Rear clunking... am I having "wheel hop"? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-17-2008, 08:57 PM
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Rear clunking... am I having "wheel hop"?

On a hard takeoff my rear is making weird "clunking" noises, that I can feel shake my car. Is this what I have heard referred to as "wheel hop?" It's a rather frightening experience, and I'm scared to accelerate as fast as I would like to.

I have a 70 Impala, and this is a new thing since I changed driveline. I ditched the original 2v 350, which was relatively gutless and pooped out with about 200k, for a new 383. While I was at it, I swapped some new richmond 3.55 gears with an Eaton posi my uncle had. I have new rubber mounts on the engine & trans. I wasn't sure if this is a result of the new-found throttle response, or possibly needing posi additive, or driveline angle being off?... My uncle had a small bottle of something from somewhere, and I put it in when I filled the rear with fluid, however I have noticed my diff cover dripping.

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Old 09-17-2008, 11:23 PM
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Eaton posi (gov-lock)from a truck????

Shane
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Old 09-18-2008, 12:08 AM
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Usually a posi that needs the friction modifier will make weird clunking noises when you make a sharp turn.

Is the car squatting excessivly? Sometimes the rear end will hit the exhaust, if it is not routed over the axle properly.

Usually wheel hop is a result of a set of tires that get good traction and the leaf springs "wrapping" up to the point that it snaps back, lifting the tire off the ground..When the tire his the ground, it usually makes some kind of spinning noise, not always squealing, but most always a chirp.

I thought that a 70 impala had a coil spring and control arm suspension in the rear. Those are not as prone to wheel hop as leaf spring suspensions are.


The driveshaft could be hitting the floor too, did you take out the rubber bumpers over the axle? (if that car had those, I don't know)

Did you set up the rear end gears yourself when you installed them?


Shane- I did not know that you could fit a truck posi in a car rear end..I know the truck 12 bolt carrier and the car 12 bolt carrier are different.


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Old 09-18-2008, 05:39 AM
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Shane, it's a regular car posi, not a gov-lock unit.

Mike, it doesn't make a lot of noise on sharp turns. Although the Impala isn't know for turning real sharp to begin with. I don't think it's exhaust because all I have is turn downs from the mufflers, right in front of the rear axle. I do have coil springs and 4 control arms. I had a driveline shop install the gears. I'll have to check on the driveshaft idea, to see if it is hitting anything. Something is hitting/shaking something, i can feel that much.

Could the driveline angles be a big factor? I replaced the trans mount (basically because the old rubber was disintegrating) with a new one from NAPA. It seemed taller than the old one, but I checked other parts stores and other B-body apps and they were all the same.
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Old 09-18-2008, 09:28 AM
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Unless you changed something drastically, like using a rear end from a different car and having the mounts be in a different place, or the mounts are ripping loose from the rear end , the U joint angle alone would not make the car behave like it does.


If the U joint angle was off so much to cause a clunking at hard take off, it would also vibrate at speed, and change the pitch of the vibration when you were decelerating.


I would check your control arm bushings, ( the rubber in those deteriorates over time, and can allow alot of movement) check your U joints for looseness and wear, check your rear trans and motor mounts for broken ones, basically make sure everything in the suspension is tight and sound. I'd be under the car looking for any sign of parts rubbing on each other, (the drive shaft rubbing the floor leaves a scratch in the paint around the driveshaft.) Grab the yoke at the trans and rear end and check for rotational and up and down looseness.



Then start looking for more exotic problems, like driveshaft and suspension geometry, (do a search here for "pinion angle", you will find a ton of threads that describe the way to check your pinion and driveline angles)


Let us know what you find out..

Mikey
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Old 09-18-2008, 04:45 PM
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You might want to check the differential/Spool bearings. I had a bearing going bad which would move in the saddle allowing the whole diff. to move around. It also caused a slight whining noise going down the road. I replaced the bearings and all was fixed.
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