4L80E W.O.T. 2nd gear up shift

[ctonton]

Hello,
Are there any transmission (4l80e) builders / gurus here who might have an explanation for my transmission shift problem? I have a 1988 Blazer with a strong 383 s.b.c engine and a built 4l80e behind that. There are only a few thousand miles on the transmission but it was built several years ago. The transmission is controlled by a Microsquirt transmission controller. Everything seems fine except for the wide open throttle 1st to 2nd gear shift. The engine pulls strong to my set shift point at 5500 RPM and then the shift feels sluggish. For maybe 1/2 of a second the engine RPM pull down a ways and then finally the clutches engage firmly. Any ideas what could be going on before I bring the transmission back to the builder or I toast the 2nd gear clutches?

 

[NickTransmissions]

Hello,
Are there any transmission (4l80e) builders / gurus here who might have an explanation for my transmission shift problem? I have a 1988 Blazer with a strong 383 s.b.c engine and a built 4l80e behind that. There are only a few thousand miles on the transmission but it was built several years ago. The transmission is controlled by a Microsquirt transmission controller. Everything seems fine except for the wide open throttle 1st to 2nd gear shift. The engine pulls strong to my set shift point at 5500 RPM and then the shift feels sluggish. For maybe 1/2 of a second the engine RPM pull down a ways and then finally the clutches engage firmly. Any ideas what could be going on before I bring the transmission back to the builder or I toast the 2nd gear clutches?

Assuming it's not a controller/electrical/electronic issue, the problem sounds like either a minor cross leak in the 2nd gear circuit or the 1-2 shift feed orifice isn't large enough given what you're trying to do, engine power, cam profile, rear gears and converter stall. I'd also wonder if the 1-2 shift valve return spring is a bit worn out, a somewhat common problem in those units. Sonnax has a 1-2 and 2-3 shift valve spring kit that I install on all 4L80Es that I rebuild (along with a boat load of other hydraulic updates).

I'd rule out anything external to the trans, including any engine-related issues then contact your rebuilder to see what he thinks, go from there.