1966 Synthetic Differential Oil

[Steeletbird]

Quick question, i removed my diff from my 1966 tbird to replace the pinion bearing and seals ( were leaking ) and replace diff fluid, some say to not use synthetic diff fluid ... i dont see why not ? any suggestions ... what to use

thanks

Scott

 

[biddle]

ome say to not use synthetic diff fluid.

Synthetic fluids/oils are all the same size molecules. Naturally occurring or refined are not. As a result, over time, non-synthetic oils can fill in compromised areas of gaskets etc. If you switch to a synthetic fluid, it will typically work out these gunked up areas that are effectively serving as a gasket sealer. What is really happening, a problem is being exposed, the gasket needs replaced, but many people choose to take the position that the synthetic oil/fluid caused the leak, when in fact all it did was expose a problem. This is typically the reason why people will say they won't use it in older cars.

The problem when a gasket gets "gunked up" it's not getting lubricated, and this is why they fail and dry out.

 

[sre]

At one time I was in charge of maintaining a fleet of about 25 Mack trucks. They were prone to pinion shaft seals leaking. A salesman was selling a synthetic gear oil. I bought a 55 gal. drum, never had to replace another seal. I would use it.

 

[cokefirst]

Quick question, i removed my diff from my 1966 tbird to replace the pinion bearing and seals ( were leaking ) and replace diff fluid, some say to not use synthetic diff fluid ... i dont see why not ? any suggestions ... what to use

thanks

Scott

The problem with recommendations for oils is that everyone has an opinion. Here is an interesting view by a seller of gear products. https://forums.fordthunderbirdforum.com/threads/1966-synthetic-differential-oil.14787/ Since this is on older car, and you are unlikely to be driving this many thousands of miles a year, I would stick with conventional fluid. Each fluid has it's pros and cons. In the end, do what you think is best but read the opinions of those in the business.