Hard Shifting finally fixed!!!!
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Joined: Jul 2007
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Hard Shifting finally fixed!!!!
I finally got my 89' 7.3l C6 to shift smooth like the day it came out of the factory. When I first bought my truck two months ago it already shifted hard. I changed the Vacuum diaphram on the back of the tranny and it made my truck downshift when I got on it, but it still would wrap out 3,200 rpms before it would shift and then slam into gear. I pondered for a month think my tranny was going out, but then I called the local Ford dealership and they told me to do what I already did and that was to change the diaphram. They told me then to order a Vacuum Regulator Valve which they have only sold one other besides mine since the 7.3l came out. The part was $120.00 dollars which made me hesitant on buying it, but I did and man I took that truck for a test drive and I had to stop with disbelief. So if you're having trouble with your truck shifting change that valve and that might fix it.
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
This can also happen from a comlpete vacuum system failure, in my case, the alternator belt snapped and since it runs the vacuum pump runs off it, I lost vacuum as well (no power brakes either).
It seems to be a built in safety, since vacuum signal also controls line pressure, its designed to default to max instead in minimum pressure. The same is true with the E4OD in the event of an electrical failure. The AOD on the other hand, defaults to low rmp upshift, and low line pressure if the throttle cable snaps, no idea why they chose that setup on that tranny.
Anyway, glad to hear you got it fixed!
It seems to be a built in safety, since vacuum signal also controls line pressure, its designed to default to max instead in minimum pressure. The same is true with the E4OD in the event of an electrical failure. The AOD on the other hand, defaults to low rmp upshift, and low line pressure if the throttle cable snaps, no idea why they chose that setup on that tranny.
Anyway, glad to hear you got it fixed!
Elder User
Joined: Aug 2007
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not so , there is no built in default on the VRV valve thay can also fail sending full vacuum to the trans which results in minimum line pressure and damage the clutches and band , they are tough though i have only replace three of them since 84
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
Originally Posted by ford trans tech
not so , there is no built in default on the VRV valve thay can also fail sending full vacuum to the trans which results in minimum line pressure and damage the clutches and band , they are tough though i have only replace three of them since 84
What I was describing, was that in the event of a vacuum system failure, ie, cut line, or dead vacuum pump (or drive belt), so that a zero vacuum condition causes a high line pressure instead of low line pressure, unlike the older mechanical AOD, for example.
In the case of the E4OD, the EPC is actually used to cut down line pressure, so at idle, the EPC solenoid is at max, and at full throttle it is at minimum.
What I meant, was that the nature of the system operation creates a failsafe to prevent clutch burnup.
