I just purchased a 1988 F250 4x4 with 7.3 and C6. According to the PO the C6 was just rebuilt but it is currently not working correctly. He claimed that when the trans was reinstalled he started the truck, shifted into reverse to back out of the garage and it worked fine but then he tried shifting into drive and it would not go. When I brought the truck home the linkage was disconnected. I moved the trans linkage up and down between the gears and seems to operate ok including turning the backup lights on/off as you pass by reverse. However, when I put the column shifter and trans both in park, the linkages would not line up. As it sits, I would have the column in park and the trans in between neutral and drive. I assume the fix here is simply to adjust the column linkage to match up with the trans?

Moving on, there is a trans cooler outside of the radiator that looks like it has seen better days so I am planning to replace it along with the lines to the cooler. I have ordered a pressure tester that should be in tomorrow or Saturday so I cannot confirm proper pump function yet.

While snooping around the engine bay I also saw that the vacuum canister had basically rusted in half. Could this be affecting the transmission shifting? I haven't traced all of the lines yet but assume one of the lines does run to the C6.

I also ordered a copy of the Haynes C6 manual that should be in tomorrow as well but any advice or help is greatly appreciated

 

Does the truck have cruise control by any chance? Does it work...?

That rusted out vacuum canister your looking at it is most likely the vacuum canister for the cruise control.

The only vacuum for the C6 is the VRV witch is on the drivers side of the injector pump, it is black in color, and plastic. There should be a line from it, running on top of the engine, running under the air cleaner bowl and heading down the back of the engine, to the transmission.

Lack of vacuum will prevent the C6 from shifting at the correct RPM's, or to shift at all. It won't affect it going in gear and moving.

 

Truck does have cruise control but I haven't been able to try it yet. I will replace the canister with a junk yard piece or aftermarket if I can't find one there. For the temporary, I used a barb fitting to put the input/output lines together and tossed the rusted out canister in the junk pile.

I will check the C6 vacuum line tomorrow both for leaks and to find its source.

 

Heres the VRV I was talking about, just to be sure you know what it is.

 

Thanks! I saw that and on my truck there is a line running back behind the air cleaner which I assumed went to the trans but also a line running to the distribution block on the firewall. That distribution block was also connected to other items such as the brake booster and rusted canister which is why I was curious if this could be a part of the shifting issues

 

How are your brakes working? Since that cruise control canister is rusted out, could of been leaking vacuum, and vacuum in the system could be to low for everything.


Were you brakes pretty hard to push?

 

Brakes didn't seem too bad but also didn't drive more than in the driveway

 

a c6 with absolutely no vacuum to it will still drive around just fine. i drove 70k miles with a bad VRV that i failed to diagnose, and just got used to manually shifting, as shifts were horribly late otherwise. i also killed 3 vacuum pumps during this time. so while you may have a vacuum problem, that certainly isn't your main problem here.

isn't there a way to adjust the shifter linkage to make it line up - IIRC there was one connection where its a bolt that goes into a slot and is just tightened down at the necessary spot, so that shouldn't be too hard to set up.

if you're getting it into drive but its not engaging, you're either too low on fluid for it to work, or theres something wrong inside the tranny and you'll have to tear it apart to find the problem

 

The only vacuum for the C6 is the VRV witch is on the drivers side of the injector pump

 

The nut on the adjuster bolt of the linkage that comes down from the shifter is pretty rusted and rounded off. I will probably cut it off and replace with a bolt/washer until I can source the correct fitting. Still optimistically hoping that adjusting the linkage and replacing the cooler makes it work as I would like to avoid a rebuild for at least a little while!

 

to set the trans linkage. with engine off and parking brake set, put the shifter in drive. use a strong bungee cord at the end of the shift stalk to hold the shifter in gear. (book says to use an 8 lb weight but a bungee cord works just as good.)
get under the truck and loosen the adjuster nut on the shift rod. (this will be on a long slotted rod.)
manually move the shifter lever on the trans all the way rearward, then forward two detents.
tighten the nut to 12-18 ft lbs torque.make sure nothing moves when tightening nut.
remove bungee and check for full range of shifter movement.

i tried scanning the pictures too, but my scanner is being difficult and refusing to cooperate with me today.

 

The fact that this all occurred upon re-installing suggests that the torque converter was not fully engaged back into the pump, & so has chewed it up when he first started the engine.

 

Chewed the pump or torque converter?

 

if this were true, it would not have reverse.
since reverse works and when the shifter is in park the trans is in neutral, i am sticking with my guess the linkage is not adjusted properly, or he screwed something up in the valve body, like possibly putting the shift rod in backwards. .

 

I wondered about the shift rod possibility...that should be apparent by dropping the pan,right.