Hey, i am driving an 88 F250 351W with a C6. My tranny is shifting late and a little hard. I was told she was rebuilt when I bought my ride in Feb (07). The fluid is clean and new and doesn't really overheat.

But, when I drive, I have to run the rpms up a little higher than i want and then let off the gas completely to get it to up shift. I am thinking that the modulator might be bad. Even if it's not the modulator, it's such an easy fix that I should probably try this before I do anything else.

However, Advance Auto parts lists four different modulators (with different colored bands -- green, purple, brown, and black). I don't know what color my current band is (or if it is even the correct modulator since I am having trouble). I know the modulators goevern my shift points by vacuum pressure, and that the colors sort of denote the shifting pressure. So, how do I know which band to get? I don't want to get one of each (~$10 - $50 each) and shoot my way in the dark.

Any advice?

 

You only need to change the modulator if it is leaking oil into the vacumn line. Pull the vacumn line, if there is no oil in the hose you can adjust the shift points. Look inside the nipple of the modulator, if there is a screw inside you can adjust it easily. Do it about 1 turn at a time till you get the shift you want. Screw it in to make the shift later and harder, out to make the shift earlier and softer. If there is no screw to adjust you can adjust the length of the rod behind the modulator. If you shorten the rod the shift will be earlier and softer. To make the shift later, make a new rod maybe 1/16" longer from 1/8 welding rod or something similar. Try to keep the rod ends round and smooth when you make a new one or shorten the old one. When you remove the modulator to get to the rod you will loose a little oil unless you jack up the rear of the vehicle to get under and work on it. Have fun.

 

RClarke

I've read a little about the adjuster screw. Is there a way to know which models of trannys or modulators have screws? I have seen some people say they don't have the screws while some do, but I haven't been able to tell what determines which models have the screw or not.

But, thanks for the help. I will give it a try maybe tomorrow and see whether I have a screw or not. I can't tell whether I think Murphy's law applies to my truck or not. After I had to change the rear axle oil seals and found out how wonderful full floating axles are, I am a tad bit optimistic about my black beast.

 

ok, I found out that I do have an adjustable modulator (thank you God) and I just backed it out a turn. It feels like that might have done the trick for the most part.

But, it still feels like I need to let off the gas completely in order to shift when driving (even when granny driving). So, I might need to adjust the throttle kick-down thing still. Anyone know anything about that?

 

I worked as a Ford Tech for 26 years and never saw a Ford manufactured modulator with a screw except maybe in the late 60's. They are all aftermarket. It does make the adjustment a lot easier. The kickdown adjustment is just that, it should be full travel at full throttle. It actually only moves the last part of the throttle movement. At full throttle it will prevent an upshift but has no effect on shifting otherwise. A normal upshift at moderate throttle will be 1-2 at 10-15mph and with the same steady throttle setting the 2-3 will be at 20-30mph.

 

rclarke,

I feel like my shift points are falling where you said, 10-15 for 1-2 and 20-30 for 2-3. the problem is that with just a little more throttle at 25-35, my truck will drop a gear (down shift). So, I think my kickdown is cutting in at a very moderate throttle, rather than the full (or close to full) throttle.

Can the kickdown be adjusted? Is it easy to adjust? I thought I saw somewhere that you need two people to do it -- one to press the throttle in and one to set the cable? Got any pointers?

 

I found the best adjustment for the kickdown lever is to pull the throttle full on and turn the kickdown lever adjusting screw to the point where there is a little play in the kickdown lever. The book says 0.060 of free play at full open throttle.

 

Check for a vacuum leak.

The transmission shift points are controlled by engine vacuum.
When the gas pedal is depressed engine vacuum drops off.
If there is a small leak the vacuum will be much less than normal and the transmission will sense the need to downshift.

Look at all the lines for a small crack or loose fitting or junk inside them.
Depending on where the vacuum source is I have seen carbon build up that will restrict the vacuum.
Then look at the kd linkage.
There must be a small return spring at the carb.

 

[QUOTE=rclarke;4981346]I worked as a Ford Tech for 26 years and never saw a Ford manufactured modulator with a screw except maybe in the late 60's. They are all aftermarket. It does make the adjustment a lot easier. The kickdown adjustment is just that, it should be full travel at full throttle. It actually only moves the last part of the throttle movement. At full throttle it will prevent an upshift but has no effect on shifting otherwise. A normal upshift at moderate throttle will be 1-2 at 10-15mph and with the same steady throttle setting the 2-3 will be at 20-30mph.[/QUOTE
I have an 88 250 c6 that is early shifting as well. I installed the correct mod, black stripe/ adjustment screw. You said you haven’t seen adjustables since the 60s. If it’s adjustable you’re saying it shouldn’t have the rod because it’s not necessary right? I keep getting different answers. A shop that’s been around for over 40 years told me they have never seen one without the rod? Help! Thanks

 

you must have the rod behind the modulator, or it will not work.

 

[QUOTE=fordforlife62;21024448]WHERE DOES HE SAY A ROD IS NOT NECESSARY?

 

I did not see that, but sometimes people will get information overload and read something that is not said into comments.

 

[QUOTE=stuart1;21024687]So I replaced the modulator and installed a rod which was missing. No changes in early shifting problem. Made several adjustments to the modulator. Help!