I'd like to replace the TH400 in my '71 Monte with a 4L85e. Anybody know about fitment issues with the floor pan? The car underside is the same as a Chevelle.

Is there a way to identify a 4L85e vs. a 4L80e?

Thanks...

 

Anybody?

 

I installed a 4l80e in my Chevelle 10 months ago.
Fitment was not a huge problem. The 4l85's should all have the rear center support tranny return line that you will need to make room for. Don't use just a regular bent line here or you will cook the bearing in the center support.
I had to dimple the tranny tunnel a bit but not near as much as I did for my 700r4, which is strange since the 4l80e should be bigger. I had a hard time getting the cross support just right, but mine is a 4 door so it just took some shimming to get it in level.
Shorten the driveshaft a few inches. You MAY be able to use the same yoke off your 400. If the splines go all the way down on the 4l80e than they need to go full length on the yoke. If they go part way and have an "o" ring you need a yoke with splines part of the way and the rest smooth for the o ring.
I am running the TCI controller. I already had fuel injection so it was extremely simple to wire up. If not, you need a TPI of some sort to give the tranny the throttle opening readings. There are kits to do this but they are not cheap.
Speedometer is electronic and won't work with stock or aftermarket mechanical. Choices are going electronic aftermarket or using a converter that runs the stock or mechanical speedo.
I personally recommend a third choice. Buy a Garmin GPS navigator and ditch the speedo completely. They have great accuracy for speed and a lot of neat bells and whistles for a little more than an aftermarket electic speedo....or one could always do what I did for a long while and run without and use a piece of paper with speeds at certain rpm
...though this would be funny to use when pulled over..."um, no officer I dont know how fast I was going. Let me get out my handy paper chart and lets see...oh, sure I would be glad to step out of the car...no, I have not been drinking, why do you ask?"
You should be able to tell a 4l85 by the tag on the side of the case. Yea, crappy answer but I have not seen one personally to give you exactly what to look for.
Thats most of the high points. Great tranny, well worth it, and the controller makes it amazingly customizable.
Get a good aftermarket torque converter like a yank or vigilante. Stock converters weigh a ton and usually have very low stalls.
Hope this helps.
Oh yea, the shifter will take some modifying. Aftermarket 4 speed will work. I had to modify my arm that goes onto the shift shaft so I could get all my gears. I only had the one for a 700r4, but I have heard the stock 350 or 400 works correctly. Of course mine was long gone by this point....

http://webpages.charter.net/buddyholly/Chevelle.htm

 

Yes, very little tunnel mod is needed. Just a bit of massaging with the BFH.
If you find the 4l85e fine, but most 4l80e's will work. Very little difference unless you are planning on towing a big trailer. I just mention it because the 4l85e's are pretty rare in my experience. Some come with straight cut gears that are a bit stronger but kinda loud.
What controller are you going with?
Either way, good luck and enjoy.

 

Yeah, the 4L85 is a stronger unit, it came behind all diesel and big block (8.1L) engines and 6.0 LS engines in cutaway chassis like for box trucks, school buses, ambulances, etc. The lower GVW top kick trucks may have them also.

It has a harder input shaft, five pinion gears for the output and reaction gear sets, and a few other things like additional clutches. It's kinda like the difference between a 4L60 and a 4L65.

You’d be hard pressed to break one of these units. The -5 in the model number is indicative of the pinion gear count.

Also just like the 4L60, the 4L80 can be upgraded with the stronger 4L85 parts. It’s just cheaper to start off with the 4L85 because the parts are costly.