My 1989 C6 shifts hard - Ford F150 Forum

sp5937 · 09-08-2010, 12:29 PM

I have a 1989 F150 Extended cab, 4x4, 5.8 V8, automatic C6...from 1st to 2nd, shifts at about 30 MPH and kinda hard, like a shift kit installed...2nd to 3rd is a kinda hard shift too, but won't shift till about 38 MPH...if I go up to about 35 and let my foot off the accelerator it shifts....would this be a vacuum modulator? Can it be adjusted to shift earlier?

I just bought this truck two weeks ago, and haven't drive it much...I don't know if it has a shift kit or not...

flareside_thunder · 09-08-2010, 01:45 PM

Are you sure it's a C6? Most of the time when a modulator is faulty the truck won't go into reverse.....check the vacuum line going to it and make sure it is fully intact.

chelios · 09-08-2010, 01:58 PM

hows the fluid?

dirtcrew51m · 09-08-2010, 06:31 PM

The modulators are adjustable, as thunder said check the vacuum line the modulator controls the operation of the trans. If it is bad, make sure you get the one with the proper color stripe.

**Just call me Sean** · 09-08-2010, 08:20 PM

Try adjusting the kickdown cable/rod.

sp5937 · 09-10-2010, 12:26 PM

Quote:

Originally Posted by Just call me Sean

Try adjusting the kickdown cable/rod.

And what adjustment would I do? How? Which way would I adjust it for proper ops?

How would I adjust the Vacuum Modulator to get it to shift earlier? I would like it to shift to 3rd at about 30-35 instead of 35-40...isn't there a screw in the end of the modulator that will turn one way or the other?

dirtcrew51m · 09-10-2010, 07:29 PM

There is a nut on the carb linkage, loosen the nut, pull the rod until it stops, give a little play, you can also adjust it so it kicks in sooner or later, you could actually un do the trans kick down for proper operation, I think if you turn the screw in the end of the modulator it makes it shift quicker.

sp5937 · 09-11-2010, 01:13 AM

Quote:

Originally Posted by dirtcrew51m

There is a nut on the carb linkage, loosen the nut, pull the rod until it stops, give a little play, you can also adjust it so it kicks in sooner or later, you could actually un do the trans kick down for proper operation, I think if you turn the screw in the end of the modulator it makes it shift quicker.

Thanks much!!! My truck is EFI, will it still be the same for the linkage?

1987 F-150 XLT 4x4 · 09-11-2010, 07:31 AM

Every C6 transmission I've driven and owned; all shifted hard.

As the others said, ensure the small vacuum hose is still on the modulator.

Pull the vacuum hose off and adjust the small screw for different shifts points.

You will have to drive your truck to determine if it is shifting where you want,
if not, adjust it the other way and drive it.

I think; screwing it in will make it shift harder and screwing it out will make it shift softer?

I would not adjust the kick-down cable rod until you try adjusting the modulator screw or if you replace the modulator, ensure it has the correct color stripe as dirtcrew51m said.

Ford calls the C6 a heavy-duty 3-speed automatic transmission built from 1968-96.

sp5937 · 09-13-2010, 01:41 AM

Quote:

Originally Posted by 1987 F-150 XLT 4x4

Pull the vacuum hose off and adjust the small screw for different shifts points.

You will have to drive your truck to determine if it is shifting where you want,
if not, adjust it the other way and drive it.

I think; screwing it in will make it shift harder and screwing it out will make it shift softer?

Thanks, I will definitely try it...I was not sure if the modulator would be adjustable, or if I had to buy one that would be...I know it takes a black stripe one.