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Disassembling Getrag S6S 420G Gearbox (From E39 M5)

47K views 45 replies 20 participants last post by  herrubermensch 
#1 · (Edited)
Hi there, i have blown up 2 gearboxes during few years. Yesterday was the day when i wanted to see what happened inside.
Tryed to google some images how to disassemble gearbox but i found only few low quality pics. This is not a DIY how to disassemble the gearbox but i have lots of hi res pics.
Lets hope they will be useful to somebody. To be hones, its quite easy to disassemble the gearbox, locking pin is only PITA thing and when assembling you have to have shift rods in right position.

Hi Res pics: Index of /~burnout_187/M5/GetragS6S420G











Locking pin (at 9 o'clock long one) small pin doesent move!!
 
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#4 · (Edited)
First one blew up when i was accelerating and diff blew up and got stuck for a second.
Second one blew up while full accelerating with 2.nd gear, i dont know was it engaged then completely. I have heard rumors that it is one weak spot for getrags that 2.nd gear does not engage sometimes "correctly". I have noticed sometimes even when driving normally when you pop out 2.nd gear that it is littlebit "harsh". Hard to explain :)
 
#8 ·
Can you specify more details on how to resassemble the tail casing? You say that the shift rods need to be in the "right" position, but what does this mean? Also, I'll ask the same about the locking pin. My spare 420g is in great shape, but the tail housing has a crack in it. I have a new housing to put on, but have been apprehensive about taking the casing off for fear that I won't be able to put it back together correctly. The pictures are great, but a bit more narrative would be great. Thanks!

Also, if you have a spare output flange and shims, I would be interested in them. I used my v8 output flange on my M3 6-speed when I put it in my 530i, so to make my spare transmission complete again, I need another v8 flange.
 
#10 ·
Thanks for the photos and time you took to take them. I'm always bad about that.

Hopefully you were ok when the diff "blew up?" I had one do that to me while on the interstate. I was going about 60mph and started hearing a noise. I did my best to get over 3 lanes to the shoulder. Well, I nearly made it and then the stuff movies are made of happened! The whole rear locked up, I went sideways, slowly looked in the rearview expecting to be rear-ended, all the while steering to avoid the guard rail. At the very last moment, I came to rest and nothing was harmed! I immediately called for a rollback and gladly paid that guy $100+ as my day could have been MUCH worse!

The biggest pain was swapping the rear out and getting to all the axle bolts because the wheels would hardly move.
 
#13 ·
Very cool stuff here. Will the mystery of DIY'ing the 420 finally be solved? Are all the fancy tools and presses just a bunch of bull? Sub'd for more details. Good work burnout.
 
#14 ·
I didnt have any fancy special tools. Regular mm socket and wrenches. Couple screwdrivers. Ok...if you want to remove gears etc then you have to have somesort special tools.
But this project is on hold now beacause i discovered today that my block is melted between cyl 6 and 7. :frown
 
#17 ·
I would love to know how to split the case half's mine is sweating from the seal. Oil leaks are a pet peve. Good work Arvi!!!!
 
#20 ·
Here are some photo's I took last time I worked on tearing one down beyond the easy stuff.
 

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#21 ·
Most recent project was the case swap so I could install the low mileage transmission into my car. I replaced the front seal, fork bushing and throwout bearing guide bushing. The "new" transmission already had the updated detent kit. I also used a thin layer of RTV on the case joints as leaks are sometimes heard of. There is no gasket between the case pieces. This work took like 8 hours because I had to fight and curse the shaft pins to align so I could get the rear cases off.
 

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#23 ·
#27 ·
Pyite,
The reality is that none of the key internal parts (bearings, synchros) are currently available, so not sure how parts may become more difficult to find. The parts that BMW currently sells (shifter balls/springs) don't generally wear out on the newer boxes and as such I don't see a significant demand for these. The only option that will be available is a used box (a gamble) or a rebuilt one from BMW/Getrag. The latter currently costs ~$4.5k, but is likely to go up in price over time. I doubt many (if any) people are going to go and buy a rebuild box now and keep it in their garage for if/when they may need it.
 
#30 ·
You are a good man to decide to replace the sleeve that the throw-out bearing slides on. I chased hard shifts into 2nd gear for 2 years. I had the detent pins replaced, as well as almost every part of the drive line. It turned out in the end of the day the throw-out bearing was not sliding well on the sleeve and was preventing the clutch from fully disengaging. I had replaced the clutch and throw-out bearing but not he sleeve.

After that my transmission shifted as smooth as any new car. Never a crunch into 2nd even on the 10 degree mornings, it was absolute bliss. Still had to shift slow on the cold days though to warm it up, it was still stiff.
 
#37 ·
M3Augy,
Interesting for you to mention this. About 2 years ago I actually emailed Permatex customer support and asked am this exact question. See below for the email stream and their response. At least in 2017 they seem to favor Ultra Grey.

From: Boris
Sent: Sunday, November 26, 2017 12:31 AM
To: Product Application <ProductApplication@Permatex.com>
Subject: New submission from Permatex.com - contact Us - Product App



Message: Hello,
I would like to get your recommendation for sealant. Specifically, I am sealing a manual transmission case that will be used with ATF fluid. I don't care about the convenience of a fast drying time because it will be at least several weeks from the time I put the transmission together until I install it into the car and add fluid. Most important to me is long-term seal without leaks.

Thanks.


Haines, Curtis <Curtis.Haines@permatex.com>

to me, Answered
Boris,



Permatex recommends Ultra Grey (Item # 82194).

It should work very well for your listed application.





Thanks,



Curtis Haines

Technical Service Mgr./Associate Innovations Mgr.

10 Columbus Boulevard, 5th

Hartford, CT 06106

curtis.haines@permatex.com

Office (860) 543-7544





Boris to Curtis
Thanks, I'll go with that. I was just curious what are the pro/cons of using an anaerobic sealant instead? Some guys on the forums claim good results for sealing aluminum manual transmission cases with anaerobic sealants.





Haines, Curtis <Curtis.Haines@permatex.com>
Nov 29, 2017, 3:01 PM​

to me
Stick with the Grey for an excellent seal.





Thanks,



Curtis Haines

Technical Service Mgr./Associate Innovations Mgr.

10 Columbus Boulevard, 5th

Hartford, CT 06106

curtis.haines@permatex.com

Office (860) 543-7544
 
#38 ·
Hey technician117,
A few questions for you. First, I am curious how you pulled off the countershaft gear. What kind of press did you use and did you have to heat the gear to get it off? Also, were you able to put it back on? Lastly, what is the black material that is clearly destroyed in the '559 picture? Looks like some plastic retainer of some sort was shredded.
 
#39 ·
That trans was run without oil, melting anything made of plastic and turning what remaining oil there was into metal soup. I got it to use the rear case for another trans I got at the same time that had the rear case broken in shipping.

I haven't done much else with these since back then. Projects like that are far to low on the priority scale, especially with a couple companies (at least one) rebuilding them. Not worth my effort. I still have a decent amount of parts which is nice for future repairs to things that are more easily accomplished.
 
#42 ·
Dan's Diff's Online does them. Not sure who else does it "commercially". Re-reading this thread, I still have the same sentiment now: These are readily available enough on the used market for fair prices that unless you have a specific goal (racing application), it doesn't make sense to commission a rebuild. I suppose if someone is well off enough and they don't care about the cost versus having a "new" transmission, then this is definitely the way to go. AFAIR, BMW no longer sells new 420g's.
 
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