After reading much transmission-related material on the diesel forum I need to ask for some help in solving a delayed 3rd to 4th shift problem, that always requires a lift-off of the throttle to make the shift occur. The shift, when it happens, is a good bit harsher than other shifts.

Here's what work I've done this trans:
1) Changed fluid and filter, with the converter being drained also.
2) 7.7 quarts of Dexron III added bringing fill level to between low and full.
(The W126 manual calls for 7.7 quarts; longer runs to cooler?)
3) Modulator pressure set at 2.9 bar/42PSI.
4) Vacuum to the modulator set at 10" at idle, drops to zero at WOT.
5) The band 2 piston has been changed to the new style and the bushing
the piston's inner end rides in was changed to the Teflon type.
6) The control pressure cable has had slack eliminated at point of initial
throttle takeup.

All shifts other than 3rd to 4th are firm and take place quickly.

My understanding of the meaning of the term "flare" is an increase in engine speed during a transmission shift that results from a clutch pack being slow to fill to cause lockup, after the releasing clutch pack for the prior gear empties its fluid. Is this understanding correct? I do not have any increase in engine speed during any of the shifts with this transmission.

Question: What can be done to produce proper 3rd to 4th shifts that don't require a lift-off of the throttle to make them happen?

(I've learned that 3rd gear in the 722. trans is achieved by clutch 1 being applied along with band 2 being applied. 4th gear is achieved by both clutch 1 and clutch 2 being applied. This from "Automatisches Getriebe 722.3 Bestell-Nr. 6510 5762 02)

I'm a bit reluctant to try Trans-X or similar because I'm wondering if this solvent might weaken the bonds between friction material and the backing metal on the clutch discs and on the two bands that clamp onto the clutch drums.

Any information will be much appreciated...

__________________
Respect, protect, and maintain complex systems - whether natural or of German design, to benefit from their full potential.

1982 300SD W126.120 with an OM617.950 from a W116.120
1984 300SD W126.120 with an OM617.951

You should be even more reluctant!!!

I would suspect The K1 spring,(kit part number 126 270 44 77).
replacement is a must, It will help with 2&3 up shifts.
and it wouldn't hurt to check the vacuum valve levers on top of the valve cover for ware.