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BillO

Changing Differential Gear Oil -- What To Do?

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I have a 1995 Vogue Motor Coach (actually built in 1994) with a Rockwell rear axle. With 145K miles I think that it's well beyond time to drain and change the differential lube, but have been getting conflicting information from truck shop "experts" regarding what lube to use (i.e. regular versus synthetic).

One shop tells me that if the oil is non-synthetic then the whole assembly needs to be taken down, cleaned and new synthetic-compatible seals installed to refill with synthetic.

Another shop says they regularly drain and refill with synthetic gear oil regardless of what the original lube was, without cleanout or new seals.

I can't find any information on what the original gear oil was. Rockwell says they shipped the axle dry and the OEM filled it. The OEM is out of business. Even though I received a complete set of manuals from the original owner they don't mention the differential fill at all.

The only point I have is one shop that tells me no one used synthetic gear oil before 1997, for which I have no confirmation.

Could anyone shed some light on this for me, either through experience with changing gear oil in the rear end of an older coach or through expertise with gear oils?

Thanks in Advance,

Bill

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If you already only need to change the oil every 100,000+ miles, why change anything. Empty, fill, head off to bed and sleep well.

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Maybe my point wasn't clear. I have no idea what to use to fill it and apparently going to wrong way can be bad news.

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Bill,

When in doubt, go to the owners manual (see link below). Meritor (who bought Rockwell) has their manuals on-line.

My brief search did NOT find any caution about not using synthetics.

Be aware that this is a 240 page document: https://s3.amazonaws.com/helm-arm-lod/mm1.pdf

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Brett,

That is a great reference. Looks like he needs to crawl under his coach and find the data plate. Is it a limited slip differential? If so you will need to add friction modifiers.

The chart on page 160 does show use of synthetic gear lube.

Bill

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Rockwell (Now Meritor) built some pretty stout and trouble free differentials for the trucking industry. When I was with Ryder we simply drained out the OE stuff and put in synthetic with no issues that I can recall. Thousands of single and tandem tractors were done and I'm sure the change had the blessing from Rockwell.

There might be an issue with a limited slip differential as it may require a specialized lube formula.

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That is also what I did with our Rockwell axle-- drained the old and went with synthetic. 120,000 miles later and one additional change after 50,000 miles, no issues at all.

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Folks,

Thanks for the feedback. The last two posts were especially what I was hoping to see.

Brett, thanks also for the reference. I can't read it right now because of access speed with my tethered 3G connection. However, as soon as I find a decent WiFi connection I will.

I am pretty sure that I do not have a limited slip differential, but will double check before changing the oil.

Not knowing what the OEM used originally, I was mostly concerned by the conflicting info from truck shop "experts" (i.e. "don't put synthetic in after regular gear oil" and "don't put regular in after synthetic"). Now it looks like the safe bet is synthetic with the caveat of limited slip differential confirmation.

Brett, did you do a second change at 50,000 miles to flush out any remaining old style oil (similar to what Allison recommends when changing to Transynd in their transmissions)?

Thanks again,

Bill

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Bill,

No, just changed it based on time-- I figured every 5 years was reasonable.

Brett

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Just a note, All synthetic oils are fully compatible with regular oil. The guy trying to tell you that you had to flush all the old oil out and change the seals was looking for a fast buck.

Bill

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