I also forgot to mention that I am not the average DIY'er. I build differentials, set up gears, do LSD/POSI installs for a living. I also build transfer cases, and have built well over 200 engines (guesstimate as I have been building them since I was a teenager), so it goes without saying that I have "some" mechanical ability. The problem with transmissions is that it seems to me that it's more "theory", and "logic" than it is mechanical.
No, I still don't have 4th gear with my 700.. However, I've been studying the hydraulic circuits and looking at the charts that show the different devices that are applied for each gear, I think I have it narrowed down to the following;
1. Sticking/stuck 3/4 valve
2. Worn 3/4 valve and/or valve bore in valve body
3. Cut/torn seal on the 2-4 servo
4. Blocked servo exhaust hole (on pan rail)
5. Potential air pocket trapped somewhere in the 4th circuit. I read on another site that if I can make it shift into 4th at least once, then it will work from that point forward. Poster said to run it up to 100+mph in 3rd gear to see if I could make it shift at least once. I'm not holding my breath on this last one.
All of this is hypothesis though. I deduce that the band is holding when it applies because I have 2nd gear. Both 2nd & 4th need the band to be applied in order to get those gears. I deduce that the clutches, and/or apply piston seals for 4th are good because 3rd gear uses the same clutches & piston so if you have 3rd, you know the circuit for 4th has the potential to hold within the drum. I deduce that the sunshell is good because I still have reverse, & 2nd gear. So that leaves the numbered items above as possible culprits. For a transmission that is 20 years old, I guess problems like this are to be expected. For 4L60e's with aluminum valve bodies, I can't imagine that they will last as long as the older 700's with cast iron valve bodies.
Folks, building clutch & planetary type transmissions is a dying art. The new double clutch units as most manufacturers are heading towards (all electronically controlled) is the distant future. I have a feeling that if I decided to learn to build these older style units by the time I got a good handle on it, the technology would be obsolete. I think in the next 10-15 years, the types of transmissions that are common now, will only be found in classic cars, antique cars, or the junkyard. CVT's are already here and though I've heard of lots of problems with them, eventually the OEM's will figure out how to make them work and when that happens you can expect everything to have one of those in it. The CVT's from what I read, are much cheaper to manufacture once you get the tooling set up. They use far fewer parts, weigh less, and are smaller than traditional clutch & planetary style tranny's. So they potentially are the successor to what we are all working on today. Does not bode well for muscle cars though.. Have you driven a CVT car? Yeck!! I hate the way they slide between ranges.
Anyway, I won't be working on my 700 again until the weekend, and maybe not again until after the first of the year depending on the holiday schedule. I WILL figure it out, it will just take some time & money.. Lot's of money I'm guessing.
I've tried looking for a replacement pack of springs for all of the valves in the valve body so I could "recondition" the valve body-but no luck. Nothing like this exists on the open market apparently.
Anyone have any ideas where I can buy replacement springs for the valve body? Even my buddy that works at a shop said he does not know of where to buy individual springs like that...
Hope I'm not hogging the post, but it's nice having a place I can vent my thoughts.