hep2jive Posted March 13 Report Share Posted March 13 Hey group! I have a 1951 Plymouth. What kind of oil should I put in the differential? I put GL1 90 oil. Seems fine but should I change it? Quote Link to comment Share on other sites More sharing options...
Adam H P15 D30 Posted March 13 Report Share Posted March 13 Save the gl1 for the transmission and just use a modern gl5 90wt oil for the rear. 1 Quote Link to comment Share on other sites More sharing options...
Ivan_B Posted March 13 Report Share Posted March 13 +1, these are hypoid gears... Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted March 13 Report Share Posted March 13 Go to your local walmart store and get the 80-90 weight rearend oil in a squeese bottle. This is what you need it is a gl5 oil for hypoid gears and is extreme pressure oil. I run this in my 39 Desoto. Rich Hartung Quote Link to comment Share on other sites More sharing options...
Ivan_B Posted March 13 Report Share Posted March 13 6 minutes ago, desoto1939 said: Go to your local Walmart store and get the 80-90 weight rear end oil in a squeeze bottle. I've also seen them sell gear oil in a soft baggy, this is actually soooo convenient, you can just push it out into the differential with your hands (under all sorts of access restrictions) no mess with cleaning the pump/hose! Quote Link to comment Share on other sites More sharing options...
Los_Control Posted March 13 Report Share Posted March 13 1 hour ago, desoto1939 said: Go to your local walmart store and get the 80-90 weight rearend oil in a squeese bottle. This is what you need it is a gl5 oil for hypoid gears and is extreme pressure oil. I run this in my 39 Desoto. Rich Hartung Rich, have you drained or changed any of that oil lately? I have been buying the walmart gallon jugs it is 85-145 gl5 ..... I ran it in my chebby truck and changed it about 6 months ago .... then again I changed it about 2 weeks ago .... while searching for a problem that did not exist 😜 The 6 month old oil was full of air bubbles. Let it sit in the pan for 4 hours and they never went away. Now I'm hesitant to recommend the walmart supertech oil. .... I do have it in my truck now and it has about 600 miles on it. I think it is possible I over filled the rear end and that is causing the aeration. .... My truck the fill level is 5/8" below the fill plug. I always out of habit fill it up til it runs out, then a couple more quick squeezes and cap it off. So technically I'm about 3/4" overfilled. Really grasping at straws thinking that is the problem. My plan is to run it for a few weeks, maybe today drain some out to get it down to proper level. If it is full of bubbles again I'm going to change brand of oil, no more walmart oil for me. I sure would like to hear a good report from someone on it ..... currently until I check it again, I'm not that person. 1 Quote Link to comment Share on other sites More sharing options...
hep2jive Posted March 13 Author Report Share Posted March 13 Thanks I'll get the gl5 gear oil. I was staying away because I know it can harm the transmission over time so I was worried to use it in the rear gear. Though I'm sure the GL1 won't hurt being in there or does it NEED the properties of a gl5? It's a slow easy going car I don't race why do I need the high pressure oil? 4 hours ago, Adam H P15 D30 said: Save the gl1 for the transmission and just use a modern gl5 90wt oil for the rear. Quote Link to comment Share on other sites More sharing options...
Sniper Posted March 13 Report Share Posted March 13 the shear dynamics in a transmission are different than in a rear axle. Hence the need for a different lube. In a rear axle you get a sliding of gear teeth across each other than does not occur in the transmission. The 51 FSM calls for an Extreme Pressures Hypoid Gear Lubricant, SAE 90 for the rear axle. Whereas for the trans and OD, it calls for SAE 80 Gear Lubricant. Back then it was GL1, there was no other choice, 2 Quote Link to comment Share on other sites More sharing options...
Ivan_B Posted March 13 Report Share Posted March 13 43 minutes ago, hep2jive said: It's a slow easy going car I don't race why do I need the high pressure oil? I will answer this question with another one: did you check the OEM manual recommendations? Quote Link to comment Share on other sites More sharing options...
hep2jive Posted March 13 Author Report Share Posted March 13 But I like GL1 😂😂😂 Quote Link to comment Share on other sites More sharing options...
Los_Control Posted March 13 Report Share Posted March 13 I will only add that as years have gone by the oils have improved as cars have improved/turned to junk. GL5 oil got a bad name for awhile because it no longer had additives in it for the softer metals such as brass. ..... Modern cars do not have softer metals in them. So it is important to read the labels and see that it does protect these metals. GL1 oil was just fine for these old cars and worked for years .... just getting hard to find because nobody really wants it .... GL5 is better quality in most peoples mind. Is available and cheaper ..... just read the label to be sure it protects soft metals. Quote Link to comment Share on other sites More sharing options...
Ivan_B Posted March 13 Report Share Posted March 13 1 hour ago, Los_Control said: Modern cars do not have softer metals in them. I would respectfully disagree with this statement. The good old brass synchros are still there, and this is probably the main reason we do not use the hypoid oil in the manual gear boxes. Although, some oil manufacturers claim that their oils are just fine, so it is definitely a good idea to read the bottle label. GL1 oil is not recommended for hypoid gears (your average differential) due to the lack of sufficient protection from metal-to-metal friction. More information is available here: https://www.api.org/-/media/files/certification/engine-oil-diesel/publications/1560-eighth-edition-april-2013.pdf BTW, the API has been around since 1919, but I could not find when the GL-1 standard was adopted Quote Link to comment Share on other sites More sharing options...
Sniper Posted March 13 Report Share Posted March 13 9 minutes ago, Ivan_B said: BTW, the API has been around since 1919, but I could not find when the GL-1 standard was adopted That's because it wasn't called GL1 back then. There was no other GL spec, so it was GL by default. Later as GL2-3-4-5 came about then numbers were added, retroactively for GL1. In any case, GL1 seems to be the oil for non synchronized gearboxes,, recently surpassed by MT-1. Since we do have a non synchronized 1st gear, it may still apply. Quote Link to comment Share on other sites More sharing options...
Los_Control Posted March 13 Report Share Posted March 13 9 minutes ago, Ivan_B said: I would respectfully disagree with this statement. The good old brass synchros are still there, I admit I made a very broad statement and it is not true in every case. Same time many cars were having issues because GL5 was not taking care of them ...... they got a bad reputation. .... Seems for the oil industry it was simple to just start including the needed additives to the oil. ..... so it was fixed. If you want to get into brake fluids .... modern fluids are not compatible with older fluids .... not such a easy fix ..... It is buyer beware or buyer needs to be informed. GL5 use to be the same way, but it was just easier to fix the problem by adding the additives ..... brake fluid is not the same way and you actually need to know something. Quote Link to comment Share on other sites More sharing options...
Dave72dt Posted March 13 Report Share Posted March 13 To say brass synchos are still there is also a broad statement. Metallurgy has changed in the synchro world. White paper reads will tell you it's gone from brass to paper lined to carbon fiber lined to sintered metal rings, depending on a number of factors. Some of these transmissions require a very specific oil because it can mess with the friction coefficient of the synchros. Read the label. Quote Link to comment Share on other sites More sharing options...
hep2jive Posted March 13 Author Report Share Posted March 13 My transmission is the same one that was put in in August of 1951! I'm GL1 Quote Link to comment Share on other sites More sharing options...
hep2jive Posted March 13 Author Report Share Posted March 13 Thanks everyone for the input. Everyone has helped me out that means a lot! May GL1 shine upon you! .....if you're a transmission from 70 years ago lol!!!! Quote Link to comment Share on other sites More sharing options...
Ivan_B Posted March 14 Report Share Posted March 14 I thought we were talking about the right oil for the differential, this whole time... 🤨 Quote Link to comment Share on other sites More sharing options...
Los_Control Posted March 14 Report Share Posted March 14 31 minutes ago, Ivan_B said: I thought we were talking about the right oil for the differential, this whole time... 🤨 We were ..... just some in class were not paying attention Gl5 is fine for the differential ..... Just be sure to read the label first and you will be fine. Quote Link to comment Share on other sites More sharing options...
hep2jive Posted March 14 Author Report Share Posted March 14 But but but there's no drain plug?! Differential plug?! To DRAIN Quote Link to comment Share on other sites More sharing options...
Los_Control Posted March 14 Report Share Posted March 14 5 minutes ago, hep2jive said: But but but there's no drain plug?! Differential plug?! To DRAIN Not sure who's rear end you are looking at ..... All Mopars I've worked on has a drain plug ..... chebbies you actually loosen the rear cover to drain oil .... Maybe you just looking at the wrong rear end? 1 Quote Link to comment Share on other sites More sharing options...
Sniper Posted March 14 Report Share Posted March 14 Later Mopars don't have a plug like the 8 3/4. My 51's had it Quote Link to comment Share on other sites More sharing options...
Los_Control Posted March 14 Report Share Posted March 14 My 49 has a drain plug ..... had to make a special tool to remove it ..... lost it and made another tool .... then found the first tool I made. If this thread was about modern mopars we would be giving different advice ..... @hep2jive just being silly and thats fine. Quote Link to comment Share on other sites More sharing options...
hep2jive Posted March 14 Author Report Share Posted March 14 I see where to fill the differential but no drain.... Any pics of rear ends plugs? Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted March 14 Report Share Posted March 14 some rear end did not have a drain plug you would take out the fill plug and then insert a suction tube and suction tool to pull out all of the rear end fluid. Some cars also had a drain plug that was on the lower left side near the bottom of the side flange. Just have to look on yours to see what you have. Rich hartung 1 Quote Link to comment Share on other sites More sharing options...
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