I have a problem with my friends 4L60E. Transmission was rebuild 1200 miles ago by me. Everything was fine but few days ago it started to bind/lock in manual low when hot. All other gears work fine like before. When it is cooled down, manual low works again without issue. After few minutes/miles when trans is getting higher oil temp I can't move the car by brake pedal release from dead stop; I have to put accelerator pedal a little to start moving. After a few more miles manual low binds constantly all the time.

Transmission has TransGo 4L60E-3 shift kit installed so I can't check first gear in overdrive range because is fmvb.

After some anlysis I figured out that propably I have crossleak from manual low circuit to manual second circuit. Am I right?

When I disassembled transmission I found that I had changed order of parts in 2-3 shuttle valve. I changed order of spring and checkball inside the valve so I put spring and then ball against wider coil instead of putting ball first and then spring as TransGo instruction advised. I thought it can't be reason of binding becasue trans worked a long time perfectly with ball and spring swapped.

After some more inspection I found a little heat signs on rev input drum, band looks good. Servo travel about 0.095. Low reverse clutch OK. 1-2 acc piston, cover, spring looks OK, I think piston and pin have nice and tight fit. Transgo shims made some signs inside accumulator cover but it's not area when accumulator piston rides. 3-4 acc looks OK - sonnax sleeve kit installed. Oil and filter is extra clean, only a little bit of stuff on magnet. VB and case gasket with no tears and spots of leaks, separator plate (TransGo 46-PLT-94) looks like new. None of VB bolts was loose. Accumulator valve and sleeve in VB also looks fine.

Transmission is from 94, VB and oil pump from 93 Chevy Astro (no difference with 93-94 4L60E).

What else can I check to find why it's not working properly?

 

Check the pressure manifold switch. Could be getting hot and telling the PMC that it is in a different gear than what it really is.

 

PSM is not active because TransGo 4L60E-3 is installed - full manual valve body without electronic control. PSM works only like a plug and all of the 5 bolts was torqued tight.

 

I can add that it was constant pressure drop on idle when first gear was selected. Manual low pressure - 50psi; second, third, fourth - 65-70psi; reverse - 120psi.

Today I noticed some heat discoloration on reverse input and overrun frictions and steels. Also input sprag has signs of wear in place where overrun friction rides and input drum has signs of wear in place where rev input frictions rides.

Any ideas?

 

I found the reason of binding something like two weeks after I had started this post. I wanted to post solution earlier but finally I'm doing this just today. Better late than never.

The reason of binding was 1-2 accumulator. When I compared new 1-2 acc assembly with that used in transmission I realized that problem was leak between piston pin and piston itself. When piston started to get hot clearance between piston and pin was too loose and created a leak between manual low circuit and manual second circuit. So 2-4 band was applied in the same time with low/rev clutch which is providing engine braking in manual low. That caused transmision to bind.

After installation of new 1-2 accumulator assembly binding in manual low disappeared. Transmission downshift 2-1 good but not perfect. You can feel a little "hit" when you downshift from manual second to first. Even if you stand still with second gear selected and quickly change to low and want to start immediately you can notice a little hit before car is moving. I think the reason of this situation is that 2-4 band is realising slower than low/rev clutch is applying. I thought about stronger servo return spring but I don't want to affect 1-2 and especially 2-3 shift because now they are really nice. The car is going to be driven mostly on the streets so it's not going to downshift 2-1 often - especially with 3.06 first gear.