Posted by Traveler on January 20, 03 at 11:46:14:
In Reply to: Re: Compare it to climbing stairs posted by Bruce on January 20, 03 at 10:20:39:
: But I would like to know the technical reasons for this.
: The fluid pumps through the transmission faster in 3rd than in overdrive. The increased volume through the cooler keeps it cooler.
Yes, 30% RPM difference in pump speed.
: On the other hand it has been brought up that there is more slippage in 3rd than in overdrive. The OD is locked up with no slippage. At least in some 700r4s. At freeway speeds it actually runs cooler in OD, at least that what some people have been saying - they have a gauge and have observed it.
It locks up in 3rd too. No slippage difference.
: I think the solution is to install a gauge and see what the temperatures are doing. Then install a cooler and see what the difference is. If it runs cooler in OD, like some have claimed to observe than I dont see why not use OD.
You have to deliver a 30% higher input torque to the trans to pull in OD. This will shorten the bearing life, TCC clutch life, and overheat the fluid in the converter until the TCC locks.
Also the OD ratio uses an additional planetary/sun gearset that is weaker than direct drive in third. Third is the strongest configuartion because none of the sun/planetary sets are carrying any load.
: I still dont see the analogy with climbing stairs. Seems like there are a lot of conflicting information out there.
A different analogy is trying to work a see-saw when you sit 30% closer to the fulcrum than your equal weight companion.