Timmaah! wrote:
Well, maybe you haven’t heard it all, yet. The judder is caused by just enough impulse torque to slip the torque converter a bit at peak impulse torque. Just after peak impulse torque the torque converter grabs with a thunk (under full hydraulic pressure). This happens at 1,800 RPM where there are 2 massive impulses with each RPM. It corresponds exactly with the beat of the engine or we are not talking about the same effect.
Can you say DUUUHHH!!! What do you think that clutch chatter is? It is described many ways; Chatter, shudder, slippage, judder, etc... In most vehicles the clutch is never under full hydraulic pressure at low rpm. In some vehicles it is a function of the pump being unable to raise full pressure at low speed, but in most, it is because of the programing.
Timmaah! wrote:
In the standard transmission there are 2 things going on that prevent this from happening. The first reason that the standard transmission clutch does not slip and grab is because it is strong enough to hold the impulse torque.
Is that not exactly the reason which I gave as an argument in pro of the TC slipping vs the other theory of torque pulsations? I think my explanation was clear enough. Perhaps you should read it again.
Timmaah! wrote:
Second reason that it doesn’t happen is that standard transmission diesels, where this would be a problem, have what is referred to as a dual-mass flywheel that is designed to absorb the impulse and not destroy the transmission.
Indeed many Manual trannys do have DMFs. However it must be remembered that DMFs are entirely ineffective outside of their tuned RPM and torque range and will either burn up because of slippage or can even multiply the hammering at certain low harmonic ranges. In our CRDs, they are tuned for the peak torque curve which is much higher than the RPM range where our shudder is occurring. In any 4 or 6 cylinder vehicle with a manual tranny. you can achieve torque pulsations by lugging the engine at RPMs below about 1200, regardless of whether or not it has a DMF.
Timmaah! wrote:
The more cylinders that a diesel engine has the more the impulse torque is smoothed so it’s less of a problem in a V8 diesel. The lowly Jetta TDI standard tranny model has a dual-mass fly wheel. In very rare cases, auto Jetta TDIs can judder. Sometimes even the Jetta dual-mass flywheels give up.
So what? This is not a new revelation, but it is another reason to suspect TC lockup slippage. If it were torque pulsations as you theorize here, 007Husky would never have mentioned the shudder improvement in the initial post. It would have had the same amount of torque as before. The only difference between before and after is the new clutch material with it's increased lock holding capacity.
Timmaah! wrote:
The CRD computer(s) try to protect the torque converter by downshifting when the torque is too high or by upshifting at a higher RPM under high acceleration. Our poor little torque converters in our CRDs have to take it all or they slip just enough to judder when conditions are just right.
So what really is your argument? Above you are arguing for torque impulses being the cause of the shudder but here you say that it is clutch slippage, which is what I initially posted as the cause of shudder.
This is fun.
