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Thread: tcu replaced, think transmission is shot

  1. #1
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    tcu replaced, think transmission is shot

    I just got this rs6 knowing I would have issues. I purchased it, at the sellers word, saying he had minor repairs completed to the front end and it was returned on a flatbed. He didn't want to mess with it so he sold it to me. TCU was confirmed completely dead. Installed a new one today. Read the measuring blocks and can see that there is no detection of movement into the trans. It reads 0 rpm. I put into gear and see no movement whatsoever but the idle changes when in any gear. So sounds like the ecu is reacting to the gear.

    I'm thinking the trans must be removed and then I'm left with a few options. 6 speed swap (most intensive and costly), swap with used trans and hope for the best with a new torque converter, part the car *cringe*. Next step, I suppose is to remove trans pan and check for metal chunks? Also, seems odd and a little unlikely that the tcu would be completely dead and the trans would both die simultaneously.

    Guess I'm just asking for thought or ideas. Anything else to look at before I start tearing everything down? Anyone with bad trans or dead TCU ever experienced similar issues? How much more difficult is it to remove the 4.2t compared to the 2.7t I've done?

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    Registered User RSoverAll's Avatar
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    Haven't had a trans issue myself... yet. But just off the top of my head. Have you checked the simple stuff? Axles? Torque convertor bolts?

    I dont think you will see any rpm in the trans measuring blocks until the vehicle is moving, don't quote me on that though.

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    How do I check tc bolts? Crawled under and can only see flywheel through a small hole. Don't see an access plate or cover for tc?

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    Registered User mik15's Avatar
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    the first thing would be to take the pan off and see if any metal chunks are present. What error codes do you have stored?
    I had a similar issue on a VW Phaeton, the car wouldn't move however some rpm variation would occur when put in D or R, but no movement at all, turned out the box was toasted.

    Also, what readings do you get when you put in D? or R? on the measuring blocks?

    TC bolts can't be checked with the gearbox on.
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    Input shaft snapped

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    Registered User RSoverAll's Avatar
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    Quote Originally Posted by DHall1 View Post
    Input shaft snapped
    I thought I read a thread with the same symptoms a few weeks ago, even had a nice pic of the sheared input shaft

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    Registered User MaxRS6's Avatar
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    Here is my snapped shaft. It would go into gear with a very large thunk. I had no codes or any prior issue on this transmission.


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    Ok. So next is to remove engine and trans. In the 2.7 found easiest to simply drop subframe with engine and trans attached then once dropped do all else that is needed. Would this be the same with the rs6? If so, I could remove front, disconnect everything from top like wire harness, etc, drop it down and roll it out. I would have access to remove trans from car then.

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    Quote Originally Posted by mik15 View Post
    the first thing would be to take the pan off and see if any metal chunks are present. What error codes do you have stored?
    I had a similar issue on a VW Phaeton, the car wouldn't move however some rpm variation would occur when put in D or R, but no movement at all, turned out the box was toasted.

    Also, what readings do you get when you put in D? or R? on the measuring blocks?

    TC bolts can't be checked with the gearbox on.
    Box meaning tcu? Just replaced it. Measuring blocks show no rpm from input or output. No codes either the ecu or tcu. Old tcu was completely dead. This one seems to read just fine.

  10. #10
    Registered User lswing's Avatar
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    You've yet to mention the adjustment/shift cable that goes to the trans...could this be disconnected?

    Also, last year Bigglez had a shutdown like this in the snow, turned out to be broken axle?

    I've had two gear boxes break on me, but sure it was the clutches both times. They still drove, just slipped and banged around, no codes.

    Rebuild TC when out also. Tozo can rebuild the lump upgraded with tc for around $4k...
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    Good luck here
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    My guess is that TCU was somehow fried intentionally to hide the real issue of snapped input shaft (or otherwise dead gearbox).
    EDIT: Yea, with RS6 you drop the whole powerplant.

  13. #13
    Registered User Bigglezworth's Avatar
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    First and foremost is to check the fluid. Ensure there is appropriate levels of fluid and that the fluid doesn't smell/look burnt. That's a starting point. Next, check for any broken axles (especially at the outer joints). Can visually look integral, but if you can turn the wheel and the end bolted to the differential doesn't turn - no worky. You've mentioned already addressing a TCU so that's out of the question. A broken drum or bad clutches will cause no movement, but you indicated the car drove in for repairs and now doesn't work? Also check something obvious like the shifter cable being connected to the PRNDL unit.

    I'm suspecious of the front end damage you eluded to on AZ and how that might be somehow related. Input shaft snapping has occurred, but is extremely rare. You can't check TQ bolts without having the starter removed. You can't easily remove the starter without dropping the entire powerplant. Unlike a 2.7, you cannot (with any sanity anyway), disconnect the tranny from the engine without having the cradle significantly lowered. The passenger turbo conceals easy access to two bolts coupling the tranny to the engine. It 'has' been accomplished, but for all the headaches, banged up hands, difficulty with the best of tools, etc., it's recommended to take the hulk out and address. Again, start with checking the fluid.

    Also guessing that because you didn't test drive the car that you got it for 'cheap' which means the problem merely moved on to the next owner. Pay now or pay later... Nothing comes for free. Best of success with your hunt.
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    Quote Originally Posted by Bigglezworth View Post
    First and foremost is to check the fluid. Ensure there is appropriate levels of fluid and that the fluid doesn't smell/look burnt. That's a starting point. Next, check for any broken axles (especially at the outer joints). Can visually look integral, but if you can turn the wheel and the end bolted to the differential doesn't turn - no worky. You've mentioned already addressing a TCU so that's out of the question. A broken drum or bad clutches will cause no movement, but you indicated the car drove in for repairs and now doesn't work? Also check something obvious like the shifter cable being connected to the PRNDL unit.

    I'm suspecious of the front end damage you eluded to on AZ and how that might be somehow related. Input shaft snapping has occurred, but is extremely rare. You can't check TQ bolts without having the starter removed. You can't easily remove the starter without dropping the entire powerplant. Unlike a 2.7, you cannot (with any sanity anyway), disconnect the tranny from the engine without having the cradle significantly lowered. The passenger turbo conceals easy access to two bolts coupling the tranny to the engine. It 'has' been accomplished, but for all the headaches, banged up hands, difficulty with the best of tools, etc., it's recommended to take the hulk out and address. Again, start with checking the fluid.

    Also guessing that because you didn't test drive the car that you got it for 'cheap' which means the problem merely moved on to the next owner. Pay now or pay later... Nothing comes for free. Best of success with your hunt.
    checked axles and movement right when I first got it home. Seems to be fine there. Checked the fluid also and that was fine. Just drained tonight and see no metal in fluid. Even ran my own magnet through the fluid after I got it in my pan and found no shavings or chunks. I will remove the valve body next after it stops dripping and see if anything strikes me as improper. Is there a way to see, without moving engine or trans, if the torque converter is actually hooked up? I just want to make sure something wasn't undone by the shop he had it into in "their" mechanical attempts to resolve a dead tcu. The body shop he took it to had to be unaware of the defective tcu because the owner ( after he got it back from the body shop on a flatbed) took it to an actual audi dealer and the dealers diagnosis was "defective tcu, replacement $1800". The owner said, at that point, "screw it, I'm buying a different car". I saw the invoice from the dealer as well. There was no other repair quote on that bill.

    I only know what the pervious owner stated. He SAID he drove it for minor body work and it was returned to him on a flatbed. Other than that who knows how much if that is accurate. My only issue with this whole thing is how likely would it be to have a completely dead tcu (which I am sure of because it was tested by a very reliable source) and for there to be catastrophic mechanical failure at the exact same time? Seems like the two issues are in a completely different ballpark.

    Although I do not know where to check it exactly, the shifter must be hooked up because I can see it change through P,N,R, and 1 in tip through group 1 on measuring blocks of tcu.

    Yes, got it "relatively" cheap for an rs and expected the worst hoped simple tcu swap was the issue. Still questioning two issues of mechanical failure and dead tcu and same time (as far as I can tell).

  15. #15
    Registered User ben916's Avatar
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    also, can you get under there and check if the gear lever is actually connected to the transmission?
    Just because the gear lever is moving and electronically "switching gears" and fuel trims to the ECU, doesn't mean it is actually moving the levers to engage a gear.

    Also, how are you moving it? If it is "P"ark, the car shouldn't move at all...
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    I can crawl under there and look. If I'm under and pulling trans pan, I should be able to get at this shifter connection? Also, vcds shows 0 rpm input and output. Isn't this relevant? When in gear, or otherwise, shouldn't the input rpm be showing something other than 0? Group 1 in trans shows engine rpm 832, input rpm 0, output rpm 0, and trans gear 1m. Car on all four stands wheels off ground, rev engine, 0 movement.

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    Someone correct me if I'm wrong, and I can't check personally since I've pulled my auto box out to make room for an 01E, but isn't the input speed POST torque-converter, and thus would be 0 unless the output shaft is also turning? Or I suppose there could be a disconnect inside, i.e. transmission in neutral.. But either way if the input speed is 0 even in neutral with the engine running, it's got to be a bad sensor or else the torque converter isn't spinning the input shaft.

    Assuming the sensor reading is accurate, it sounds like a disconnect between the engine and the transmission.. Or am I missing something here?
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    Quote Originally Posted by P1054 View Post
    Someone correct me if I'm wrong, and I can't check personally since I've pulled my auto box out to make room for an 01E, but isn't the input speed POST torque-converter, and thus would be 0 unless the output shaft is also turning? Or I suppose there could be a disconnect inside, i.e. transmission in neutral.. But either way if the input speed is 0 even in neutral with the engine running, it's got to be a bad sensor or else the torque converter isn't spinning the input shaft.

    Assuming the sensor reading is accurate, it sounds like a disconnect between the engine and the transmission.. Or am I missing something here?
    Yes. Exactly. Would be nice if someone could expand on this. -EDIT- not necessarily expand but confirm or deny what these readings mean exactly.

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