"Klunk" when shifting to R

Transmissions and Rear Ends

  1. Toro67

    Toro67 Well-Known Member

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    Hi guys

    My 79 Lebaron runs and shifts just fine when going forward, but when shifting into R the is a rather loud "Klunk" or sometimes a metallic "Klang" like the shift happens with too much force or something. Reversing works fine once the shift has been made.
    From what I can read in this transmission forum I have a 904 or a 998. (I know it has lock-up)
    The car has done 51K miles. Could it be something is worn in the rear diff or does the Reverse function need adjusting ?
     
  2. Dr Lebaron

    Dr Lebaron Well-Known Member

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    Worn U joint.

    Bet you can Google it and say Bingo.
     
  3. Toro67

    Toro67 Well-Known Member

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    Well my car has 1 of the 4 most common symptoms of a worn U-joint, so I guess that could be it.
    However, there are no vibrations, no leaks and no squeeking sounds when driving.
     
  4. Oldiron440

    Oldiron440 Well-Known Member

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    I had a 727 that went into reverse hard even after a rebuild but I'd say ujiont.
     
  5. volare 77

    volare 77 Well-Known Member

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    What rear is it? Sounds like it could be the backlash.
     
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  6. Poly

    Poly Well-Known Member

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    Are the rubber seals dry rotted on your u-joints ? You wanna keep the water and dirt out as much as possible.
     
  7. Toro67

    Toro67 Well-Known Member

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    I was under the car yesterday, put it in N and tried to provoke a noise from the joint by turning the propshaft back and forth. However I could not see any play in the joint or hear any metallic noises. I have ordered new U-joints all the same.
    One thing puzzles me though: If the U-joint is worn, why do I only hear the noise when putting it in R and not also in D ?
    I read once in a transmission thread here that when putting it in R, the hydraulics divert a lot of force towards the rear diff, and if this force is excessive due to misadjustment, it could break the the diff eventually. Anyone heard of this ?
     
  8. Toro67

    Toro67 Well-Known Member

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    What is the Backlash ? English is not my native language :)
     
  9. Dr Lebaron

    Dr Lebaron Well-Known Member

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    Mopars always goes clunk in reverse.
    Wish I was more video savvy and let you listen to all the clunks from other Mopars.

    Two Mopar transmission tips that work very well for me.
    Back the the car in to avoid the every day reversing with a cold transmission.
    Put it in N for a bit before shifting and driving away.
    The transmission pump doesn't run in P.
     
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  10. AJ/FormS

    AJ/FormS Well-Known Member

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    IMO
    this is side-gear to pinion backlash, very common in open diffs. All the engine power is transmitted to the crosspin, and from there to the spiders then to the sidegears and out the axles.As the parts accumulate mileage the backlash becomes excessive between those guys. Peg-legging it, or running two different rear tires, or major differences in air pressure, accelerates the wear.

    A temporary solution I have used is to install extra washers either on the pinions or behind the side-gears. This takes the clunk out of it.
    But in a lot of cases there is also wear on the cross-pin and in the pinion bores. And finally, many cases are beat up by the cross-pin and the saddles become "wallered out". These are ticking time-bombs; the pin could be ejected at any time. But they don't usually come completely out, but instead get jammed up in there and lock up the rear wheels, usually while the car is moving and being abused, and with unpredictable results.
    So I suppose the prudent thing to do is to remove the cover and inspect the parts.
    And yes, backlash here will clunk,thunk, and clang, totally unlike U-joints. If you back up the car just a few inches and lock the brakes, then shift into manual low, it will clang too, as the torque coming into the case slams the spiders all the way to the bottom and then back up to the top. The shock travels back up the driveshaft, and to me it has always sounded like the sunshell gets a smack and rings like a bell. But I suppose the clang could be in the driveshaft, but IMO the pitch is wrong.
     
    Last edited: Jul 22, 2018
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  11. Toro67

    Toro67 Well-Known Member

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    Hmm I have no idea what that means, but it sounds like the problem is in the diff ? If that is the problem, is it easy to fix ?
     
  12. AJ/FormS

    AJ/FormS Well-Known Member

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    Yes inside the diff; the sidegears are splined to the axles and the pinions ride between them, on the cross-pin. I would put a drainpan under the cover and pop it off for a look-see
     
  13. volare 77

    volare 77 Well-Known Member

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    You didn`t say what rear is in the car but if it is a 7 1/4 rear they are fairly weak when compared to the other rears mopar used. If they are driven hard it will do them in kinda fast. They seem to last ok behind slant six cars. Burnouts around corners seems to tear up the pinions and side gears. I agree take off the cover and take a look. Post some pics if you like. If it is not your problem then it probably could have used a fluid change anyhow.
     
    Last edited: Jul 22, 2018
  14. Justwondering

    Justwondering Well-Known Member

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    Toro67

    Clangs, klunks, swooshes, etc.
    Wouldn't it be nice if we had a library of sounds so we would know that my klunk sound is what you would say is a clunk?
    lol
    My brain is in a weird place today.

    JW
     
  15. Oldiron440

    Oldiron440 Well-Known Member

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    Maybe it's a junk in the trunk klunk!
     
  16. AJ/FormS

    AJ/FormS Well-Known Member

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    junk in the trunk don't clunk,...... nor klunk,klonk, klink,or klank;
    it wiggles and jiggles,and generally just drives men wild. Well not me,I'm more mature than that,lol
     
  17. Oldiron440

    Oldiron440 Well-Known Member

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    I've got a 8.8 LS in a bucket that goes klunk once in a while in the back of my Expedition.
     
  18. Toro67

    Toro67 Well-Known Member

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    I actually had the cover off in February when I changed the fluid. Took a picture of it to determine whether it had LS diff or not (so I would get the right oil).
    Don´t know if it´s the 7 1/4, but Im sure you guys can tell from the picture.
    I dont think the car has been driven hard at any point in its life. A 2-bbl carb and a lean-burn system will keep that in check .. Many people here in Denmark soup up their engines just to be able to do longer burnouts - not me though.

    IMG_3547.JPG
     
  19. volare 77

    volare 77 Well-Known Member

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    8 1/4 with a suregrip
     
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  20. AJ/FormS

    AJ/FormS Well-Known Member

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    And that almost rules out side-gear to spider backlash, leaving the cross-pin as the likely culprit
    Unless the wheel lugnuts are loose,lol.
    Or the idle speed is excessive.
     
    Last edited: Jul 27, 2018