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Thread: Getrag 420g Problems

  1. #1
    Join Date
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    Getrag 420g Problems

    Hello all,

    I am having have issues with two 420g transmissions that I own:

    (Transmission #1) Last May, I purchased a 2000 M5 (93k miles), knowing there was a problem with its Getrag 420g transmission. When the car is either on or off, shifting the transmission both into and out of both 5th and 6th gear is very difficult. I can maneuver in and out of all other gears normally. I own a 540i 6M, so I can safely say the problem is definitely not the “notchiness” accompanying the 420g, or that a fluid change is needed (I put RP in box shortly after purchase). It takes, like, 7.5 out of 10 (scale of 1-10, 1 being minimal effort and 10 being as much force a normal-sized adult male can physically muster) in terms of the sheer force/effort required to get the car into and out of the two gears. There isn’t any grinding, so I don’t believe it’s a synchro issue. I have put ~600 miles on the car and the problem has not worsened, though.

    In researching and reading through several threads on problems with the 420g, I understand that the spring/arrester ball combo(s)(see #17 here: (http://www.realoem.com/bmw/enUS/show...diagId=23_1411) on the top of the rear, passenger side of the box can malfunction (i.e. spring breaks into pieces and jam something) and make it difficult or impossible to shift gears. Would the spring breaking and jamming in the detent notches on the 5-6 shift rail be indicative of the problem I am experiencing? Can anyone describe what their experience with a broken arrester ball spring was/felt like?

    Also, would malfunctioning of either #8,9,10 or #14,15,16 cause this problem? I understand how the spring mechanisms of #17 work, but I am a transmission noob and not sure how, exactly, parts 8,9,10 and 14,15,16 work and what purpose they actually serve. I know that they do not control the resistance when moving across from resting neutral towards Reverse or towards 5 & 6; that is not a problem with my box, as the resistances for these cross-movements are normal.

    I will also add that there is a lot of “slop” in the shifter linkage, and linkage definitely needs to be rebuilt, but the sheer force involved makes me think it is not a linkage issue, unless something is really bent, misaligned, etc., which a quick inspection while underneath the car did not reveal.

    (Transmission #2) Anticipating that the M5 box might be beyond repair without a teardown & rebuild (~$5k) at one of the, what, TWO shops in the U.S. that can do this, I purchased a used 420g from a ’98 540i (timing chain guides broke) w/120K miles. Here’s the thing: with the trans on my workbench, I can put a screwdriver through the hole in #7 (see: http://www.realoem.com/bmw/enUS/show...diagId=25_0009 ) and pull the selector shaft in and out, but I cannot rotate from, say, 10 to 2 if looking at a clock, so as to move over and catch the 5&6 rail or the 1&2 rail. I also tried gripping pliers on the rod joint,but this did not work to rotate the selector shaft. Fiddling around and not knowing any better, I attempted to open the sealing cap covering the detent/ball combo (part 17 in first realoem link above). I loosened each bolt of the cap a little at a time, but as I was loosening the one bolt I could see the spring closest to the passenger side looked like it was pushing on the cap (from spring pressure) and would shoot out if I proceed to completely remove the cap. Having read horror stories about locking things up on this trans if a pin misaligns or, or bearing ball falls out, etc., I stopped, tightened everything back up and went to research a little more. Apparently, per TIS, the trans has to be in first gear while attempting to play around with the spring/ball combo, or you will lock things up? I did not know this and had no idea what gear the trans was in at the time I tried to pull off the sealing cap. Uh-oh.

    Is it possible to have damaged anything (i.e. misaligned something, allowed something to move out of place, etc.) by attempting to pull the cap? Do you think the rod joint would rotate if I hooked up linkage and tested (while on trans on workbench)? Could the fact that the trans fluid leaking out while I was transporting the trans home from the seller have anything to do with it?

  2. #2
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    The repair kit was originally intended to fix the problem of being unable to shift out of 3rd. It may also fix your problem.

    Be sure to shift into 1st gear before removing the cover.

    You may be in deep doo-doo.
    Last edited by edjack; 01-18-2019 at 07:27 PM.


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  3. #3
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    Quote Originally Posted by edjack View Post
    The repair kit was originally intended to fix the problem of being unable to shift out of 3rd. It may also fix your problem.

    Be sure to shift into 1st gear before removing the cover.

    You may be in deep doo-doo.
    The more I think about it, I don't think semi-opening the cap retaining the spring/ball combos caused any further problems, given that the spring pressure was never fully relieved and, so, theoretically, the metal ball stayed in the rail detent and nothing really moved/misaligned??? Also, TIS implies that if the repair is performed incorrectly (i.e. not putting into 1st gear beforehand), the cap would not fit back on. This is not the case with mine, as it fits without issue. Trying to source a shift carrier to set up linkage on tranny; already have a UUC SSK and DSSR, so all I need is the carrier to test.

    I will be super pissed if Trans#2 is locked up! $400 was a decent price, IMO, and the seller was local.

  4. #4
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    Bump for more input, especially on transmission #1.

  5. #5
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    Manual transmissions are fairly simple, why not just crack open your original trans, find whats wrong, and fix it?

  6. #6
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    Quote Originally Posted by MotorMouth93 View Post
    Manual transmissions are fairly simple, why not just crack open your original trans, find whats wrong, and fix it?
    From what I understand the 420g is not simple to even open up the casings, let alone service/disassemble it. I have read through the two or three primary disassembly/repair threads over on M5Board.com and would not be comfortable, given my lack of experience with transmissions- and I am by no means afraid of undertaking more involved repairs on my e39s.

    I guess my next move should be to post over there. Was just seeing if anyone had an experience(s) similar to either of the two I am currently having .

  7. #7
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    Everything you either wanted or didn't want to know about taking apart the 420g:

    https://www.m5board.com/vbulletin/e3...-assembly.html

    Enjoy.

    -Paul
    2003 "M5" - Full M5 conversion, AMG C63S 6 piston front calipers, Porsche Panamera 4 piston rear calipers, GC Coilovers,
    Eibach ARBs, UUC Evo3/DSSR, Borla Exhaust w/Muffler Delete, BMW NBT with Carplay/Android Auto, Bi-Xenons, e38 Style 37 M-Pars, e60 Hubs 530i 6-speed swap build thread
    2005 Range Rover 4.6is (M62TU Powered) - 4.6is Engine Swap from X5, BMW NBT with Carplay/Android Auto
    2006 Porsche Cayman S - Soul Performance Competition Headers and Exhaust, H&R Coilovers, 718 Boxster Spyder wheels, Rennline 35mm rear spacers

  8. #8
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    Quote Originally Posted by blackknight530i View Post
    Everything you either wanted or didn't want to know about taking apart the 420g:

    https://www.m5board.com/vbulletin/e3...-assembly.html

    Enjoy.
    Quote Originally Posted by MotorMouth93 View Post
    Manual transmissions are fairly simple, why not just crack open your original trans, find whats wrong, and fix it?
    I for one want to know more. These trans are certainly not simple.
    I was fortunate to get a good working unit (until the supercharged s62 did a burnout) to take apart.
    My hope was to harvest 3rd gear synchro out of it.
    To get to this point, I used the YouTube video showing how to get the case apart, then every puller that I had. Needed a 10ton 12" 3jaw to get the one pressed gear off the main shaft.
    I have searched the internet and gone to transmission shops hoping to find any info on rebuilding one. I can't even find a chart that shows parts, gear position, or of which gear is which in the gear path.
    The synchros have more parts that most manuals, with spring loaded ball dedents on the shoes and just parts everywhere.
    Opening up a 420 past case removal could lead to it never going back together. ( In my opinion, and I'll try anything)
    I'm still looking for more info on assembly, or another bad one to experiment on. 20190121_120506.jpg

  9. #9
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    Ah gotcha, that's definitely nastier than the manual transmissions I've rebuilt in the past. Should be an interesting project if mine ever fails.

    Edit: Okay after more reading the 420G seems to be much worse than expected. I take back my initial statement of "itz eazy to rebuild11!1."
    Last edited by MotorMouth93; 01-22-2019 at 12:03 PM.

  10. #10
    geargrinder's Avatar
    geargrinder is offline Having No Trouble Here BMW CCA Member
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    Quote Originally Posted by wagons ho View Post
    Needed a 10ton 12" 3jaw to get the one pressed gear off the main shaft.
    ...<snip>...
    Opening up a 420 past case removal could lead to it never going back together. ( In my opinion, and I'll try anything)
    ^^^^ DIS RIGHT HERE ^^^^

    Ho'man hits on the issues really:
    1. Critical gears are interference press-fit onto their shafts
    2. Getting them on/off requires serious presses. Above and beyond what many tranny shops have. Not to mention the tooling & jigs to press safely.
    3. There's no charts or parts lists published

    ...I've also been told...
    4. Proper disassembly/re-assembly requires special jigs (above and beyond the pressing issue), although thats one item I suspect is a little over blown and could be figured out given a well equipped shop and a careful mindset.

    ...and then of course... worst of all..
    5. There's no parts sold, period. You can only buy rebuilds via BMW who gets them from Getrag.

    There are shops that can rebuild them but its practically a state secret to try to find out who and where. I have spoken to one of them and he gave me the info above but that was only after I worked my way through a bunch of contacts at the same rebuilder (aka "oh you gotta talk to Don he's the only one who knows the deal with those"). That shop, (any shop really) has to rely on harvesting parts out of other used dead boxes even if they do rebuild them.

    If there was a big enough market clearly you could take critical parts and have them manufactured, but E39 540/M5 and E46 M3's aren't enough critical mass it seems.
    2003 M3CicM6 TiAg
    2002 540iT Sport Vortech S/C 6MT LSD TiAg
    2008 Audi A3 2.0T DSG (the daily beater)
    2014 BMW X1 xDrive28i (wifemobile)

    Former:

    1985 MB Euro graymarket 300SL
    1995.5 Audi S6 Avant (utility/winter billetturbobattlewagen)


  11. #11
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    Quote Originally Posted by MattyL View Post
    (Transmission #1) Last May, I purchased a 2000 M5 (93k miles), knowing there was a problem with its Getrag 420g transmission. When the car is either on or off, shifting the transmission both into and out of both 5th and 6th gear is very difficult. I can maneuver in and out of all other gears normally. I own a 540i 6M, so I can safely say the problem is definitely not the “notchiness” accompanying the 420g, or that a fluid change is needed (I put RP in box shortly after purchase). It takes, like, 7.5 out of 10 (scale of 1-10, 1 being minimal effort and 10 being as much force a normal-sized adult male can physically muster) in terms of the sheer force/effort required to get the car into and out of the two gears. There isn’t any grinding, so I don’t believe it’s a synchro issue. I have put ~600 miles on the car and the problem has not worsened, though.

    In researching and reading through several threads on problems with the 420g, I understand that the spring/arrester ball combo(s)(see #17 here: (http://www.realoem.com/bmw/enUS/show...diagId=23_1411) on the top of the rear, passenger side of the box can malfunction (i.e. spring breaks into pieces and jam something) and make it difficult or impossible to shift gears. Would the spring breaking and jamming in the detent notches on the 5-6 shift rail be indicative of the problem I am experiencing? Can anyone describe what their experience with a broken arrester ball spring was/felt like?

    Also, would malfunctioning of either #8,9,10 or #14,15,16 cause this problem? I understand how the spring mechanisms of #17 work, but I am a transmission noob and not sure how, exactly, parts 8,9,10 and 14,15,16 work and what purpose they actually serve. I know that they do not control the resistance when moving across from resting neutral towards Reverse or towards 5 & 6; that is not a problem with my box, as the resistances for these cross-movements are normal.

    I will also add that there is a lot of “slop” in the shifter linkage, and linkage definitely needs to be rebuilt, but the sheer force involved makes me think it is not a linkage issue, unless something is really bent, misaligned, etc., which a quick inspection while underneath the car did not reveal.
    Did you ever get to the bottom of the problems with transmission #1?
    I've recently purchased an M62B44 converted E30 that has the M5 420g box and like yours 5 & 6 are near enough impossible to use, 1-4 inc rev aren't an issue at all.

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