View Full Version : Topping off Trans/Transfer Case fluids, but don't know what's already in there?

07-23-2020, 04:37 PM
I bought an M38A1 a month or so ago. I need to drain all the fluids and start from scratch because I don't know the history on it. Some of my gaskets are leaking underneath so it'll be a good time to just change out those gaskets all at once. In the meantime, I've enjoyed driving it. I've been getting some puddles on the garage floor so I wanted to top off my trans/transfer case so I could continue driving it until I had a free weekend to change everything and replace those gaskets. I've ready all the threads about different lubs.

Main concern is, I don't want the trans/transfer lub to run dry while I'm driving it until I have time to change out the gaskets. I have noticed that it's not shifting as smooth lately and I know there isnt' a ton of oil in there to begin with.

Here is my questions, if I don't know what type of lube is in the trans/transfer case is it OK to top it off with something like the Royal Purple Max Gear Syn 75w90 oil to get by in the meantime? I feel like it currently has a gear oil and not regular motor oil in it, because the spots dripping on my garage floor have that sulfur smell of gear oil.

07-23-2020, 05:57 PM
Doc Dana - this one is yours

07-24-2020, 08:19 AM
No One65r, do not put hypoid oil in your trans and transfer case. Max Gear will work well in the Axles however. Here are two links to get you started. If you want to top it off use the right lubes. If it has been sitting that long, I would drain ALL the fluids ALL of them, and replace with the correct stuff. The things that happen to sitting lubes are not good for your baby. Drain them out and start with new, even if you don't have time to do the repairs to the leaks. The damage that water causes in there is just not worth it. I would not drive it all with 8 year old lubricants that have been sitting. They don't get the opportunity to heat up and evaporate condensate water. Acids can build up in the lubes from sitting and just ruin things like the sitting gas did to the carb. In sitting additives can separate and the lube can become a poor excuse for lubricant.


07-25-2020, 11:40 AM
Thanks, makes perfect sense. I’m just gonna dump and replace all the fluids tomorrow afternoon and then replace any gaskets when I have time. At least if I do need to top any of them off, I’ll know what I’m adding too.

On the trans/transfer oil, can you tell me an exact manufacturer/specs on what your using. Or even post a picture of the container :D

07-25-2020, 12:02 PM
I use Red-Line MT-90 https://www.redlineoil.com/mt-90-75w90-gl-4-gear-oil

It is pricey. It's just one of those things I have used under some extreme circumstances. Good stuff.

07-25-2020, 05:06 PM
A Doctoral Dissertation Indeed!

Carson Childs
08-03-2020, 02:49 AM
"It is pricey. It's just one of those things I have used under some extreme circumstances. Good stuff."
I always trust bmorgil with his recommendations, so you can bet that this is a very wise advice.

08-12-2020, 09:38 AM
Thanks Bmorgil. I got a chance to swap out all (transfer, transmission, oil, both differentials, coolant) the fluids 2 weekends back. Good thing I did. The oil reservoir had some black tar sludge built up in the bottom of it unlike anything i've ever seen. I think it could have been part of the filter that broke down and settled in the bottom.

So here is my question, it shifted really good/smooth/firm prior to changing out the transmission/transfer case oil. Never grinded going into 1st or had any issues going into 1 or R. I used the Redline MT90 that you had mentioned above. I noticed the difference immediately after changing the transmission fluids. It just doesn't shift as smooth and if I'm shifting into R or 1, I feel like I have to ease it into gear to keep it from grinding. Is there a chance that my transmission just doesn't like this new mix of oil? Should I try something else? I've put a couple hundred miles on it since changing the fluids. It drives great and no issues going into 2 or 3rd. It's just gotten finicky about going into 1 or R and it happened immediately once I changed the fluid. It never pops out of gear or makes any crazy sounds. You can just feel it grind some as i'm going into 1st and sometimes you have to work it around to get it into 1 or R.

08-12-2020, 11:42 AM
You have the right fluid in there now. The 1st reverse grinding is probably a few things. I am assuming it had some pretty thick gear oil in it before.

The first and reverse gears are not synchronized. When you swapped out the lube the Redline is probably quite a bit less "thick" than what was in there. The thick lube probably helped slow the gears down when attempting shifts into first or reverse. If it is grinding because you are trying to shift into first or reverse while moving, or you are not waiting long enough to engage from neutral to gear when disengaging the clutch when stopped, it will always grind.

Here is the test, Start it up in neutral and from idle and stopped, disengage the clutch and count to 4 slowly. Then attempt to shift to first or reverse (The un-synchronized gears). If the transmission has not stopped spinning, the gears will clash. If they do, the clutch is not completely disengaging. The clutch should be adjusted for complete disengagement.

Let me know what happens.

Just remember this is an old transmission. It can only be shifted into first when moving by double clutching. To get it into reverse you must be stopped and the transmission must stop spinning. It will go into the synchronized gears while moving or, even if the transmission has not stopped spinning with the clutch in. I would say that the thick lube slowed the gears down a little and allowed a quicker shift from neutral to 1st or Reverse. The lube you have now will require you to let the transmission stop spinning before you try to put it into the un-sychronized gears. You will have to bump these old trans missions from time to time to get the gears to line up.

08-12-2020, 05:59 PM
Thanks for the input. I'll do some of those tests tonight. I will say, I have never tried to shift into 1st or Reverse while moving. It's always been while I was completely stopped. I also have made a point to "slow shift" with the pedal all the way to the floor. Even after a fresh start @ idle (not moving) or at a stop light once it's warm (not moving), I still have to baby it going into first if I don't want it to grind.

08-12-2020, 08:56 PM
Bmorgil has great advice. The clutch adjustment should do the trick to get the transmission back under control.

08-18-2020, 08:23 PM
Ok, so I did your 4 second test above. If I hold it in 4 seconds, it doesn’t grind at all. I thought I was babying it before, but I guess I just need to slow things down another couple seconds.

08-19-2020, 07:36 AM
Easy on the old girl! You are far better off with the correct lube and waiting a few seconds that's for sure.

10-04-2020, 05:53 PM
Do you use Red Line in your diffs as well?

10-04-2020, 07:21 PM
I am a fan of Mobil 1 Synthetic https://www.mobil.com/en/lubricants/for-personal-vehicles/our-products/products/mobil-1-syn-gear-lube-ls-75w-140/ It has a nice range and has a good heavy high end at 140w in case things get hot. In testing in the lab, there was a reduction in operating temperature in Hypoid gear driven axles when we used the Mobil Synthetics. That said I would not hesitate to use Red line. It is difficult to move away from something you trust however. I have not had the opportunity to see how Red Line axle lubes perform. I have seen it in the winners circle!

The little 134 engines produce so little power compared to the axles capability. It really doesn't take much to keep the Dana Axles cool. 80w is all you need.

10-05-2020, 04:43 PM
Thank you!

10-05-2020, 06:53 PM
Anytime dalero!