GM Quad Driver Chart C3 and P4

**1project2many** · 10-10-2014

Well, it sounds like a very common 700R4 problem. It sounds like the trans is shifting out of 2nd but you have a mechanical problem. The trans will default to 3rd gear if the shift solenoids have no power so the problem likely isn't electrical. The Sun shell splines maybe? Try manual upshifts and see if you find an unexpected neutral where third should occur.

**1project2many** · 10-10-2014

So when you see these in these AFTERMARKET SCAN TOOLS, they NEVER verify each engine/trans selected. They just put it all in just in case. They don't have the resorces and knowledge of the OEM and why.
These Mode Words in the Data stream are sometimes refered to as a bit packed word (of 8 bits).

I've talked with some s/w guys on the aftermarket scantool end. They license a datastream and get a definition, then make sure the scantool can display what the definition shows. That's it. If the datastream def. info says the engine is a 3200 hp turbine and the trans is a 125 then that's what they believe. Hacks, internet info, and other guys' scantool info are all off limits since it wasn't acquired through agreement. One guy had personal version of commercial scantool that would plug into edge card connector of C3 like Dynamic EFI's Lockers for scantool data, but could not share software at all.

The definition files I'm talking about were directly from GM. Not sure what was used to built the Tuner-pro definition files.

**kevinvinv** · 10-11-2014

Originally Posted by 1project2many

Well, it sounds like a very common 700R4 problem. It sounds like the trans is shifting out of 2nd but you have a mechanical problem. The trans will default to 3rd gear if the shift solenoids have no power so the problem likely isn't electrical. The Sun shell splines maybe? Try manual upshifts and see if you find an unexpected neutral where third should occur.

Both my builder (in chicago) and a local shop think that the overrun clutch drum is bad. Not sure how this could happen with only a 1000 low stress miles on this thing. Oh well.

Can I get one clarification though? When people say "manual upshift" for example... what is meant by that? If I shift up via the lever does the PCM still do something? I guess I don't really understand how the lever and the PCM work toghether... I actually wonder why the lever even goes to the tranny at all if the PCM can handle the shifts through solenoids etc...

**RobertISaar** · 10-11-2014

Originally Posted by kevinvinv

I actually wonder why the lever even goes to the tranny at all if the PCM can handle the shifts through solenoids etc...

there are still a lot of traditional parts still in newer(but not necessary all newer) transmissions....

parking pawl is entirely cable operated
reverse may use the shift solenoid combo for 1st gear(though IIRC, it won't matter, it is just for anticiption of getting out of reverse and into a forward gear), but the manual shaft needs to be in the R position to send pressure where it needs to be to engage reverse instead of 1st.
the manual shaft can do some interesting things depending on the transmission.... for instance on the 4T60E(and 4T65 derived from it), if you disconnect the circuits of the shift solenoids, putting the shifter into reverse will still allow reverse, putting the shifter into 1 or 2 will cause 2nd gear, putting the shifter into 3 or 4(or D/OD) will cause 3rd gear. all of these are because of how the manual shaft(which is directly controlled by the shifter cable and therefore, shifter) causes certain things to happen in the transmission.
actual line pressure can also be significantly effected by shifter position. what could normally be ~65PSI idling in gear, pulling the shifter down into 1st may bump it up to the 200PSI range.

**1project2many** · 10-11-2014

Not sure how this could happen with only a 1000 low stress miles on this thing.

Because it's a 4L60E!

I'll admit that I have a very strong negative bias. It's because I was around when Chevrolet first released the 700R4 on us poor technicians. It's taken GM and the aftermarket over 30 years to get this transmission "fixed" but getting a good trans overhaul can still require a lot of hard part changes and $$. I've got the same trans in my Suburban and when it fails again I'm hoping to swap to the 80E. It's not a cheap or simple changeover but I'd estimate it's 90% effective as a fix in stock and mild applications.

Can I get one clarification though? When people say "manual upshift" for example... what is meant by that? If I shift up via the lever does the PCM still do something? I guess I don't really understand how the lever and the PCM work toghether... I actually wonder why the lever even goes to the tranny at all if the PCM can handle the shifts through solenoids etc...

Manually selecting a gear is an indication that conditions are not typical so additional/different functions are enabled. In the 4L60E engaging 1,2,or three supplies pressure to the overrun clutch to provide engine braking. In OD when driveline speed is greater than engine speed the engine automatically "disconnects" from the gears. The manual position also provides a mechanical limit to shifts. As to the question of why, the transmission began life as a fully mechanical transmission but was modified to remove most of the electronic controls. Sometimes change is slow to happen, and as described by billygraves, oftentimes left over functions or items not required to be changed are ignored. Newer transmissions have greatly reduced functions through the manual shaft as they are being designed primarily for electronic control.