TCM Tuning .... again

[turbo_bu]

Don't know if this is an old question, but my TCM tuning has to deal with the part throttle shifting. I've noticed that for my truck, (stock '04, LB7 with stock Allison 5 spd), that the part throttle shift points don't match up with what EFI Live shows. Basically, the truck will shift at a higher MPH than what is commanded in the TCM tables. This is pretty consistent across the board for all gears.

I know I've read that this is most likely due to gear ratio in the TCM being 4.10 instead of the actual 3.73. This tends to cause some confusion when people want to adjust their WOT shift points. I on the other hand would like to drop my part throttle shift points to help increase my fuel mileage some.

Do we know that this is the reason for the shift points not matching my TCM tables? If so, can I go in and manually edit them to adjust for the actual gear ratio of the truck.... in so doing drop down my actual shift point to what is commmanded in the TCM??? Or would this be bad for my tranny?

 

[malibu795]

there is a speedo for the dash and a speedo for tcm shifting. the dash is in the ecm and the tcm is in the the tcm.

the tcm probly still thinks you have you have 245/75R16 tires.

part throttle shift is pretty easy to figure out..

you can manually adjust iirc there is auto adjust option there..

i did hte manual adjust on my truck.. took my 3-5 tune to get everything how i wanted. i woul recommend you work on 1-2 shifts at a time..

another thing if you want to get fance about it. set up a liner gragh that show the mph range of each gear from say idle to wot shift. that way you can get a nice idea one the overlaps of the gear during part throttle.
example wot 1-2 shift with 35" tires and 3300rpm is ~20mph and at 10%tps 1-2 shift is 5-8mph. then blend from top to idle.
TC clutch works the same way. for engageing and disengaging speed.

 

[turbo_bu]

Actually, I really still do have the stock small tires (245's) on the truck. I am looking at going the tall single route for my next set (235/85R16).

But it sounds like yes, the TCM is reading a different speed than what I am actually going.

Soooooo, the big question is if I adjust the part throttle shift points to match what is in the TCM tables ... example - reduce the 4-5 shift point from current 38 mph down to 34 mph like is in the stock TCM table ... will the Allison have any problems?

I know that I am lowering the shift RPM which will probably have an effect on the line pressure, but if it is in the TCM shouldn't that still be safe? Or did Allison already put the lowest shift point speeds in the TCM software from the factory?

 

[MaxPowerLB7]

I think the RPMs are set to match the turbo's operating range so if the shift Rs are dropped i'm pretty sure performance will suffer.. But maybe not i don't know.

 

[malibu795]

I think the RPMs are set to match the turbo's operating range so if the shift Rs are dropped i'm pretty sure performance will suffer.. But maybe not i don't know.

depend on what he is doing.. towing a load yes short shifting will hurt the performance. driving around empty probly not.

for me under 20-30% throttle i set it up to short shift alot. 30-80% is normal to wider shiftting anything above 80% is consider WOT

i also how downshifting set pending speed to down shift with minimul throttle increase

ie going 35-40mph cruising im in 4th or even 5th pending TPS% it doesnt take much to down shift 1 to 2 gears to pull out and pass or to get in a said opening.

i aslo set the upshifts and down shift to my driving style.

 

[turbo_bu]

Yes, this would only be for unloaded conditions (20-30% TPS). I guess my only concern is can a stock allison take short shifting?

I mean, all I am asking it to do is shift the actual speed that is programed into the TCM. Unless, the Allison guys have already out thought me, and have the "adjusted" speeds in there correctly.

 

[malibu795]

nope shift it early/short shift it is not going to hurt the tranny