Texas82GP's GMT900 4L80E Swap

Texas82GP

Texas82GP

Geezer
Supporting Member
Apr 3, 2015
5,077
113
Spring, Texas
I changed the harness in my 80e. Easy peasy.
Thanks for the reply and the reassurance. I'm glad to hear it. Scott was kind enough to send me some pics of when he swapped the harness in his 80E (on the stand) and it didn't look bad. The builder commented that it was a bit fiddley getting it around the park rod, but that was it. The tool is on the FedEx vehicle for delivery so I should be all set to tear into it tomorrow morning.
 
Texas82GP

Texas82GP

Geezer
Supporting Member
Apr 3, 2015
5,077
113
Spring, Texas
Got it running.

Saturday didn't go totally to plan. My Dad and Step-Mom broke down the previous Sunday morning about 250 miles away from home. They were driving home from visiting my step-sister in Midland. They were in my Step-Mom's 2005 Saturn L300. It has right at 100k miles on the clock. It was my Grandma's last car. I talked to Dad on the phone for about an hour trying to help him figure out what was going on. He didn't have any tools and nothing was open that early on Sunday (was about 7 when he called) so they ended up putting it on a wrecker and my step-brother met them about half way with a truck and trailer. I did some reading up online and it started to look to me like it was a bad crankshaft position sensor. It appears to be a common problem on those cars. The sensor wasn't available locally so Dad ordered one online when they got home Sunday. He worked all week and never got around to putting it in. Then Friday, he suffered a fall and sprained his right wrist pretty bad. I went over to his house Saturday morning to install that sensor. I read the codes first and low and behold it did have a crankshaft position sensor code. I left Dad's a little after 11 a.m., picked up some lunch and went back to my house to eat. I got over to the storage at noon.

I ended up draining the transmission, pulling the mid section of the exhaust, the transmission heat shield, and the shift cable to be able to get the pan down. Replacing the harness was pretty easy, especially with the tool to get the case connector pushed through the case. Then I put it all back together. Nothing difficult, but getting the exhaust all situated just right and snugged up is a bit of a chore. There are a dozen fasteners to tighten. I got it all back together, cranked it up and started working on getting it filled up. I had a tough time reading the dipstick. For some reason the fluid doesn't sit in the windows when you pull it like it does when you dip it in a quart of transmission fluid. At 15 quarts I took it for the first spin around the storage property. I was able to confirm three forward gears. Everything seemed o.k. but I was concerned it wasn't full. I kept adding fluid, a 1/2 quart at a time, trying to sneak up on the level. I think my biggest issue was that there was so much fluid on the walls of the fill tube and that was screwing with the reading. I may just be a dumbass. Anyway, I ended up with it overfull. It was about 9 PM by then so I shut it down and locked up the storage. Sunday morning I went back over and drained some of the fluid out of it and got the level where it needs to be. Then I took it out on the road. Everything seemed fine so I took it to the carwash. I got it all cleaned up and then went to the gas station and filled it up. By then I had about 10 miles on it. I parked it in the driveway to cool down so I could get under it and check everything out. Everything seemed fine and I took it to the grocery store and back. Then the Astros game came on and that was as much work as I was going to do with my day. Didn't leave the house yesterday. I drove it in to work today. Everything seems fine. No strange noises, no warning lights, no leaks.

Unfortunately, I think the stall speed is way too high for my liking. I'm going to drive it at least a few more days before I decide. I went with 3600-3700 thinking it would help with the really high first gear ratio. I think I should have probably gone with 3000-3200, which is what I had in it with the 4L65E. It just slips way too much below 3000 with the way it is. My gut says I'll pull it back apart to swap the converter. We'll see.

I don't like the gearing of the 4L80E compared to the gearing of the 4L65E, but I knew to expect that. 1st gear is too tall and overdrive isn't as tall as the 4L65E so I'm turning more RPM at highway speed. I think I'll get used to that just fine. I just don't think the converter I have in it right now is suitable for daily driving it on the street. Oh well, sometimes you have to learn the hard way.

The tuner did a great job. The tune flashed right to the TCM and between what I did to the wiring (following the sloppy mechanics write up I linked to earlier in the thread) and what he did with the tune, it's as if the truck came with a 4L80E. I'm going to go ahead and send him a data log to look at but I don't think there is anything for him to work on. The transmission shifts when it should and the speedometer is correct.

So far I like what the builder did with the transmission. It shifts fast and crisp but not harsh. He said I'd be able to feel it bite with those redline frictions and Kolene steels and I can.

So, mixed feelings. I'm really happy to have the truck back on the road but I think I screwed the pooch on converter selection. I'll drive it a few more days and then decide. It has about 50 miles on it now.

That's it for now guys. I'll update with a decision or if there is news to report.

Until then,

Best,

Jared
 
Turbolq4

Turbolq4

Royal Smart Person
Sep 25, 2017
1,374
113
Nampa Idaho
Loud exhaust amplifies the slippage annoyance from high stall converters. I don't like them when I'm trying to cruise or just out for a drive but they make up for it when you beat on it. I agree with you on the gear ratios of the 80e. I think the 60e is a superior piece from a driveability standpoint but it fails hard everywhere else. Hard decisions to make, fast usually comes with trade-offs like the converter. I really like your truck.
 
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Texas82GP

Texas82GP

Geezer
Supporting Member
Apr 3, 2015
5,077
113
Spring, Texas
Loud exhaust amplifies the slippage annoyance from high stall converters. I don't like them when I'm trying to cruise or just out for a drive but they make up for it when you beat on it. I agree with you on the gear ratios of the 80e. I think the 60e is a superior piece from a driveability standpoint but it fails hard everywhere else. Hard decisions to make, fast usually comes with trade-offs like the converter. I really like your truck.
Thanks for the compliment. I'm glad to have the truck back. I totally get it on the compromise. I do want it to be a hot rod but I think I might have gone just a little too far for it to be ideal for a daily driver.

I have 150 miles on the swap at this point. The vast majority of that is from my 25-mile (each way) commute to and from work. My commute is about 1/2 city street and 1/2 highway. About 1/3 of the highway driving is stop and go. I'm starting to get used to it and understand what to expect from it. I don't think the loudness of the exhaust is what bothered me starting out, rather it was the mushiness/unresponsiveness at anything below about 3000 RPM. I'd been driving a completely stock 2013 Impala LTZ for the prior three months and I think part of my reaction was culture shock.

I still think I would have done better to go with a lower stall speed, like 3000-3200 or 3200-3400 but I'm going to keep driving it for now. Everything that I complained about before is bothering me less.

The polyurethane motor mounts are a big improvement. They increase NVH but they are holding the drivetrain steady which is helping with drivability (the unstable drivetrain was causing idle issues with the DBW throttle body).

The transmission cooler is definitely big enough. The highest transmission temperature I've seen is just below 150°. At this point, I'm concerned it might be too cool for the winter.

I like how the transmission shifts so far. It's not harsh at all. I think the high stall speed has softened the shifts relative to what they would be with a lower stall speed converter. So far so good on the overhaul and installation. No leaks, no odd noises, no problems. I'm very impressed with the tune. He really nailed it. The worst I can say is it doesn't hot restart that well with the A/C turned on but if you start it with the A/C turned off (like you should), it cranks right up.

That's it for now I think. I'll follow up in a week or so and let you guys know what I think. Moving forward I want to do the coilover conversion on the front and some routine maintenance (all new cooling system hoses, flush the power steering system). I did have an ABS light for part of a day. I don't think I spun the rear tires so I'm not sure what that was about. I haven't gotten on it super hard but I have run through the gears at 4500 RPM and no complaint there.

As always, thanks for the feedback and interest.

--Jared
 
Anubis

Anubis

Royal Smart Person
Mar 30, 2012
1,778
113
I still think I would have done better to go with a lower stall speed, like 3000-3200 or 3200-3400 but I'm going to keep driving it for now. Everything that I complained about before is bothering me less.
--Jared
Its a good thing you went with Circle D. They will re stall your converter for free within one year of the purchase date....ask me how I know
 
Texas82GP

Texas82GP

Geezer
Supporting Member
Apr 3, 2015
5,077
113
Spring, Texas
Its a good thing you went with Circle D. They will re stall your converter for free within one year of the purchase date....ask me how I know
I wasn't aware that they would re-stall it for free so that's good to know. At this moment, I don't think I am going to pull it back out to re-stall the converter. I've pretty well gotten accustomed to it and it doesn't seem nearly so extreme at this point.

I ordered a new code scanner from Amazon to read the ABS codes. I have an Actron scanner that I bought probably 15 years ago that reads domestic OBD I and all OBD II but it doesn't read ABS codes. I bought a OTC 3208 scanner Friday evening for $53 shipped. They delivered it late Saturday night. It's amazing how affordable the scanners are now. I think I paid over $300 for that Actron Scanner back then. It was a big hit at the time as I was much younger and poorer, but I was proud to have such a nice tool.

I scanned the codes Sunday morning. I had:

U0073 - Control Module Communication Bus A Off

and

C0055 - Rear Wheel Speed Sensor Circuit

I was surprised by these codes. I expected/hoped to have a code on a bad front wheel speed sensor. I poked around the internet on both of these codes and decided to erase them and see if it sets them again. I also removed the main electrical connector on the truck's side of the harness at the transmission and sprayed it out with electric contact cleaner and compressed air, which I should have done when I replaced the internal wiring harness in the transmission. I also sprayed and blew out the case connector on the transmission. When I replaced the internal harness, I just wiped the fluid off of the connector from the truck's side of the harness. I'm hoping that cleaning it will solve the problem. My gut tells me the issue is in that connector. If the code comes back I'll open it up and make sure I got all the pins back in it right when I repined it for the swap. There hasn't been any problem with the transmission shifting or with the operation of the speedometer so I don't know. I also think it is possible that I could have had the key on with the connector unplugged at some point and that may have thrown the code. Not sure. I do think the two codes are definitely related. If anyone has experience with this or feedback on it, I welcome the discussion.

I also worked on the fluid level. It was still ever so slightly over full so I pulled the drain plug and drained a bit more fluid off as I raced to replace the copper washer on the plug and get it back in the pan. I'm real happy with the level now. I still don't know that it has ever gotten up to 'hot' temperature as I don't think I've seen 150° degrees yet and it mostly runs in the 120°-140° range.

That's it for now. It's funny how negatively I felt about it after the first few days driving. I really feel pretty happy with it at this point. It's really running and driving pretty darn well.

Thanks friends.

Jared
 
motorheadmike

motorheadmike

Comic Book Super Hero
Nov 18, 2009
4,249
113
Ottawa, Ontario Canada
I have been reserving comment until you settled in a bit and acclimatized. Congrats on mission success. That said, I cannot stress enough that now you need a supercharger.
 
Northernregal

Northernregal

G-Body Guru
Oct 24, 2017
912
93
Red Deer AB
You don't have a huge cam, maybe a 2500-2800 would make it more street friendly and still fun to drive. Might also tame the tall 1st gear of the 80e.
 

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