4l60e

[fortcarp]

Ok one more trans question guys....Looking at the Sonnax performance site I see they have a "corvette" 2nd gear servo kit. Supposed to provide increased apply area to it thus firming up the shifts, especially 1-2. I mean mine is ok, just a little sluggish for my taste. You think this will work? I assume the servo cover is on the left side just above the pan....judging by the instruction pic anyway. They make a bigger one still, but looks complicated. http://www.powerglide.com/parts/parts/77701-04K.htm Anyway I guess GM put a bigger servo in the 'vette applications? Check this site out & let me know what you think. Thanks

[rodeo02]

That's odd your 1-2 shift is slushy. Many GMT360 chassis owners complain of too harsh a 1-2 shift. It's a jolting shift on my 2005, especially when cold. It was on my 1998 K1500 4.3L 4L60E as well. I'm not sure if you can get at the accumulator piston on a GMT360 w/out dropping the trans.

Joel

[fortcarp]

Mine shifts fine when cold, it's only spongy when warm and in the throttle hard. I've read on here it's prolly just the programming. I will check out the servo location when I do my tranny service. I know my old 727 in my mopar had a 1-2 adjustment nut on the side of the tranny, made adjustment easy. Came accross that vette servo & figuered I'd ask you if you know anything about them? Says on the site that fluid can leak past the stock servo causing delayed band engagement? That make sense? Anyway....looks pretty easy. Thanks

[fortcarp]

Well after more research it appears using the larger vette servo piston will increase pressure too much causing "bang shifts" and limiting 2-4 band life. Not good....Well I hope when I change the fluid, including pump out, discussed previously, the 1-2 shift will firm up. You think a pcm update will help? It is an '03. Thanks for your input

[maxwedge]

Remember this trans has adaptive shift capabilites thru the pcm, continued hard driving after a battery disconnect will allow the trans to shift somewhat firmer. The GM reprogramming kind of softens the shift and removes that slight hesitation/overlap. BTW overadjusting the kickdown band on the 727 can cause shift over lap /bind up on the 2-3 change, unless the valve body is modified. As you can see by the race car, tried all the tricks with that trans and wound up with a custom VB to eliminate the usual o/lap that unit always experienced.

[rodeo02]

Carp, the software for our trucks also dumps ignition timing at certain points between shifts etc, to soften the blow to the drivetrain. We also don't have full control of the throttle since the throttle by wire is also controlled by software. These engines would really be something with a cable actuated throttle and no programmed "torque management". The stock drivetrain wouldn't last too long that way though.

Joel

[fortcarp]

Totally agree with you there. The I6 has good mid-high range torque, suprised me the 1st time I drove one. However the low end torque leaves something to be desired, the 3.73s definatley help I suppose. I bet the 4.10s are even better, at the sacrifice of mileage tho! But we are dealing with a very heavy vehicle. Certainly not looking for race car performance from an suv, just want it to be as efficient as possible. I appreciate you guys' knowledge. Thanks

[ScarabEpic22]

The 1-2 shift sucks, it is really unpredictable. Cold is firm but can be harsh under hard throttle, warm is slow and slips horribly.

Easy fix: PCM tune. Best money you can spend on a TrailBlazer period. Change shift points, firmness, remove speed limiter, optimize VVT settings, a a ton more.

I have a Corvette 1-2 servo and it really helps firm up the 1-2 shift nicely, but coupled with a tune it is a good firm shift and gets you into 2nd really well.

Also, the GM Torque Management system that pulls a ton of spark timing stock is heavily tweaked (aka almost completely removed) with a performance tune, it makes the power after the shifts much better plus the initial lag experienced off idle is all but removed.

[fortcarp]

Yeah I really want a Wester's tune, but soooo damn expensive! I guess the torque management as explained by Joel & others really does suck. So did the servo ALONE help your shifts? Or did you do it together with the tune? Any recomendations besides Westers? Thanks