86 Champion 8400 transmission fluid

I'm curious whether switching from straight 10 weight to a 10-30 TO4 oil could help with gear slipping. Also, could old oil that needs changing cause slipping issues? My track loader's manual calls for 30W, but the shop suggested 10-30 works better across different temperatures. Now with this grader that has an 8400 transmission, it originally called for ATF but they found out pretty quick that ATF caused slipping when things warmed up. It came with upgraded clutch plates too. I know the oil and filter have been changed since it was new, probably multiple times. I'm not sure if the transmission itself has ever been serviced, but a couple bolts are missing off the transmission guard, so something's been done to it at some point. How much of a difference could fresh or different oil actually make? Would synthetic offer any benefit in an older transmission like this?

I run 15-40 in the summer. When I'm using it a lot during winter I switch to trans hyd tractor fluid. If it's already slipping, I'm not convinced that heavier oil will solve it. Champion issued a recall pretty soon after the 8400 came out—they changed the O-rings in the clutches to address clutch slipping issues.

I've never come across 15-40 TO4 type transmission fluid before.

Does the slipping happen all the time or just at startup, when it warms up, that kind of thing? I don't reckon oil's going to fix a slipping problem in those transmissions for the long haul. You could give the 30W a shot and see how it behaves. I've always thought synthetic belongs in newer machines, and once you switch to it you should stick with it. Running it in older high-hour stuff tends to cause leaks and other issues, though maybe that's different now. Not sure.

The grader was running at full operating temperature when it started slipping. Maybe I should've downshifted more?

Yeah, modern ATF is really about 3.5 to 5wt fluid, and THF might help with the clutch loads and help deglaze the steels if you've been getting some slipping. Going up to that TO4 spec fluid wouldn't hurt anything. Heat's the enemy with any transmission though. I tend to rev the engine more on these graders rather than lugging them, because the transmissions in these machines aren't as stout as you'd think. Higher RPMs give you more torque multiplication, better fluid pressure and volume, and better cooling.

Yeah, old transmission fluid can definitely cause slipping once it loses its shear strength and the viscosity improvers and friction additives break down from use and heat. Once that happens, it just can't hold the clutches anymore.

I remember reading that it's important to follow the recommended intervals for changing trans fluid and the filter. Since my grader is an '86, it might have come with ATF from the factory, which apparently caused slipping issues. The manual specifies it should use 10W trans fluid though. I topped it off a bit, but I should really drain it completely and replace it with fresh fluid. I'm pretty sure it's been changed at some point since it has a NAPA filter on it, but I have no idea how many hours ago that was or what exactly was put in there. Maybe mixing the top-off oil with whatever was already in there contributed to the slipping problem?

I've got both AFD Petroleum and a new Petro Canada lubricants facility about 10 minutes away from me, and they both stock TO4 spec oil. The Petro Canada place might just be a wholesale warehouse, but I picked up the top-off oil at AFD. If I remember right it was around $127 a barrel, which seemed reasonable at the time. Prices have probably gone up since then. Hopefully a full fluid change will help fix the issue.