I have been reading here on SS for quite some time about what fluids in my 977. I changed the motor oil from the 10w-40 to straight 40 weight. I was still getting different comments on the fluids in the rest of the truck. I read where some changed the trans fluid to dextron or such. I sent Oshkosh a email and this is what they told me. In the trans, OE/HDO 15w-40, the transfer case is OE/HDO straight 40. And the rear ends are GO 85w-140. What do you guys think. My 977 trans runs a little warm even when I am putting around. Would the dextron help it run cooler or just leave what is in there alone? I also don't want to screw something up by a change if what is in there is ok. Any suggestions?
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M977 Fluids..........
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dk8019
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There's been a number of threads on transmission, but don't use 15W-40, the military did, but only because they convinced Oshkosh to let them. The engine was the same deal. In the transmission use a TES-295 fluid only. On the engine oil, make sure it is straight 40W rated for 2-cycle Detroits.
Thanks... Yep on the engine I got straight 40 in it. I know detroits don't need a multi weight. What do you think would be good in the transfer? I am going to do that first since I have a output shaft seal leaking and now would be a good time to drain and refill with the new seal. Thanks again....
dk8019
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On the engine, straight 40 isn't quite right sadly. From what I've been able to find, the best reasonably available oil that meets the requirement is Delo 100. The spec you are after is CF-2, hopefully what's in it is rated that way. otherwise a change might be in order.
On the transfer case my document says straight 40, so perhaps the oil out of the crankcase could be used. Mine looked great, so I haven't changed it yet.
On the transfer case my document says straight 40, so perhaps the oil out of the crankcase could be used. Mine looked great, so I haven't changed it yet.
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Delo 100
Elideclan2
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Also don't trust the temp sensor for the trans.
Both of my Hemtts show 190-200 on the gauge
but if I use a laser thermometer they show 170-180.
I use the laser often to check.
Both of my Hemtts show 190-200 on the gauge
but if I use a laser thermometer they show 170-180.
I use the laser often to check.
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I found the water temp gauge to lacking.
I changed mine to digital
I changed mine to digital
Yea, my water temp and trans temp show almost what I would call hot but I figured they might be off. Who's idea was it to start with really low numbers on the gauges and have huge jumps in the numbers but up where the running temps would be the gauges go from 180 to something real high in a small space. If you just look down real quick, looks light the water temp and trans are maxed out until you look a little closer. I think new gauges might be in my future along with the new fluids. Had a car show a cruise two weeks ago and took the M977 in the city cruise and loved driving this truck. You can't stop smiling....
dk8019
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Yeah go figure on the gauges. I'm used to it now, some digital gauges would be nice in the future though!
JDToumanian
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DELO 100 is available in 30 and 40 weight but 30 should only be used in cold climates; it's not suitable for summer heat.
I concur with dk8019. A friend of mine has a Detroit+Allison powered coach. There's a retired Allison engineer who hangs out on his bus-nut forum, he wrote the lube specs for the HT740 back in the 1970s (or was it the early 80s?), and said the U.S. govt. forced them to allow motor oil to be used under warranty because they didn't want to stock the TES-295 fluid. He said the truth is that motor oil dramatically shortens the life, but the military didn't care. For us who DO care, use TES-295 fluid... But if your trans has been on motor oil for a long time, switching to the TES-295 seems to have killed off a few Allisons. That's why I have a NOS spare in the can.
For the transfer, I have the Oshkosh manual for the 55000 series cases and it says straight 50-weight motor oil, so that's what I'm using there. Shell Rotella T1, 50 weight.
I concur with dk8019. A friend of mine has a Detroit+Allison powered coach. There's a retired Allison engineer who hangs out on his bus-nut forum, he wrote the lube specs for the HT740 back in the 1970s (or was it the early 80s?), and said the U.S. govt. forced them to allow motor oil to be used under warranty because they didn't want to stock the TES-295 fluid. He said the truth is that motor oil dramatically shortens the life, but the military didn't care. For us who DO care, use TES-295 fluid... But if your trans has been on motor oil for a long time, switching to the TES-295 seems to have killed off a few Allisons. That's why I have a NOS spare in the can.
For the transfer, I have the Oshkosh manual for the 55000 series cases and it says straight 50-weight motor oil, so that's what I'm using there. Shell Rotella T1, 50 weight.
I have read here the same thing about the trans oil change causing a problem after. I would really like to change it if I can. The temps are just to high to me and the change from what I hear will get temps down. What are the odds or chances the change will give me trouble? By the way, I have a MK48/14 also and it only has 100 miles on since the "remanufacture". Don't they stick a new tranny in when they do that or at least a rebuild? I think I would be safe the swap that oil out on that one.
JDToumanian
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I would go for it, especially with that low a mileage... But it seems to be a crap shoot. I changed the fluids on mine in Louisiana before driving it 1,700 miles home, and I've put a few thousand more on it since then and had no problems. I don't have any data to compare my temps to, since I changed the motor oil out of mine right away, but I live in the desert, and the hottest I've ever seen it get was driving up Cajon Pass last summer... It hit 200 on the trans temp gauge. It's usually much less.
I think I am going to just go for it on both. I think I have found a NOS trans in case but I want the 10w40 out. I can believe only 200 on the temp guage. On a hot day mine will get that hot sitting or just putting around. How many times to drain and change do you think to get the old out? Drain and fill and run twice do it? With the filter change too of course. Thanks for the help....
JDToumanian
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My plan was to change it in Louisiana, drive the 1,700 miles home, and then change it again. When switching, Allison considers the transition 'complete' after that 2nd oil change... But I haven't done it yet, so I'm still at like 80% TranSynd. It's on my to-do list!