Geoff Weeks

Larry, SAE 50 (synthetic or mineral) has the same viscosity range as 90 GL. 40 SAE is close to 80 GL so no change in "thickness". Gear lube and engine oil are "rated" on different scales. EP additive package in GL increases "tackyness" in the lube so it tends to stay on the gears (and syncro) better, not an advantage with syncro's. An important thing in hypoid and amboid gearing. SAE 50 or 40 are approved by Eaton and I have used both. SAE oils have better heat tolerance then gear lube and are preferred for that reason. Synthetic oil has better heat tolerance than mineral based SAE oil. If you look though what Eaton has put out about lube for their heavy manuals, all three types of oil are approved depending on market. When run in the highest heat load conditions, over 1950 ft/lbs and/or extended drain, Eaton says that the top tier of oil has to be used if you want them to warranty it. You also have to keep the oil temp below their limit with and oil cooler. If you are running below those limits and follow "std" oil change protocol, they will warranty with mineral oil as well. In third world regions they still allow gear lube to be used. Every step up in oil is better but not required for proper operation as long as oil temp is kept below X (I'd have to go back and re read to find the limit). In short, the syncro still works with all three types of oil.

Bolton, Manchester area.

"bleeding, bloody, etc" was an expletive descriptor, "the bleeding nut was so tight, I had to get the smoke wrench".

You sound like an Englishman I used to work with!😀

It is hard to know which way to turn, when only one set of eyes are on the truck, and we only "see" what is written. This isn't a knock on the poster, just if a clue isn't passed on, we will not know. @fjh said long ago that oil sample analysis would be prudent at this point, and I 100% agree, it will show what is in the pan even if no moisture/antifreeze is "seen" in the oil.

Eaton calls for many choices, it is right there in their manual. I am not recommending something that Eaton does not. Larry wasn't happy about paying the expense for synthetic and according to Eaton it isn't required. I found no info saying flushing was required at any point in the manuals I read when changing lube, if it isn't there (it may be and I missed it?) I can't point to it. If you can point to where it is required, I will accept that. When you made the the statement that syn was required it was something I had not heard or read, so I went to the source to see if my understanding was incorrect, it was not. So I linked the source material for all to read. IF you want extended drain intervals and you want Eaton to warranty it, then and only then does Eaton require its use for warranty purposes. On a used transmission none of those apply. All the oil I listed are approved by Eaton for their HD manual transmissions. By your reasoning deleting the oil cooler would also void any factory warranty. But they are not required below 350hp, although you pointed him to the delete plate. By the title of this thread, he is well below that. Transmission lube has an easy job compared to other boxes, no combustion gases, no hypoid or amboid gearing, little chance of moisture accumulating, just spur gearing, roller bearings and one double ended syncro.

I wouldn't give SAE 50 a minute of thought before filling the trans with it. Your call. SAE 50 is listed as approved. Any used transmission syncro is going to "be saturated" with what ever was run before, It will not make a difference, but as I say, your money, your call.

You can disagree with Eaton, that is fine, I went to the source to make sure I gave the correct info. further more it is a used box, so you have no idea what it was filled with. Eaton doesn't mention a need to "flush" if a different or unknown lubricant is being replaced by something else. Synthetic has better heat qualities than SAE 50 which has better than GL-1. Each is a step up. In this application, which is so far down the scale from the transmissions rating, SAE 50 would be fine. Even GL according to Eaton would be ok, but I would not recommend it. They list it as acceptable in other parts of the world (in the same transmissions)!

What is missing from that list over the "old days" is 80w90 GL-1 which is not approved any more. GL was not preferred lube since SAE 50 became common. Higher GL (2 and up) were never recommened due to their friction (EP) additive package. Here is a link to the manual you can read it yourself. I doubt that engine will exceed 1850 ft/lbs! Eaton Lube requirements. Eaton lube spec's Edit: looks like they approve GL-4 in Asia?? I guess I was wrong about that!

Larry, SAE 50 is fine according to Eaton's list dated 2023. Synthetic is only required for extended warranty /drain interval. Here are screen shots from Product Specification Manual Eaton® Lubrication TCMT0021 EN-US

No matter what suspension, how the load is distributed on the trailer make a much larger impact on ride than what the suspension type is. For best ride, if a concentrated (dense) load, split in 1/2 and place 1/2 over front and rear. For less dense, you'll need to place the load through out the trailer in order to get it all in. Worse thing you can do is "belly load" a dense product, placing the load in the center of the trailer, it will ride like hell and that sound like what you have. Doesn't matter what the product is, rock or iron, how load will make a big difference. The problem comes with a rear dump, where you wouldn't want to have the weight concentrated at the front and rear and try and dump it. In that case safety of unloading trumps ride comfort unfortunately. try to avoid mounding it in the center of the trailer. In short it sounds more like the product being hauled, not the truck or trailer suspension.

Here is a chart (may be the one you looked at) 2070-2080 that shows the ratio, in both cases 1st in direct is 5.24:1 which would be fairly high starting gear. Somewhere between 3rd and 4th (if you count the lowest gear as 1) on an Eaton. I think you'd still want the compound for starting.

I do not remember. I was looking for a parts breakdown of the BM9 and found some chart that showed it obsolete and the new 150BMP that replaced it.

Yes, I wasn't saying your had a snap ring just the the two models used differing retaining methods. Since air starters are made in right and left rotation (noted in your model number) having a left thread on RH rotation, means they had to make another part with a right thread for LH rotation, explains why newer models went with a snap ring retainer, works for both rotations.

Cats of that vintage and 400 hp could be water aftercooled, that is one place it could be leaking. Coolant doesn't just disappear, so I would put some time into finding where it is going. head/spacer plate gasket is another. .6 OD puts a lot of heat (and power) into the transmission oil. You have a large OD and can drop the rear ratio quite a bit to move "in the mud", and still get down the highway at decent speed. My Marmon will top out at 80 with 4.11's and .78 OD, how much more do you need? If you have gears you can not use most of the time, but are paying a penalty for not having low enough gears at the same time, you are not making the most of what you have. Flying when empty, is a poor tradeoff for working well when loaded. Look at the total ratio, not the individual boxes, make the best compromise over the total ratio, so you are likely better off with a ratio that tops out at 80 mph but gives you a lower starting overall ratio.