So, I am trying to gather my thoughts around the servo deal in the 4l60E. First I am going to assume some things so bear with me a moment
We all know, that the stock 2nd gear servo is the least desirable 2nd gear servo to have especially if it came out of a 4.3L transmission.
We all know, that the vette 2nd gear servo is desirable in pretty much any application as an upgrade.
We all know that the billet servo, either the set or separate, is for extreme purposes.
We all know that the 2-4 servo set is also an accumulator of sorts for the 2-3 shift... or something like that
What I can reconcile in my head is, what is the chief main job of the 2nd gear and 4th gear servo's. Is it shift feel? Is it the shift in general. Is it band apply pressure that directly affects the holding power of the band?
I have an idea that it is mainly there as the latter. The servo has the most affect on clamping force and therefor holding power of the 2-4 band. All else being equal, a servo with more apply area equals more holding capacity. Is that about right? I know there can be a combination of mods that will also affect the end result. I just want to fully understand the servo and why we upgrade them theory.

 

Apply force=line pressure x apply area

Larger apply area means more apply force

This affects the shift feel, timing, and holding capacity of the band.

 

All else being equal(hole sizes, boost valve, pump mods, afl mods, epc) it still affects all of these areas. In your experience, Does it affect one more than the other? Like, could I have a gentile shift feel with small feed or apply holes but really high holding capacity with increased pressure rise rate? Or am I looking at this the wrong way? Thanks for your help
Side note, am I using affect/effect correctly? I need the grammar police

 

Having a small hole will give you a softer shift and yes retain the holding to an extent , You will have more slipping during the actual apply but the same holding once the drum is stopped. Well as long as the hole doe not become so small you are leaking to much out as everything leaks . Probably best way to acheive that end would be a combination of accumulator set up and hole sizes , But in any case soft shift equals more slip during shift as that is literally what a soft shift is and thus more band wear and heat.
Also consider that the servo is the 3rd accumulator also. Me I use a TH400/4L80E int servo return spring in place of the stock it would play in a small degree with both too,
Also on the flip side a smaller servo with a large hole might give you a quicker firmer light throttle shift than the corvette simply because of less area to fill.
That is where accumulators and springs come in.
Me I do all my units the same .083 second feed second to servo, .083 accum feed for 3rd and corvette servo but also with the sonnax when I do use one (Primary reason for using the th400 return spring is the sonnax with DRINGS and the VET servo I noted they would be stuck in partially applied position on tear down off the dyno not fully releasing on the 2-1 because of the drag of the DRING.
I am a little different on the vet servo I would rather use the teflon rings and as far as leaks am more concerned at this point with leaks of 3rd clutch, 4th feed oil arround the band pin in case which I have noted playing arround can be considerable, This is why I pretty much strictly use the sonnax pin with the little teflons. though I can only hope they seal better once hot as while better than, They still leak a good bit in that area. Been looking for either a rubber or solid ring alternative or even considering getting the sonax tool so I can bore the hole and use the oversized pin they offer.
I have wondered if small rubber orings could be used in place of the little teflons but worry they will roll and destroy themselves though pin travel might be limited enough with a close set up to avoid that.
Then we have pancake servos , They are equal area both sides. They do offer max hold but getting a reasonable shift is hard though the ones with the cushion spring do a little better in any case they tend to be clunky feeling are very very agressive on the band and with the exception of what little accumlation they offfer due to the retrun spring no 3rd accum at all another clunky feel at light throttles. I only use those in the most extreme applications. They are not my preferred at all other wise. I have heard some say with the cushion they have accumulation not true at all they have the same but not quiet as hard on the band. Like I said not a fan except in extreme applications where comfort is not a consideration at all.
Ok My 2 cents lol

 

Great feedback guys. Thank you

 

Hope I didnt ramble to much. I tend to do that on explanations.

 

Nothing I couldn't get through lol. I appreciate the time.