BenzWorld Junior Member
Date registered: Mar 2013
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722.3 722.4 Transmission Shift Problem & Adjustment
Hi there people,
I'm an old retired technician who doesn't really do much work on cars now, but here's another story about 722 transmission shift problems and rectification.
Mercedes and Transmission specialist will probably hate me for this because they loose out on an expensive transmission rebuild, but I don’t care. I care more about reducing landfill waste and not sending good old cars and other still useful things to scrap.
It's an interesting read for those having issues with this transmission as there is a plethora of information I have found on this site so far, but little regarding these faults of (1). and (3). Reference images included.
I have worked on pretty much everything from a 1901 American through to the most recent of modern vehicles.
All in all I spent about 2 days working through these faults, but the actual time required is little more than that of a transmission filter change.
Prior to undertaking these rectifications the oil and filter were changed as a first step to no affect upon faults.
1. Unable to shift into reverse or park when cold
2. Flaring between 2nd and 3rd up-shift
3. Uncontrolled downshift from 4th to 3rd, then 3rd to 2nd, No upshift after.
(1). After trawling through various factory technical data I found reference to the same faults (1). and (3). and subsequent rectification involving removal of the centrifugal governor. I didn’t feel like pulling the box out of the car, so I cut a hole in the transmission tunnel and removed it quickly with little ease. Yes you can do this if you wish! After checking its operation it appeared all good/clean, so I refitted it and tested the car. Same fault, no change.
Eventually I found the “Reverse Block-out Pin” to be sticking when cold. I removed a C clip and extracted the return spring and bushes. (The block-out pin cannot be removed without removing the oil feed pipe for lower valve body). I replaced the original return spring with one of slightly more tension (old inkjet printers are full of really useful stuff they are). I refitted the return unit and tested the unit’s operation….
Time in action required to change spring:
10 minutes once sump and filter is removed. (very easy fix)
Time in action to remove governor:
20 minutes once transmission oil is drained. (refer to later details)
(2). This was an easy fix by fitting the K1 spring kit. (refer to other posts)
Time in action required to fit kit:
10 minutes once sump and filter is removed. (very easy fix)
(3). This was a real challenge but was really simple in the end.
Removing and cleaning the governor did not rectify this fault although the activity did point toward a loss of governor pressure causing an uncontrolled kickdown with no upshift afterward.
I first isolated all ancillary controls to the transmission; Bowden Cable, Kickdown Solenoid, Modulator Vacuum Line and I released the mechanical adjustment to the modulator till there was no tension on the internal spring.
Further reading presented various strainers located within the valve block. So I contemplated pulling the valve block off and dismantling it. But I thought further and decided against it.
Obviously the valve block was suffering wear. The fault only existed when the oil was hot and thin. (“it’s tired” as they say). So I searched for a thicker ATF oil… None available; they’re all rated about 7.5 viscosity at 100C. How was I going to thicken the transmission fluid?
Returning to my training where I was told that if you use anything else other than ATF in a transmission it will unceremoniously ruin the entire unit; especially EP Gear Oil (due to friction additives)…. So, what about engine oil then?
Off I went and studied the chemical makeup off ATF (Wikepedia). Up to Dexron III is basically made of 36W-7.5W mineral oil with a few friction additives and red dye for easy identification. (Did you know ATF used to be made from Whale Oil!)
Nearly all modern engine oils contain additional friction reducing additives; so these would not be suitable and may result in clutch and band slipping. Hydraulic oils are even thinner than ATF; so no good there.
I turned to the garage shelf behind me where sat a 5 litre can of Penrite Shelsley Medium 40W oil. Hmmm, now Shelsley doesn’t have any friction additives; formulated for extremely antique engines. Hmmm this might work!
Formulating a 50:50 mix of Shelsley and Dexron III ATF worked out well with no separation.
What have I got to loose I figured. The box as it is is cactus!
Up went the car on the stands, out came 500ml of ATF and in went 500ml of Shelsley, down came the car off the stands and out I went for yet another test run.
The result was not perfect. After giving the oil time to mix up and heat up I got on the motorway and let the gearbox do its thing. Down it shifted from 4th to 3rd, but this time it didn’t shift down any further. Additionally after stopping and restarting the engine the transmission shifted normally for a while, then it would downshift again and stay there until an engine restart.
I checked the viscosity of the now heated and mixed oil. Hmmm not much thicker than standard ATF.
Up went the car on the stands again, out came another 500ml of ATF, in went another 500ml of Shelsley, down came the car again and out for yet another run.
After giving time to mix and heat the oil, out onto the motorway we went…
Subsequent reconnection of the kickdown, Bowden cable and modulator vacuum line. With adjusting of Bowden cable, the car was now driving better than I could ever remember while I owned it!! Smooth as silk. I cannot even feel it downshift when coming to a stop.
Time in action to drain and fill 1 litre of ATF and Shelsley:
This is a great fix for anyone suffering a transmission with a tired valve block and problematic shift pattern issue. It should be used as a last resort before removing the gearbox or valve block for either overhaul or replacement. The slight increase in viscosity is used to counter balance operative wear within the valve block assembly and will not result in differences of operating pressures within the transmission. It is very possible a reduction adjustment of the modulator pressure will be required post activity to counter years of service adjustment that may exist.
Token End Statement to negate liability induced by peoples of useless superficial and non-realistic nature of unhelpful hindrances:
Please Note* I do not recommend this for all transmissions and, especially not for anything beyond 722.4 series with hydraulic valve block shift solenoids. Mixing of ATF and other oils and use within your transmission is done so at your own risk.
Everyone is now standing!!! Thank you