Strange shifting under light acceleration
 

When I floor it all the way, I get the firm, crisp, shifts throughout the range. However, when driving it nice and easy, there is a slight harshness from the 3-4 shift. Hard to describe, but it seems to engage noticeably slower, compared to the other gears.

Additionally, I get an occasional clunk when letting off the throttle and coasting. This is the flex discs, correct? Is it a "must" to replace these things ASAP or can they wait for a while?

Flex disk or rear tranny mount (between crossbar and transmission at the back). Crawl under and look -- if the bolts on the flex disk aren't in the center of the "cutouts" in the disk it is shot -- you'll see what I mean -- the angular relationship of the transmission and driveshaft ends shouldn't change very much under load. Tranny mount can separate, you will only see this if you jack (gently!) on the transmission or remove the crossmeber. You will need to support the transmission if you take the crossmeber loose -- you don't need to in order to change the mount. It can also get soft and mushy, allowing the tranny to move too much. They are cheap and easy to replace. Flex disk is about $90 or so, cheaper on older cars.

No real rush, but causes vibration. Don't wait till your youngest child gets married.

Check the vaccuum lines going to the vaccuum modulator on the transmission -- hard, late shifts at light throttle can indicate a vacuum leak. Will also cause harsh downshifts.

Peter

Thanks for the reply. Where's the first place to check for that vacuum leak? My locks operate flawlessly, and the engine has no problems shutting off. What do the transmission modulators / vacuum controllers look like? They're probably covered with dirt and gunk...

Speedy:

Will describe the turbo setup, na just has the throttle linkage stuff.

Vaccuum supply (usualy white plastic) to a rectagular box on valve cover or IP with another line going to a blue thing (vaccuum amplifier) that looks like a car horn with four hoses on it, one labeled TRAN. That one goes to the vacuum modulator (plastic thing on tranny).

The scoop is that this is a "cheap" way to avoid a special tanny for the diesel. The rectangular box is a valving system that supplied full vaccum to the tranny to mimic a gas engine at idle. The wider the throttle, the less vacuum. Signal is modified by boost pressure via the blue "horn" on the fender.

Check all the rubber ends on the hoses -- if they haven't been replaced yet, they need to be. 6/16" hose works ok, but if you can find some with the same internal diameter that is a little smaller outside it is better -- the boost side hoses are all clamped and the 5/16" is just slightly too large to fit well.

If you have a mityvac or similar hand pump, you can easily check that the whole deal holds vacuum, and what vacuum you get with the throttle open.

Big leaks give full throttle shifting -- hard and late. Typical good condition shifts are noticable but don't bang at light throttle -- if you get very firm shifts at low speeds and light throttle, my bet would be that the vacuum lines are bad, especially the rubber parts. Easy fix.

Peter