Rear diff is inside the transmission. It uses any GL4 gear oil. It must be GL4, and *NOT* GL5. GL5 has sulfur additives and it will eat the brass synchros in the transmission. Many products are labeled as "GL4/GL5" because GL5 is supposed to be "backwards compatible" with GL4 uses, but only if brass is not used. Do not use anything labeled with anything saying "GL5" on it anywhere. A relatively easy way to tell if you will have issues is just to smell the oil. If it stinks, it has sulfur. If it basically smells like nothing more than engine oil, then it will be fine. Redline MT90 is a relatively popular GL4 oil that is suitable. CRC also sells "Sta-Lube Gear Oil 85W90" that works well too. I think Royal Purple makes a suitable product, but they tend to be rather expensive. You can use any gear oil in the front diff, since there is no brass inside. Any GL4 or GL5 will do the job.
I changed the transmission fluid recently in my 1997 Sambar 5 speed. I used SEA 140 (GL-4). Seems a little sluggish when first driving. Almost like the parking brake is slightly on. Is it possible that the 140 is too thick? If so, opinions on if this will damage anything inside.
I also have this symptom even after warmed up. Haven't found the fix yet but gear lube that is too thick can cause unnecessary wear during high speed/constant operation. The gear lube will start to create a thicker than necessary film between gears and the separation forces that are happening will be similar to that of hauling a heavier load. The oil may also be too thick to flow properly through the meshing gears causing metal to metal wear. Of course operating temperature plays a large role but operating temps for specific weight oils have a pretty large range and you are most likely already covered by the weight oil that's recommended. Additionally, fluid friction also exists, and your gear lube will heat up faster and to a higher temperature which causes it to break down quicker as a result. As a result, higher temperature will cause faster degradation over time with most mechanical things. All that being said, I wouldn't worry too much. I haven't seen anyone anywhere mention exploding axles on these things. They appear to be quite resilient! Also, I just want to make sure what I'm hearing is that Redline MT-90 (GL-4) is safe to use in front/rear differentials as well as in the transfer case/transmission? Because if so, that simplifies the process for me. 1990 S83P 4 speed 3" lift
We need GL-4 in the Sambar because of the use of brass synchros.. a Hijet could be a very different story. I have no idea what a S83P Hijet calls for. You may want to ask this question over in the Daihatsu sub-forum instead of the Subaru Sambar one. As for @Kie s question, the OE oil is 85W90, so I would guess that SAE140 is "too" thick. Will it damage anything? Probably not.. but I am sure that the trans/diff are working harder than they need to to spin around in that significantly thicker oil.
Thanks for keeping me straight! I didn't realize I found a Subaru forum with the search function. I'm new here
The manual for my '97 calls for "75/80 GL-4" in the transaxle, and "75W-90 GL-5" in the front diff. I would not use the same GL-4 in both. And I would definitely not use SAE140 anywhere in the truck. Hypoid gears in the front diff are better protected running GL-5, which shouldn't be used in the transaxle for the reasons others stated above. I'm using Red Line 75W-90NS GL-5 in the front diff. Red Line MTL GL-4 is about to go in the transaxle when I find a minute. The product data sheet for MTL even states it's not for use in hypoid diffs. From Castrol's website: API GL-4 – Intended for gear sets with light to heavy load and sliding forces. GL-4 lubricants are often used in syncromesh manual shift on-road and off-road truck transmissions. API GL-5 – Intended for heavily loaded gear sets with high sliding forces such as hypoid differentials. GL-5 lubricants contain high levels of extreme-pressure additives to provide protection under boundary lubrication conditions. Common heavy duty applications include differentials in on-road and off-road trucks, differentials, final drives in Caterpillar scrapers, and differentials and planetaries in Euclid haul trucks. Some manual-shift transmissions can use GL-5, but typically should not be used in synchromesh-type transmissions, as the EP additives can be corrosive to yellow metals found in those transmission types. Limited-slip differentials also typically require a specific lubricant with a limited-slip additive.
I was about to use a 75W-90 GL-4 in both the transaxle and differential, but the information you shared makes a compelling argument to get some GL-5 just for the differential. Thanks for sharing this.
No problem. I’ve seen a couple YT videos where the guy puts GL-4 in front and rear or GL-5 front and rear and I just cringe. Both are easily available at any auto parts store or online so why not use the correct fluid?
What manual are you referring to here? Both the owners manual and original service manuals I have gives several options for front diff oil, including both GL4 and GL5 options. While I am not at all saying that you should not run GL5, but GL4 is certainly an acceptable option.
The original pink Sambar 660 manual that came with my 97, published April 96, calls for GL-5 in the front diff. No other options. Maybe it has changed over the years.
Pennzoil Synchromesh and Valvoline Synchromesh are the two manual transmission lubricants I'm thinking of that I frequently see on store shelves at AutoZone or Oreilly.
