John and Andy,
In my experience (not backed by any polymer chemistry),
we should change the gearbox and diff oils. However,
not more frequently than every 3 to 5 years or 50000 miles. This is for
standard gear oil in normal driving, I don't know about the synthetics or
about cars used heavily (racing, autocross, etc.) When the
distinctive sulfur-like smell fades to a sour or burned smell, its time to
change the stuff.
I worked at a Jiffylube-like place to pay for college and I've drained
30 year old gear oil. Believe me you don't want that stuff in your car.
It looks and feels like its reverted to its original form (crude oil.)
Since its a real bear of a job to drain the diff (and to refill the tranny),
call around to the local lube shops and ask if they have a vacuum
tank that removes the gear oil. Basicly it sucks the oil out of a probuscis
(word of the day) that you stick in through the filler plug. Most shops also
have a pump to refill and can do the tranny lots easier than the average
owner. For me it was worth the $20 I spent to have the lube shop
do these jobs.
Be sure to warm up the oil by driving around for an hour or so first,
which of course is the easiest part.
At 11:25 PM 8/25/98 +0100, jonmac wrote:
>
>On August 25, Andy Mace wrote:
>
>> Gearbox and differential oil don't need to be changed at all -- only
>> topped up as needed.
>
>Andy, I'm not challenging in any way what you have written and I know this
>is what the factory recommended in days of yore. However, I have long been
>of the opinion that this was a shortcut on Triumph's part to reduce owner
>servicing costs - and I'm not too convinced whether it was really the right
>way
>to go about things.
>When I last removed the diff plugs on my cars to check oil levels, I stuck
>my finger in the holes and took a sniff at the oil sticking to my digit. In
>layman's terms, it reminded me that possibly a herd of tomcats had been in
>there for far too long - and any oily aroma had long since gone.
>Over the years, I've speculated on how long an oil can reasonably be
>expected to last and still do the job. I know nothing at all about the
>chemistry of the oil industry but I know things called polymers are present
>in oils which presumably are there to protect and keep the oil in good
>order. What happens to these polymers through the undoubted shearing action
>they must encounter as the diff or gearbox is working? The tooth loading on
>a crown wheel and pinion must surely be many tons per square whatever and
>how long can an oil REALLY last? I have to say I've never subscribed to
>this 'lifetime' oil claim and I've changed the oil (with difficulty) on a
>number of occasions because I don't see how it can be expected to go on for
>ever. Does anyone want to comment and allay my concerns?
>
>John Mac
>
>
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