding overdrive to one of those is to swap to a 5 speed. Reason being that the automatics are a bit large and the car is small. Manual transmissions tend to be slim and trim. The go-to automatic overdrives for those are the AOD or the 4R70W. I haven't done one myself on a '74-78 car (my Mustangs are older and newer) but I understand you have to modify the transmission tunnel a bit (big hammer) and trim off some non-essential protrusions on the transmission case. And it will still be a very tight fit.

I like AOD's for being more simple and not requiring a controller kit but for the trouble I suspect you might have to go to anyway I recommend spending a bit more for a 4R70W setup. Depending on what you can actually find, of course. No way you'd ever recover the money it would cost with the gas savings in a car. But when you are on the highway and it drops down into overdrive at about 50 mph it sure is sweet. I'm addicted to overdrive and want it in everything nowadays. Manual or automatic. I bought a VW Caddy years ago (driving it today as it happens) and one of the first things I did was source a five speed from a Golf to swap into it.

Changing the content of this post for this reply only, I am reading that it may be easier to upgrade my MII than the Chevy G30, which wasn't my original intention and that the 4R70W will need the electronic controller?

 

[Kevin D Pem]

All modern "many" speed transmissions have, and need, a computer because the day of hydraulic shift valves are history. The ZF in my truck also relies on electric control of the throttle so braking clutches are not needed.

 

[GypsyR]

Hard to say about "easier". I have frankly no idea the difficulties you face finding the needed parts for either. But if I had to guess, I'd say a Ford transmission for the II swap would probably be easier than the 4l80E. The 4L80E you need is pretty specific where you could use the 4R70W in my 1994 F150 truck or one from a 1998 3.8 liter Mustang and some others too. Also if you wanted to skip having to use a separate computer there are the Ford AOD options.
The Mustang II's are actually even a bit rare over here too but people have swapped 4R70's and AOD's into all sorts of other Fords and Mustangs that you can read about and get a fair idea of what you would be getting into.

There's also info about people putting 4L80e's into antique cars and such but that's kind of overkill for you. You could potentially park a 1992 G30 with the 5.7 and 4l80e next to your RV and almost just swap the parts from it onto yours and with the addition of the computer kit be done. It's not like trying to put a tractor engine into a Volkswagen or an airplane. It would be pretty straightforward as such things go. If your coach has a TH400, some of the internal parts are even shared with the 4L80E. The 4L80E design was very much based on the 4L80E.

 

[Tony302]

Thank you all for the contributions, it is really appreciated
My decission will definitely depend on what I can source over here, however there is no rush, I might just enjoy it for this year and plan for next year

 

[Joe Hogan]

This article might be useful Installing a 4L60E Transmission in an Early A-Body

 

[Tony302]

This article might be useful Installing a 4L60E Transmission in an Early A-Body

Interesting............

 

[GypsyR]

A local transmission rebuild shop has referred to his 20 year old transmission shop as "the house that GM built" because for the first ten years ailing 4L60E's and 700R4's paid more than their fair share of the bills. The 4l60e's coming coming into the shop for rebuild outnumbered every other make and model of transmission by like two to one. You could make one work, but.......just saying.

 

[Tony302]

The automotive industry was the same over here in those days, quality control was not as good and to some ectent we accepted that