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Synthetic ATF goes into both.
 

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Discussion Starter · #5 ·
I am finding it hard to believe that synthetic was a requirement in 1990. We barely had anything more than Mobile One for engines then.
 

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Discussion Starter · #6 ·
Of course that would explain why it is so freaking hard to shift.
 

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Not likely. There were several problems with ZFs back then; particularly, the force required to operate the clutch diaphragm. It cracked transmissions AND firewalls. If your truck's firewall isn't reinforced, look up the TSB about it here:
Search Technical Service Bulletins

And check the Aluminum casting for the pedals - they can crack. Then look at the MC pushrod eye and the pedal shaft bushings...
 

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Iirc, there was a tsb stating the switch to synthetic.
I believe the gasser versions still ran plain atf.

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Synthetic is recommended in trans and differentials nowadays for it's better ability to withstand extreme temps plus other benefits over non-synthetics. And the rumors years ago that switching over to it caused seal leakage proved to be nothing but an old (mechanic's) wives tale.
 

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I had an engine run dry after switching to full-synthetic.



I think it doesn't happen any more because full-synthetic oils no longer contain any synthetic oil.
 

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I think it doesn't happen any more because full-synthetic oils no longer contain any synthetic oil.
Right, every one of those oil companies are lying to us and I just hate it when that happens. :)
 

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Synthetic is recommended in trans and differentials nowadays for it's better ability to withstand extreme temps plus other benefits over non-synthetics. And the rumors years ago that switching over to it caused seal leakage proved to be nothing but an old (mechanic's) wives tale.
I'm going to have to disagree with you on that one. Some of the old synthetics did in fact cause gaskets to leak though I never saw seals leak. They would just pour out the gaskets, when the only thing that changed was synthetic oil after a long period of running common oil. The theory was that it washed all of the build up from the gasket surfaces and the brittle gaskets couldn't make up the difference.
 

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Right, every one of those oil companies are lying to us and I just hate it when that happens. :)
So you think it has never happened, right?

Synthetic Oil vs. Mineral Engine Oil - Changing from Mineral to Synthetic Oil
Shell & Castrol Settle FTC Charges ? Royal Dutch Shell plc .com
JobbersWorld Online
Esters In Synthetic Lubricants - Bob is the Oil Guy

That last one is pretty technical and dry to read, but the relevant line is: "In automotive applications, the first qualified synthetic crankcase motor oils were based entirely on ester formulations and these products were quite successful when properly formulated. Esters have given way to PAOs in this application..." , which means synthetic esters are not used in "synthetic" automotive oils now.
 
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