tranny experts: what to do about leak on high mileage tranny

[jrd]

Here's the dilemma.

I have a 1987 300D turbo with 210k miles that has been a great car to own but somewhat of a money pit. After three years of this, however, it is in great shape with new paint and alternator, water pump, vacuum pump, tires, brakes, battery, glow plugs, and many other parts. It's set to go for a long time.

But the transmission leaks. It has since I bought the car. The thing is, it leaked a little 30,000 miles ago. It also intermittently slipped between second and third. I got the fluid changed at the local MB shop and it has been fine ever since. Actually, the shift into third is a little harsh. For a while the shifting was somewhat mushy first thing in the morning, but I found and bypassed the circuit that adds vacuum in cold weather (whose idea was that!) and, after the modulator diaphragm failed, a new modulator made the shifting fine again. Now I am happy with the shifting because it is crisp and timed right.

At this point, however, I have to add fluid every 100 miles because this particular unit shifts poorly if the fluid gets more than a cup low. It's driving me crazy, and the landlord is not happy the 14" diameter puddle on the floor that results from leaving the car parked for more than two days. I have to keep wiping it up, and I cannot go more than a couple hours before stopping to check the ATF!

I can have my mechanic install a good dyno tested rebuilt unit for a total of about $1550. This is a great deal for a good rebuilt transmission. But I have put enough into the car (two major repairs 6 months apart) this year and would much rather put some miles on it and enjoy it for a while. I really cannot afford to throw too much money at a problem that might be fixable for next to nothing. I have a complete set of metric tools and 6 ton jack stands and whatnot, and I can buy or rent a tranny jack for a very reasonable price. I have an able bodied friend indebted to me for other reasons who is willing to come up and help me pull the transmission so that I can replace the seal.

Transmission rebuilders would rather sell me a rebuilt transmission, claiming that the existing tranny will start to leak again if I replace the seal. The Aamco and Cottman guys are shaky at best, but the local MB guy will do the front pump seal (the leaking point) for $650, which is a good deal for the labor involved, but that seems like a poor use of money for a high mileage transmission, since it will cost $750 to do the servo seals too, and that still leaves old seals inside the transmission. I have heard of automatics developing "morning sickness" or slipping in the gears in cold weather due to bad internal seals, and I do not want this to happen to me after lots of expense. I do not currently notice morning sickness on the transmission.

This leaves three options, as far as I can tell:

1) The most affordable thing: to get my friend up here and replace the pump seal and B2 piston and drive the car another couple years if I can, at which point a rebuitl should be more affordable if I need one. Is this something that can be done in a Saturday? Do I have to replace the front pump too? Pump bushing? Anything to be concerned about with the torque convertor? I am figuring $40 for the reseal kit, plus tools, so maybe $100 for this option. What is generally involved in this task?

2) Install a rebuilt myself ($1000) which gives me all new seals and clutches and bands and whatnot, and I don't have to disassemble anything.

3) Pay the independent to install the same rebuilt for the cost of the rebuilt plus his $485.

Does the typical failure mode (if there is one) for these transmissions provide some warning such that I am not risking catastrophe? Can I, a reasonably competent DIYer , complete a reseal in a long day? Is it really likely to leak again from the front pump? When I am not masquerading as a student, I work in the refrigeration industry , where compressor seal failure usually signifies a bad bearing. Someone suggested to me once that I do the front pump bushing as well as the o-ring. Yet another person has suggested replacing the whole pump! Is that overkill?

I would like to take care of this soon because I am losing patience, but I want to strike the right compromise between "doing it right" and staying within my limited budget. Would anyone who has pulled one of these trannies care to comment on the job? Am I approaching this correctly?

Thank you!

[engatwork]

I would pull the tranny and replace the front seal myself and I do have it on the "to do" list for my 300D. I am having to add a little fluid once/week. I put some tranny seal stop leak in it during one of the fluid changes about 6-8 months ago and that did slow it down a little but it needs a new seal. Make sure you get the car high enough to roll the tranny out from under it or get a tranny jack that is low profile. You could probably pull the torque converter and change the seal under the car but it will be more of a pain in the butt. Check your flex disc while you have it out. When putting everything back together make sure you keep your friend over until you get the exhaust/muffler back in place. You may even want to consider replacing the engine rear main seal while the tranny is out. Take your time and you will be fine. It took me three 6 hour days to replace the rear main seal on my E320 but I was working by myself. Make sure you get the torque converter "latched" in during the reassembly.

[kowached]

Justin, at different times when I was on a student budget I maintained a 1997 Truimph TR7 & a BMW 320i and I could kick myself for some of the corners I cut to "just get by". If you are going to keep your MB for the long haul, by all means go for the rebuilt trans and do it yourself to save some $ and besides no one will make sure that all of the little things are done right like you, after all you have to take to old one out to replace the seal anyway. Just replacing the seal is a lot of work to do and still be left wondering how long the trans is going to hold up. Put Amsoil ATF (or Redline) in the rebuilt trans, and know that your going to have a reliable MB for years to come.

[Mr. BILL]

All three are good options. I think you have to decide what is appropriate for your wallet, now. $1500 for a rebuilt tranny is cheap, if it's done right, and if you can afford it.

Personally, I hate to crawl under any car and wrestle anything that weighs more than me. If you are comfortable with that, go for it, you will save yourself over $500. I wouldn't install the rebuild myself because if there are problems, they will say you did something wrong installing it.

I had a 300D that developed a pretty severe leak at 160K. I too struggled with the decision. I decided to have the dealer re-seal the tranny,($900) and yes, seal the other end while it's out. I decided to re-seal it because with the right fluid level, it shifted properly. I think that's they key, if it shifts well, seal it. I drove mine another 30K and sold it to a friend. It has never leaked a drop.

Good luck,
Bill

[stevebfl]

I wrote an article recently about adjusting diesel automatics. The point to much of the adjustments was to compensate for internal leaks that change the rate of filling of clutch packs and band servos. (The article is not yet in print but I noticed that it is archived already for those that read such things: http://www.babcox.com/editorial/ic/ic20242.htm )

The point is that all the rubber in the trans is the same age and in your case all at the point of causing trouble. We advise resealing and rebuilding anytime the car has over 150k. But, that is mostly due to labor costs. Resealing the front of the trans is 9 billable hours that is a little over half the labor to do everything; not practical if labor has value.

[dpetryk]

I agree with Steve. With the mileage on your transmission surely a complete rebuild is near. Do it right the first time and you wont be sorry. If you do just the minimum now you will be cursing your decision in the near future. Its pay me now or pay me later. It all depends on how long you plan to keep the car.

[jrd]

Other things I will be tending to are the differential mounts and the rear subframe mounts. They're not too bad, but the rear end rattles over bumps and it is not the exhaust, and I believe it is because the rubber is rotted out in the little mounts.

If I have the independent install the transmission, can I put off the differential mounts for another few months until I can do them myself? I have the parts already. (In fact, they have been sitting in the trunk for over a year.) Would the rattling of the differential damage the new transmission? I assume I need a special MB tool to do the diff mounts myself.

I think I will order a transmission today and have it shipped to the independent.

Thank you for your responses!

Justin

[engatwork]

Check out the rear sway bar connecting "links" before you go changing the supports on the differential. They are inexpensive and may well be where the noise is coming from - they have been on my 300D and E320.

[loubapache]

Good call, engatwork.

These $7 links are the first to check for suspension noises. Replace them first to see if the noise goes away as they are cheap.

My 91 300E had some noise over bumps and replaced these two babies and it is very quiet now.

[300EE320]

As J.H. indicated in a separate post, the differential mounts are a bit of a PITA. If you have a good set of tools and can handle some easy fab work, it's not so bad. I wrote up a little how-to article when I did them.

Differential Mounts: Follow-up

Good luck,

[jrd]

It's in for the tranny now. I've asked the tech (30 years experience with MB) to check the assorted items in the back. Based on my description of a light clanking, he's betting on the sway bar links, which have been replaced in the past but perhaps are due again. The differential mounts are still in mediocre condition, but I would like to put those off untill summer so that I can crawl under there on a Sunday afternoon and mess with it myself.



On the transmission, I asked about synthetic ATF and the tech didn't think it was worth it. Would it be a good idea to service the trans after 3,000 miles or so and THEN convert it to synthetic? If not, I think synthetic might be worth it now, since i am already buying the tranny and 80% of the car's operating time is in city conditions.


Any reason to mess with the rear main seal?

Justin

I have a 300D. I recently had a Transmission leak too! I had put this stuff called "No Leak" for transmissions in. You can pick it up at Wal=Mart for about $5.00! It takes a few hundred miles to work, but it really works! I also use the one designed for oil leaks in the engine. Just for fun, you might want to try this. Until you have the courage to spend the $$$ on a rebuild!

Good Luck!

Chuck