Bowtie70SS Posted May 22, 2006 Report Share Posted May 22, 2006 I recently installed my Zippy shift kit. I already had a vette servo installed, and have been holding off the billet servo install to see how it acted. My question is how hard does your truck shift at very light throttle...almost idle? Mine seems to shift pretty hard, and even kinda goes into gear hard. You can tell there's a lot of line pressure (that's what it seems like to me anyway). I am almost scared to install the servos. Could my tune be messed up? I did send my spare PCM in for a retune and installed it with the shift kit. Other than that it shifts hard 1-2 and real firm 2-3 and 3-4. I'm happy with that part. Thanks Dave Quote Link to comment Share on other sites More sharing options...
BenKey Posted May 22, 2006 Report Share Posted May 22, 2006 Under light throttle, I wouldn't want "hard" anything. Quote Link to comment Share on other sites More sharing options...
misterp Posted May 22, 2006 Report Share Posted May 22, 2006 (This is a guess) Most likely not. I've got the same behavior (bangs into second at low speed/light throttle) and the answer is exactly the opposite, it's not that you have too much pressure but rather that you do not have enough in the accumulator at low tranny pump RPMs (to offset the action of the servo). It is not damaging to the tranny at all, just annoying. BMan has discussed with me a fix he has developed for this in his own SS, I've riden with him and the light-throttle 1-2 behavior is completely domesticated in his shift kit. Install the billet 4th apply servo, and contact BMan about his 2nd accumulator mod. Mr. P. Quote Link to comment Share on other sites More sharing options...
BenKey Posted May 22, 2006 Report Share Posted May 22, 2006 FWIW, I installed my shift kit without any changes to line pressure and the 1-2 did not bang at low speeds. It was firm, but no bang. Quote Link to comment Share on other sites More sharing options...
zippy Posted May 23, 2006 Report Share Posted May 23, 2006 If you're getting a hard shift with the corvette servo and that shift kit the line pressure is cranked. it should shift almost stock at part throttle with that setup. Quote Link to comment Share on other sites More sharing options...
detjoe Posted May 23, 2006 Report Share Posted May 23, 2006 (This is a guess) Most likely not. I've got the same behavior (bangs into second at low speed/light throttle) and the answer is exactly the opposite, it's not that you have too much pressure but rather that you do not have enough in the accumulator at low tranny pump RPMs (to offset the action of the servo). It is not damaging to the tranny at all, just annoying. BMan has discussed with me a fix he has developed for this in his own SS, I've riden with him and the light-throttle 1-2 behavior is completely domesticated in his shift kit. Install the billet 4th apply servo, and contact BMan about his 2nd accumulator mod. Mr. P. <{POST_SNAPBACK}> what does this mod do??? is it secret Quote Link to comment Share on other sites More sharing options...
Krambo Posted May 23, 2006 Report Share Posted May 23, 2006 My $0.02 I had line pressure cranked with a STOCK tranny and 3000 stall. The shifts under any throttle were Very hard. Now I have stock pressure, a HD2 shift kit (built 65E) and a 2600 stall and the truck is VERY tame under light throttle. WOT shifts are as hard as my stock tranny with cranked line pressure. I kind of like it this way... Quote Link to comment Share on other sites More sharing options...
misterp Posted May 23, 2006 Report Share Posted May 23, 2006 what does this mod do??? is it secret It's BMan's mod, not mine - ask him and I know he'll tell you all about it! Tranny hydraulics 101: A servo is the hydraulic component that applies pressure to the friction material - it is what 'grabs' the next gear. The Vette servo is more aggressive than the OEM servo, installed in place of the stock piece it exerts a lot more holding force on the friction material to prevent slippage. On the 'opposing side' of the servo is the accumulator, which is a hydraulic component tuned to absorb the attack or 'hit' of the servo. If you have a highly energized accumulator then the servo will hit really soft but still deliver the same clamping force; an accumulator not energized enough will allow the servo to act/hit faster, again with the same clamping force against the friction material. The issue being discussed here is that in some transmission shift circuit calibrations there is very little fluid pressure being pumped into the 2nd accumulator at low pump output (low engine speeds), resulting in a 2nd accumulator that is not energized all that much; when the Vette/billet 2nd apply servo acts it does so almost completely unopposed/controlled by its accumulator and the result is a violent shift. Remember this is happening at very low engine speeds (under 1500-RPM) so the real-world case is idling around a parking lot and the tranny bangs into second, fortunately the engine is only putting out low torque so there's not enough torque to damage anything. What BMan has done is experiment and develop a simple 2nd accumulator mod that adds just enough spring preload to the 2nd accumulator it opposes the action of the Vette servo at off-idle so the truck feels completely stock idling around a parking lot yet still delivers the same assertive hit and clamping force at mid and high RPMs. Mr. P. Quote Link to comment Share on other sites More sharing options...
BenKey Posted May 23, 2006 Report Share Posted May 23, 2006 I got a banging 1-2 at low speed from a B&M shift kit. This was because all the springs are taken out of the accum. and metal spacers are put in their place - is that what you have done to yours? This was on stock pressure in my last truck. Personally, it was f'n annoying. Hated it. Quote Link to comment Share on other sites More sharing options...
misterp Posted May 23, 2006 Report Share Posted May 23, 2006 I got a banging 1-2 at low speed from a B&M shift kit. This was because all the springs are taken out of the accum. and metal spacers are put in their place - is that what you have done to yours? This was on stock pressure in my last truck. Personally, it was f'n annoying. Hated it. This is exactly the accumulator set-up in the TransGo Kit. Mr. P. Quote Link to comment Share on other sites More sharing options...
BenKey Posted May 23, 2006 Report Share Posted May 23, 2006 I got a banging 1-2 at low speed from a B&M shift kit. This was because all the springs are taken out of the accum. and metal spacers are put in their place - is that what you have done to yours? This was on stock pressure in my last truck. Personally, it was f'n annoying. Hated it. This is exactly the accumulator set-up in the TransGo Kit. Mr. P. <{POST_SNAPBACK}> Not in the HD-2 kit it isn't. You only add washers, up to 3. Quote Link to comment Share on other sites More sharing options...
Bowtie70SS Posted May 24, 2006 Author Report Share Posted May 24, 2006 I have the Zippy kit, which if I'm not mistaken has this accumulator mod. There is a spring on each side of the acc. and yes it is metal. I'm getting more used to it now. I sold my 70 Chevelle wagon to a buddy of mine and I had a 700R4 in it. It shifted so hard it felt like you got ass ended...gotta love it. I think I'm gonna put the billet servos in, I love the "firm" shift. Dave Quote Link to comment Share on other sites More sharing options...
zippy Posted May 24, 2006 Report Share Posted May 24, 2006 The kit he's running still has full use of the 1-2 accumulator. There is a stiffer spring in there, but it does not reduce the volume of the accumulator as the Transgo, B&M, and TCI. This is one of the reasons I use the Superior Products brand valve body kit. I know hydralic's pretty well and I don't like the idea of reducing the volume of the accumulator to make a harsh shift. With the vette' style servo, .490 boost valve, and upgraded valve body kit which is how my towing kit comes it leaves the desired shift all in the programming. If you put this kit in a truck and left the stock programming in it would hardly be noticable until you were heavy into the throttle. With a minor bump in line pressure and reduction in shift timings you can make it shift very noticable and solid at all speeds. Quote Link to comment Share on other sites More sharing options...
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