4L80E conversion
 

Have the wonderful 700 in my 91. Needing something a little more heavy duty. Anybody done this swap? Aside from the obvious t-case spline and driveshafts. I'm more inquisitive about the electronic part. I know I'll need a harness to the trans, so what about the computer? different one or just a PROM swap? How will the harness plug in? This is a 91, the first year available with the 4l80 if it were a 3/4 ton

Re: 4L80E conversion
 

You've already got the correct instrument cluster. What's it going in?

Re: 4L80E conversion
 

Back then the ECM didn't control the 4l80e. There was a separate TCM (trans control module). The easiest way for you to go about this will be to find a '91 in the scrap yard with a 4l80e and get the wiring and TCM, or (my preference) just get an aftermarket controller. Either way, you are going to have some wiring to manage. As John stated, you already have an electronic speedometer so that part should be fairly simple.

Mike

Re: 4L80E conversion
 

Suburban..... couple of years ago I had a 1990 and was really sorry about a month or so after I sold it. I had changed out the 700 3 times after they were supposedly 'built up' (yeah right, its a 700). Anyways I had the pan off this current 700 a few weeks back and there was a lot of debris in the pan (150K on the speedo) and I plan on towing with this like I did the other. My thought was to just step up and put the 4l80 in. Being a 91, this was the first year of the 4l80. Looks like it's getting complicated. My other alternative is a t400 with a gear vendor. I am however going from the 28% overdrive of the 700 to the 22% of the vendor unit. The 4l80s overdrive is 25% plus the torque convertor lock , which with the 4.10 gearing will put me at a 3.07ish final drive, and the gear vendor being a 3.19

Re: 4L80E conversion
 

The other alternative is keep the 700. I think that there are some places that rebuild these 700's with a good track record. Several tips for making these 700's last is good cooling and never towing in overdrive. This transmission is particularly weak in overdrive but strong in direct drive. My previous 1982 Suburban 6.2 diesel had a rebuilt 700 in it that lasted many years towing a 26 ft Airstream. The 6.2 diesel was particularly hard on these transmissions because of the higher torque at low rpm's but keeping it out of overdrive while towing attributed to the 700 not falling apart.