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Stephen_ha

Need help diagnosing noise.

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I have recently swapped out my l28 on my 280z with and sr20, and replaced my old diff with a 300zx diff. When I am reversing the car or downshifting it makes a weird clunking noise, and I can't distinguish where the noise is coming from. I have a video from underneath the car while I was in reverse, if anyone can suggest where I should start that would be very helpful, thanks.

 

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It is rotational and it is only in reverse correct?

 

It doesn't seem like it is the axle or the axle input into the diff as the movement seems smooth, at least on this side.

 

If we think about it, when you are in reverse short of your revers gear engaging and the drive shaft and wheels spinning the opposite way, the only thing that changes is the load. When you accelerate the rear squats and the front lifts. When you put it in reverse the rear would pickup a little bit. It is rotational so it can only be in a couple of places.

 

I would check your axles or your drive shaft or areas around it for witness marks. You might be lifting the rear up and in reverse and at that angle your axle is rubbing your sway bar or the front of your diff mount might be pushing down and your drive shaft or flange might be contacting your exhaust. 

 

A helpful test would be to go up a hill, make sure it is clear and let the car roll backwards with the car in neutral and the car in reverse and see if the noise is only there under one condition or the other. That would help determine if it is load based.

 

Additionally a picture would help here quite a bit an SR20 swap usually entails a transmission swap, means conversion drive shaft, trans mount, lots of things change and it could be something obvious like poor drive shaft engagement or driveshaft angle or something of that nature which would be difficult to guess.

 

It sounds too distinct to be like a wheel bearing grumble or like skipping teeth. Sounds like the axle is hitting bolts or loose control arm mounts skipping with traction, hard to tell. 

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32 minutes ago, Stephen_ha said:

I have recently swapped out my l28 on my 280z with and sr20, and replaced my old diff with a 300zx diff. 

 

 

Did you do both at once or did you just throw in the part about the SR20?  In other words, did it work well with the SR20 and transmission before you installed the 300ZX diff?

 

You might try rolling backwards down in a hill in neutral to see if it's a load thing or a direction thing, or both.  If it makes the noise in neutral, no load, it might tell you something.

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Good idea with the Cell phone Camera. It sounds most like a dry U-joint to me. When you reverse, the U-joint loads the needles and cages in a different direction. It can make this creaking noise. If the U-joints have grease nipples. Add some grease and see if noise goes away. 

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Sounds like the video was shot in the shop, no?  (I.e. Car on a lift, and no load on he drivetrain.)

 

Ard you sure you got a good diff?  Those noises on the video sound a lot like a differential with internal issues.  What differential is it, and is it open or LSD?

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