What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Any 4l80e gurus on here?

Magikal

Magikal

1/2 ton status
Joined
Nov 25, 2007
Posts
402
Reaction score
103
Location
North Idaho
Last night suddenly out of nowhere my 4l80e lost reverse. If i put it in reverse and give it high rpms it will sort of move on flat ground. 5 minutes prior to it failing it was working fine. After some homework on the internet this morning i did a few in vehicle tests. If i put the shifter in first gear i still have movement, very firm and solid. I did the engine braking test and that's working fine. All forward gears are working fine as they should. I tried each gear manually and everything works fine except reverse.

Fluid is clean and full as it should be. Recent filter a few months ago.

Please help
 
Factory torque converter? Also check the simple things, check the shifter cable and make sure it's moving freely and is adjusted correctly. It could be not fully engaging reverse and could be half way between reverse and park or reverse and neutral.
 
Converter will have absolutely nothing to do with this, as if it has issues/fails, it's going to affect all gears, not just one of them. While a cable _COULD_ be out of adjustment, it's highly unlikely that it also won't affect other gears as well.

Also going to be harder to diagnose without further info on the trans/install. Factory trans in something? Swapped into your K5? Set up with factory style ECU/TCU? Aftermarket controller? Or, like mine in a full manual configuration with no ECU/TCU period? Things that can fail and cause reverse to drop out on a TCU controlled trans will have zero effect on mine.

My initial guess, based on your symptoms of "will kinda move with high RPMs" is that you have an internal leak, and is going to require tear down to fix. Similar to what happened to my 1st 4L80 - engine overheated, and afterwards it needed 2000+RPM for a good 30 seconds to even begin moving, and would drop out of gear at idle, but more or less worked OK once I got moving until I stopped again. I haven't pulled it apart yet, but I'm positive I will find some trashed seals in there somewhere.

Also, a decent diagnosis path - https://www.sonnax.com/tech_resources/88-diagnosing-the-elusive-no-reverse-with-the-4l80-e
 
Tranny and 7.4l vortec are swapped into my k5. On second tranny, got cheap off Craigslist. History unknown. Engine harness and ecu reworked by team208motorsports a few years ago. Don't think he touched any of the tranny stuff in the computer. It's been fine until now. Tranny is all stock to best of my knowledge. Running cable shifter and just verified its set correctly. Did line pressure test this morning and everything checks out well within specs.

Gonna drop pan i guess and examine the rear apply pin and see what i can see. Just want to do any in vehicle road tests before i drop the pan.

Honestly, I'm sick of automatics. If i have to drop this tranny out I'm going to install the sm465 sitting in my shop instead. Lower gears and less headache once installed.
 
On a different note, i was wondering if i were to swap in the sm465 would i need to have the computer adjusted since i wouldn't be running the electronics for the transmission anymore? Computer was tuned years ago by @Team208Motorsports and all the emission crap deleted, etc. If all it would do is cause a MIL, i could live with that...
 
Magikal said:
On a different note, i was wondering if i were to swap in the sm465 would i need to have the computer adjusted since i wouldn't be running the electronics for the transmission anymore? Computer was tuned years ago by @Team208Motorsports and all the emission crap deleted, etc. If all it would do is cause a MIL, i could live with that...
Click to expand...

Manual trans and autos put different loads on the engine. The ecm/pcms are tuned differently for each.
 
As i ponder this situation while i wait on gaskets for the 4l80e to arrive I've been debating the sm465 swap. This morning it dawned on me that i would have no vss for the ecu to use. Tcase is just old school 203/205 doubler. No vss there. How is everyone handling similar situations?
 
sweetk30 said:
www.offroaddesign.com

Labor to Machine Customer's NP205 Speedometer Housing for GM VSS, Tone Wheel, Plug, Speed Sensor and Pigtail Included

Labor to Machine Customer's NP205 Speedometer Housing for GM VSS, Tone Wheel, Plug, Speed Sensor and Pigtail Included Return shipping is calculated in cart. Shipping from you to us is not included. Please ship with all your contact information included and/or a copy of your order. Shipping...
www.offroaddesign.com www.offroaddesign.com
Click to expand...
Yeah. I saw that. Any other options?
 
imiceman44 said:
I don't know if it's cheaper but there are vss options that go on a mechanical tcase, I know Dakota digital among others offer that
Click to expand...

That's what I was running on the 205 that was in my Scout some years ago to provide a VSS signal to the ECU as I had swapped in an LT1. Was basically just a mechanical pass through type deal with a tone ring in the middle. So the mechanical speedometer still was being driven via the cable, but also had a electrical connector on it to feed a VSS pulse signal to the ECU. Still had to reprogram the ECU to handle it, as the pulse count was different than factory GM stuff. I don't recall what the specific numbers were as it was quite a few years ago, but I recall it was significant enough of a difference that not retuning for it would have been worse than just not running a VSS at all.

That said, it won't be absolutely required to run it, as the ECU will cope without a VSS signal. But it won't be ideal, and will cause the ECU to revert to some default numbers in the fueling and timing maps so that you're likely to lose some power and MPGs doing it.

This is the adapter that I was running - https://www.summitracing.com/parts/dak-sen-01-4160
 
urbex said:
That's what I was running on the 205 that was in my Scout some years ago to provide a VSS signal to the ECU as I had swapped in an LT1. Was basically just a mechanical pass through type deal with a tone ring in the middle. So the mechanical speedometer still was being driven via the cable, but also had a electrical connector on it to feed a VSS pulse signal to the ECU. Still had to reprogram the ECU to handle it, as the pulse count was different than factory GM stuff. I don't recall what the specific numbers were as it was quite a few years ago, but I recall it was significant enough of a difference that not retuning for it would have been worse than just not running a VSS at all.

That said, it won't be absolutely required to run it, as the ECU will cope without a VSS signal. But it won't be ideal, and will cause the ECU to revert to some default numbers in the fueling and timing maps so that you're likely to lose some power and MPGs doing it.

This is the adapter that I was running - https://www.summitracing.com/parts/dak-sen-01-4160
Click to expand...
The price is right on that setup.
 
You must log in or register to reply here.

Latest Posts

Top Bottom