300SD, shift problem, HELP!!

[n4xft]

Last week 3/4 of the way thru a 10 hour trip my beloved prize became haunted by demons. Stopped for fuel and found while getting back on the road that the xmission decided to not shift {and very harsh when it does} till about 3200 rpm 1-2-3 and wont go into 4th at all unless I go to neutral and then back to drive, then it goes into 3rd for a second and then 4th. This is a xmission that has never had any issues and had a fluid and filter change about 20,000 miles ago. I have searched the posts for 2 days and checked everything I could find. Fluid level right on the top mark hot. Unhooked the kickdown at the pedal and also the xmission, checked the vac- 12 in at the feed to the modulator which drops to near 0 as throttle is opened, modulator holds 12 inches on the mighty-vac for as long as i cared to watch it. No other vac leaks found {envy me??} I think that I saw in my search that a blocked filter causes some kind of pressure rise but I can't find it again. Does anyone think a fluid and filter change might help or would I just be barking up the wrong tree?

[Brian Carlton]

You have certainly covered your bases well.

I was hoping for another kickdown switch.

The fluid and filter would almost certainly accomplish nothing if it was done 20K ago.

Take a look at the Bowden cable. It might be possible that this cable is hanging up. If the cable was pulled to a typical position when heavy pedal is used, the shift would be delayed until over 3000 rpm. This is normal.

Now, if the cable fails to return to its stop, due to internal friction, the transmission thinks that you have stomped on the pedal again and delays the shifts.

If the cable fails to solve the problem, it is likely a problem internal to the transmission. However, this is the least likely scenario.

[n4xft]

Thanks for the reply Brian, I should have mentioned in my first post that the bowden cable adjustment makes no difference to the shift point, all the way out or in on the adjustment and it acts just the same. Have you or anyone else ever changed one of these cables? Mine seems to pull to a stop when I try it by hand unhooked from the throttle so I feel that it is still hooked up in the tranny but maybe a return spring or something has gone south. I feel this just has to be some sort of mechanical issue instead of pressure or vac.

[Brian Carlton]

Originally Posted by n4xft

Thanks for the reply Brian, I should have mentioned in my first post that the bowden cable adjustment makes no difference to the shift point, all the way out or in on the adjustment and it acts just the same. Have you or anyone else ever changed one of these cables? Mine seems to pull to a stop when I try it by hand unhooked from the throttle so I feel that it is still hooked up in the tranny but maybe a return spring or something has gone south. I feel this just has to be some sort of mechanical issue instead of pressure or vac.

Can you check the connection point at the transmission to determine if the cable is moving properly all the way down? Seems like a longshot, but might be worth a look. I'm not positive, but, I would guess that the trans must have a return spring to pull the cable back to the idle stop???

I have not changed one of them. However, if you disconnect the cable at the transmission and the problem remains, you have effectively ruled it out.

I agree that it is not vacuum related. Now, governor pressure is a different story.

[t walgamuth]

how about a faulty kickdown or a faulty electrical connection to same?

[Brian Carlton]

Originally Posted by t walgamuth

how about a faulty kickdown or a faulty electrical connection to same?

........

Originally Posted by n4xft

Unhooked the kickdown at the pedal and also the xmission,