87 GN 2004R, 2-3 shift, car slows down.

[chevellejoe]

Recently rebuilt the trany with a kit from CK performance. Drove it for a week, everything worked correct but the Throttle Plunger was getting stuck after warmed up. I decided to add the CK performance Valve Body recalibration kit while I changed out the Throttle Plunger with a sonnax kit. The issue with the plunger was fixed. Shift points stay constant. Unfortunately I gained a new issue. During 2-3 shift, the car slows down for a sec. before going into 3rd. All other shifts feel great. I’m going to look into servo, maybe its not releasing the 2nd band. Has anyone else had this issue after installing the recalibration kit? This kit eliminated the 1-2 and 3-4 accumulators.

 

[34blazer]

so it's binding up on the 2-3 shift?

 

[chevellejoe]

Yeah most likely. It feels like I tap the brakes as it shifts to 3rd. Its not a smooth transition.

 

[34blazer]

Yeah that seems like its binding up pretty good, maybe the band is not releasing fast enough? I don't have an ATSG or FSM to look at the elements applied/released. Sorry Im not much help

 

[TurboBob]

contact Chris, every kit developer has their own strategy for timing that shift. The 2-3 shift has the band being pushed off and the direct clutch engaging. Its the same supply of oil that does both, and the timing of the shift and amount of overlap is controlled by passage volumes, accumulator (the servo is the accumulator for the 2-3), and hole sizes/checkballs in the separator plate.

Bob

 

[INEEDAGN]

Did the kit come with a new plate?

Is it binding or does it feel like its freewheeling (going back into first momentarily when the band releases too early)

If it's binding (and assuming a new plate) open up the 3rd accumulator orifice in the plate a little at a time until it goes away. 3rd accumulator orifice controls how fast the band releases, bigger hole knocks it off faster. Likewise, if it's freewheeling/overrevving, peen the hole closed and redrill it smaller.

Start with .110and go from there. Lonnie says with billet servo and dual feeding to start with .125 (point of reference).

 

[chevellejoe]

Thanks guys,

Chris has been very helpful like usual. I took the servo out and are going to see him today. Its an aftermarket billet design. Which is differnet then stock. Ill see what he says before I start to drill out the orifice. (its a new plate and is binding)

 

[mikestertwo]

Is the direct clutch dual fed or stock?

 

[chevellejoe]

The direct clutch is stock.

I picked up a servo from Chis. The aftermarket servo I removed eliminated the intermediate servo cushion. The pin was attached directly to the outer intermediate piston. The CK version is a stock design with a larger intermediate piston (I beleive). Ill find out later if this was the issue. .

 

[chevellejoe]

I followed the procedure to properly set the intermediate band clearance and installed the CK performance servo. This corrected the issue.



I attached a picture of the two different servos. The top servo was the one I removed. As you can see the pin is connected to the piston. The bottom servo, CK performance, was a stock design utilizing intermediate servo cushion set up (the piston was in the cap). As you can see two different designs. It seems like the valve body recalibration kit that I installed from CK performance wasn't designed to be used with that aftermarket servo.


Thanks for your help guys.

 

[INEEDAGN]

What do you want for the one that came out of it?

 

[mikestertwo]

I can see why you had the binding problem with the top servo. It has a very large apply area and a very weak return spring. The combination of the two is a recipe for binding without modifications to the hydraulic circuit.

 

[Steve V]

Looks like a sonnax to me.

 

[Ttype6]

I can see why you had the binding problem with the top servo. It has a very large apply area and a very weak return spring. The combination of the two is a recipe for binding without modifications to the hydraulic circuit.

Correct. We can increase the diameter of the apply side of the piston,but we can't increase the size of the release side of the piston. As the diameter of the release side becomes closer to the size of the apply side,the band will release slower which effects the timing of the two events that must be coordinated to produce a proper 3rd gear shift. All larger servos release slower and must be assisted with a stronger release spring to get the 3rd gear timing correct. In this situation,a weaker return spring was used which slows down the release of the servo even more. This timing could have been corrected by using a stronger return spring on that first servo. I know that Chris,Dave,and Lonnie all sell a stronger than stock return spring.