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Old 03-01-2002, 04:04 PM
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Join Date: Apr 2001
Location: Central Oregon
Posts: 91
Cool W126 trans leak(s) - DIY or not

All these posts/discussions have inspired me.

My 85 500 SEL has a few leaks and is not going to get better on it's own. I have been reluctant to DIY in the past because of time/space limits. Now I have a company car to use daily, and a larger garage to work in. My plan is:
1) Clean the underbody to pinpoint the leaks
2) Review the MB CD for direction and parts ID
3) Order what I need from FastLane
4) Get to work!:p

What I don't want is to
1) Spend $$ on a lot of "special tools"
2) Have to take apart several auxillary items to get at the probems, or mess with the internals.
3) Do any damage when I turn the key for the first time.

What I know to date:
1) There are at least two distinct leaks - one around the pan, and one forward.
2) The car shifts heavy in the lower gears, but fine in the other two.
3) At stop lights, it is sometimes reluctant to disengage into ?standby? When this occurs the car will lurch slightly, and then settle right down.
4) When I maintain proper trans. fluid the car is very appreciative and these symptoms all but go away.

Your input on what to look for/avoid, lessons learned by others, and tips on removing/keeping contaminants out of the work is greatly appreciated.


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Old 03-01-2002, 05:22 PM
Posts: n/a

I had the same problem before. The Mercedes garage in Austin told me that there was a leak around the transmission front pump and it would cost me $900 to re-seal the pump.

Later I found out myself that it's not the front pump. It's the transmission pan gasket which is leaking. It took me around 2 hours to drain the fluid, install the new filter and install a new gasket. The cost is $24 dollars.

After this, no more leaking and the transmission runs like a champ.

I was even thinking to have my tranny rebuilt which will cost me more than $2000.

I used to have the problem of hard shifting. After the new gasket and fluid change, all of these problem went away.

The leak is really hard to trace. Sometimes, it seems to be the front pump but you want to make sure this is really the case before you spend big bucks.

Hope this help.

85 380SE
Austin, TX
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Old 03-01-2002, 07:32 PM
Mike Murrell's Avatar
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Join Date: Feb 2000
Posts: 2,580

I'm not versed in the ways of a 500-SEL; I suspect that in many ways my 300-SEL W126 and yours are similar with regards to tranny fluid change:

In my case, the following tools were required:

27mm six-point socket - 12 point will work if that's what you have
17mm socket
5mm allen head wrench/socket
Philips screwdriver

Place front of car on ramps or as Larry Bible has done, drive car up on to 2x12 boards. You need to elevate the front end so you can crawl underneath it.

Use the 27mm socket to turn the engine over manually. Turn clock-wise facing the front of the car. You place the 27mm socket on the end of the crankshaft-front of car. Before you do this you will need to remove the large plastic shroud underneath in order to gain access to the under-carriage. In your case, I do not know what size bolts secure the shroud.

The is a cross-member that runs across the car that covers part of the auto-tranny converter. In my case, there are 3-17mm bolts holding each side in place. Remove these bolts and the cross-member. With this out of the way you can now turn the engine with the 27mm socket mentioned earlier. You'll do this until the converter drain plug is at the bottom of the converter. You'll see it through an opening at the bottom of the converter once the engine has been rotated enough to bring the converter drain plug to the bottom. The 5mm allen-head takes this out. The converter will now drain. I believe it's round 3.0 to 3.5 qts.

Further back is the tranny pan. 13mm bolts hold it up and access in my case is unobstructed. Before removing the pan, remove the drain plug on it - also uses 5mm allen-head to get it out. 3.0 to 3.5 qts drains out the pan - this is an approx. measurement.

Wih pan drained and removed, remove the tranny filter. I forget the number of phillips screws holding it, but it's around 3-4.
Remove and replace filter.

Be advised that the drain plugs have washers that should be replaced. One uses a silver washer and the other a copper-colored washer. I forget which uses which. I would definitely replace these.

Reassembly is reverse of this. Pour approx. 4 qts Dexron in through the tube where your tranny fluid level dipstick is. Start is up and slowly add the rest. Go slowly - do not overfill.

Remember that it takes about 15 miles of higway driving to warm up the tranny enough to check the fluid level. After this much driving, the fluid level should be up to the HOT mark.

This is an easy task.

Good luck.

Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
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