Noisy Diff on C5?

[BobbyV8]

I have a whining noise from the rear of my C5 which I fear may be the diff. Since I have had the car there was always a very slight whine at around 60mph but any where above or below this speed was fine.

Recently this has got quite bad and now it makes a lot of noise at 30 to 40mph and again at 50 to 60mph but 70 it is hardly noticeable.

It doesn't do it on acceleration or slowing down just on a light throttle.

The previous owner had changed all the fluids including the diff but I did do it myself last week. The oil I drained out was clean and I put it through a filter and there was no sign of metal parts or bearing material.

I will try to upload a video of the sound it makes but any thoughts on what other parts could be making a noise would be much appreciated. Cheers.

 

[teamzr1]

GM requires a special diff fluid additive to the rear-end lube to lessen the noise
Or what I use on my 1999 C5 is Mobil I synthetic diff lube, and it already has the right mixture as noise would be more using a 3.73 ratio I put in place of the stock 3.42 gear which will smooth out gear meshing and reduce and noise

Without this the diff will be noisy, and it could be yours needs new lube and fluid additive
Most places sell this diff fluid or a GM dealer should sell it

 

[teamzr1]

Here is the additive

Limited slip additive

 

[BobbyV8]

GM requires a special diff fluid additive to the rear-end lube to lessen the noise
Or what I use on my 1999 C5 is Mobil I synthetic diff lube, and it already has the right mixture as noise would be more using a 3.73 ratio I put in place of the stock 3.42 gear which will smooth out gear meshing and reduce and noise

Without this the diff will be noisy, and it could be yours needs new lube and fluid additive
Most places sell this diff fluid or a GM dealer should sell it

Thank you. I changed the fluid with Royal Purple 75w90 with the additive already in but made no difference to the noise. Maybe I should get the other additive and start again.

 

[teamzr1]

There have been cases where people did not use GM's limited slip fluid and noise did not go away,
so I do not know if what is in what you used works correctly with the Corvette transaxle

Maybe should check it the noise is within the transaxle, side shafts or maybe something else back there ?
Checked the tranny fluid level and quality of it ?
I also use Mobil I Synthetic tranny fluid limits noise (My case M6 tranny) but also works for the A6)

If all else, maybe a shop that can work on C5 transaxle can replace and adjust leashing with shims.

If in doubt you might try Blackstone testlab, where on their website (if it supports the UK) you can order a free testkit
they mail you
You then put a sample of oil or fluid from car in and send back to them, and they fully analyze, and full report to their findings
including if any metals are found
I have been using them for my Corvettes for like 20 years as engine oil and tranny fluids.

Blackstone Lab

Here is an example of results on my C5 tranny fluid

 

[BobbyV8]

There have been cases where people did not use GM's limited slip fluid and noise did not go away,
so I do not know if what is in what you used works correctly with the Corvette transaxle

Maybe should check it the noise is within the transaxle, side shafts or maybe something else back there ?
Checked the tranny fluid level and quality of it ?
I also use Mobil I Synthetic tranny fluid limits noise (My case M6 tranny) but also works for the A6)

If all else, maybe a shop that can work on C5 transaxle can replace and adjust leashing with shims.

If in doubt you might try Blackstone testlab, where on their website (if it supports the UK) you can order a free testkit
they mail you
You then put a sample of oil or fluid from car in and send back to them, and they fully analyze, and full report to their findings
including if any metals are found
I have been using them for my Corvettes for like 20 years as engine oil and tranny fluids.

Blackstone Lab

Here is an example of results on my C5 tranny fluid

View attachment 13742

Cheers and thanks for the info. I think I'll get someone to check where the noise is coming from although I know this can be difficult sometimes to narrow down.

 

[teamzr1]

BobbyV8,
Maybe try doing tight left and then right slow speed turns and see if that helps to pinpoint where the noise is coming from ?
See if it is worse in cold or hotter weather

 

[Oneball]

Does it do it in all gears? If it does that’ll go some way to ruling out the gearbox.

 

[BobbyV8]

Does it do it in all gears? If it does that’ll go some way to ruling out the gearbox.

It's an auto box and the noise doesn't change whatever gear it is in so I'm sure it isn't the box. It may be a wheel bearing but that's usually more of a rumble than a whine.

 

[Custom exotics]

Have you checked the rubber prop shaft bushes inside the torque tube these can perish and split causing noise from the torque tube area

 

[BobbyV8]

Have you checked the rubber prop shaft bushes inside the torque tube these can perish and split causing noise from the torque tube area

No haven't got that in depth yet. It's a bit of a major job to do at home but yes that could be a possibility. The car is low milage and probably stood around most of its life so may have perished. Thanks for your input.

 

[Stingray]

My diff would sometimes make noises but never anything that I would describe as a whine. I assumed it was "gentle graunching" from the limited slip mechanism when making tighter turns in town.

 

[BobbyV8]

Here a link to the noise it is making:

 

[teamzr1]

Wow, yours sure sounds loud, should be real quiet like my 99 C5
I never hear the rear gear in mine

Here I was being good and just cruising around (ignore radar detector keep going off

Seriously, what a job yanking out the drivetube and then the driveshaft

Maybe cheaper is replacing rear end fluid, add the GM additive
Then find a parking lot and make several tight figure 8 turns and then go the other way with figure 8 turns to work additive in
and see if that is different.

 

[BobbyV8]

Wow, yours sure sounds loud, should be real quiet like my 99 C5
I never hear the rear gear in mine

Here I was being good and just cruising around (ignore radar detector keep going off

Seriously, what a job yanking out the drivetube and then the driveshaft

Maybe cheaper is replacing rear end fluid, add the GM additive
Then find a parking lot and make several tight figure 8 turns and then go the other way with figure 8 turns to work additive in
and see if that is different.

Maybe I need louder pipes and a cam too .

I will try the new fluid and the additive first which will be here next week and take it from there but I believe it is the ring & pinion shot.

Enjoyed your videos and a bit jealous of your roads. If mine was a manual I wouldn't get out of first around here

 

[teamzr1]

BobbyV8, you got my clue !

Get better mufflers and your problem will be solved for good (and your ear drums
I run a 3.73 rear gear with M6 tranny and bounce the rev limiter all the time and many a run down the
drag strips and never had a problem with the ass end so really would be rare that diff goes bad

I can understand your roads, knowing you can go full north to south on that island and run out of road quickly
If you noticed in those videos how rare it was to come upon any traffic and cops are too busy at some coffee & donut shop !

Make sure you do those figure 8s to push that additive in
When under there look closely at 2 known issues

1. The end links of rear sway bar is known to go bad and cause odd sounds
2. Also, the mounts for the mufflers, the rubber goes bad on them and makes odd sounds.

 

[BobbyV8]

BobbyV8, you got my clue !

Get better mufflers and your problem will be solved for good (and your ear drums
I run a 3.73 rear gear with M6 tranny and bounce the rev limiter all the time and many a run down the
drag strips and never had a problem with the ass end so really would be rare that diff goes bad

I can understand your roads, knowing you can go full north to south on that island and run out of road quickly
If you noticed in those videos how rare it was to come upon any traffic and cops are too busy at some coffee & donut shop !

Make sure you do those figure 8s to push that additive in
When under there look closely at 2 known issues

1. The end links of rear sway bar is known to go bad and cause odd sounds
2. Also, the mounts for the mufflers, the rubber goes bad on them and makes odd sounds.

Thanks for the info

 

[BobbyV8]

Hi all. Update on the diff is that the noise is getting worse now. I am looking for recommendations please on the go to people for working on c5 diffs? I am in Norfolk but not worried about distance to travel. Thanks.

 

[Rich]

Ignoring your location I would suggest Topcats Racing or Parts USA. However they are quite a way so how about asking Neil Williamson to put out a plea to the Region via Mojo as someone more local may have a recommendation.

 

[BobbyV8]

Ignoring your location I would suggest Topcats Racing or Parts USA. However they are quite a way so how about asking Neil Williamson to put out a plea to the Region via Mojo as someone more local may have a recommendation.

Thanks Rich