Good evening.

I submitted a thread last month "88 Ford F350 with electrical issues" and I'm not sure that this issue isn't related to my previous post but the symptoms only came up (according to my son, the driver) in the last week or two.

He said it didn't feel like it was shifting properly. Not that the trans jerks or slips but that when accelerating it doesn't seem to up-shift when it felt like it should

I drove it around the other day and it seems like it takes along time to get into 2nd and 3rd.

We did a transmission fluid drain and refill with a filter change to see if that would help and to see if there was anything amiss in the pan.

The fluid was dark but not burnt and there was only very minor residue in the pan -- no metal shavings that or any loose material that I could detect.

We bought the recommended trans fluid and the level seems to be towards the top of the 'hatch' when checked after running 15 min and on a flat surface.

I've read some threads about transmissions and I'm not sure where to look next.

 

On the back of the trans is the vacuum modulator. It has a vacuum line attached. Pull the line off and see if there is ATF in the line. If so, the modulator needs to be replaced.

 

Will do, thanks.

I was also reading about transmission solenoids but I haven't much idea on how to troubleshoot that...

 

Truly, when I got under the truck and found the vacuum control modulator and pulled the hose off, i got a dose of fluid on my hand.

 

Is the modulator located on top of the trans? I have a 1990 e4od with similar symptoms but cant find a vac line exiting the trans

 

Yeah I was having trouble with it too but I found a YouTube video some guy made and it shows it pretty clearly and once I saw it it was easy to find

https://youtu.be/4ySIaM3gsy8

 

Just realized they are only on C6 not e4od thanks anyways

 

There are no solenoids on a C6. It uses a modulator.
There is no modulator on an E4OD. It uses solenoids.

 

That's interesting.

So, I got the part at Autozone and tried to put it in... couple of things... they gave me a part that looked almost right but wasn't. It was missing the flange that is used by a clip to hold it in place.

They found another one (last one in stock) that had the right flange. Funny how they both came from boxes with the same label.

Now, dumb question asked after the fact -- how do you know how to adjust the thing?

My son drove it a bit and says it seems to shift quicker but may not be right. It's too late to mess with now so I have to figure out what adjustment needs to be made -- how far to adjust it.

 

That's something I've never done. My background in automatics started just after the C6.

 

If I recall, you can pull the vacuum line off the modulator and use a small flat head screw driver to adjust a screw in the modulator, which will depending on which way you turn it will speed up or slow down your shifting. DO NOT GO CRAZY WITH THIS ADJUSTMENT. Make very small adjustments, and test drive until you are happy with it.

That said, the C6 is a heavy duty trans with just 3 forward gears and requires a lot of energy just to turn so manage your expectations.

 

Ok... let me tell you something rather stupid... we've been trying to adjust this new vacuum modulator to no effect.

Today my son and his friend traced the vacuum tube from the vacuum modulator up to the engine compartment and discovered that it had somehow come disconnected from whatever it's supposed to be connected to.

Clearly this is a problem.

I've been googling to find out where this vacuum hose is supposed to terminate in the engine compartment.

Do you happen to know what it connects to?

 

It connects to the vacuum tree, probably on the rear of the intake manifold. Look for an empty vacuum connection.