GM 5 speed into 504
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  1. #1
    Fellow Frogger!
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    GM 5 speed into 504

    Hi all,

    Following on from my previous thread, does anyone know if the GM 5 speed that mates to the 3.8 V6 fits into the 504 tranny tunnel witout a hack and chop job?

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    Torque tube, this is just a driveshaft, right?

    Chipper

  2. #2
    Guru davemcbean's Avatar
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    Chipper,

    A torque tube is not just a driveshaft, but a driveshaft enclosed within a housing which acts as a suspension arm (usually the only suspension arm) on a live rear axle car.

    The 504 sedan doesn't actually have a torque tube (although alot of people call it that) because the tailshaft housing does not act as a suspension arm (because it has IRS), it only houses the tailshaft, and joins the diff to the gearbox as one rigid unit. So it actually shares more in common with a Porsche 924/944/968/928 tailshaft than it does with the torque tube fitted to 404s and 504/505 wagons, etc.

    I actually came across a mechanic once who had never seen a torque tube suspension system before (didn't say much for the textbooks he had at TAFE). Almost every car made before the second world war had torque tube rear suspension, because it is simple, and also easy to fine tune, to get the car to handle nicely (they explain why in race car dynamics textbooks).

    Anyway, to join a Commodore gearbox to the 504 tailshaft housing, you will probably have to have a flange welded to the extension housing of the gearbox. I don't think this is too difficult. You will also have to have a commodore tailshaft spline welded to the front of a shortened 504 tailshaft and you will also have to shorten the tailshaft housing (most likely). As I have had this shortening done before, I know it costs around $300 (not including tailshaft balancing).

    I think the commodore gearbox should fit in the transmission tunnel of a manual 504. I'm sure it will fit in the transmission tunnel of an automatic 504.

    Dave
    NZ Fleet
    1976 504 Ti
    1984 205 GT twin carb
    1991 205 SI 1.6GTI motor
    1994 106 Xsi
    1996 Mondeo V6
    Aus Fleet
    1955 203C
    1997 Civic Cxi (great allrounder- revy, flexible, nimble, comfortable , economical, simple and durable )

  3. #3
    Gone Fishin' Ray Bell's Avatar
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    It's the bellhousing section that is so tight on the 504, hence the auto bellhousing has to have extra clearance otherwise the torque converter just wouldn't fit... But I think the Commodore bellhousing might be bigger again. Just imagining it to be more like the size of a bellhousing for a V8 or a Ford 6.

  4. #4
    Fellow Frogger!
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    Thanks guys for your replies.

    Chip

  5. #5
    Fellow Frogger! Ralph's Avatar
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    <font face="Verdana, Arial" size="2">Originally posted by davemcbean:
    Chipper,

    A torque tube is not just a driveshaft, but a driveshaft enclosed within a housing which acts as a suspension arm (usually the only suspension arm) on a live rear axle car.

    The 504 sedan doesn't actually have a torque tube (although alot of people call it that) because the tailshaft housing does not act as a suspension arm (because it has IRS), it only houses the tailshaft, and joins the diff to the gearbox as one rigid unit. So it actually shares more in common with a Porsche 924/944/968/928 tailshaft than it does with the torque tube fitted to 404s and 504/505 wagons, etc.

    I actually came across a mechanic once who had never seen a torque tube suspension system before (didn't say much for the textbooks he had at TAFE). Almost every car made before the second world war had torque tube rear suspension, because it is simple, and also easy to fine tune, to get the car to handle nicely (they explain why in race car dynamics textbooks).

    Anyway, to join a Commodore gearbox to the 504 tailshaft housing, you will probably have to have a flange welded to the extension housing of the gearbox. I don't think this is too difficult. You will also have to have a commodore tailshaft spline welded to the front of a shortened 504 tailshaft and you will also have to shorten the tailshaft housing (most likely). As I have had this shortening done before, I know it costs around $300 (not including tailshaft balancing).

    I think the commodore gearbox should fit in the transmission tunnel of a manual 504. I'm sure it will fit in the transmission tunnel of an automatic 504.

    Dave
    I'm curious!

    Why connect the diff to the gearbox with a rigid outer tube when they are both bolted to the floorpan as is done in Peugeots with IRS? Surely this would negate any effects due to torque.

    What is the correct terminology for this setup and what are the benefits?

    Is this a misnomer similar to referring to shock absorbers when they are actually (oscillation) dampers?
    On the internet, no one knows that you are only wearing a fez.

  6. #6
    Gone Fishin' Ray Bell's Avatar
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    We are speaking here of an IRS car, I'm sure. And there are a number of things that would have to be done to overcome any change to a normal tail shaft.

    First, the differential will have to be more solidly mounted, as the torque reaction of the turning motion of the final drive is normally cancelled out by the torque reaction of the motor, this cancelling being done by the 'link tube' as I'm told it's called. Without this the differential mounts will tear out. Experience has shown this. And that was with a torque tube bolted to the diff to take the torque in the normal direction... ie the twist on the axis of the axle... the diff in this case twisted itself on the axis of the tail shaft and tore its mountings out.

    Next, the steps involved, engineering steps, will be more numerous and expensive than modifying the box and shaft to suit the arrangement. You would need to make a protective cover over the nose of the diff, and mount a flange on it for a tail shaft. A similar thing would have to happen, though it would be simpler, at the gearbox end. Then a tail shaft would be required to be fabricated, and it would need a sliding joint. And the back of the gearbox would need to be supported, so a mount would have to be fabricated and the floor modified (though only slightly) for it to be secured.

    See the extent of things?

    I think in this I have at least partly explained the benefits of the system. There are fewer mounts to the chassis (it's not really mounted to the floorpan at all!), the mounts are lighter because they do less, the mechanicals are protected from the elements to a greater degree and, in addition to this, the size of the lump that's rubber-insulated from the body is greater, so the insulation from the noise and vibration is better. That's a mass thing, I recall reading somewhere.

    [This message has been edited by Ray Bell (edited 03 August 2001).]

  7. #7
    Guru davemcbean's Avatar
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    Ralph,

    As Ray said, the correct name is "link tube", although few people refer to it that way.

    I think it is safer than having an exposed drive shaft which can break a universal joint and do crazy things under your car as you're moving along.

    The big disadvantage of the "link tube" system is that the splines on the tailshaft have a greater tendency to wear away, which leads to drive train lash and eventually loss of drive. To avoid this molybdenum grease should be used on the splines, but it's still difficult to find a 504/505 that doesn't have atleast some tailshaft spline lash.

    I met one fellow who had a 504 which had no lash in the drivetrain. When the car reached about 22 years of age the splines eventually wore enough that there was a very slight amount of tailshaft lash, but it was still better than any other 504 I had ever driven. He thought it was terrible though, because he was so used to it being nice and tight. I don't think he was too happy when I told him it would be next to impossible to make it any better than it was. He had been wondering why no mechanics could feel anything wrong with the car. This was because they (like myself) had never ever driven a 504 without some drivetrain lash. I've noticed that this lash can be disconcerting to people who've never experienced it before. People who only ever drive FWD cars seem to notice it the most.

    In 26 years of family driving 504s, we have had 2 tailshaft splines completely strip. I know now, when they a getting near the point of stripping, so I can change them. It's apretty easy job. Just undo one rea driveshaft, remove the diff, slide the old tailshaft out, slide the new one in, and put everything back together. 504 automatics are generally easier on their splines, due to the smoother drive. I have a couple of spare second hand ones of these. Sometimes the auto ones do strip, but it only happens when they leak transmission fluid into the link tube, which washes the grease off the splines. In that case it will usually be the rear spline that wears away, whereas manual cars usually wear the front spline away.

    I bought a 505 a couple of years ago which had heaps of tailshaft lash. When we got the car home and pulled the tailshaft out, it only had the faintest hint of a front spline left. I think we were lucky to get it home without it stripping.

    Sometimes the splines chew out due to the link tube flanges coming loose and the drivetrain sagging, putting a large uneven load on the splines.

    New tailshafts are available, but I'm not sure of the cost.

    Dave
    NZ Fleet
    1976 504 Ti
    1984 205 GT twin carb
    1991 205 SI 1.6GTI motor
    1994 106 Xsi
    1996 Mondeo V6
    Aus Fleet
    1955 203C
    1997 Civic Cxi (great allrounder- revy, flexible, nimble, comfortable , economical, simple and durable )

  8. #8
    Guru davemcbean's Avatar
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    I know somebody who's interested in this thread, so I'm just boosting it to the top again.
    Dave
    NZ Fleet
    1976 504 Ti
    1984 205 GT twin carb
    1991 205 SI 1.6GTI motor
    1994 106 Xsi
    1996 Mondeo V6
    Aus Fleet
    1955 203C
    1997 Civic Cxi (great allrounder- revy, flexible, nimble, comfortable , economical, simple and durable )

  9. #9
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    This is a bit late, but what the hell...

    To answer a question from above--the IRS sedan's torque tube is also a necessary structural member because there is no separate trans mount. In other words, the trans is suspended via the engine and the torque tube. It also helps in serious crashes as it fortifies the passenger area of the car.

    -Joe

  10. #10
    Gone Fishin' Ray Bell's Avatar
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    Yes, a small point that could be overlooked... but only till the back of the head banged on the firewall the first time!

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