All about the Transfer Case
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01-31-2007 | 11:49 PM
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All about the Transfer Case
A lot of people see the Evo TC as a weak spot.... He's some background on the USDM Evo TC.
The transfer case issues on the early Evos was real. In Japan, all Evos from the Evo 7 and up had ACD and a Front Helical LSD. When Mitsu introduced the Evo to America they did not include ACD, and the cars had open front differentials.
You will hear varied opinions, but the general concensus is that the 03-04 Evo GSR's (not the 04 RS) had an open front diff because they did not have ACD and they DID have ABS. Without an ACD, ABS can wreak havok on a true AWD car (LSD's at front, rear, center). This is one of the reasons Mitsu felt comfortable releasing the 04 RS with a front limited slip, it has no ABS.
In 05, Mitsu started shipping all Evos with ACD, as an indirect positive benefit is that they all also came equipped with front LSDs as well.
Why is that such a benefit? The open front diffs on 03-04 Evos are WEAK, the spider gears are made from powdered metal, which is a very cheap manufacturing process which results in a metal that is not strong when subdued to drivetrain shock (I.E., hard launching). The helical LSD found in the 04 RS and 05+ Evos completely replaces the powdered metal gears (it is not an insert into the spider setup like a phantom grip), so that weak point is eliminated.
The majority of failed TC's in 03-04 Evos were due to broken spider gears. The rest of the failures were due to actual ring and pinion gear failure.
The ring an pinions fail in ALL Evos for one simple reason. Mitsu had a drivetrain problem to solve, and in my opinion (and any other engineer worth his weight in salt) they solved it poorly.
The Transfer case houses a ring and pinion gear, but unlike every rear differential in the world, in the Evo TC the Ring gear drives the pinion gear. (big gear drives little gear). Why is this bad? Helical gears were not designed to transfer power in this manner, and as a result the generate a ton of heat. If you've ever looked at an Evo TC, the bottom side of it is covered with heat sinks, and the undertray on the Evo is designed to direct air to those fins to aid in cooling.
The second downside is the low fluid capacity of the TC. The oil is what transfers the heat off of the gears, and when there is less fluid to wick away the heat, the fluid cooks over time (especially high speed driving). The upside is that the direction of rotation of the Ring gear picks up the oil and the immediately lubricates that pinion, unlike in a rear diff where the oil needs to travel all the way around the ring and then hit the pinion. More oil on the pinion means it will be cooled more. (good thing)
Bottom line, change your TC fluid at every other oil change if you want your Evo's TC to live a long happy life. And when you change it, use ONLY Mitsubishi Diaqueen Gear oil, it was designed to live in that high heat environment and will be happer taking that heat than the other options out there.
On another note, my 03 lived at ~400WHP for the majority of it's life. I changed the oil with Mobil 1 every 3k and used Mobil 1 filters as well. I changed my TC fluid every othe roil change. My car was still running very very strong when I traded it in (50k miles) and it did not use any oil.
Keep on top of the maintenance, and the Evo will treat you well. If you're going to abuse it, reward it with fresh oil every 3k, fresh TC oil every 6k, tranny/rear diff oil every 12k, and keep an eye on your pads, rotors, tires, and alignment.
Borrowed From SuperHatch NE Evo
The transfer case issues on the early Evos was real. In Japan, all Evos from the Evo 7 and up had ACD and a Front Helical LSD. When Mitsu introduced the Evo to America they did not include ACD, and the cars had open front differentials.
You will hear varied opinions, but the general concensus is that the 03-04 Evo GSR's (not the 04 RS) had an open front diff because they did not have ACD and they DID have ABS. Without an ACD, ABS can wreak havok on a true AWD car (LSD's at front, rear, center). This is one of the reasons Mitsu felt comfortable releasing the 04 RS with a front limited slip, it has no ABS.
In 05, Mitsu started shipping all Evos with ACD, as an indirect positive benefit is that they all also came equipped with front LSDs as well.
Why is that such a benefit? The open front diffs on 03-04 Evos are WEAK, the spider gears are made from powdered metal, which is a very cheap manufacturing process which results in a metal that is not strong when subdued to drivetrain shock (I.E., hard launching). The helical LSD found in the 04 RS and 05+ Evos completely replaces the powdered metal gears (it is not an insert into the spider setup like a phantom grip), so that weak point is eliminated.
The majority of failed TC's in 03-04 Evos were due to broken spider gears. The rest of the failures were due to actual ring and pinion gear failure.
The ring an pinions fail in ALL Evos for one simple reason. Mitsu had a drivetrain problem to solve, and in my opinion (and any other engineer worth his weight in salt) they solved it poorly.
The Transfer case houses a ring and pinion gear, but unlike every rear differential in the world, in the Evo TC the Ring gear drives the pinion gear. (big gear drives little gear). Why is this bad? Helical gears were not designed to transfer power in this manner, and as a result the generate a ton of heat. If you've ever looked at an Evo TC, the bottom side of it is covered with heat sinks, and the undertray on the Evo is designed to direct air to those fins to aid in cooling.
The second downside is the low fluid capacity of the TC. The oil is what transfers the heat off of the gears, and when there is less fluid to wick away the heat, the fluid cooks over time (especially high speed driving). The upside is that the direction of rotation of the Ring gear picks up the oil and the immediately lubricates that pinion, unlike in a rear diff where the oil needs to travel all the way around the ring and then hit the pinion. More oil on the pinion means it will be cooled more. (good thing)
Bottom line, change your TC fluid at every other oil change if you want your Evo's TC to live a long happy life. And when you change it, use ONLY Mitsubishi Diaqueen Gear oil, it was designed to live in that high heat environment and will be happer taking that heat than the other options out there.
On another note, my 03 lived at ~400WHP for the majority of it's life. I changed the oil with Mobil 1 every 3k and used Mobil 1 filters as well. I changed my TC fluid every othe roil change. My car was still running very very strong when I traded it in (50k miles) and it did not use any oil.
Keep on top of the maintenance, and the Evo will treat you well. If you're going to abuse it, reward it with fresh oil every 3k, fresh TC oil every 6k, tranny/rear diff oil every 12k, and keep an eye on your pads, rotors, tires, and alignment.
Borrowed From SuperHatch NE Evo
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