I have an 89 F150 with a 351 and a three speed automatic. It will not upshift when I have it in drive. If it put it in first and then shift manually it does ok. It will downshift on its own but not back up unless I move the shifter down and back up.

Any thoughts on this? Do you think it is an internal problem with the transmission or could it be a solenoid or something electrical?

 

assuming the fluid level is correct, i do not know what this could mean or how to fix it. try changing the fluid

 

Nothin electrial on the mighty C6 tranny. I would look to a bad vacuum line to the modulator.

No need to mess with the fluid on the C6.

Adrianspeeder

 

Pull the vacuum line off of the modulator and see if any transmission fluid comes out of the vacuum line. If it does the diaphragm inside the modulator has ruptured and you will need to replace the modulator. Also check the rubber vacuum lines at the engine because the trans fluid will cause them to swell and deteriorate.

 

The vacuum modulator is on the side of the transmission near the transmission oil pan?

One other question, I took the truck to a Quickie Lube type place and asked them to change the fluid for me. They told me that this was a bad idea because in older models that had not had the fluid changed regularly that deposits would build up inside the trans and that putting in new fluid (which contains detergents) would cause this stuff to break loose and make the situation worse. Do you think this is right or do you think he just did not want to have to do that job on a saturday?

 

C6 is a whole different animal than the newer electronic trannys that like regular fluid changes. Leave the C6 be.

Adrianspeeder

 

You seem to be a fan of the C6. I was hoping that this tranny would be more reliable than the latter models since it does not have an overdrive. Should be better for towing too...

 

It is the only automatic I willingly like to have. Basicly you can't kill it. Who knows what higher power come to Ford and granted them the C6. Like the 300six, model T, and 9" rear, the C6 is one of Fords greatest inventions.

 

They should have kept the 300 six.

 

Couldn't be made to meet emmissions, and it is harder for an inline six to meet crash standards.

Moment of silence for the mighty 300...

Adrianspeeder

 

Government ruins everything eventually....

 

OK, I changed the modulator and it will now shift on its own rather than having to manualy shift it. It does not shift well though. To get it to make the shift from first to second you have to run up the RPMs and then let off the gas completely, usually three or four times, then it will shift and jerk pretty hard. You have to repeat this process for the shift from second to third although it does not jerk as hard. It seemed to improve a little as I drove it home from my dad's house where we changed the modulator.

I was thinking of putting one of those additives in it to see if that helped it shift better. Any advice??