The ultimate DIY - or am I crazy ?
 

I am considering rebuilding my automatic transmission from my 87 420sel. The PN# is 722.324. I have managed to get a service manual from the ATSG group and also have the information from www.transonline.com in my arsenal of weaponry. I am confident that I can get the thing apart, replace the friction parts and seals and back together with no problems. My experience has been that MB cars are built to be serviced and im sure its true of the transmissions as well.

My question relates to the various upgrades that need to be applied to bring the transmission up to date with all the latest fixes and improvements. I have talked to several transmission shops and they all elude to doing some upgrades during the rebuild. Where can I get information on these upgrades? Does the www.transonline.com information contain them? Are the upgrades only done in the valve body? I have not found any information related to adjusting the transmission after the rebuild is complete other than the modulator pressure. Are there any other adjustments internal or external other than the modulator pressure and the bowden cable?

Mercedes does not publish any information about their transmissions to the public. They seem to want to keep their transmissions a secret. All the more reason to do it myself. I am doing this just as a personal challenge and to enjoy the satisfaction of success should I accomplish the mission. Am I crazy and in for the hassle of a lifetime or is this a doable deal? If you guys have any opinions, warnings or otherwise, I would love to hear them.

The internals of an automatic Trans. are like a womans mind...best left to people who know em' best:D As far as upgrades...any parts you would be replacing would more than likely be already built/changed to the new specs. Concerning any further upgrades that would not be covered by the replacement parts, the best place to start would be a higher end Import shop for the info or where to look.

is there enough detail in that manual? on the online version there is mention of upgrades. i would think if you have lots of time and have the tools then maybe it's worthwhile. i believe Steve B. knows some of the ATSG people and would be able to give you advise...

I took on this challenge on a Saab 900 slushbox...
 

and after several iterations, it came out quite well. I initially only went "in" as far as needed to address the specific flaw (leaking seal) but with each foray grew bolder. The third time came about 9 mos. later when the torque converter lunched necessitating complete teardown for the sake of cleaning. I had a complete overhaul kit that eventually all got installed along with clutch friction discs, springs etc. Some things were upgraded in the kit but there are many version changes to the hardware so-to-speak that I addressed on a case-by-case basis. I had several others for parts. As a novice, you really need a cooperative expert on the unit you are doing to guide you as to the relative merits of the upgrades and to provide general tips. I found one in Nat Wentworth who owns Eriksson Industries in Saybrook, CT. They have a superb reputation in the Saab community and I believe they rebuild MB trannies as well. Nat never hesitates to spend time on the phone with me, always has the parts at excellent discounts, has a lot of used parts and can offer services for those things that can make one weak in the knees (exchange valve bodies!). He also told me to never reuse a torque converter from a trans that failed as they are relatively inexpensive and impossible to clean internally.

Good luck!

Rebuild a tranny in 10 easy steps...
 

1. Find a clean work area. A metal top bench that's about 8 foot long might do you.
2. Book several weekends, better yet, take a week off from work.
3. Read the manual cover to cover and write down the name and part number of every tool.
4. Buy or rent the tools. Some, like the 4 pin wrench on the tail shaft are completely benz-specific and cost about 50$.
5. Get recommendation from expert as to where to buy rebuild kit (and then buy it).
6. Pull motor from car.
7. Clean case (leave no dirt behind).
8. Take unit apart.
9. Put it backtogether again (using new parts). You can use vaseline (!) as an assembly lube.
10. Reinstall in car.

Note, steps 6-10 may have to be repeated a few times before you get it right. Also, Prior to final valve body assembly, the unit can be checked for basic operations with compressed air. It sure beats repeating steps 6, 7 & 10 a lot.

-CTH

Thanks CTH, sounds like you have been there done that. I assume that you meant to "pull the tranny" rather than "pull motor from car".

I have the tranny completely disassembled. I am working on replacing the hidden O rings in the clutch packs and waiting for the seal kit to arrive. Case is completely clean, and I am working on a stainless steel top workbenches. I have no time constraints on completing the job so I can take as much time as is necessary. I ended up buying all the parts from the dealer cuz they were the least expensive. Figured I could not go wrong.

I am very interested in knowing how to do the air checks that you mentioned. I assume that you pressurize the various pistons to actuate the brake bands / clutch packs and check that it shifts as it should. Is this correct? Do you have any specifics on this preceedure?

I have a basic assumption - tell me if it is true. I assume that if the case is done correctly ( all clearances correct ), and if I have shifting problems, then those problems are in and can be solved at the valve body. The valve body is easily removed so I have no reservations about having to deal with wierdo shifting problems after the unit is back in the car. Is this a valid assumption or is it typical to have to remove the tranny from the car a number of times?

Anyway, to everybody who responded, I appreciate you insite and thanks for the responses.

Dave
I say go for it. I have always done my own automatics and find they are not as mysterious as people think. Important is clean clean clean. do use lint free cloths during reassembly. do get yourself a 1/4" torque wrench, as it is very important to correctly torque the valve body. did I mention clean is important. one grain of sand or one hunk of lint can hang up the sliding valves in your valve body. I can usually completely rebuild in one day. I used to pull rebuild and reinstall in 8 hours, but that was 20 years ago. I try to think in terms of small groups of parts. this will help uncomplicate things. I don't know about a BW tranny. carefully check the placement of the check balls. There is nothing one man can build that cannot be repaired by another man. Have fun;)

Thanks JB for the encouragement. Im well under way. I have the clutch packs, primary oil pump and reverse clutch piston overhaul completed. I am staging for re-assembly. Ill let you know how it comes out. Im taking my time, checking and double checking, having a fun time and learning how an automatic works. Im saving the valve body for last.

Big B_ _ls!
 

Fascinating Thread! as I am pondering the eventual rebuild of my 1987 SDL tranny! Generally what is the opinion of the manual you bought ? Great? Fair? Worthless? The transonline site seems to provide enough info to make it seem like a methodical, mechanically inclined, fearless fool (me - not you), armed with a manual, a rebuild kit, some relatively simple tools and the b_ _ls could accomplish a moderate miracle. I have noticed that Partsline carries more than a few tranny parts as well as a rebuild kit ($187) for starters. Any opinions as to the completeness of your rebuild kit and what other parts you needed would be interesting to know. I'm rather new to the forum and just found this thread through a search but I notice it's been a couple of weeks since the last post so I'll be checking back regularly to get your updates. P. S. When I found this forum it was exactly this depth of understanding, interchange, and accomplishment that I was looking for. Mastery over those elements of our lives that genuinely matter, is a truly noble quest. Be brave and good luck!

been there, done that. It was my 84's 380 SEL about 5 years ago. It took me two trials. Initiallly, the car wouldn't go forward. 1st trial got it but it wouldn't shift to 3rd. 2nd trial replaced one of the band(B2?) and it solved the problem. It was impossible to put the planetary unit back together with the new seal unless you have a press. I ended up taking it to a tranny shop and paid $25 for that. Anyway, if you are going to do the valve body later may be you'll be interested in this shift kit

I'm planning to do it on my 300sd next tranny fluid change

Update - The tranny is completely back together and on the car. The entire project was a success. Here is the story.

I had the transmission on my 91 420 fail suddenly. I took it to a reputable shop to have it rebuilt. He quoted $3000 to put in a factory rebuild and $2000 to rebuild the one I had. I didnt have much choice since my primary vehicle was out of commission. I let him rebuild the thing and it ended up costing $2600 by the time it was over. So I said to myself "this is nuts". My price on a factory unit was $1800 so I didnt understand why it took another $1200 to put it in. He would not explain it either. So after rebuilding my own, I understand why he wanted to rebuild the one that was in the car. Its because it is easy and very profitable. Assuming that no hard parts are needed and B2 is reusable, the parts cost about $200 - $300 for the complete unit.

So I decided that I was going to learn how to do it myself. I located a junker tranny for $200. I figured the most I could do was f__k it up. I accumulated as much information as I possibly could. Then I proceeded to open the thing up. It turns out that this tranny had water in it so it was a complete rebuild. The seal kit was $100 and the friction parts added up to $250 because the B1 & B2 bands had to be replaced. Normally B2 never needs to be replaced. I proceeded to follow the ATSG manual for the teardown proceedure. I found it to be complete and accurate. However it did not detail how to replace the hidden O rings as is done at www.transonline.com. And the O rings were not in the kit either. I had located a rebuilder near me www.jie.com and he had all the parts to do the hidden O rings. Screws, taps - everything. I did have unused parts in the gasket kit. So after I finished replacing parts, I took it to him for a dyno test. The dyno test cost $80 and it proved that a novice can rebuild a MB tranny right the first time. He checked and set the pressures and I was on my way. I have been driving the car and it shifts like it should. The best part is that it dosent leak any fluids now. I replaced the rear main engine seal while I was in there. I have the tranny that was in the car rebuilt as well. It was much easier and less mysterious the second time around.

The moral of the story is; If you have the time and inclination to atempt such a task, I say - go for it. The information at transonline is not complete and does not detail the tear down & assembly proceedures. But the ATSG manual does. So both sets of information are needed. Also the ATSG manual details the valve body which is necessary if you should happen to misplace some of the check valve balls or other small parts. But the hidden O ring information is not included in the ATSG manual SO there you have it. You need both. And it helps to have an expert standing by.

Overall it was a worthwile investment for me. I am well equiped with tools and I have doing my own auto work since I was 16. I always wanted to understand how automatic transmissions work. I certainly have achieved that goal and I have a spare tranny that can be used in either of my 420's at a minimal investment. I have found that everything associated with MB cars are designed to be serviced. Even the electronics is very repairable. They are great cars.

Good luck, let me know if I can be of assistance.

Now that's cool, and an inspiration. I personally have always been afraid of AT innerds. Unfounded fear I guess. Might be a fun project just to practice on a junker tranny.

Dave,
I stand in awe!!

Have you compared how much cash you saved to how much time you spent?

Mitchell Automotive Service Manuals
 

Congrats on your successful auto trans overhaul! Sounds like you found the needed info and professional help to ensure the trans worked the first time (nothing like the frustration with a failure and the subsequent R&R to correct the problem).

I found a wealth of info on the M-B auto trans. servicing/testing/internals/overhaul procedures in the Mitchell Automotive Service Manuals. I found the Mitchell manuals at my library for my 1977 W123 and other models, but how far up in model years covered by the Mitchell manuals is unknown to me - I do recall seeing info into the mid 1980's. The trans manual I copied covered the W 4B025, W 3A040, and W 3B050 auto trans. Include are: trouble diagnosis info, road test info including shift points in MPH for various loads, stall speed specs, hydraulic pressure tests, removal and disassembly info with lots of pictures of various sub-components including an exploded view of the valve body assembly/governor assembly/etc., special tools, clearance and band adj. specs., torque specifications, and more.

I do not know if the Mitchell manual is as complete as the info you have, but it is certainly worth a look for those that do not have the info you have and are wanting to see what the overhaul procedure is before deciding to dive into it. Also, I found lots of other great info about maintenance/repairs on other components that I have not found in the official M-B service manuals (print & CD), the Haynes and Chilton manuals. Plus, the info is free from the library (at least our libraries in San Antonio)!

My, very cheap, $0.02 worth!
Tom