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What causes harsh shifts apart from sprags in a 722.6?
I finally opened up my 722.6 with ~ 180k kms / 120k miles to do some minor refresh, and I was surprised to see both F1 and F2 in perfect health. I say surprised, because the car has the harsh shifting symptoms described in the MB documents as strongly related to the sprags.
Frictions were inspected, all are around 2mm thickness.
A single friction has a small piece chipped away (picture at the bottom).
Solenoids all measure within spec.
Symptoms
An abrupt engagement in D / R when warm. There's no build up, it's not the smooth gentle hunkering of the back end. It feels more like a car covered in pillows rear-ends me at 1mph :-) HOWEVER - when cold, it engages as smooth as you'd expect.
When engaging D driveshaft spins, backs off, then spins again. Happens when driving as well - kickdown to first and I get slammed in the seat, then something lets go, then I get slammed again and then take off.
Kickdown to 2nd gear produces a loud thunk, sometimes with refusal to shift. I think it's from 4th to 2nd, since I believe 5th to 2nd is not possible.
Various occasional harsh upshifts and downshifts.
Shudder around 40mph when cold. Reconditioned torque converter with Sonnax return springs is ready to go in to hopefully rectify this.
Any opinions are welcome. I'm trying to do the least amount of repairs, to hopefully narrow down the exact culprit, but if something is screaming at me I will tend to it.
I bow to anyone willing to doctor transmission hands on. This is the most complex mechanical assembly that requires the most skills and experience.
While you're in there do the best service you can with a complete rebuild kit parts + seals besides your torque converter.
Did you find any clutch steel that got overheated blue??
So many factors affect the shift qualities. Shifting perfectly well is a coordinated act.
The frictions packs and brakes are....
driven by oil pressure
driven by the valve body
driven by solenoids
driven by the TCM
driven by tranny sensors plus ECM data!
so eventually not every shift will happens in a timely fashion!! Harsh engagement is better than slippery but denotes something's not right.
Luckily the tranny computer has some habilities to learn from past-shifts for multiple ATF temperatures.
So a perfectly good gearbox can work poorly due to non-mechanical factors such as:
sensors coated with magnetic sludge
dirty solenoids screens
poor ATF qualities
wonky external modules can impact ECM/TCM CAN-C COM's.
ATF viscosity is affected by the engine heat through heat exchanger - So engine cooling thermostat better be working right to prevent thinning ATF and with that dropping pressure.
Last edited by CaliBenzDriver; Sep 19, 2024 at 09:07 PM.
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