C3 Rear End Noise

[Don kelley]

[David M.]

Re: C3 Rear End Noise

When you replaced the pinion yoke you may have mess with the pinion pre-load. Noise on no-load or deceleration is an indicator of this. If your not familiar with the proper set-up of these rear-ends take to someone who is. You will damage the ring and pinion. It may be corrected with a new crush sleeve and proper pre-load on the nut. Something to mention to who ever you take it to. If it needs to come apart again consider doing all new bearing/races and seals. I know thats not what you wanted to here. Anyone else?

[Mike McKown]

Re: C3 Rear End Noise

I'd say you're very likely right on the money.

[Joe L.]

Re: C3 Rear End Noise

Don, Dave and Mike-----

Yup!

[Michael H.]

Re: C3 Rear End Noise

Don,

If you have gear noise at float and coast, but not when under acceleration, it most likely indicates that the pinion nut is not seated and tight. There is lash, or clearance in the pinion bearings. This allows the pinion to move slightly and change it's depth in the ring gear. The reason it's quiet under accl is because the pinion is forced forward, back to it's correct original position, but at float or coast, it's pulled the other way, or forward, which upsets the original gear mesh. If you haven't driven the car more than around the block, I don't think you have any gear damage and I would suggest trying to tighten the pinion flange nut to eliminate all lash, but not to the point of over loading the bearing preload. Check to see if there is any movement of the pinion gear or flange. I suspect you will find there is a bit of for/aft movement. It should have zero movement with a very slight preload.

[Randy Krohn]

Re: C3 Rear End Noise

Just curious - I have a '72 454 automatic (sorry - I'm in my office - couldn't quote you the rear end ratio) with the opposite condition - quiet on coast, whines on acceleration. I believe it's the original rear end with 96xxx miles. It did this when I bought it, and didn't change with a rear-end flush/re-fill (with the suggested additive - name escapes me at the moment).

Is this normal?

Thanks

Randy

[Don kelley]

Re: C3 Rear End Noise

Thanks for your response. I did not make it clear however. There is no noise at coast or Acceleration only just at float.

[Michael H.]

Re: C3 Rear End Noise

Don,

I misunderstood your original question and assumed you had a problem with the pinion bearing preload but it sounds like it's a little deeper than that. Clearance, instead of a slight preload in the pinion bearings, will create a whine at both float and coast. If you hear it only at float, that's a different problem. There are several things that can cause this sound at "float", including incorrect pinion depth and backlash but incorrect ring gear backlash is the most likely.

[Michael H.]

Re: C3 Rear End Noise

Randy,

The Whine you hear on acceleration is not normal. I think you may have some internal differential problems. A bad rear pinion bearing can cause a noise on acceleration that may sound like a whine and be silent on coast or float. The gear set can also cause this same problem but typically, if the gear set is that bad, you would hear some noise at all ranges of driving, not just acceleration. If the pinion bearing is loosing dimension and allowing the pinion to move, that will give both a slight grinding sound and the gear set whine on accl.

[Randy Krohn]

Re: C3 Rear End Noise

Thanks for the information.

Randy

[Don kelley]

Re: C3 Rear End Noise

Thanks Michael for the information.

Any idea why the sound at float only is just now showing up? Some history: It came out of a 4 speed C3 car and installed in an automatic C3 car. The automatic transmission is from a C4 car not a C3 if that makes a difference. This rear end was overhauled a few years ago. It has probably less than 2,000 miles on it( which might be the problem). I should have driven the car more.

Also, If the noise is at float only, will it cause any additional damage between now and when I have it repaired?

[Terry M.]

Re: C3 Rear End Noise

It is common for high-mileage differentials to wine on float. In those cases it is due to wear creating high backlash clearance. Tightening up the backlash by adjusting the carrier shims will cure those cases, but doing nothing creates no real problems (other than the noise) either. All that said there are, as someone else said, other reasons for whine on float. The only way to tell is to take it apart and do some inspection/measuring. Given yours is not a high mileage item you are right to wonder about the cause. Measuring backlash and making an impression of the contact between pinion and ring gear teeth -- see the FSM for instructions and drawings -- will be necessary to diagnose the noise. Diagnosis by Internet is a futile pursuit for these kinds of issues.

[Michael H.]

Re: C3 Rear End Noise

Don,

I don't have a good explanation as to why the problem started when the units were swapped. If the pinion flange was installed properly, there isn't anything else that could cause this change at the time the units were exchanged from one car to the other.

If a diff gear set makes noise at any load, or lack thereof, there is definitely something incorrect, either in pinion depth or ring gear back lash. Pinion depth can/will change as power is applied if the pinion flange nut is slightly loose but you mentioned that this was not the case. If you hear the "singing" only at float, it's likely one of the two gear settings we talked about.

If a new or rebuilt diff assy makes gear noise when fresh, it's likely it will continue to make noise for the rest of it's life. New cars off the assy line didn't have gear noise. There is a break in period for a new gear set but that period wasn't intended to quiet an incorrect mesh. I know that many rebuilders wil tell you that you have to put several thousand miles on a new gear set before they quiet down but that isn't exactly true.

If a new ring/pinion set is allowed to run at incorrect settings, it will eventually destroy the set. We've reset pinion depth on near new vehicles with aprox 100 miles and had some success but after a several hundred miles, or several thousand miles, it wasn't possible to save it.

Setting proper pinion depth is usually a LOT more work and a LOT more complicated than many mechanics want to deal with and typically, they just reuse the same pinion bearing shim that they removed from the old gear set. Even if the same gear set is used, a new rear pinion bearing can definitely change the depth setting of the pinion.

One thing to remember is the fact that a diff in a C2 or newer Corvette will transmit more gear noise to the pass area than just about any other vehicle built in that era because of the location and mounting method used. Even a slight, almost normal whine, will sound much worse in a Corvette than that same noise in a passenger car that has the diff mounted several feet rearward of the driver compartment and not bolted directly to the frame.

When you changed the pinion flange, did you happen to notice any slight load, or drag, on the bearing after you retorqued the nut? In other words, did the amount of rotational force required to turn the flange/pinion change? If I remember correctly, there should be 5 INCH lb resistance with used bearings. This figure is only supposed to be used for the the pinion only with no ring gear installed but it may help us determine if the nut s indeed seated and there is some load applied to the flange.