S420 transmission trouble - Mercedes-Benz Forum
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#1 (permalink) Old 09-14-2012, 11:47 PM
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Angry S420 transmission trouble

I was driving my s420 for the last week or so and I noticed a jerk in shifting around 35-40 mph and when slowing down. I took it today to a transmission shop, the diagnosis is erratic and hard shifting between 2-3 3-4 ,3-1 3-2 downshift. Also, the mechanic mentioned internal clutch pack failure. The estimate to rebuild the tranny is around $2500-3k or buying a remanufactured transmission for $3200... Any advice on how to proceed? I am thinking of trying another shop for an estimate. Also, would the use of Lucas transmission slip fix help with my tran. Issue?

Thanks for the advice!
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#2 (permalink) Old 09-15-2012, 06:35 AM
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Check out mercedesdismantlers.com I hear they are good.

They have your tranny and torque converter for $2500 with a two year warrenty.

Good luck!

Getting there in a W140 is only half the fun....
the return trip is the other half!
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#3 (permalink) Old 09-15-2012, 07:53 AM
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Aboabdo,

I would not throw in the towel for a rebuilt or re manufactured transmission yet!!! But you got some of your home work first, and not let your mechanic direct your decision yet !!!

OH... No mechanics in a Bottle-bad news for the 722.6....!!!

1) Check your oil, is it good? recently changed? Do you have the Mercedes measuring dip stick? Do not have one? You should have one for piece of mind - regardless if you work on your S420 or not!! Though fluid(Im guessing) is not your problem, but you need a clear foundation to work from. If you need to change it, than wait a bit..

2) You also need to inspect if the connector at the transmission has broken it's seal, and see if you do not have fluid up at the Transmission Computer located up on the car on the passenger side of the engine bay-Its the big cover with screw. It should be dry. Not wet of transmission fluid. Again, need a clear reference to start from. You cannot advance further if this computer and connector are wet.

3) If the transmission computer is dry, and connector is dry too; Fluid is good and at proper level.

4) Your problem is probably the pressure regulation spring(cheap and DIY fix) on the valve body, but before we jump into the problem. Did you get any check engine codes-did the check engine light turn on? If the check engine light came on, the conductor plate probably has to be replaced, but the codes must be read with Carsoft or MB Star.

5) No check engine light, than it is an easier fix.

Here is a drawing of the valve body:

It is piston/springs No.4 pressure regulating Sonnax P/N 68942-1

http://www.sonnax.com/downloads/valv...edes-722-6.pdf

While your add it with the valve body, Replace the shift pistons, so you have sweet shifting, 68942-05k

Here is the list of parts of the sonnax parts:

Sonnax - Aftermarket replacement transmission, torque converter, and high performance automotive parts[make]=11&filter[unit]=221&product_line=trans

While your down there, change the conductor plate connector, by it from Mercedes only!! P/N 203-540-02-53. If you have not changed the conductor plate, I would change it, but if want to solve your problem first. You can do it later.


Check out this video:


Installation of valve body-must be torqued down


This is a DIY that is not hard, but a little tedious, and something most shops will not do as they cannot charge you big bucks. If all you do, go after the spring. It's five to ten bucks, and re use your old oil. If you exchange your fluid(meaning get all the fluid out, and replace it with fresh fluid), and filter. Do the sonnax shift($70) kit. No conductor plate. You are in it for less than $200.

Let us know how it turns out? What you decide?You can DIY this. I have the process to do a fluid exchange on you S420, so you get 100% of the fluid out.

Best of luck,

Martin
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#4 (permalink) Old 09-15-2012, 05:44 PM
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Thanks for the great info... I will definitely look into the fluid and the computer box... I believe the fluid is full according to the mechanic who checked it out, not sure how new it is though... I just purchased the car few months ago.. no check engine lights on.. the car seems to drive fine, just the jerking when shifting and down shifting. again thanks for the help.. i didn't want to give up just yet.. and your advice is a great way to start.
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#5 (permalink) Old 09-15-2012, 09:18 PM
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Aboabdo,

You are welcome

Get your self the 722.6 test dip-stick test tool. measure the fluid, and smell it. If you have to compare the fluid smell, get your self a quart of Valvoline MAX-Life ATF(in the red bottle). It will get you close to what it smells.

You can do this for cheap, but the test dip stick may cost you fifty bucks. The Mercedes Part number to the spring is 140 993 58 01

The 722.6 transmission is very rugged. How many miles on the clock?

Martin
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#6 (permalink) Old 09-15-2012, 10:58 PM
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141k


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#7 (permalink) Old 09-16-2012, 08:48 PM
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Mileage is still good for 722.6. My S500 has 185k and my E320 153k they shift great; Both of those have 722.6
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#8 (permalink) Old 09-17-2012, 11:01 AM
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Man i wish i would have saw this thread when i was trying to figure out what was wrong with my tranny rebuild. Does the w140 change trannys thru the years?

1995 S500
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#9 (permalink) Old 09-17-2012, 05:21 PM
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Mr Fresh,

On the W140, It changed three times. All the cars with the 722.6(all electronic-no brake bands in it) are drive by wire W140(meaning the throttle cable goes to a electronic sensor in-front of the brake booster, and not the throttle body like the other versions) Here is the list of years:

mercedes transmissions

In my opinion, the 722.6 W140's are easier to troubleshoot, but the early ones are more elegant.

Martin
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#10 (permalink) Old 09-17-2012, 06:53 PM
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MAVA. You have provided excellent advice and information. I agree with your sequence completely.. I had harsh shifting that was cured by my changing the fluid and filter. I have done this every 35K miles since 80K miles. Now have 175K and it is still as smooth as silk. I was not a beliver in the "lifetime fill" marketing tag. Fluid wears, gets dirty and filter clog. Also caught my leaking connector in time "prior to it walking up the wires by capillary action" and taking out my controller. Seth
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