Intermediate Servo Travel

[BradTSS]

I am installing the CK servo with 1 large shim and a pin that has 3 grooves on the tip.
What is the most accurate way to measure the servo pin travel? Some say install with small spring but not the cushion spring and some say no springs. Where do you take the measurement?
I have been using the pointy end of a caliper to measure from the edge of the servo cover to the edge of the transmission case and it is very hard to get consistent results. Sometimes it is .060 or less and other times it is .100 or somewhere in that range.
What should the clearance be with all springs and gaskets installed on the servo?

 

[77 cruiser]

When I did mine I put it together as it is going to be run, & measured between the cover & snap ring. Push in on the cover till it stops & measure. I used .06 I think, so a 1/16 inch wire welding rod or whatever you have.

 

[TexasT]

We put ours together without springs or orings and measured with a feeler between the cover and retaining ring. We also did .060 clearance. Had to pull it apart several times and grind on the pin until we got the clearance we wanted. We used a sonnax servo.
Once we had the clearance we put the springs and orings on for a final assembly.

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[chris718]

If your servo requires a cushion spring and you check clearance with it out it will result in excessive clearance. There is a crush on the cushion spring and that is not included,nor should it be in the .060".

 

[TexasT]

Might be I guess, but it shifts good so I'm happy with it.

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[gunzandgearz]

Hey chris just curious, unless the spring went into stack or coil bind why would it change the reading.

 

[chris718]

Might be I guess, but it shifts good so I'm happy with it.

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I am sorry, I misrepresented my idea there. I shoot for .060" plus the crush of the cushion spring . I found that .060" travel with the cushion spring crushed results in reduced clearance. This results in spin losses in first and high gears when the band is knocked off. Over time the additional friction at the bands drum surface and the band lining can result in band and drum failure. The band also has to be loose enough in its free state to allow the servo to accumulate up on a 3-2 downshift to reduce excessive slippage during apply. This is because the servo was placed by the engineers on the passenger side of the transmission case for a reason. In first gear the anti rotation of the drum is in the same direction of the servo apply force on a 1-2 upshift. If it was on the drivers side the drum would attempt to push the servo out of the bore on the 1-2 upshift resulting in rapid band failure. In high gear the drum is turning in the same direction as the input shaft but on a forced 3-2 kickdown the drum tries to fight the servo from applying because the forces of the drum attempt to fight the servo from stopping it. For this reason art throttle and full throttle detent oil is also used to raise line pressure when the kickdown ports at the plunger are open. It is for this reason GM ENGINEERS allowed the servo piston pin to float in the servo piston rather than be attached to it.This allows the band to encounter less resistance to apply pressure during a 3-2 kickdown byloading the band anchor just enough.

 

[chris718]

Hey chris just curious, unless the spring went into stack or coil bind why would it change the reading.

My method applies just enough pressure to apply the band during the check w/out compressing the spring. The spring must crush its prescribed amount before it will push the pin enough to apply the band.Best thing to do is to look at an OEM servo to understand the concept.

 

[gunzandgearz]

By the way wasn't trying to bust youre chops I know you've built a few of these in youre career just thought maybe im missing something.

 

[chris718]

By the way wasn't trying to bust youre chops I know you've built a few of these in youre career just thought maybe im missing something.

I need my chops busted otherwise my blade gets dull. I am getting old and whiny.

 

[TexasT]

I'm just glad you show up and share your knowledge. I'm saving up for the th400 book so I can learn some more.

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[SS/GN]

So Chris with cushion spring installed and compressed what should the clearance be?? As others have said,thanks for the input

 

[gunzandgearz]

I understand that,as a shop owner myself we do numerous transmissions not just performance we also work on regular auto repair, rear ends , electrical,driveability you name it but I enjoy your input as well because I know you've put a lot of time in these units and its good to bounce stuff around.

 

[chris718]

If it is being checked between the servo cover and servo cover snap ring I go for .125". I push in the cover with a homemade tool and insert a .125" wire between the servo cover and servo cover snap ring, adjusting pin length until it just slips in and out.Then I blow air into the case at the 3rd accumulator / band knock off passage to fully knock the band off and make sure it wiggles.

 

[gunzandgearz]

Good info, because if it doesn't wiggle it will still be partially applied and will smoke the band in a relative short time.

 

[chris718]

Good info, because if it doesn't wiggle it will still be partially applied and will smoke the band in a relative short time.

Wiggling is good.

 

['75]

So with the cover relaxed against the snap ring, I should be able to push it in .060" and the tail shaft will lock, then push it in further and compress the cushion spring till the cover stops and should be around .125" total movement. Then release it and be able to wiggle the band and turn the out put shaft. Correct?

I have noticed that with the factory servo, the apply pin touches the cover when relaxed, all the ones I have seen have wear in the cover from the pin. With the Superior Super Servo and also the BTO billet servo, the pin is held away from the cover by the piston, so when setting the band clearance, the pin needs to be ground off more.

 

[chris718]

Good info, because if it doesn't wiggle it will still be partially applied and will smoke the band in a relative short time.

Imagine the heat generated as the band drags in 3rd and fourth gear for 20 to 30 minutes or more at a time at highway speeds. This causes friction eleent bonding agent to come undone, concentrate itself in the friction material and wreak havok in an instant.

 

[chris718]

Good info, because if it doesn't wiggle it will still be partially applied and will smoke the band in a relative short time.

Imagine the heat generated as the band drags in 3rd and fourth gear for 20 to 30 minutes or more at a time at highway speeds. This causes friction eleent bonding agent to come undone, concentrate itself in the friction material and wreak havok in an instant.