To change or not to change Transmission/Diff/Tcase oil

[MalcolmY]

Obviously in a normal healthy-ish car the answer is always drain and refill with new oil.

But what about the beat up units, or the ones you have no idea the history about?

Where I come from every seems to oppose changing these oils (manual transmission, Diffs, transfer case). And especially on older cars. The "procedure" is to add oil if not enough. At least when it comes to older cars everyone agrees with this, owners and mechanics!

Recently I replaced the front Axle seals on my 1991 FJ70 because it was leaking since I got it. I filled everything with 140w oil as the mechanic's recommendation (hot climate etc). Interestingly the rear diff was almost dry, with no leaks visible.

I have no symptoms with this drive train except moving the shifter front Lo back to high is difficult.

Is the above mentioned belief correct in any way? If I drained and filled this oil in an old diff/trans/Tcase am I going to harm it or start to have symptoms?

(is 140w way too heavy even for a hot climate?)

EDIT: I'm willing to bet the oils in this car have never been changed since it came out of the factory. Maybe previous owners just added oil as they went along. Car has 274k km almost.

 

[coldtaco]

Don’t know why they would say not to change the oil. Sounds like want to save money. The only way I can see posible problems would be putting synthetic in an old unit if it only had dyno oil. I would run what Toyota recommends.

 

[jblueridge]

I do know that gear oil "weights" are not valued on the same scale as engine oil.

I would change out the oils as coldtaco suggests.

 

[roscoFJ73]

Is the above mentioned belief correct in any way? If I drained and filled this oil in an old diff/trans/Tcase am I going to harm it or start to have symptoms?

Landcruisers last a long time ,even when suffering abuse. But they last a hell of a lot longer when they are maintained to a high degree.
If you are buying new every few years, you could save money by ignoring maintenance and pass the wear and tear onto the next owner, thats the only logical reason I can see for not doing oil changes.
But astute used vehicle buyers may also seek out vehicles that have a documented maintenance history and be prepared to pay a premium.
And why would clean oil free from contaminates and metal particles and with its molecular sheer strength intact harm the components?
People who promote these tales are either lazy, tight asses or lack mechanical knowledge.
Would you fly in a plane knowing its maintenance has been let go?

 

[HomerOz]

G'Day Fella's,

MalcolmY, it is best to change all of the oils, at least you then have a bench mark to work from.
The reason I suggest this is, oil does degrade with time and use, so unlike Herpes virus, it doesn't last for ever.

I have two TLC's, one (BJ73-1989) I have had from new and another (FJ60-1982), that I got off a mate for $700.00 in 2016.
When I got the FJ60, I asked my mate how long had it been since the Diff's, G/box and T/case oils had been changed (along with other details).
He told me he didn't know, but that it would have been a long time ago. FYI, the G/box whines at 80 Kms/50 Mph and the G/box it a bit loose to the feel.
On the other hand, I have changed the Diff's, G/box and T/case oils on my BJ-73 every 30,000 Kms.
It still runs nice and quite, and the the G/box is still tight to the feel................ so that will do me.

Hope that helps

D'oh!
Homer

 

[MalcolmY]

Thank you all.

One of the reasons people here give for not replacing old gear oil is that old crusty oil and contaminants hold the gear teeth in place. So if you drain the oil you will dislodge this stuff and problems will arise (slip, noise etc). Sound good or bananas?

 

[Willis]

Thank you all.

One of the reasons people here give for not replacing old gear oil is that old crusty oil and contaminants hold the gear teeth in place. So if you drain the oil you will dislodge this stuff and problems will arise (slip, noise etc). Sound good or bananas?

I get the logic here, but I think that's a crutch to a bigger issue. I would prefer to know and repair what needs to be fixed, than hope my truck is held together with "old oil".

 

[ca18sean]

Thank you all.

One of the reasons people here give for not replacing old gear oil is that old crusty oil and contaminants hold the gear teeth in place. So if you drain the oil you will dislodge this stuff and problems will arise (slip, noise etc). Sound good or bananas?

I've heard of this argument with automatic transmissions, but never with manuals. Some older guys have told me that extra metal particles suspended in the auto trans fluid helps the clutches grip together better and prevent slip in older transmissions. I have no idea if it has any validity or if it's just an old wives tale (old mechanics tale?) but even with any automatic I've ever owned, I've always had good luck changing out old fluid with fresh stuff. If changing the fluid kills the transmission it was on it's last leg anyways IMO.