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  1. #1

    Default Why does driveshaft orientation matter?

    I've read a lot of posts talking about marking the driveshaft and rear end so it's re-installed in exactly the same way.

    I'm about to install a new rear end and so wondered, will it be out of balance since I am obviously starting fresh?

    Why is it important? What do people do when they install new rear ends or driveshafts?

    Thanks.

  2. #2
    FEP Power Member
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    The factory had a method for balancing and installing the driveshaft to be in balance with the rear end. Simply match up the yellow paint marks. It may be ok if installed 180 degrees out, just depends on the tolerances that day. Have a problem? Just rotate it.

    FYI just about all new tires are marked for out of round and balance. Notice the red dot and yellow dot/circle on the sidewall? Align the yellow dot (light side) with the valve stem hole when installing tires on the rim. The red dot is for out of round (high spot ) and it is also aligned with the valve stem. It takes priority over the yellow.
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    FEP Super Member gr79's Avatar
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    Most, me included, bolt and go. OEM marks long gone.
    Visually rechecking the 4 bolts back there every now and then.

    Flywheel is balanced never seeing the engine.
    One piece driveshaft is balanced independent of axle.
    Ds never sees the axle it will mate to until installed.
    Handled properly, stays balanced during an axle swap.

    Shop manual mentions scribe marks on ds and axle flange but does not elaborate.
    Maybe due to axle companion flanges having multiple holes.

    Ford Racing makes no mention of indexing their new aluminum driveshafts.
    Or rear axles.
    Only Loctite on the 4 bolts.
    Last edited by gr79; 06-15-2018 at 02:19 PM.

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    FEP Power Member Ourobos's Avatar
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    ^ except a flywheel can only bolt on one way due to the counter balances of the crank and dampener for that matter..

    On the driveshaft, it is odd that a balanced piece would need to be bolted on in one orientation, but I have seen it make a world of difference.
    1986 CHP SSP Coupe

  5. #5

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    Ha, with the amount of rust on everything below, I would guess any line-up marks were gone sometime in the Reagan administration.

    Thanks for the info everybody! Sounds like I should just hook up to the new rear end and rotate if I feel vibrations.

  6. #6
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    Quote Originally Posted by gr79 View Post
    Most, me included, bolt and go. OEM marks long gone.

    Ford Racing makes no mention of indexing their new aluminum driveshafts.
    Only Loctite on the 4 bolts.
    Maybe, but there is a yellow paint mark on the Ford Racing driveshaft.
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  7. #7

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    I still have a hard time with this. Maybe I've just been super lucky, but I've blown ujoints and chucked driveshaft after it beat the crap out of the tunnel. Every time I've either swapped the whole driveshaft or just replaced the u-joint. No problems either way.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  8. #8
    FEP Senior Member BMW Rider's Avatar
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    The orientation of the driveshaft to the flange on the differential would have no effect on balance. The driveshaft is balanced as a unit on its own prior to installation.

    The only issue with driveshaft orientation is with three piece drive shafts where there is a slip yoke in the middle. The u-joints must be in phase to cancel out the oscillations. If you were cutting and re-welding your driveshaft to shorten or lengthen it, you would also need to pay attention to phasing the u-joints for the same reason.

  9. #9
    FEP Power Member Ourobos's Avatar
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    ^ In theory, sure.. But having used over 100 different stock driveshafts over the years, it CAN matter with a bone stock piece that is fully intact.
    1986 CHP SSP Coupe

  10. #10
    FEP Super Member erratic50's Avatar
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    the other thing is you can have varied amounts of corrosion buildup on the flange on the pinion. If you put the driveshaft on with holes that have never been used before you can get rust and grease and grime between the driveshaft and the flange on the pinion.

    I had a bolt hole get funny on the pinion flange on my original 1986 GT rear diff. some dip at the Ford dealer in Norfolk NE had replaced the clutch and transmission on my 1986GT but when they did they used locktight and cranked every bolt down as tight as they could with an impact.

    I went through 5 12 point 12 mm sockets of various brands, a breaker bar and a 1/2" ratchet on a 3' cheater bar.

    I was finally able to get them broke loose with my 3/8 drive SK ratchet with the cheater bar with a craftsman socket and a touch of heat. the threads looked quite worse for wear so I picked a different hold on the pinion flange when I put it back together. I didn't scrape it down with a razor blade and it was a bit messy -- it ended up vibrating like hell if I was going 65 or faster.

    I took the driveshaft back off and cleaned everything up good with a wire brush and razor blades, etc. put it back. All was well from there. No vibration at any speed. And I tried really hard a few times before that rear diff gave up the ghost and had a bearing fail.....

  11. #11

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    James touches on it there. The rust. The same can be said for doing your brake (not break... man that irritates me)job. We've all seen the rust on a hub when you pull a rotor. Especially when there are holes on the hub. That extra thickness of rust can add run out to the brake system unless put back the same or completely cleaned off. The drive shaft is balanced long before it meets the car. But the rust could cause a vibration the same as your rotors. My .02

  12. #12

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    Not read the first response so this may have already been said. It matters for sure without a doubt. I had a Ranger that I put a new driveshaft in because the OEM damper on it broke loose. The new one vibrated like mad. The whole shifter was shaking so hard you couldn't hold on to it. I took it out and rotated it a quarter turn and it was tons better. I rotated it another quarter (which was a half turn in the end) and the vibration was gone. So the orientation of the driveshaft totally DOES matter. No other changes were made and vibration was gone

  13. #13
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    Quote Originally Posted by homer302 View Post
    Not read the first response so this may have already been said. It matters for sure without a doubt. I had a Ranger that I put a new driveshaft in because the OEM damper on it broke loose. The new one vibrated like mad. The whole shifter was shaking so hard you couldn't hold on to it. I took it out and rotated it a quarter turn and it was tons better. I rotated it another quarter (which was a half turn in the end) and the vibration was gone. So the orientation of the driveshaft totally DOES matter. No other changes were made and vibration was gone

    Many times people come here with a vibration proble. More often than not, the problem gets solved by doing exactly this. It may not make sense to some of us. Maybe Ford had an engineering reason behind it. Not every engineering reason is a good one. As some are probably to keep costs down.
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  14. #14
    FEP Power Member 81coupe's Avatar
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    I just bolt and go also. If I get vibrations, then I will turn it a 1/4 turn until it smooth out. If it still vibrates then the driveshaft is out of balance and needs addressing.
    1981 Mustang Coupe: Rebuilt 91/306, Ported E7's, TF Spring kit, E-303 Cam, RPM Intake, Eddy 1406 Carb, FMS Dual Roller Timing set, March UD pulleys, Summit LT Headers, Summit 2-1/2" Chambered Mufflers w/ 2-1/2" FlowTech H-Pipe/ Flowtubes & 2-1/2" LMR SS Tailpipes. C4 trans with 8.8/ 2.73 Rear.

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    FEP Super Member erratic50's Avatar
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    One other thing to check is make sure it’s not twisted along the seam and make sure the U joints are good.

    if the shaft twists the u joints won’t be square to one another and it will never — ever quit vibrating. It doesn’t have to be far off to vibrate like a bitch.

    Also, Ive had u joints that were bad right out of the box. Took them out of the box and tossed them in and they shook worse than what I took out. Ifthey are missing one needle in the cap that’s all it takes. Double check them as that’s the most likely culprit.

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