Transmission or rear end?

JasonNCJasonNC Posts: 889Expert Adviser
Took the 49 out for a test drive after making a few changes to the engine.  The car ran well except for when I either accelerated rapidly or let off the gas quickly, at which point it the car would lurch and make a loud bumping sound.  I can't tell if the "bump" sound is coming from the rear end or the transmission.  I wonder if the driveshaft is engaging the rear end too hard or if the clutch is slipping.  When decelerating quickly, when the hard thump sound occurred, the car would sway slightly.  Any ideas? 

Comments

  • boothguyboothguy Posts: 109Senior Contributor
    I would check the trans mount and the carrier bearing mount first
  • GlowplugGlowplug Posts: 1,850Expert Adviser
    edited November 2019
    Did you look under the car?   The outcome of what you see may point to the problem quickest.  GUESS from afar....the center bearing has has come loose from the mounting insulators, one or both?   
  • JasonNCJasonNC Posts: 889Expert Adviser
    Thanks guys, I'll check it out Monday and let you know....

  • Ken U-TxKen U-Tx Posts: 3,732Senior Contributor
    Did the car veer to left or right when accelerating /decelerating? If so, in addition to the aforemented areas to check, check the rear spring shackles and where they go into the frame for looseness, breakage. Check the rubber front eye bushings of the rear springs, these can be gone. Also check the U-Bolts that hold the leaf spring to the spring pads on the axle, and the rubber isolators, they should be tight but can loosen if the rubber isolators are bad. Also check the Panhard rod (lateral stabilizer bar) rubber bushings. One other thing, check the leaf springs for broken leaves!
  • JasonNCJasonNC Posts: 889Expert Adviser
    Ok guys I have checked the center bearing and the mounting insulators and they are ok.  Ken I really can’t see if the front eye bushings are bad because the cover blocks my view, but my guess is they need to be replaced.   I assume by isolators you are referring to what Wildrick Rubber lists as spring mount bushings #103.  Correct me if I am wrong . Thanks.
  • GeoffGeoff Posts: 3,683Senior Contributor
    Check U-bolts holding the diff to the springs, universal joint nuts,  axle end nuts. 
  • Jon BJon B Posts: 6,975Administrator
    I don't know your level of mechanical expertise, so please don't take offense if you've already checked this, but have you rotated the drive shaft to see how much play there is back at the rear axle?  I am not sure what the acceptable play is, but I would think that if it's too much, you'd get a "thunk" back there when accelerating or decelerating .
  • JasonNCJasonNC Posts: 889Expert Adviser
    Jon B said:
    I don't know your level of mechanical expertise, so please don't take offense if you've already checked this, but have you rotated the drive shaft to see how much play there is back at the rear axle?  I am not sure what the acceptable play is, but I would think that if it's too much, you'd get a "thunk" back there when accelerating or decelerating .
    I have done this and there is quite a bit of play back there.  Is that going to be a problem down the road.  As far a mechanical expertise is concerned, I'm a lawyer by trade and a wanna be shade tree mechanic by night...

  • JasonNCJasonNC Posts: 889Expert Adviser
    Geoff said:
    Check U-bolts holding the diff to the springs, universal joint nuts,  axle end nuts. 
    Thanks Geoff.  I had tightened the U-bolts with an air wrench months ago and thought that they were tightened to the max.  Turns out that when I started to tighten by hand, they were a lot looser than I wanted them to be.  I will see if that cures the problem once I get the car off the jack stands and back on the road.  
  • bob wardbob ward Posts: 1,079Senior Contributor
    Are your back axle U bolts double nutted? 
  • JasonNCJasonNC Posts: 889Expert Adviser
    bob ward said:
    Are your back axle U bolts double nutted? 
    Yes they are.  I took the second nut off.  Tightened the inner nut an then put.the second nut back on. 
  • Ken U-TxKen U-Tx Posts: 3,732Senior Contributor
    We should hope we all have our second nuts.....monorchidism ain't no laughing matter....
  • JasonNCJasonNC Posts: 889Expert Adviser
    Good one Ken.  I had to Google that word to see what it meant.....

  • barrysweet52barrysweet52 Posts: 478Expert Adviser
    Some times the second nut is not close to the first. In this situation its called, One Hung Low.
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