1984 6.9 shifting problems - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 4 (permalink) Old 10-16-2010, 09:50 PM Thread Starter
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1984 6.9 shifting problems

I have a 1984 F 250 6.9 C6 trans. It shifts @ 35 MPH to 2nd and 55 mph to 3rd. I replaced the vacuum pump, vacuum regulator valve, and vacuum modulator. Pump first, it was bad, no breaks/ heater etc... that is all working fine now, shifting was still bad. Modulator next, poor shifting continued I adjusted the screw in the inlet tube and eventually took it all the way out to see what would happen, it never changed the shifting problem. Although it does down shift @ 45 mph which the stock modulator did not do. Replaced the VRV no difference in the shifting Checked all hoses, swapped the two hoses on the valve top for bottom no difference. I bypassed the VRV altogether and still no Difference even with direct vacuum to the modulator! ANY IDEAS!!!!!!! I'm tired of playing with it. It shifts firm and seems to be fine mechanically just very uncomfortable to drive like this!
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post #2 of 4 (permalink) Old 10-18-2010, 02:42 AM
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Your VRV valve needs calibrated to shift at the correct RPM. Did you do that or just put it on?

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post #3 of 4 (permalink) Old 10-19-2010, 04:17 AM Thread Starter
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location doesn't matter

It doesn't seem to matter where the adjustment is on the vrv shifts the same no matter where
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post #4 of 4 (permalink) Old 10-24-2010, 01:28 AM
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No vacuum to the Modulator Valve will result in both harsh and late shifts.

Be sure to check all the vacuum lines for leaks, even a small leak can keep the VRV/MV from working correctly.

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