Who knew a “simple” thing like what type of gear oil should be used in the transmission and the differential would be so time consuming!!
Answers all over the place and nothing clear.
So…
1969 4-speed toploader - what oil?
Does the differential get a different oil or the same as the transmission? Standard differential.
I’ve lost my way on GL-4 vs GL-5, dino based or synthetic.
Seems most people say NO synthetic. But there are limited choices out there for GL-4 organic products.
You can get GL-4 from Summit Racing or David Kee Toploader Transmissions and others. Summit has PennGrade (BradPenn) and Richmond Gear in a GL-4. Both state they are safe for soft metals.
Currie Enterprises assembled my Detroit locker with a 3:50 gear. There was a big highlighted piece of paper that said using synthetic gear oil would void my warranty. I called and asked why. Basically synthetic molecules are so small that they don’t provide enough “shock/cushion” protection for the gears. Dan Williams rebuilt my toploader and he recommended Shell Rotella non synthetic gear lube 75W-90 for the street or 85W-140 for the track.
My '08 Mustang (with 8.8" Traction-lok) came with synthetic oil in the differential from the factory. I wonder what’s different about the Currie setup that would make them void the warranty with synthetic. My Cougar currently has Mobil 1 synthetic (75W-90) in both the differential (9" Traction-lok) and the Toploader. I’ve used it for many years, dating back to the early 90’s when I started using them. The Toploader is all original and the synchros still work fine. I don’t know exactly how many miles either the transmission or differential have on them, as they were both used when I got them. I’ve put at least 20k on both. I’ve used both Mobil 1 and Royal Purple synthetics in transmissions and differentials without issue.
Every Ford dealer sells the appropriate gear lube and the friction modifier. Unless you are in Antarctica or someplace really remote you should be able to go to the nearest Ford dealership and get what you need.
Thanks Royce. I honestly would have never thought Ford dealers would carry gear oils for 50 year old cars.
And… maybe I need more coffee but that picture you sent has contradictory “cautions”.
So conventional, non-limited slip diff get the special modifier according to Caution #2?
The Valvoline I had for years. It was a GL4 rated lubricant. I know they are constantly changing. Brad Penn products are of the highest quality and I have been using them since the early 80’s. Better known as Kendall. The green oil.
From what I was able to discern from “the internet”… GL-4 and GL-5 are not compatible. In other words GL-5 doesn’t cover GL-4 as well. So, I would say no-go. But me being to OP I obviously can not be relied upon
