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Discussion Starter · #1 ·
Have a rebuilt by me C4 behind my rebuilt by me 289. Runs great but I have a slow 2-3 shift. It takes long enough that I get a rev during the shift but the 1-2 is great. Is this accumulator related or something else?
 

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From the shop manual:
Engine Overspeeds on 2-3 Shift B G W E F (transmission in vehicle). r (trans out)

B Vacuum Diaphragm Unit or Tubes
G Intermediate Band
W Perform Control Pressure Check
E Valve Body
F Control Pressure Regulator Valve

r Reverse-High Clutch Piston Air Bleed Valve

Full disclosure: I'm just a guy with a book. Not sure how to diagnose any further, but this may point you in the right direction.
 

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Books are fine but save time and put a shift kit in the valve body. The shift timing is off . The second gear band is releasing too early and or the high gear clutches are applying too late.
 

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Discussion Starter · #4 ·
Thanks for the suggestions. First I think I will check the band adjustment since that is pretty easy.
 

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Does the servo effect the 2-3 flair?




.
 

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The intermediate servo does play a role in the 2 - 3 shift engine flare. The servo is releasing the band before the Rev/High clutch is fully applied which technically puts the transmission in neutral for a split second. I've found the main cause of 2 - 3 flare is excessive Rev/High clutch clearance. The FSM calls for 0.050 - 0.066 clearance for all applications. I like to have 0.012 - 0.015 maximum per friction disc. Which with 4 frictions will put you at 0.048 - 0.060. The event timing of the intermediate band releasing & the Rev/High clutch fully applying is critical for long transmission life.
In my '68 C4 I have 5 Rev/High frictions clearance is 0.060 a TransGo 47-2 reprogramming kit & a Sonnax C intermediate servo. No engine flare ever on the 2 - 3 shift.
 

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Discussion Starter · #8 ·
The intermediate servo does play a role in the 2 - 3 shift engine flare. The servo is releasing the band before the Rev/High clutch is fully applied which technically puts the transmission in neutral for a split second. I've found the main cause of 2 - 3 flare is excessive Rev/High clutch clearance. The FSM calls for 0.050 - 0.066 clearance for all applications. I like to have 0.012 - 0.015 maximum per friction disc. Which with 4 frictions will put you at 0.048 - 0.060. The event timing of the intermediate band releasing & the Rev/High clutch fully applying is critical for long transmission life.
In my '68 C4 I have 5 Rev/High frictions clearance is 0.060 a TransGo 47-2 reprogramming kit & a Sonnax C intermediate servo. No engine flare ever on the 2 - 3 shift.


Thank you for that info!


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Discussion Starter · #9 ·
Sooooo the plot thickens. Spent the day working on timing and carb tuning along with looking at the trans. verified the kickdown linkage is fully engaged so I'm thinking I forgot something when I reassembled. Also I think the valvebody is messed up as the only way I get 1st gear is with the selector in L. With it set to either drive or green dot it starts in second. So I think I need a valvebody reprogramming kit. Any suggestions? I also checked the band adjustment and they were both spot on.
 

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Discussion Starter · #10 ·
So I tore into the valve body to make sure I installed the shift kit properly. Found out I forgot to drill a hole in the separator plate so I took care of that. Shift is significantly better but still flairs a bit. Shifting too low so need to adjust the modulator a bit.
 

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Discussion Starter · #11 ·
Posting an update in case this may help somebody else.


So I spent the day fine tuning the timing and carburetor and looked at the trans again. I re-read the shift kit and realized they recommend 1 1/4 turn out for the front band so I adjusted that. No change. Then I started cranking the vacuum modulator 1 1/2 turns in at a time. Went 4 turns total and honestly could not tell a significant difference. Not sure why but I decided to fashion a 1.625 pin for the modulator and swapped in another new modulator just for grins. Test drive was a SIGNIFICANT improvement. 1-2 shift is so smooth I can almost not feel it. The 2-3 shift is quick and smooth. I really like the way it is shifting now. Need to drive it for a while to see what I thing. Any thoughts on running the longer pin?
 
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