Difference Between differential fluid Vs. transmission fluid

The difference between differential fluid Vs. transmission fluid - Why do we need to understand the difference between differential fluid Vs. transmission fluid in cars? The reason is many of us may think that differential fluid Vs. transmission fluid is the same.

This assumption is indeed difficult to avoid because several things could be the cause, including:

Differential fluid and transmission fluid are generally changed at the same time (for example, the replacement time is every 25,000miles or every 24 months).
Differential fluid and transmission fluid look the same at first glance, either color or thickness.
It's equally used as a gear lubricant.

Difference Between differential fluid vs transmission fluid

These two types of fluid have significant differences. So, if there is an error and mistake in selecting the type of fluid, it can cause damage and wear that should not have happened.

So what are the differences between differential fluid Vs. transmission fluid in cars? And why should we use a different fluid between transmission fluid and differential fluid? Below is a complete review of the difference between differential fluid Vs. transmission fluid.

1. Different lubricated working area

Transmission fluid is used to lubricate all components in the transmission, such as acceleration gear (1,2,3, R, etc.), linkage shaft, idler gear, synchromesh, and differential gear (for FWD manual transmission). The difference between differential fluid Vs. transmission fluid that is most easily distinguished is the different working areas that are lubricated.

Transmission fluid itself is also divided into two types, manual transmission fluid and automatic transmission fluid. The automatic transmission fluid is divided again into several variants, including the planetary gear version of the automatic transmission and the CVT version of the automatic.

Likewise, with differential fluid, differential fluid is used to lubricate all components in a car axle, such as ring gear, pinion gear, side gear, and others.

There is regular differential fluid (used for open differential axle type), special differential fluid for locking diff type, and special Limited Slip differential fluid (axles that already use LSD). Each of these fluids mostly differs in the type of additive used. In general, the differential axle has the same typical fluid, but there are still have differences, especially at differential axles type.

So here, we can clearly distinguish if the transmission fluid is used for transmission and differential fluid is used to lubricate the differential axle.

2. API service specifications are different

The second difference between differential fluid Vs. transmission fluid is the API service used. Although, in general, the API service between differential fluid Vs. transmission fluid is the same, using API service type GL (Gear Lubricants). Both have different levels.

For transmission fluid generally use API service GL-4, whereas transmission fluid with API service GL-4 has a lower additive level than differential fluid. One reason is the use of brass for synchromesh components. This lower additive is intended to keep the synchromesh from wearing out easily.

As for the differential fluid, API Service GL-5 uses a higher additive level than transmission fluid. This higher additive protects the axle gear from wear due to very high working pressures. Simply put, transmission fluid uses API service GL-4 while differential fluid uses API service GL-5

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3. The SAE spesification are different

The third difference between differential fluid Vs. transmission fluid is that the SAE specifications are different. For manual transmission fluid, usually, the SAE used can be varied. Manual transmission can use fluid with SAE multi-grade 70-80 to 90 or use single grade SAE90 type.

If the transmission is automatic, the SAE level is lower when compared to manual transmission fluid. However, it only uses single grade SAE specifically for differential fluid, such as SAE 90 only or SAE 140 (especially for heavy-duty vehicles such as trucks).

4. The amount of additives added is different

The difference between differential fluid Vs. transmission fluid that we know is the number of additives added is different. That is in line with the many differences in the components used between the transmission and the axle.

This type of GL fluid for transmission or axle usually uses phosphorus and sulfur additives. Its function is so that the gear can withstand high working pressures. As already mentioned in point no. 2, if the transmission fluid has lower additives, this is because of the synchromesh component, while the axle does not use synchromesh.

If there are too many additives in the transmission fluid, the synchromesh can wear out quickly. Vice versa, if the additive content in the differential fluid is less, then the gear in the axle will wear out quickly because it is defeated by high working pressure. Therefore, there is a difference in the number of additives between transmission fluid and differential fluid.