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Diff re-build 4.08 FD whine issue...


andygore

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Hi Guys,

 

I have recently stripped by diff fitted a 4.08 final drive and rebuilt it. I changed all of the the bearings and rebuilt this as per the factory manual. I checked all of the tolerances and they were all spot on and the contact patch of the gearing is perfect.

 

I then refitted the diff and filled with 1.4 liters of Red Line 75W90.

 

I then took the car for a quick spin and I've noticed a whining from the diff. This has never been there before and I have only changed the diff so I'm guess this is the issue.

 

The whine starts around 40 mph and get progressively louder and higher pitch as the speed increases. If I go into neutral and coast around 70 mph this noise gets a lot quieter. When the cruise control is on at 70 its quite loud.

 

Before I did the diff rebuild I had no noise, the wheel bearings were fine and I had no noise from the gearbox or diff whatsoever.

 

Anyone have any ideas what it could be, has anyone fitted this final drive and is it normal to get more transmission noise?

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Does no one have any ideas?

 

I really don't want to take the diff off again its a ruddy nightmare!

 

I think ill try and drain/refill the fluid to make sure I have enough in there.

 

Has anyone changed the fluid on the diff, if so what did they use?

 

I know sometimes different oils can be louder/quieter than original oils.

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Redline is good stuff so I don't think that's the issue. I take it you refitted the OEM VLSD and just swapped the FD.

Start by putting it up a ramp and inspecting and hearing where the noise is coming from. Then drain oil to see if any metal bits.

Next I would open it up and and check nothing is eating itself to death. Cheaper in long run. With the FD backlash is very important. Did you make sure this was within specs.

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Redline is good stuff so I don't think that's the issue. I take it you refitted the OEM VLSD and just swapped the FD.

Start by putting it up a ramp and inspecting and hearing where the noise is coming from. Then drain oil to see if any metal bits.

Next I would open it up and and check nothing is eating itself to death. Cheaper in long run. With the FD backlash is very important. Did you make sure this was within specs.

 

Ill give all that a go cheers! I checked the back lash it was right in the middle of the spec. I'm going to spend a few hours and take off/inspect the diff. Ill keep you updated if anyone is interested! lol

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  • 2 weeks later...

Just an update,

 

I have pulled apart the diff again and I have found the backlash to be way out, I need to get a dial gauge on it but it looks to be about 2mm rather than the 0.10 to 0.15 mm.

 

So I need to increase the shim size on the pinion. I am not sure on the size needed though. Does anyone know of a backlash to shim chart, or is it as simple as 1mm of backlash is 1mm of shim size?

 

Cheers guys!

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