The automatic tranmission on a 1989 420 SEL, 242,000 KM, is leaking fluid all over the front cage around the torque converter, a 722.355 model. It leaks about 4 diameter circle, when stopped. The torque converter drain nut is on tight and is definately not leaking. I took it to my independent mechanic and he says it is leaking from the top of the transmission, at the forward pump and recommends dropping the tranny, and replacing all of the gaskets and seals, not just the forward pump gasket/seal. He also said the the front pump may be scored and may need to be replaced. I was looking at the breakdown of the tranny, and trying to figure out how the pump gets scored. Is the front pump scoring a common problem?

This leaking only started after the last oil change, which was to synthetic Walmart brand tranny oil, about 3K KM ago.

Comments?

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1989 420 SEL

I have the leak on the back and side of the tranny, PO has warpped the tranny pan. A new pan-gaskit and pan fix the main leak. I had to replace 2 Orings on the back to fix the minnor leak. It did seems like that it was leaking from the front. Make sure about the source, I cleaned the outside with parts cleaner, dried it, Started the car and crawled under the car occassionally to find the source of leak. Took few tries but finally was able to resolve the issue. My 420sel has 156K miles and no pump issue neither I heard this before.
Now if I can figure out how to reseal the steering boxk, I will not have any leaks at all.
I hope it helps, keep us posted.
Thanks

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87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)

BenzMatic brings up some interesting points.

The torque spec for the tranny pan bolts is only around 5-6 ft. lbs. I believe the Newton rating is about 8 which is the same thing. If the pan bolts are over-torqued, a circular-shaped ridge is worn into the areas where the bolt heads meet against the pan, so you have as many opportunities for this to happen as you have pan bolts. The transmission fluid then seeps out through these ridges. It could be the pan bolts up front are leaking. With wind blowing through there, the fluid could be all over, giving the impression the leak is coming from higher up.

Before you spend $$$ having the transmission pulled, pull the pan yourself and examine it for what I just described. If ridged, you might be able to smooth out these areas with a brass hammer. That work and a new pan gasket may solve your problem.

The transmission fluid on the 126 cars is very easy to change. Elevating the front of the car with a set up ramps will give you clear access to everything.

I fixed this same problem on my Dad's 300e this summer. There is a large o-ring that fits between the tranny case and the front pump. It is a 4 dollar part, but the only way to change it is to drop the tranny out of the car and pull the front pump. The o-ring was cracked all around the pump. It took me about 8 hours to pull the tranny, change the o-ring, and re-install the tranny. It is now dry as a bone. Some people also warned me that the front pump could chew up the bushing where the torque convertor rides, but mine was fine.

Well, I took it into the mechanic. He dropped the transmission out, sent it to the Mercedes machine shop. They replaced all of the exterior gaskets/seals, and checked it to make sure it performed to specifications. The machine shop guy said the big piston was gone, and needed to be replaced, so it was replaced. Front pump was OK. It was bench tested and reset to Mercedes specs.

The total bill came to C$1,100, which included the piston replacement, new fluid and filter, and installing 2 new cooler hoses, which connect to the rad. I had previously bought the hoses, so the C$1,100 does not include the hoses. The piston replacement was C$350, C$300 labour to drop and install the tranny, fluid and filter, replace hoses; machine shop charges with seals was C$280. Elapsed time for the job was 2.5 days.

Comments?

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1989 420 SEL

You got treated very fairly. No unnecessary work was done, all that was necessary was, and costs were very fair.

You should feel good and be sure and send each of the parties a written thank-you note (its amazing what a small peice of paper does to ones spirits -President George Bush Sr always practiced this kindness and it earned him great regard and respct around the world)

Before the tranny work, when coasting down a hill with the car in D, if I shifted to neutral, the car would go faster in N. The tranmission seemed to be dragging.

Now, after replacing the seals and piston, shifting to neutral, the car travels at the same speed as in gear. Also, it seems to coast longer in D, after leting up on the gas.

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1989 420 SEL

How's your transmission holding up? Do you know the name of the Mercedes machine shop?

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

The tranmission has no leaks, whatsoever. Clean and dry for tranny fluid.

According to a rebuild manual, these transmission start in 2nd gear. When accelerating slowly, it shifts hard into third. When accelerating rapidly, it shifts quite smoothly.

I do not know the name of the machine shop. The mechanic is Charlie McNally. He said the shop was near his garage. If you call him, he may even tell you who he uses.

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1989 420 SEL