722.3 722.4 Transmission Shift Problem & Adjustment - Mercedes-Benz Forum
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post #1 of 11 (permalink) Old 03-13-2013, 06:57 PM Thread Starter
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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.

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.

Rectification:

(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….

Problem solved!!!

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)
Problem Solved!!!

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.

No change.

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…

Problem Solved!!!

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:
5 minutes.

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

OG
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post #2 of 11 (permalink) Old 03-14-2013, 12:46 AM
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Nice write up there OG and interesting.

No clue here on the use of your mineral oil. Motor oil would have everyone telling you to run not walk or Tow :-) the 190 to the nearest Jiffy Lube to have it all pumped out. Fried clutch packs and stuff. Though I had seen one fellow who did just that, added a qt to thicken it up a bit and claimed it worked well.

Just as a thought, I recently change my Son's 1985 BMW trans fluid with an unknown real mileage, could be up around 200K. I used Valvoline MAX Life, as advertised for over 75,000. Well, in the BMW there was a noticeable change for the good and it was pretty good going in. No issues but it just felt better. Can't say what's in it or IF it's any thicker, looks normal but I think I will give it go on my next change for me.

I did the K1 spring a few years ago. This took care of most the 2-3 flare, only happens now on a hot day and hot trans being driven a bit hard, otherwise it's good. I have not had the other issues you had,,,yet.

I still have a new Modulator I bought years ago sitting in my tool box.. :-(

edit: I trust you found the excellent everything you want to know about Transmission troubleshooting in our FAQ section. If you scan down all your symptoms are listed and the cause or fix.

Regards
Dan

Last edited by Logon_Bob; 03-14-2013 at 12:50 AM.
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post #3 of 11 (permalink) Old 03-14-2013, 04:43 AM
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Did you try replacing the K2 spring? It's on the front of the valve body, opposite the K1, and can cause various 3-4 problems.
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post #4 of 11 (permalink) Old 03-14-2013, 08:17 PM Thread Starter
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Thanks for the feedback guys.

I thought about the K2 spring Frank but my search abilities failed to find anything on the site. Interested to read and learn a bit more. Maybe you can post me the link here so I can have a read; would be appreciated.

Fresh oil usually makes a big difference as the viscosity does break down with age. However the valve blocks can suffer internal wear; one tiny scratch in the bore can cause all kinds of challenges. That's why they are seldom overhauled in a service warranty situation; we would just throw them in the bin.

I like your comment there Dan about running to the nearest Jiffy Lube. My father looked at me in amazement when I turned to him and said
"oil is oil" after nearly 40 years of working on cars... Average normal engine oil would probably cause the issues as mentioned, which is the reason I had no problem using Shelsley; its a straight mineral oil without any additives; it has no friction reducing materials to cause problems. EP Gear Oil on the other hand is full of friction modifiers. I'm told a transmission will last about 5 minutes before a no-go situation with even small amounts added. I've seen 1st year apprentices do this one.

Leave the modulator in the tool box. The only time I've ever needed to replace one is if the diaghram breaks. The car will blow a screen of white smoke if this happens. Its a good party trick but not very environmental.

Regarding changes to viscosity. They are minutely incremental; just enough to simulate oil running at a cooler temperature; moving it from a 7.5w to around 10w @ 100C.

Friend is happy. We all helped save her much loved Mercedes from the scrapper.

Thank you everyone who contributes here.

Happy Happy

OG
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post #5 of 11 (permalink) Old 03-14-2013, 11:49 PM
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Hey OG

You didn't say but it appears from the items you checked you did see Hattenators trans trouble shooting complaints/fixes in out FAQ section, post #4

Going through the list for fun. I didn't see where you mentioned anything on the Magnetic Valve.. or if it can even be got to without disassemble.
Possibilties for 1
Doesn't say anything about reverse or cold.

Complaint:
Parking not engaging.
1. Check rear engine mount and renew if required.
2. Check adjustment of selector rod and correct.

Complaint:
Selector lever positions R & P cannot be engaged.
a) engine running.
1. Clean centrifugal governor and make operable.
b) engine stopped.
1. Make detent piston in lower cover operable


Possibilities for 3 Doesn't say no upshift afterwards.

Complaint:
Automatic unwanted downshifts outside partial throttle downshift range without
actuating kickdown switch.
Cause/Remedy
1. Remove the kickdown magnetic valve. Check O-ring on mag valve for damage.
2. Check whether kickdown switch sticks in pushed position and renew if required.
3. Check whether mag valve sticks in opened position and renew mag valve.
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post #6 of 11 (permalink) Old 03-15-2013, 04:36 AM Thread Starter
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This is where language muddles and fuddles things for us. This is why it is important to be your own guru. As long as you are talking and standing with only yourself there can only be complete understanding while completely standing still!!

Ok, let's clarify things here. Heads are looking toward the ground and not the sky.

This particular transmission had more than one fault at the same time.

Two of the faults acting together pointed toward a faulty centrifugal governor. These faults persisted even after, as mentioned, all ancillary controls were disconnected; i.e vacuum line to modulator, supply cable to kickdown solenoid at the solenoid and disconnection of the pressure regulator cable at the throttle linkage. Hence removal and inspection followed by refitting and road testing. The kickdown solenoid was also removed and inspected for correct operation and refitted prior to thickening the oil (I did not mention this; well pointed). It was however not suspected due to particular fault at full temperature. (grit in the needle and seat would still affect things at lower operating temperatures)

Regarding the magnetic valve you mention there Dan. The reverse blockout pin is hydraulically operated and supplied by the governor pressure. The return spring is used to return the pin to zero position after governor pressure drops off, i.e coming to a full stop. No you cannot remove the pin unless you first remove the oil pipe seen in the picture. You can only remove the return spring and plunger that resides within the inside of the pin itself. The spring felt weak in relation to perceived governor pressure, so I up rated it slightly. I also sprayed the pin with carbi cleaner and worked it around a bit which made a big improvement to its free movement; you can move it about 10 mm by hand.

Not sure if I came across Hatternator's FAQ's. I still cannot find them. I just use the search window and hop for the best!

Checking the rear engine mount takes less time than to write this sentence and was not a concern on this occasion. Nor would I associate an engine mount with faults affected by differences in operating temperature.

Still, I had fun doing the impossible and learned a great deal on the way.

The great thing about these forums is the sharing of new ways to do the same thing.

Again, I must say that thickening the oil was a 'nothing to loose' last resort to undertaking much more involved solutions that would have taken more time, physical effort and expense.

OG
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post #7 of 11 (permalink) Old 03-15-2013, 09:21 AM
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OG

The FAQ section is right there on our Home Page with a Sticky.
https://www.benzworld.org/forums/w201...l-replace.html

Go down to post #4 and you will find the Complaint/remedy guide.

I didn't know IF the Mag Valve was actually the same as Rev Blockout or not.

Don't discount the Engine Mounts. Years ago I argued and argued no way was that going help my issues. In my humble opinion my engine started well, smooth idle.... yet at a stop light the back of the hood would shake but the main issue was a big bang 1st to 2nd. Change the front motor mounts,, no say I that can't be. They appear just fine.. I gave in and then had to eat humble pie. Hood was now still and the shifts were very much improved. Not saying that will fix your issues but it's a consideration.

I looked up the MDS sheet on this Miracle trans fluid I mentioned, Valvoline Max Life. Unfortunately at 100C it is mmm low 6, 6.2 ,6.3 or there abouts. I didn't write it down as it was less than your 7 ish.

My Trans is doing wonderful except in the summer fully hot after some freeway driving I can still get a 2-3 flare. Not that bad but I don't like it. I am wondering how and where I could install a Trans Cooler, that is in a location it would actually get some air on it.

I understand you were in a last ditch effort, you "Done Good"... at least so far as it hasn't failed.... :-)
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post #8 of 11 (permalink) Old 03-15-2013, 03:56 PM
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Quote:
Originally Posted by The Organic Guru View Post
Thanks for the feedback guys.

I thought about the K2 spring Frank but my search abilities failed to find anything on the site. Interested to read and learn a bit more. Maybe you can post me the link here so I can have a read; would be appreciated.
This is the only reference I have for it:

My Superior Shift Kit thread (W124 300DT) - PeachParts Mercedes ShopForum

When I did this job, I bought the Superior kit, which includes replacements for every spring in the valve body. I began with the K1 spring, which I found to have fallen apart, due to the plastic keeper uncoupling. The K2 had a physically broken spring. Replacing both of these completely resolved my erratic shift problems.

The K2 repair is exactly the same as the K1 repair. The K2 spring cover is located on the rear of the valve body, opposite the K1. It looks exactly like the K1 cover, four screws takes it off and exposes the spring. I don't know the part number for the replacement spring, but the Superior kit replaces K1 and K2 with single springs rather than the compound spring w/plastic keeper as used in the original.
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post #9 of 11 (permalink) Old 03-16-2013, 01:39 AM
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Hey

From the list of complaints, 2-3 flare. What are your thoughts on remedy #2, and or, what the hell does that mean???. Temp. installed?? Up to working temp? Is there a thermometer in there somewhere?

As mentioned, upon changing out the K1 a few years back all is wonderful until it gets hot is why I am wondering about Check Temp.

Complaint:
Transmission slips during 2-3 shift, or slips at first and then grips hard.

Cause/Remedy
1. Check modulating pressure and adjust.
2. check whether temperature is installed.
3. Exchange shift valve housing.
4. Renew inner plate of clutch K1, recondtion clutch according to condition.
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post #10 of 11 (permalink) Old 03-16-2013, 05:42 AM
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My symptoms were erratic shifting...flares and hard shifts...and much worse when the transmission was cold. I guess it has to do with the viscosity of the fluid changing as it warms.

Not sure how you "install temperature", but maybe they are referring to the tranny cooler.
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