Differential Noise Part II

[Oliver S.]

Hello
last year the diff was out to replace the front seal. New diff oil was filled in with one bottle of positraction additive. After that I experienced diff noise when turnig left or right after driving a longer distance. Driving 8x clckwise and counter-clock wise and '8' didn't improve the situation. Finally another additive bottle was added. Since then I've had the impression of improvement - until today. After driving for 50 miles the diff. started to make noise while driving through left and right curves on our Black Forrest tour. Furthermore it was driving like on a bag of nuts. It felt as if the car wobbled at the rear. Now I have got 2 questions:
I know that the filled in diff. oil was another spec. I don't recall which one, but seems to be one that is used for modern cars. Could it be that - despite two bottles of posi fluid - this oil may cause this effect? Before the fluid change it wasn't a problem.
Does the 8- clock, counter-clock wise and'8' procedure have positive effect even after the fluid was added some hundred miles before.

Oliver

https://www.forums.ncrs.org/showthread.php?87720-Turning-right-sometimes-there-s-a-noise&p=563730#post563730

[Domenic T.]

Re: Differential Noise Part II

Oliver,
The diff may not be the problem, you probably have bad bearings on your axle or half shaft depending C1 or C2 +.

DOM

[Oliver S.]

Re: Differential Noise Part II

DOM,

the problem only occurse when the car has bee driven for some miles. Therefore I assume it's the posi

[Domenic T.]

Re: Differential Noise Part II

DOM,

the problem only occurse when the car has bee driven for some miles. Therefore I assume it's the posi

That does point slightly more towards the differential, excluding the posi clutches, but as bad axle bearings get warm from the friction caused by being bad, they start to growl.

Take some lube out of the differential and see how much metalic you have suspended in the oil.

A posi unit will have some after age but a lot will tell the story.

DOM

[Paul D.]

Re: Differential Noise Part II

You may be able to pull the filler plug on the diff and run a telescoping magnet in there. See what you find. Could also be t-arm bearings.......P..

[Michael W.]

Re: Differential Noise Part II

It could be one of a hundred things, including the parking brake assembly falling apart or any one of the six universal joints. Sticking posi clutches don't sound like driving on a bag of nuts. Get the car up in the air and have a look.

[Oliver S.]

Re: Differential Noise Part II

Depending on turning left or right the inner corner wheel causes the noise and wobbling. I assumed the wobbling to be caused by internal friction issues.

[Michael W.]

Re: Differential Noise Part II

I wouldn't assume that- or anything.

[Gary R.]

Re: Differential Noise Part II

A lot depends on what was done to the diff. The noise could be rear bearing related, posi clutch related, or something else in the IRS.
Typically posi hammering is felt and heard starting up from stop and cornering. The stock spring tension and tight spider lash will cause the clutches to grab, just like a 4x4 rock climber will. The additive and the following figure 8's are to allow the additive to work in between them and allow them to slip enough not to chatter on a corner. This has been a problem since 1965 in corvettes and continues with the current aftermarket setup. In 1971 the clutches were changed to the "snowflake type" which is just a name I call them because they look like flakes. The clutches were opened up to allow more additive in between them. This failed to achieve the results hoped for and in HP usage they broke apart. Those that think the new fiber coated ones are the answer are also mistaken, that material comes off in your hands.

If you track the noise to the diff and the additive doesn't work then you either live with it or drop the diff out and tune the posi.
If it's rear bearings, that noisy, then you better check the feel on them now, before they lock up and wreck the spindle and possibly cause an accident. You will feel a lot of play and rumbling from them if they are bad.

[Oliver S.]

Re: Differential Noise Part II

Today the car hase been on the hoist at the garage. All bearings are ok. The garage owner attributes the problem to the posi. He has said that even the bag of nuts driving behaviour when cornering (and after the car has been driven for a while) is caused by the posi. He wants to change the diff. oil again - and use 80W 90 fully synthetic this time - and start with one bottle posi fluid. As mentioned - last year the diff was out and sealed - and since this time the problem has occured. A second bottle of posi fluid helped only temporarily.

Oliver

[Gary R.]

Re: Differential Noise Part II

Shifting or hammering taking a corner typically is the posi clutch setup, lash and spring tension is tight. I never use sythetic oil in the diff but others do and it leads to interesting discussion at times. I use only Lucas gear oil, 85-140 most times, and 1 bottle of additive. 2 bottles may work but if not then you probably won't get it corrected unless the posi is tuned.

[Kurt G.]

Re: Differential Noise Part II

If you did a Schwartzwald Tour, hope you hit Triberg. Wunderbar. Anyway, Gary R is the guru here, and I believe what he says, don't use synthetic, 85W90 Valvoline or Luca oil and then two bottles of GM posi additive. Other additives only work for awhile. GM is by far the best additive. Had my diff rebuilt this last winter, used Valvoline and GM additive. Did 3 figure 8 patterns and have had not clunking or grinding since.

[Timothy B.]

Re: Differential Noise Part II

I want to add to Gary's post #11 about Lucas oil and additives. My daily driver is a old 1999 Mercury Sable that has a transmission shifting problem since 30K miles. When it shifts from low to L-2 sometimes the engine revs free like it's caught in neutral if your to hard on the acellerator pedal.

Had it flushed/filled at Ford dealer and still same problem until just recently added a bottle of Lucas transmission fix and within a minute all is fine again. Car has been shifting occasionally like that for 10 years and now it's fine. Anyone that knows me knows I am not a fan of additives so I don't know if it's the quality of today's fluids or what the Lucas product contains but the bottle states it can be added to fresh fill to condition a serviced transmission or add to new.

Made a believer out of me so I second Lucas products, my cars are all maintained very well by me.

[Oliver S.]

Re: Differential Noise Part II

Based on another post by Duke Williams I ordered 80W 90 GL 5 - the modern equivalent to the initial mil ?... . Brand I chose is Valvoline. My garage mentioned the same spec except GL5 to use. The mechanic said that he would only add one bottle of posi fluid since this type of oil is actually ment for usage in a diff with posi - without additional posi fluid. I'll give it a try. If it doesn't fix the problem I'll do as proposed here.
I hope the posi is not damaged now since before the diff was out last year there hadn't been a problem - and now I have been driving 1000 miles.

Regards