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Clanking While Coasting

Discussion in 'Early CJ5 and CJ6 Tech' started by Ns0mniac, Jan 22, 2020.

  1. Jan 22, 2020
    Ns0mniac

    Ns0mniac New Member

    San Clemente, CA
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    Searched around but couldn't find anything conclusive, found a thread on a similar problem on Pirate but it wound up being a U joint problem, which I'm fairly certain it is not.

    Installed my new Tom Woods rear driveshaft (XC long life splines, 1310 u joints), installed a new rear yoke on my Dana 18 (non-parking brake type), new fluid for Dana 18 and flushed my transmission (SM420). Put like a whole tube of grease into the new driveshaft, tapped with a hammer to seat the U joints outward. New u bolts. First drive got some driveshaft noise when I'd let off the throttle in gear, more grease fixed it.

    Now my Jeep's started to make a new noise, sort of like a clanking sound. At first I thought it was my exhaust hitting something but ruled that out.

    The most peculiar part is that it only makes the noise when I'm going around 30 or more miles an hour and giving slight throttle. If I'm fully off the throttle or on it more than 5% (measured by the TPS on my Holley Sniper EFI) the noise disappears. Only if I'm under some load but low load. The noise is constant, I swear it sounds like something is flopping around down there banging into the frame or something. The noise doesn't change with engine speed (RPM).

    Tomorrow my plans are to check for anything loose hitting the valve covers or something under the hood, regrease the rear driveshaft (gotta do the front anyway) and if I can't figure it out from that I'll chock the front wheels, put the rear axle up on jackstands and have my wife work the throttle for me while I listen. I'll be careful, I promise!

    Nothing is low on fluid, I have Warn lockouts on my Waggy front Dana 44 so it's not the shafts up front. Any ideas?
     
  2. Jan 22, 2020
    Twin2

    Twin2 not him 2020 Sponsor 2019 Sponsor

    Virginia Beach, VA
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    have you checked spring bushings
     
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  3. Jan 22, 2020
    PeteL

    PeteL Member 2020 Sponsor 2019 Sponsor

    Hills of NH
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    Motor/transmisson mounts? Maybe allowing exhaust pipe to be hitting something?
     
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  4. Jan 22, 2020
    Ns0mniac

    Ns0mniac New Member

    San Clemente, CA
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    I'll add those both to my list. I checked to make sure none of my shackles had loosened, their nuts are all still tight and the witness marks are good but I didn't really look closely at the bushings, good catch. I also have fender exit headers so it's very possible they could be tapping the frame if my motor mounts are bad. I'll rock the engine around and see if I can replicate it.
     
  5. Jan 22, 2020
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    Tell us more about the driveshaft. Standard? Double cardan?
     
  6. Jan 22, 2020
    Ns0mniac

    Ns0mniac New Member

    San Clemente, CA
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    Standard, XC greasable splines with greasable 1310 Tom Woods "golden seal" U joints. I've got my D18 shimmed down 6 degrees, rear 44 shimmed up 6 degrees to match, actual driveshaft operating angle is about 6 degrees at ride height. Old driveshaft that was in there worked just fine, it was just too short after the yoke swap to the non parking brake yoke. Only changed yokes because I had a leak from the D18 output, didn't have a functioning brake anyway.

    I greased the driveshaft until it was clearly showing new grease coming out of the dust cap on the splines, greased the U joints until grease was visible from all caps. Tried re-seating them with a block of wood and a hammer to make sure the caps are fully seated outward, cleaned the inside of the yokes before I installed it.
     
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  7. Jan 22, 2020
    BadGoat

    BadGoat How High Can You Climb?

    St Croix, USVI
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    How is the torque arm mount on the transfer case? They do wear out.

    Mike
     
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  8. Jan 22, 2020
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    Just to cover these bases...
    The shaft is phased properly? If you were to lay the shaft on a bench, the flats on both u-joints lay flat on the surface?

    And the t-case output bearings and pinion bearings are shimmed to spec? No play?


    Is this rattle consistent with bumps in the road?
    Is it reliably consistent at 30mph?

    You might just need to go hunting. It might just be the right speed to rattle something against something, and pinpointing it to a general location will be step one.
     
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  9. Jan 22, 2020
    Ns0mniac

    Ns0mniac New Member

    San Clemente, CA
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    T case bushing is good, I have an extra transmission/tcase mount too so drivetrain is solid, haven't inspected engine mounts yet though. Driveshaft is balanced and phased properly and drives smooth. The rattle happens regardless of bumps but does happen whenever I hit a bump. I haven't checked the transfer case shims but it worked fine before I put a new yoke and seal on it, I'll check that if I'm unable to locate the problem elsewhere.

    Also, the noise happens at any speed over 30 MPH (roughly 30 anyway, speedometer doesn't work but according to my gearing and engine speed it should be around 30). It doesn't change with vehicle speed either.

    Looks like I've got quite the laundry list to go through after work today! Thank you all for your suggestions.
     
  10. Jan 22, 2020
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    I mentioned that because these have a tendency to make a racket around 30mph at low throttle if there is slop in the driveline. The t-case output yoke is what applies the preload to the bearing, and if the wrong yoke is used, the nut could be bottoming out before applying proper preload. Just a thought.

    I hope it’s as simple as a muffler. Good luck!
     
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  11. Jan 22, 2020
    Ns0mniac

    Ns0mniac New Member

    San Clemente, CA
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    I think that the shims will most likely wind up being my problem. I had initially thought that the symptoms resembled slack in the driveline, your description of the problem and others I've found online fits what I'm experiencing very well. I'll report my findings tonight!
     
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  12. Jan 22, 2020
    Ns0mniac

    Ns0mniac New Member

    San Clemente, CA
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    Solved! It's the shims. Looks like a Dana 18 rebuild is in my future. Now to decide whether I want to upgrade to the tapered intermediate bearing or not. Decisions decisions.

    Thanks to all for the advice! Your suggestions actually lead me to discover a few more... Err.. Areas of potential improvement for my Jeep. Cheers!
     
  13. Jan 23, 2020
    NCRenII

    NCRenII yellow fever

    Far Nor Cal
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    I've been away from site and as a follow up would like to offer a couple observations of my driveshaft angle follies.
    When checking angles add weight to the vehicle. Adding weight will change angles, especially with soft springs).
    Driveline angles change with axle wrap (worn spring bushings and engine/transmission mounts too). As soon as power in applied to driveline in forward gears the (rear differential) pinion rotates up and in reverse downward. The effect on the front axle is reversed, i.e. pinion down on forward power, upward on reverse). As NsO discovered playing around with shim angles often times cam eliminate driveline noises and rumble.
    fwiw I find most often it's necessary to set the rear pinion just a bit below the measured "optimal" angle (or straight line with a double cardan driveshaft) to elliminate driveshaft rumble. I find the front angle is not as problematic as 4x tends to be used at lower speeds. Yet for optimal u-jt life the front pinion angle can be set just a fough above the measured optimal angle. All this based on premise rear pinion rotates up and front downward when load is applied. Final observation is super stiff springss wrap less and softer wrap more. This is mentioned as the stiffer springs require less static angle (angle set with vehicle at rest
     
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  14. Jan 23, 2020
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    Just a note... Weight shouldn’t change the actual pinion angle if the leaf springs are symmetrical (centering pin is centered in the leafs). The front and rear of the spring will flex equally, and the angle of the pinion will remain unchanged through the spring’s travel. The driveshaft angle will change obviously, but it will change the angle of the fore and aft u-joints equally.
     
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  15. Jan 23, 2020
    NCRenII

    NCRenII yellow fever

    Far Nor Cal
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    Technically correct the pinion angle won't change, yet the driveline pinion output shaft angles will change.
    i.e. frame (including engine, transmission and output shaft) lowers and changes angle. So much is going on with the angles, especially with soft springs, centers, shackles, etc., that it's easy to add weight to chassis and measure the angles before adding shims. I think it's important and easy enough to do when investigating rumbles.
    I'd be interested for NsO to report what shims were used in his case.
    I'll guess he retained the 6* down on the D18 and went with between 5* to 4* up on the rear.
     
  16. Jan 23, 2020
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    If the frame angles down in the rear 2 degrees with weight, the t-case output might go down 2 degrees with it, but the springs are also attached to that frame, angling the axle with it to match.
     
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  17. Jan 23, 2020
    Tom_Hartz

    Tom_Hartz Member 2020 Sponsor 2019 Sponsor

    North Carolina
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    Also remember on the front pinion angle you need to keep the caster of the alignment in mind.
     
  18. Jan 23, 2020
    NCRenII

    NCRenII yellow fever

    Far Nor Cal
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    Lots of variables to consider. I'd like to leave my adding weight suggestion as-is as adding weight will end up compressing each spring a different amount and the frame may or may not settle one end or the other or left or right more or less than a similar jeep. I've found adding weight and making measurements, then leaving the rear pinion slightly down relative to zeroing out the angles works very well.
    Tom Hartz makes a good point. Front angles are hard to set especially in lifted jeeps. Often cutting and welding of perches is the only cure.
     
  19. Jan 24, 2020
    BadGoat

    BadGoat How High Can You Climb?

    St Croix, USVI
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    A common solution for the front axle is to ignore the pinion angle and just work to get the caster/camber alignment correct. The front driveshaft is usually disengaged for normal high speed driving. The driveshaft u-joint angle offsets are far less important at low off-road speeds.

    Rewelding the perches can help.

    Cutting off and rewelding the C's on the ends of the axle and then aligning the perches is the best way to optimize both the pinion angle and the caster/camber, but it's more effort to do correctly. Custom built axles (Currie, Dynatrac, etc.) can be ordered with the pinion angle and C's preset, but you do need to know your final ride height and be able to either measure or calculate how they should be configured.

    Mike
     

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