shifty diesel
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shifty diesel
i have an 84 f250 diesel that downshifts irractically (will suddenly down with out warning). gets worse under load it also shifts hard. downshift linkage appears ok. acts like vac mod valve but didn't think diesels had one
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Joined: Jan 2001
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From: Virginia
Your diesel still shifts with vacuum. So your vacuum system needs to be working. If your power brake system is working though, usually your vacuum pump is ok.
Up on the throttle lever at the injection pump, you will see vacuum lines. This is a gizmo that varies the vacuum signal to the tranny according to throttle position. Then the vacuum line runs down the backbone of the tranny to the modulator on the rear pass side of the tranny just like a gas engine.
I would check all the vacuum lines for cracks, including the little one at the modulator valve. Also look over the variable vacuum thing on the throttle. You can mark it's position and adjust it to see if it makes any difference.
Up on the throttle lever at the injection pump, you will see vacuum lines. This is a gizmo that varies the vacuum signal to the tranny according to throttle position. Then the vacuum line runs down the backbone of the tranny to the modulator on the rear pass side of the tranny just like a gas engine.
I would check all the vacuum lines for cracks, including the little one at the modulator valve. Also look over the variable vacuum thing on the throttle. You can mark it's position and adjust it to see if it makes any difference.
