Does the trans tunnel or firewall need to be modified to put a 4L80E in a 71 Cutlass Supreme? If so, what needs to be done?

 

The floor pan is the same as in a Chevelle. Yes, it needs to be clearanced. Google 4l80e chevelle and you'll get the info.

 

Try and find a 91 or earlier 4L80 core. The cooler lines on the later “center lube” models are a much tighter fit, and the rear cooler fitting take a special fitting. The early models have the cooler line fittings in the normal location, and can use regular flare lines.

 

1991 was the first year for the 4L80E, there are no earlier cores. The 91-96 cases all have the front lube connections. The 97-up cases have the center lube mod. There were a whole host of minor mods each year, so do your research before selecting one.

 

Buy banjo fittings and run stainless cooling lines, it will fit like a glove. I just test fitted my 6.0 with 4l80e. Didn't touch the tunnel or the firewall.
Banjo fittings on ebay
For an BOP/4l80E adapter, check with ckperformance.

 

I was thinking the 95 was the first year for the center lube 4L80, don’t know WHAT I was thinking when I typed 91. In the ATSG manual I have on the 4l80 it highlights all the production changes. Things like dimensional changes for pinion gears in the carriers (and the required changes to bearings, thrust washers, sun gear and annulus gears) enough changes that someone could get into a world of trouble mixing up similar looking but incompatible parts.

I never have gotten a good explanation for the center lube redesign. For the most part, the early 4L80 is 400 with a overdrive clutch in front of the forward clutch. The 400 is obviously a proven design. I’m kinda curious why Hydromatic decided to fix what ain’t broke.