R180 whine at 45-50 solution.

[djwarner]

My 3.54 R180 differential had the usual whine between 45-50 that changed pitch from driving to coasting. The FSM says it was due to excessive wear between the ring and pinion. This is usually blamed on pinion bearing wear. My solution is somewhat different.

The clearance between the ring and pinion can be affected by the fore/aft movement of the pinion shaft. Differential rebuilding calls for inserting shim washer to adjust this clearance. In actuality, the shim assortment is used to accommodate machining variation in the manufacturing process. Since the bearing tolerance is much tighter than possible machining castings, you can normally replace the bearings while re-using the existing shims.

Because the ring/pinion gear is essential a bevel gear arrangement, there is a second way of introducing excessive clearance between the ring and pinion. Namely by shifting of the differential carrier left or right through output bearing wear. The outer race of these bearings are held in a bearing cap. Again, shims are used between the bearing caps and differential housing to account for manufacturing tolerance. The FSM gives formulas to determine shim thickness by measuring the machined surfaces.

These formulas are calculated to establish a proper preload to ensure proper operation as the differential warms up.

This was a clue to my wear issues as the differential was quiet when cold and became increasingly noisier after a 20 mile warm-up. With this knowledge, I ordered a set of output bearings. Upon tear down, I found that some mechanic tried to cure a leak around the bearing cap by packing the o-ring joint between the bearing cap and differential housing with RTV. Some RTV was even found between the shims, reducing the bearing pre-load.

This delayed re-assembly two days waiting for new O-rings. Fortunately, during the previous mal-maintenance, the shims were weren't mixed side to side. To anyone attempting this bearing replacement I would suggest ordering new O-rings with the bearings.

Replacing the output bearings was straight forward after removing all the RTV. Once done I verified the ring/pinion free play was back to factory specs, though near the high limit. Being in Florida, I refilled the differential will the heavier grade of oil. The net result was that I all but eliminated the whine. In fact, it was now almost as quiet as my wife's 350Z with only 30,000 miles.

But now the final solution. I tried putting Zmax in my automatic transmission and was impressed with how it quieted the 180,000+ mile unit. Recently, I read about someone reducing differential whine by going to a lighter weight synthetic oil. So I thought why not add some Zmax into the differential.

Now Zmax is pricey. A search for its MSDS indicated its only components is mineral oil and a coloring dye. Zmax claims that is doesn't remain in suspension but soaks into the metal surfaces. So I decided to experiment with baby oil instead. - Again a note to anyone trying this. Verify the ingredients listed on the label say mineral oil and fragrances only.

Based on the ratios Zmax recommended for the transmission, I added 1 ounce of baby oil to the one quart of differential oil. I must say the results were almost immediate and dramatic. I can't believe how it quieted the differential.

As for those of us who poo-poo the use of additives, Zmax was originally introduced as an oil additive for light aircraft engines. For those who know, the FAA is very particular about modifying aircraft and operations from the certified standards proven by the aircraft manufacturers. Even manufacturers of aftermarket devices have to specify exactly how their products are to be used and prove their products do not compromise safety. Considering that an aircraft engine failure is a much more serious event than in a car, the FAA came down on Zmax, demanding proof of Zmax's claims and safety. The end result, after extensive tests, Zmax (now sold to the aviation market under the trade name AV-Blend) is actually an FAA approved additive.

To summarize, after replacing the output bearings and verifying the ring/pinion free play was restored, I had a differential that was mechanically sound. I would have been satisfied with the performance, though still short of perfection at this point.

However, it was the dramatic difference after adding the baby oil that prompted my taking the time to write this post. YMMV.

[Pop's Z]

Very interesting post. FWIW you can buy pure mineral oil (no fragrances) at some kitchen supply or retail stores. It is used for maintaining wood cutting boards. I've been using RedLine for the diify. I think I will add a little mineral oil to the diffy and see what happens. It isn't too noisy, but there is some whine.

Cheers, Mike

[Zed Head]

Seems odd. It's just low viscosity oil. It should just blend right in and lower the gear oil viscosity by a fraction.

Side note - isn't it odd that people rub a petroleum distillate on their babies?

Oil culture.

[zKars]

Read the MSDS at zmax itself

www.zmax.com/documents/msds_105_avblend.pdf

There is a single ingredient listed. Mineral Oil, >99%

Now is "Mineral oil" a generic term, or is there a single or any number of compositions for Mineral Oil....

You decide:

Mineral oil - Wikipedia, the free encyclopedia

Edited August 27, 2014 by zKars