Hello,

I have a 4L60E pulled from a 2003 Silverado 2wd, I originally rebuilt it and everything was fine, had all forward gears but I blew a seal on the servo and roasted the band, losing 2nd and 4th. I pulled the pump threw a band and new drum in, buttoned everything up, and now.. no forward gears but reverse is strong. Strange, so I grabbed the tech2 and commanded gears one by one. 1st and 2nd, no response. 3rd and 4th work great when commanded via the tool, but not manually via the shift lever or drive range. I checked all solenoids as well as resistance on them, everything seems good. I've built a handful of these units and run into all the common problems over the years, but this one has stumped me. I went through hydraulic schematics and haven't found anything yet. Threw a new harness in it this morning, no difference. But disconnecting the harness does cause it to run in 3rd (limp mode).

Any ideas?

 

So you are saying it does not move at all forward in any gear position unless you either command 3 or 4 or unplug harness forcing 3 ?

 

Very strange indeed.
Did you remove the valve body? I ask because installing the longer bolts in the wrong place gives strange (and bad) results. I find it a lot easier to anchor the band with the valve body out.
Or did you only remove the pump, reverse drum, band; and not even remove the input drum?
The next diagnostic step might be to connect a pressure gauge and see what the line pressure is in 1st and 2nd. Heck 3rd too with the harness disconnected.

 

I removed the pump and reverse/input drums only yes. Valve body bolts are all in the right places, don’t think I’ve made that mistake in years (not to say I couldn’t have, but it worked fine before replacing band)

I’ll grab my gauge from storage and check once I get a moment

yes

 

Inspect the Turbine-Shaft Teflon Sealing-Rings...

 

I could be wrong be on this trans isn’t the only port in use the forward clutch apply port which is on for every forward range?

 

I cannot for the life of me think of a scenario that would yeild this result. Moving with 4th command I get because the FWD clutch and sprag are not doing anything, But 3rd? If it was in the 3rd gear position only then yes as the overun clutch would be on and able to sub for the sprag or fwd clutch. Even with an overun mod of some sort on then you would have 1-2 too so thats is out . Low roller possible but then it should move in manual low 1 1st commanded,
Unless you tore the ring between the fwd overun and 3-4 clutch. Then fwd oil would dump via the 3-4 clutch circuit and only be prevented when the 3-4 clutch was applied which would be in 3rd and 4th gear my only issue here is the overun clutch is between them? Well unless maybe it has the sonnax HD 2-3 valve blocking the venting of the overun oil particulary if the gasket cut method was used during install the leak to D3 might be small enough to allow the forward clutch to apply.
I would have to agree look at the rings on the shaft it has to be there.