Differential whine

[mrsnak]

I'm starting to get a good whine at about 50mph from the rear end. Only when accelerating. What parts do I need to go about replacing? Being here in the US, looking for the easiest solution as finding a replacement diff will not be easy. Everything's in the uk, but shipping is an issue. TIA

[bmcecosse]

You may be able to adjust the pinion mesh with the crown wheel to help reduce whine. Do check there is EP90 in the final drive ... There must be Spridget units out there - you want a 3.9 ratio - it's a straight swap.......

[mrsnak]

Thanks very much for the reply. You might remember me as being the one who had the "sealed" diff- no fill plug, only the breather valve higher up. At that time I had questions about the fluid level. Ended up making a little "dip stick" to gauge when the fluid level was around 1/3 or so (maybe a little more) from the bottom of the housing.I have been using Limited Slip Hypoid SAE 75-90 wt oil in there. Pretty much the standard gear oil available in all stores here. Do I need a straight 90 instead? My area has warmer temps than the UK. Will need to check my manual, but can you direct me to where I might learn how to adjust the crown wheel.
Thanks as always.

[bmcecosse]

I think that oil will be fine - but you could always try some STP in there........ The final drive adjustment is detailed in the Manual. Of course they specify 'special tools' - but if willing to do trial & error you may make an improvement.

[mrsnak]

Thanks! A quick look at the manual tells me that because I need to go inside, and replace seals, etc, anyway just to inspect and reassemble, might as well try and do it properly when it gets bad enough. I will try the STP. This seems to have happened SINCE I did the differential fluid change, so I might need to revisit levels. Normally don't take the truck on freeways (above 50mph), so not a critical issue at the moment. I do hate not having it right, though

[mrsnak]

Here's what I'm think of doing. I picked up some Royal Purple 75-140 gear oil. Diff questions from many US forums point to this as being a top brand (Redline is another-the Lambo people love this), and the heavier viscosity should work well in my climate.
Worth a shot. Doing this next Saturday and will report back on the results. Please scream if I am committing a gross error. ;-)
Once again, I am only going to fill the diff about 1/3 or so from the case bottom (since I need to use the breather cap hole to fill).
Thanks!

[bmcecosse]

It will just create more friction drag - costing you performance and fuel.....and getting hot. I would add STP to the existing oil - especially if I lived in USA where STP is King!!

[mrsnak]

STP makes a zillion additives and nothing I saw in my local auto parts store was close to being this kind of additive. Performance is not an issue (I have a 2 bbl Doge Dart carb on the 1400 Nissan motor that sucks the gas like no one's business), but high temps could be. Fuel is half the price (even in California - the highest of all the US states) of what you pay. Just spent a week from London to Dorset and then Birmingham, and feel your pain.
Will go with your advice on the oil viscosity and go back to a good 75-90. Heard nothing but good about the quality synthetics vs petroleum and probably should go with well-rated brand. Lucas makes a good 75-90.
Thoughts?

BTW- got a chance to make a "pilgrimage" to Brooklands. The highlight of my visit

[frame][/frame]

[mrsnak]

Okay. I replaced the diff fluid with fresh quality 75-90 wt and added a little over half cup of STP Oil Treatment.
No change at all in the whine whatsoever. Comes on at about 50 mph and actually seems louder now, but always only on acceleration. Quiet in deceleration. Is there a chance that the diff bearing could be more the culprit? Is it okay to live with this problem for a while?

[bmcecosse]

It just needs adjusting.......The more it whines - the more the gears will be worn. But unless doing many hundreds of miles I wouldn't be worrying about it too much. My own 3.7 final drive whines slightly - I don't let it worry me !

[mrsnak]

Many thanks as always for your kind advice. If I were to go in and adjust, what seals and gaskets will be required to close it back up?

[bmcecosse]

Just a nose seal - and a casing gasket -and of course new gaskets for the half shafts because you will need to pull them part way out to release the final drive unit.

[mrsnak]

Super, thanks - time to order up some parts so that I have them ready