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Thread: Any way to soften shifts a little after corvette servo? 2008 4l60e T42

  1. #1
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    Default Any way to soften shifts a little after corvette servo? 2008 4l60e T42

    2008 4l60e rebuilt with beast sunshell, alto z pack 3-4 clutch pack and Superior shift kit.

    First rebuilt of a trans for myself so I was surprised when all the gears worked after I installed. The ONLY thing I noticed at the time was when warmed up the 1-2 shift would 'shudder' a bit starting at 25% throttle or more. It also shudders when manually shifting into second with load on engine. I had read that the vette servo may help this and was a good upgrade so I bought it and installed it. Shudder is still there but 1-2 if much stiffer (borderline tolerable) and 2-3 got SUPER stiff. I wasn't expecting any change in the 2-3. I figured I'd go back to the stock servo and at the same time I did that I put a new cam in my 5.3. So when I got it all back together I was out with a heavier foot and now with the stock servo I notice the shifts are smooth again (still has the shudder) BUT I now notice a 300-400 flare on the 2-3 under moderate acceleration. I can even see it in the log file as a little curved up ramp on the RPM. Once again, I put the vette servo back in and now the flare is gone but I have very stiff shifts again. (my biggest worry as I lost 3-4 before after 170K and all I can picture is the frictions burning up everytime it flares)

    My question is, is there anything I can do on the tuning side of this while keeping the vette servo? maybe soften/slow down the 1-2 a little AND 2-3 as well? I almost want something right in the middle of the stock servo and the vette servo. Right now I have stock settings in my tune.

  2. #2
    Joe (Moderator) joecar's Avatar
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    Post your TCM tune file and any log files you have.

    Make sure your ECM tune is not under-reporting VE/MAF and/or TQ.

    The shudder on 1-2 and the flare on 2-3 is a worry (slippage), monitor the color/smell of your ATF on each drive.

    2-3 should not have gotten stiff (hmmm, let me look it up).

    Attach an external pressure gauge (0-300 psi) on the line tap on the side of the case, monitor this as you drive (the GMSM has specs on this).


    When you assembled the clutches/servo did you air test them (blow clean shop air into their apply hole, watch/feel for apply movement)...?

    What band did you use...?

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    I will get the trans tune up shortly.

    I did pressurize the clutches when I assembled. All engaged and held. I did not test the servo. I replaced band with a stock band from a transtar rebuild kit. The servo pin is the stock pin. I have not verified the band clearance yet. My shift kit didn't come with any shims for it.

  4. #4
    Joe (Moderator) joecar's Avatar
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    Usually you would use a wider band, for example find band under here: http://www.sonnax.com/landing_pages/gm_4l60e

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    Here is my t42 read file. All stock


    t42 read stock.ctz

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