4L60E Manual Mode Downshifting 3-2 & 2-1

[TRANNYMAN]

I need some help understanding how Manual mode works. What factor/table determines when 3-2 and 2-1 downshifts are completed when shifting in MANUAL mode?
1) According to the GM Hydra-Matic Technician's Guide (page 9), Manual 2nd can be selected anytime but will not complete the downshift until vehicle speed falls below approx 62 MPH. Does this speed correspond to OEM 3-2 shift table value of 62MPH @ WOT? Wouldn't the part-throttle table control the shift point (e.g. at TPS value of 0, wouldn't the speed be more like 20MPH or whatever the shift table speed value at 0 TPS is set at?)
2) Again, according to the Guide, Manual 1st can be selected at any vehicle speed. If 4L60E is in 3rd or 4th gear, it will immediately shift into 2nd... I assume the actual downshift into 2nd will not occur until speed meets criteria from item (1) above. The Guide goes on to state that the actual 2-1 downshift will not occur until speed drops below approx 30 to 35 MPH. I have same question - does this speed value correspond to OEM 2-1 shift table value of 35MPH @ WOT?

thanks

[cmitchell17]

Yeah I thinks thats right. There are tables in my truck calibration that limit when it will downshift if you force it into gear.

[joecar]

TRANNYMAN, welcome to the forum... :cheers:

In the tunetool look at these tables (single values):
D0928 2->1 manual shift speed
D0933 3->2 manual shift speed

These are not the WOT parameters; they are the manual downshift criteria mentioned by the HMTG.

[TRANNYMAN]

Thanks JOECAR.

I found the table with the following values:
2-1 Manual 44 MPH {D0928}
2-1 WOT 42 MPH

3-2 Manual 0 MPH {D0933}
3-2 WOT 90 MPH

This looks to me that 3-2 Manual Downshift is disabled (0 MPH)...Can you explain why this should be disabled?? (WOT speed is 90 MPH)

[TRANNYMAN]

Any ideas on why this is disabled?

[joecar]

Any ideas on why this is disabled?I don't know why it would be disabled, I don't think it would have come from the factory like that.

Maybe the box is having a physical problem with manual 3->2 downshifts.

[jfpilla]

That value is a factory setting.
Might be to protect the trans from a hard downshift when off the throttle.

[joecar]

I looked more closely at the description of D0933:

If the vehicle speed is below this value then the PCM will allow a manual downshift to 2nd gear from any higher gear.
Early programs used TPS as a reference, later programs use a single value.

The part in red may possibly have to do with it... that could be why it's factory set to zero.

TRANNYMAN,
- what year/model is this...?
- when you pull the lever into 2, does the trans actually downshift...?

I'm learning stuff all the time... :cheers:

[jfpilla]

Joe,
I think 2001 and newer have D0933 in the table.
Wouldn't it be nice if anyone with a question had their cars specs in their profile?
Joe

[joecar]

Yes, otherwise a person would then have to make assumptions which might be invalid...:doh2:

altho, I see my sig is lacking information... :lookaround:

I'll reprimand myself...:cucumber: