I just picked up a fairly clean 88 F250 4x4 7.3IDI C6 last week. I'm loving it compared to my old ranger!

Looking through the archived here has helped me fix most of issues that have accumulated over the past 21 years but I have one I cannot find any info on:

I am having problems with the transmission, the linkage going to the injector pump was detached and I was told it was "bent" when the previous owner had the pump replaced. I have got it hooked back up although it does not allow the transmission shift into 3rd at all. With it disconnected and in drive I only get 1st, and I can manually shift it into 2nd without an issue and it will start off from a stop in 2nd without a problem. Issue comes when trying to get it into 3rd at over 35mph I have to shift from 2nd --> D --> 2nd--> D then it will shift right in without issue. Once in 3rd when slowing down it will downshift fine and if I have not come to a complete stop it goes into 2nd all I have to do is move the lever from D --> 2nd--> D and it will shift right back up again. I am going to try and find a new linkage at the salvage yard, but I am concerned it might be no better than what I have and would not fix the problem.

Is there any way I can get this back into adjustment myself? I don't really want to write a blank check to a transmission shop right now.

Can I keep running it this way? Or am I slowly destroying more than I think I am?

Any and all help would be greatly appreciated!

 

The problem sounds like you have no modulated vacuum supply going to the transmission.
There is no manifold vacuum in your diesel so they fit a vacuum pump. A supply is taken from this pump to a valve on the injector pump and from there to the trans. The valve varies the amount of vacuum according to throttle position.
So to cut a long story short you need that valve attached to the injector pump and the two vacuum lines hooked up to it.
The valve is adjustable by loosening it and rotating it on way or another.
Check also the vacuum pipes are good and attached at the transmission. Pull the pipe off at the trans and check that there is no fluid in the end of it.

 

WOW I think you hit it spot on, the valve is there on the pump but has no vacuum lines attached to it. Would you know which line goes to which port on the valve? What's the Alluminum rod for?

I am going to play with this when I get home today.

 

I can`t remember which pipe goes where but I will look at mine later for you and post back. I also can`t picture the "pod" but will look for that also.
But I think you have found the problem, the C6 shift points depend on a vacuum supply.

 

Ok, my truck returned and I got a look at it. ON the top of the injector pump modulating valve there is a small plastic fitting (like a miniture beer can) with two vertically stacked vacuum connectors. The top one of these is connected to the vacuum supply and the rubber pipe is all black. On mine this pipe runs from somewhere near the vacuum pump along the top of the passenger side of the engine, around the back of the air filter and forward again along the drivers side valve cover and plugs onto the valve.
The other pipe is black with a yellow stripe and after plugging onto the valve it runs back along the pass. side of the engine and disappears between the engine and firewall.
My truck is `87 so the pipe layout may be slightly different on yours.
Hope this helps to get that trans shifting as it should.

 

Thanks a ton for all the info.

 

I found the vac lines today, they had folded them back behind the air cleaner. Hocked it up and is shifting great.

Thanks for all the help!

 

LOL, doesn't supprise me but glad it was an easy fix.

 

More of those pesky vacuum lines the factory put in there that we supposedly don't need.