Merry Christmas everyone,

I am helping a buddy with his 4l80e that we went through a year ago for a project that he recently got running. It came out of a 1997 and had a burn up direct drum initially. The drum was replaced and we did the following mods:

Dual feed
Sonnax AFL reamer / oversized valve
drilled the separator plate shift holes a bit larger

Overall a fairly simple rebuild. We've done about a dozen or so 4l80's, most of which are modified well beyond this one so am surprised this is giving us so much trouble. If the selector is left in D3 or D4 everything is fine in 1st/2nd but once it hits 3rd the rear tires immediately drag the truck to a stop until it downshifts back to 2nd. My guess is that the rear band is applying and assumed there was a leak resulting from the feed hole that gets blocked when dual feeding. When using HP Tuners and commanding 3rd or 4th from a stop it's completely locked up, yet immediately frees up once 1st or 2nd is commanded instead.

We took the transmission out this week and tore it apart, finding nothing obviously wrong. I expected the issue to be related to plugging the wrong feed hole or leaving the wrong seal off the center support but upon inspection, all was as it should be. 2nd seal down on the center support omitted as well as the seal under the piston on the drum. The correct feed hole has also been plugged per the many examples online.

If anyone has a guess as to what might be the issue, I'd appreciate hearing it.

 

my guess would be the intermediate sprag is backwards, And yes was probably on the new drum that way ran into it before , That will caus it to lock down on the 2-3 shift and of course 4th to as 3rd direct is still on.

 

Sprag backward. Made the same mistake on my first 80. Was a fairly quick fix and trans was fine after.

 

This was exactly the case - thank you gentlemen for offering the solution. This will obviously be something I pay closer attention to going forward.

 

Yes I have gptten a few over the years that were already assembled and backwards, So i always check says alot fo effort later. Never trust anyone but yourself