Meesh Posted February 20 Report Share Posted February 20 Please let me know your recommendation on which brand/type of fluids that you use for your 720. I have especially been having a difficult time knowing which gear oil will work for my 1985 truck. Also advice on which fluids are OK to go synthetic with or which you recommend going conventional. Quote Link to comment
datzenmike Posted February 20 Report Share Posted February 20 Everyone says synthetic doesn't leak but every time I used it I had to replace the seals to stop it. Transfer case output then the top input from the transmission. Put synthetic blend in my differential and the pinion seal began to seep so new seal. Put one qt. of synthetic engine oil in to top up and a drip started to form on the timing cover seal. If you have good or new seals go for it. My rear transmission seal gets changed once a year because I like the shift quality of my gear oil. GL-4 for transmission and steering box. MUST be GL-4 or say compatible with copper alloys or 'yellow metal' safe. DEXRON ATF if automatic and in the power steering.. GL-5 for differentials. DOT 3 for brake and clutch hydraulics. All oil brands are about the same. All have to pass a minimal rating, some are slightly better than others but cost more. For engine oil you should use an oil high in ZDDP as today's oils have reduced this anti scuff additive since '92 to almost half what the 720 came out with. I use Shell Rotella T4 which is a diesel oil which is exempt from this and has a 1,200ppm ZDDP level. It comes in 15w40 and 10w30. Quote Link to comment
Meesh Posted February 20 Author Report Share Posted February 20 2 hours ago, datzenmike said: Everyone says synthetic doesn't leak but every time I used it I had to replace the seals to stop it. Transfer case output then the top input from the transmission. Put synthetic blend in my differential and the pinion seal began to seep so new seal. Put one qt. of synthetic engine oil in to top up and a drip started to form on the timing cover seal. If you have good or new seals go for it. My rear transmission seal gets changed once a year because I like the shift quality of my gear oil. GL-4 for transmission and steering box. MUST be GL-4 or say compatible with copper alloys or 'yellow metal' safe. DEXRON ATF if automatic and in the power steering.. GL-5 for differentials. DOT 3 for brake and clutch hydraulics. All oil brands are about the same. All have to pass a minimal rating, some are slightly better than others but cost more. For engine oil you should use an oil high in ZDDP as today's oils have reduced this anti scuff additive since '92 to almost half what the 720 came out with. I use Shell Rotella T4 which is a diesel oil which is exempt from this and has a 1,200ppm ZDDP level. It comes in 15w40 and 10w30. I know that the gear oil has to be yellow metal safe GL four but I've been about to buy an oil and it also says meets GL five specifications which doesn't make sense to me. I need to know the right brand to buy. Like is the royal purple stuff going to work OK? Amsoil? MT90? etc… Quote Link to comment
datzenmike Posted February 20 Report Share Posted February 20 Yes GL-5 is much superior to GL-4 but what makes it so is the reason you shouldn't use it. GL-5 has more of the anti scuff sulphur additives in it than the GL-4 and it breaks down over time into acid which attacks the copper alloy bronze synchros in the transmission. This does not happen over night and takes time but it adds up. Owners seldom change their rear oil when they should... every 3-5 years. Differentials don't have brass in them and because of the type of gear, need more protection. Must say yellow metal safe or GL-4 just to be sure. Quote Link to comment
Meesh Posted February 20 Author Report Share Posted February 20 I'm more hoping for like Amazon links to fluids that you'd recommend. For example I found this on Amazon: https://a.co/d/bp5W1Hd Has anyone had any experience with this Ultra 1Plus brand? For the dexron power steering fluid, is it ok to use the dexron ATF? (Which I already use in my other vehicle) Quote Link to comment
Stoffregen Motorsports Posted February 20 Report Share Posted February 20 ATF in power steering is usually fine. It tends to be thicker and has more gear oil in it, which can help if you have a leaky box. If you ever have an hour to kill, do some google searching for ATF compatibilty. It's pretty shocking to find that most any trans can run fluids other than recommended fluids. There was a year break when auto transmissions started to require synthetic fluids (around the late '90s), but even then, with a bit of knowledge, you can spec your own fluids based on your needs. Being "in the industry" I have played around with different fluids for years and I'll say this, with a word of caution, it doesn't matter as much as we all think it does. Sure, our race cars run Redline race oil in everything, but most of my street builds get Napa brand oils and filters. Aside from the transmissions, which I will use Redline MT90 for manual trans and synthetic ATF in auto transmissions that get heavy and hard use. Quote Link to comment
Meesh Posted February 24 Author Report Share Posted February 24 Well maybe someone could tell me if the Royal Purple 75-90 is safe to use? The whole reason I started this thread was to find the right gear oil that wouldn't damage my transmission because ever since I did a gear oil change and I believe I used the wrong type of gear oil my transmission's been acting funny. So I want to do another one and I just want to make sure that I don't spend another $50+ on something that's not gonna be good for my transmission. Quote Link to comment
datzenmike Posted February 24 Report Share Posted February 24 On 2/20/2024 at 9:20 AM, Meesh said: I'm more hoping for like Amazon links to fluids that you'd recommend. For example I found this on Amazon: https://a.co/d/bp5W1Hd Has anyone had any experience with this Ultra 1Plus brand? For the dexron power steering fluid, is it ok to use the dexron ATF? (Which I already use in my other vehicle) Synthetic is fine. Royal Purple and a few others are all probably from the same root stock, just a coloring agent added. I use the GM Delco friction modified synchromesh transmission oil. Same thing. You may notice that the synthetic oil may begin to seep at the rear seal where the drive shaft enters. A new seal should fix this. DEXRON ATF is recommended by my Nissan FSM factory service manual, yes. Quote Link to comment
Stoffregen Motorsports Posted February 24 Report Share Posted February 24 I use Royal Purple in my Cummins powered Ram truck. Quote Link to comment
Foxhound Posted February 27 Report Share Posted February 27 I'm using Redline MT90 75w90 in my transmission and transfer. For my front and rear differentials whatever GL-5 80w90 they have at the store. MT90 is brass safe and a decent price. 80$ for 4 quarts. (2 1/8 quarts or 2 liters for FS5W71B manual transmission, 1 1/2 quarts or 1.4 liters for T100L transfer.) My transmission seals have been slow leaking since I got the truck and I don't know what was in there before I changed it, but it did shift smoother after. It was probably low to begin with. Can't say it helped the leaks, but didn't hurt either. Edit: The service manual states GL-4 for the transfer, but GL-5 is ok from what I've read here and at least half the cost and probably more effective with its extra extreme pressure additives, but I have to wonder why Nissan would specify GL-4 as opposed to 5. What did they know that we don't? Your choice. https://www.amazon.com/Red-Line-50304-2PK-Manual-Transmission/dp/B00NT5V8RW/ref=mp_s_a_1_2_maf_2?crid=3KI29MQIEG7MT&dib=eyJ2IjoiMSJ9.S-Kq1qhzEqlAZALwTO5leQIydgkORicjKgBLZkotiGj7yUyeUuukfB06amypwBTYVbsz2ayDzCBicJPtJAPrKd42wa4HwXkJXtIfOuQLhu9UXEWhzAWaMVsxCkjRVFosk6tUusYgoxljj_hOjEr6cCNRHPfacciL1UlmD4wj4V7QTYMOVFKZgnAU-lTOGcsRocYCy62dYeCe-etMq_jgtQ.EcvumyWJCM8JfPMqdoRKlUtNQBsm2GAzSHzKBm0iYac&dib_tag=se&keywords=mt90+redline&qid=1709014119&sprefix=mt90+redlin%2Caps%2C547&sr=8-2 1 Quote Link to comment
datzenmike Posted February 27 Report Share Posted February 27 Differentials have different style gears and how they mesh together. They transmit power through a 900 bend necessitating more anti scuff additives. Transmissions on the other hand transmit power axially and have bronze or brass synchro rings. Generally GL4 has about 4% of the sulphur bases anti scuff additive package and GL5 about 6%. It would seem the 2% difference would not make that much difference but 6% is 50% more than 4%, a big difference Quote Link to comment
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