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If I understand it right, the tighter the clearance (longer the pin) the longer the band takes to gets released?
No.
The less Servo Clearance...
The sooner the Servo will stop, since it runs out of room to move.
It does not matter if the Servo is Applying or Releasing.
Please be patient but, how does a shorter Servo travel improve the 2-3 timing issue in relation to the band being released?
it would seem that the band would be released even faster? Or is it an oil volume issue, less volume on the servo, so most oil goes to apply 3rd gear cavity/piston and thus applies quicker?
Two things regarding the Further that the Servo can Travel...
The Greater the Volume of fluid will be to move the Servo to apply the Band (Larger space to fill with fluid).
Also the greater the amount of time it will take to have moved the Servo.
For the 2-3 Shift...
Oil that has to go to the 3rd Accumulator Circuit, is essentially oil that the 3-4 Clutch can not have.
Look at the diagram again:
Last edited by vorteciroc; Mar 20, 2023 at 02:14 PM.
Two things regarding the Further that the Servo can Travel...
The Greater the Volume of fluid will be to move the Servo (Larger space to fill with fluid).
Also the greater the amount of time it will take to have moved the Servo.
Then wouldnt the band release even faster and further exacerbate the issue if the clearance is reduced? What I'm understanding from prior posts is that the band is releasing before e 3rd gear frictions can apply?
larger clearance=greater servo stroke into the bore=smaller amount of volume needed to fill the 3rd accum circuit
Smaller clearance=shorter servo stroke into the bore=larger amount of volume needed to fill the 3rd accum circuit
larger oil volume=delay before the band is released
The physical travel needed to release the band is prettymuch the same regardless of clearance. It's clamped, then about .020 worth of travel and it will release
The big point of contention with the shift timing comes down to the oil volume
Because if servo clearance is .150 vs .050 the band itself only really knows on or off.
So consider band on to be 0
Then band off will be .020 ish
past that .020...the rest of the travel doesn't "matter" for the band because the band is no longer clamping the drum
it does matter for the hydraulics...but not the band clamp
so the one scenario you get .030 worth of travel past released
and the other you get .130 travel past released.
This whole conversation isn't easy to articulate and it's part of why all synchronous shift units are a bit of a bear to make shift right.
Powerglide flares see the same issues and are different because they don't have a positive release area, they have a pin biased negative release area and rely on a spring for release.
You'll find this same conversation happen with 727, 46/7/8 rh and re, c4, c6, etc
Adding a shim changed your clearance...but not the depth of the servo in the case when the band is applied. To change the servo depth when applied the only way to do it is with a longer pin
Now...with all this said...you could still end up not quite reaching the shift timing you want...and you'll have to use a different method to change that.
3/4 clearance
servo release bias %
oil orifice sizing
etc
I believe a longer servo pin will be the easiest thing to change and try to achieve the desired result...but you might not be able to quite fix the flare with just that
larger clearance=greater servo stroke into the bore=smaller amount of volume needed to fill the 3rd accum circuit I tried to look at the diagram that vorteciroc posted and follow how a smaller amount of volume is needed to fill the 3rd Accumulator circuit, but I just can't seem to make sense of It. The cavity is bigger if the servo has more travel, so more volume would be required is it not?
Smaller clearance=shorter servo stroke into the bore=larger amount of volume needed to fill the 3rd accum circuit the same question as above, but opposite. Less volume would be needed to move the Servo..right?
larger oil volume=delay before the band is released
The physical travel needed to release the band is prettymuch the same regardless of clearance. It's clamped, then about .020 worth of travel and it will release
The big point of contention with the shift timing comes down to the oil volume
Because if servo clearance is .150 vs .050 the band itself only really knows on or off.
So consider band on to be 0
Then band off will be .020 ish
past that .020...the rest of the travel doesn't "matter" for the band because the band is no longer clamping the drum
it does matter for the hydraulics...but not the band clamp
so the one scenario you get .030 worth of travel past released
and the other you get .130 travel past released.
This whole conversation isn't easy to articulate and it's part of why all synchronous shift units are a bit of a bear to make shift right.
Powerglide flares see the same issues and are different because they don't have a positive release area, they have a pin biased negative release area and rely on a spring for release.
You'll find this same conversation happen with 727, 46/7/8 rh and re, c4, c6, etc
Adding a shim changed your clearance...but not the depth of the servo in the case when the band is applied. To change the servo depth when applied the only way to do it is with a longer pin
Now...with all this said...you could still end up not quite reaching the shift timing you want...and you'll have to use a different method to change that.
3/4 clearance servo release bias % is this what you mean by getting a super servo? (I know its a bandaid) but where does the bias come from? The added weight? The shape of the servo? Different volume? oil orifice sizing what oil orifice size would help this issue? Bigger 2-3 hole?
etc
I believe a longer servo pin will be the easiest thing to change and try to achieve the desired result...but you might not be able to quite fix the flare with just that
thank you for that! I follow everything else except the bolded section
The 3rd accumulator cavity gets SMALLER as the servo is pushed deeper into the bore.
You typed up basically the inverse of what I had typed which you were replying to.
Yes servo release bias % is the ratio of apply vs release area.
A super servo will have a smaller bias % which by its nature will slow the release of the band.
And for oil orifice sizing you could block the #2 checkball and let that control the rate at which the band is released by limiting the oil volume to the 3rd accum area.
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