Red Line 75W80 API GL-4 Manual Transmission Lubricant

This product is nothing short of awesome! I have been a sports car enthusiast for 30 years, and in that time I have owned many performance cars, as well as working in the automotive field for 20 years. I used to live by the rule that their is no chemical fix for a mechanical problem, but this gear oil did do just that in my situation. I purchased a 2007 Civic Si a little over a year ago, just to have something a little sporty to drive around town, and also be reliable (Honda 😉 ). I learned that the third gear synchronizer in these cars were notorious for problems, and there was even a service bulletin issued by Honda that recommended replacing the synchronizer in the transmission, which calls for around 12 hours of labor. I have always ran synthetic oil in my vehicles, and after researching gear oil I came across Red Line, and also read some reviews by other Si owners stating this product solved their 3rd gear problems. Well, I gave it a shot, and yes it did fix this specific issue! This is also the first time I have used synthetic gear oil in a transmission before, and I can say that it is nothing short of amazing in the difference when it comes to shifting between all of the gears! Other than the 3rd gear issue in the Honda 6 speed I had no problems before changing the fluid, and their was only a little resistance to speak of when shifting gears. After the change, there is almost no resistance at all! Smooth as silk when shifting gears now. I would highly recommend Red Line to any car enthusiast, and though it did resolve my synchronizer issues as I said, this product is not a miracle fix for all transmission problems. I will be replacing the manual transmission fluid in my 525 horsepower muscle car to Red Line next.

Great for both bearing protection and smooth gear changes
Redline are also very helpful and responsive to email queries.
First class outfit making first class products

I’ve owned my 02 Acura RSX Type S since new in August 2001. It is still the best and most fun car I’ve ever owned in my 50 years of driving. The only complaint I’ve ever had was shifting from 1st to 2nd gear. The speed of the car, whether sedate or aggressive didn’t seem to matter. The ratio jump between 1st and 2nd gears is substantial and it was always clunky, sometimes grinding. Down shifting was never an issue from 3rd to 2nd.

In the last few years I’ve tried several things to improve the shifting. I started with a short throw shift lever from B&M which seemed to help, but in reality caused the shift cable end to bend, because of the design of the lever. What had helped was the removal of the rubber bushings that mounted the shifter housing to the floor of the car, the B&M kit included aluminum bushings to replace the originals. Mounting the housing solid took out unnecessary movement and wasted motion.

This past February I swapped out the entire shifter mechanism for a billet aluminum unit that definitely improved things along with new shifter cables from the same source, K-tuned.

This past Tuesday, I drained the Honda manual transmission fluid for the Red Line MTL. Almost immediately the shifting is smoother with no clunky 1–2 shifts.

The car has 92,000+ miles on it. The trans oil has been replaced according to the manufacturer’s outline, so this last change was 30,000 miles early.

I really wish I’d known about Red Line MTL ten years ago. This stuff really works.

Update: August 31. Since replacing the Honda manual transmission fluid with the Red Line MTL, I’ve been to Michigan and back and Wisconsin and back to St. Louis. I did normal maintenance on my car last weekend. Checked the transmission fluid and it was as clean as the day I installed it and shifting is smooth, almost effortless.

I used this on my daughter’s car when I refilled the manual transmission after removing and replacing it to install a new clutch. It’s working great.

The most important bit of info I ran across was the difference between GL-4 and GL-5 spec. GL-4 tends to be for manual transmissions and transaxles whereas GL-5 tends to be specified for differentials and transfer cases. GL-5 contains additional additives that are harmful to typical synchronizer material in manual transmissions. Bottom line: use what is specified for your application.

The majority of 75W gear oil that I found for sale at auto parts stores and online tended to be GL-5 and marked “includes additive for limited slip differentials” so this GL-4 Red Line synthetic gear oil was exactly what I needed!

Great product, arrived on time.