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: New SC IV Has Hard Downshift P.Beaver 03-20-2009, 10:35 PM I had the all the hard parts changed as well as a new S/C IV installed today and it downshifts very hard to the point it squeeks the back tires on the last downshift when you pull up to a light.This is doing the same thing my last one did just before it blew up.Any ideas about what is going on?We reset the taps but its like it is not relearning gtmax 03-21-2009, 10:45 AM Was the TCM relearned after the new trans was installed? Maybe the bad habbits of your previous trans (that blew up) are now controlling your new trans. Sometimes I've had to do the relearn procedure (Tech 2) more than once, in addition to individual tap cell clearing. generalwar 03-21-2009, 03:54 PM Was the TCM relearned after the new trans was installed? Maybe the bad habbits of your previous trans (that blew up) are now controlling your new trans. Sometimes I've had to do the relearn procedure (Tech 2) more than once, in addition to individual tap cell clearing. x2 get your guy to use the Tech 2 and relearn the trans.. DrHolliday 03-21-2009, 06:39 PM Samething happened with mine, even after the taps where reset. After about 100 miles of driving and shifting up and down it started to omprove then 3 or 4 shifts later it was perfect. The broken trans had the shifting tables all messed up. scramHD 03-21-2009, 09:15 PM Doesnt sound like a taps thing to me. The hard 2-1 downshift will likely be there after break in and taps resetting. gtmax 03-22-2009, 08:38 AM During the 2-1 downshift the C1 clutch remains on--C4 (2nd gear) comes off and C5 (1st gear) comes on. What causes this to happen? The TCM. There are also downshift taps which can be cleared, perhaps if you did a lot if 2-1 downshifts the TCM will relearn this and correct itself. The installation or the C4 and C5 clutches are straightforward and I couldn't imagine a problem there. scramHD if not the taps what to you think it could be? wilsonck 03-22-2009, 09:50 AM who did your trans? scramHD 03-22-2009, 02:37 PM Dont know. If taps does not clear it you will have to live with it, or tear it apart. Too many unkowns right now. Who rebuilt it? Just the kit replaced or any hard parts, pistons, etc.. replaced? Mine has always done this. I was able to lessen it drastically with EFI Live by changing torque tables, idle rpm, etc.... Can you pull any codes from the tcm? What about the temps? Does it do it in TOW/HAUL too? P.Beaver 03-22-2009, 03:58 PM I still havent got 60 miles on it yet . my tranny guy s name is Scott and is very knolegable with the allison.He wants me to put some miles on cause he thinks the last tranny has something to do with the shifting also.We reset the taps with a GM tech 2 twice.will let you know the outcome . beach_33 03-22-2009, 04:05 PM yeah drive soem more and see if it gets better. if not could be a valve sticking. there are two valves that controll the pressure going to the clutches (atrim and btrim) these are what actuall turn teh clutches off and on. if one of these is sticking it will cause this. i had this problem and i just went with a new valve body. problem solved hardcoremxer7 03-22-2009, 06:30 PM I just rebuilt my suncoast 4 last week and reset the taps with EFIlive and it was shifting hard from 2-1. It seems like it done it more when cold, but it has smoothed out and feels pretty good. It took mine a few days to pan out.... Hope it smooths out for ya. | ||