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Driveline clunk when changing direction


crazyd

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'92 LQ1 DOHC.  I'm getting a clunk from the driveline when i change direction forward/reverse.  Doing the motor mount test, I saw a lot of movement from the engine in reverse, so I figured the rear engine mount.  Pulled it out, checked it over, yanked and tugged on it, no sign of a problem.  The replacement I got looked worse than what was there, so I put it all back together as it was and made sure all the mount nuts were tight.  Yet the problem persists. As soon as I back up - clunk.  As soon as I go forward again - clunk.  The trans mount is a new 282 mount and all its bolts/nuts are tight.  Same with the front mount and the dogbone.  It's hard to tell where it's coming from because no matter which side you're sitting on it sounds like it's coming from that side, but it seems to be right in front of the firewall. Anyone else had this problem?  Any ideas?  Is it normal for the DOHC to move up a lot more in reverse than forward?

 

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Dave:

 

to clarify, this IS a manual trans car?, you're getting a clunk when you let out the clutch?, how aggressive are you being on the clutch pedal?

 

You said that you checked the *rear* engine mount, did you also look at the *forward* engine mount as well?

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My suggestion is to try this.....you'll need 2 individuals, one in the car, you under the open hood (beside the car), pull up on the parking brake all the way, block the front wheels on both sides (if you can), your partner in the car with engine running is releasing the clutch in the same manner you are doing to duplicate the issue. You watch under the hood for movement of the powertrain, try to narrow down where the bulk of the movement & the clunk is located. Go from there.....

Edited by 55trucker
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woof woof bone....lol

If you disconnect the dogbone & duplicate the maneuver how much movement in the engine At the dogbone is there?

Mine's an auto but if I do a mild converter brake/torque there is approx 1" movement at the dogbone. 

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  • 2 weeks later...

I got under the car again over the weekend.  I tested the other two mounts (lower front, lower trans) by putting it up on jackstands and applying pressure with a jack. 

There was slight movement in the lower front, so I pulled the radiator fan and got a wrench in there to tighten it.  It took a couple of cranks on the front nut, but I couldn't access the rear nut without pulling the compressor.  Retested, and it seems tight and not broken.

Then I tested the trans mount.  Since this is a manual (284) it's a little different than the auto mount, with the two bottom studs where it attaches to the crossmember/cradle and then two long bolts on top that come in sideways, or laterally.  I had hit these with a normal 3/8" ratchet a couple weeks ago and they were snug, but upon doing this jack test I was seeing way too much movement.  I got an extra-long ratchet and started tightening the two bolts and it actually took several turns to get them tight with a lot of force. The short ratchet wasn't applying nearly enough torque and fooled me into thinking they were tight when they weren't.  Re-tested and the mount is good, and the bolts are tight.

The clunking/popping is now worse than it was before.  If I hard accelerate in 1st or 2nd gear, it clunks as soon as I push in the clutch, or if I let off the gas suddenly.  No, it's not the clutch that's doing it.

So, the dogbone story.  I had been going through dogbones like door-handles.  I finally figured out that they were skimping on the way the rubber is molded inside the bone.  It looks the same on the outside, but on the cheapo parts-store ones there is almost no rubber inside the bone.  It would last maybe a year and then get all loose and wobbly.  First I tried a poly dogbone, but the poly was too harsh and noisy for my taste.  So I got a new stock rubber one that I believed was better-made a couple years ago, paid several times the normal price for it, can't remember if it was a Pioneer or an AC Delco.  It was nice and snug at first.  I'd say it's now got maybe 3000 miles on it, and it too is now loose and wobbly to the point that I can move the bone around by hand against the rubber.  I'm going to replace it again.  But it's not the cause of this noise. 

There's only four mounts.  None of the three on the bottom appear to be the culprit and the one on top isn't either.  I don't think a tie rod or ball joint could do this, both are good on both sides, and I believe the control arm bushings are good too as I just put the car through three consecutive alignments and the alignment tech said his only complaint was the right-side ball joint, which I replaced three weeks ago.  The right-side axle is new as of 2018, and the left-side is older, replaced maybe 10k miles ago, but has what I would consider normal movement and the symptoms don't seem to match up to this being an axle problem.   

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a simple inexpensive cargo ratchet strap will suffice, one end fastens to the rad header, the other end to the engine lift hook, ratchet up the strap, see how much movement the engine actually allows.

Edited by 55trucker
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  • 2 weeks later...

It's slightly offset; the brackets don't precisely align for some reason.  You can see it, and how much play there is in the bushings after only a few thousand miles, in the below pic.  Incidentally, I did use a jack handle to yank around the engine fore/aft while the dogbone was out, and it was moving maybe 1/2-3/4" (13mm-19mm).  Snug.  

20201121_090708.jpg

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something you could try to *align* the engine side is..

to remove all of the paraphernalia 1st & then back out the engine lifting bolts & slip in some hardened washers in between the head & lift support to move it away from the head slightly to true up the alignment.

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  • 2 weeks later...

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