1976 F-150 4wd, C-6, NP205, 428 propane

my fishing truck started doing a strange thing, when i lift offf the throttle in drive itshifts into 2nd like going into a corner.

it does this almost right away.

i check the vacuum line and it appears to ok, i do have a aftermarket floor shifter. there is no downshift linkage with my propane mixer and holley base plate.

tranny does get hot going up hills at hwy speed (65mph) and does have a large oil cooler, tranny has lots of miles and years on it but seems to work fine otherwise

any ideas

 

So you are saying it downshifts from 3rd to 2nd when you let off the throttle going around a corner?

How fast are you going and what RPM is the engine running at when this happens.

These transmission do downshift on their own according to speed and rpm.

You could always check the vacuum modulator for adjustment.

There is a screw (allen?) inside the nipple where the vacuum line connects to.

Since this is a specific trans topic you may find answers in the drivetrain forum.

 

sounds like maybe the governor is stickin, thats what controls the actual shifting points, workin alongside in partner with the modulator, did ya pull the hose off the modulator? if so did any fluid come on out? like the million dolllar man said, there is an allen screw or some have a very smalll flat head screw in em to adjust what poiint under part throttle conditions shift points, i've built a few c-6's in the past, they really are a good trans, but when and if you have a problem they kinda are finiky to trace

 

thanks for the replys

i will start with the mod.

this happens around 20-30 miles and hour when it just gets into to drive and then if you let off the throttle it goes right back into 2nd. does it on straight, corner

i did have a muddy 4 low camping trip awhile back and i think it started after that.

will post what i find

 

i have a 79 f150 that i just rebuilt a 460 and c-6 tranny. The tranny now slips in drive and reverse. Can any one give me any ideas

 

was it professionally rebuilt at a shop?
If so take it back?

need way more info overall though.

what where when ???

 

no we rebuilt it ourselves started this right off the bat

 

when you rebuilt the tranny did you replace the entermediate band and if so did you readjust it?

 

bronco II 460, c-6- goes forward in all gears even park. all linkage internal ok. any Ideas?

 

Why dredge up a two year old post? Just start a new one with your question.

But to answer your question, most likely the shift linkage has been disconnected from the manual valve on the valve body.

 

Thanks for reply mark, just tore it down, forward clutches welded together. Guess I should not stand on 514 cid in high range.
Mark