Please help 1500rpm judder, what is it ?????

[ChaosMaster]

I am just hazarding a guess it may have been changed when in for its services but im not 100% but going to change it. Why would this only cause judder at 1500rpm in 5th and be ok every other time?

If you knew how a Torque Converter works, then it's pretty simple. If I had to dumb it down, I would say, think of a river and it's currents. At low speeds, the currents are relatively weak, but at high speeds, it can knock back just about anything. In a torque convertor, the engine creates currents in the transmission. At low speeds, the currents is weak, thus when you stop at the lights, it feels like the car wants to move forwards (it does when you let go of the brake), but it isn't much. When you accelerate, the engine speed increases, thus the current increase, which in turn pushes the car forward.

Now, here's the important part, I guess. Torque converter efficiency increases with engine speed. Efficiency I'm talking about here is transferring power from the flywheel to the transmission. They have been designed so that at 1000 rpm, the efficiency is low (e.g. 20%) while above 2000rpm, the efficiency is high (e.g 95%). The reason for this, is because at 1000rpm or idle, the lower efficiency means less stress on the engine, thus more fuel efficient, where at higher rpm, you basically want to get all the power from the engine to the wheels.

Now here's the problem, as the oil ages, it wears out. So at 1500rpm, when it's efficiency should be say 90%, it's now only 70% (again, figures are purely for demonstrative purposes). At lower gears, it's fine, because the engine isn't producing much power/torque at 1500rpm anyway, and the lower gears multiply the input, so the load isn't that great (think gears on a bike, lower gears are much easier, but higher gears require more muscle). At 5th though, which is the tallest gear, the ratio is actually taller than 1:1, meaning the load is much higher. In this case, because the oil's efficiency is much lower, it's slipping, thus causing the judder or w/e sensation you're feeling. At say 2000rpm though, the efficiency is much higher, so even though the oil is worn out, it's still able to transfer 85% which is enough to avoid slipping.

This is in theory anyway, it's a bit difficult to explain simply and accurately, but I think you get the idea. Of course, all transmissions are different, especially Honda's ATF, but this is the general idea.

[Jasemas]

If you knew how a Torque Converter works, then it's pretty simple. If I had to dumb it down, I would say, think of a river and it's currents. At low speeds, the currents are relatively weak, but at high speeds, it can knock back just about anything. In a torque convertor, the engine creates currents in the transmission. At low speeds, the currents is weak, thus when you stop at the lights, it feels like the car wants to move forwards (it does when you let go of the brake), but it isn't much. When you accelerate, the engine speed increases, thus the current increase, which in turn pushes the car forward.

Now, here's the important part, I guess. Torque converter efficiency increases with engine speed. Efficiency I'm talking about here is transferring power from the flywheel to the transmission. They have been designed so that at 1000 rpm, the efficiency is low (e.g. 20%) while above 2000rpm, the efficiency is high (e.g 95%). The reason for this, is because at 1000rpm or idle, the lower efficiency means less stress on the engine, thus more fuel efficient, where at higher rpm, you basically want to get all the power from the engine to the wheels.

Now here's the problem, as the oil ages, it wears out. So at 1500rpm, when it's efficiency should be say 90%, it's now only 70% (again, figures are purely for demonstrative purposes). At lower gears, it's fine, because the engine isn't producing much power/torque at 1500rpm anyway, and the lower gears multiply the input, so the load isn't that great (think gears on a bike, lower gears are much easier, but higher gears require more muscle). At 5th though, which is the tallest gear, the ratio is actually taller than 1:1, meaning the load is much higher. In this case, because the oil's efficiency is much lower, it's slipping, thus causing the judder or w/e sensation you're feeling. At say 2000rpm though, the efficiency is much higher, so even though the oil is worn out, it's still able to transfer 85% which is enough to avoid slipping.

This is in theory anyway, it's a bit difficult to explain simply and accurately, but I think you get the idea. Of course, all transmissions are different, especially Honda's ATF, but this is the general idea.

You must spread some Reputation around before giving it to ChaosMaster again.