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Which is better when at a stop light with an automatic?
To shift it into neutral and put it back to D when green light comes or make it stay in D the whole time?
I know if you just put it in D and hold your brake, it will put a lot of force and the engine sounds different than idle, will that shorten the life of the trans. in general?
At the other hand, is it bad to shift more? (from D to N to D). every time I shift, the car shake(which is normal for automatic), so I assume it is just like more wear to the trans.
Please share your opinion with me. Thanks!
I know if you just put it in D and hold your brake, it will put a lot of force and the engine sounds different than idle, will that shorten the life of the trans. in general?
At the other hand, is it bad to shift more? (from D to N to D). every time I shift, the car shake(which is normal for automatic), so I assume it is just like more wear to the trans.
Please share your opinion with me. Thanks!
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Regarding heat, the friction occuring when the clutch engages generates heat. Almost all automatic transmissions/transaxles are liquid cooled, sharing a common radiator with the engine. Normal transmission pan temp. is about 185 F. (coincidentally about the same as the engine thermostat setting). If the engine is overheating at stop lights, shifting to neutral allows higher engine RPM, higher water pump RPM, and improved coolant flow. Otherwise, leave the trans in gear. There is no benefit in shifting to neutral.
Regarding to change the trans. fluid, I also heard that sometimes, if you change it, it will start to leak, but that only happens if you didn't change it for, say, 50k or more. So, is it safe to say that if you change it every 30k, there is very little chance that it will leak, if it were not before?
Automatic transmissions use an engine driven pump to develop hydraulic pressure which applies clutches and bands to control a compound planetary gear set (except Saturn, Honda, Acura).
Clutch and band control (shifting) is determined by engine load from the throttle valve cable, manifold vacuum modulator, or TPS & MAF/MAP & coolant temp & RPM, and by vehicle speed from the governor or VSS.
Transmission "special hydraulic oil" is required to apply clutches and bands, regulate the rate of friction element lockup for smooth shifts, transfer energy in the torque converter, provide cooling, lubrication, cleaning, etc, etc.
Torque converters allow slip at low engine speeds, allowing the trans to remain in gear without engine stall. As RPM and centrifugal force increase, higher vortex flow is generated which strikes the turbine vanes, forcing the turbine and the trans input shaft into rotation. WHen appropriate speed and load conditions are met, a clutch locks the turbine to the converter housing to eliminate slip.
That's my understanding of automatic transmissions, based on 32 years of rebuilding them and 21 years of teaching their construction, operation, overhaul, and diagnosis at the technical college level.
Thanks,
Al
After the pan is removed to replace the
fluid, a worn out reused gasket (a lot of them
are supposed to be reuseable), a defective new
gasket, or an improperly installed gasket or
pan (out of alignment, mistightened, etc.)
could cause the trans to leak.
As far a rebuilt trans goes, in theory some could
actually be better than a new one. A properly
rebuilt transmission should have all the parts
checked out to make sure they're within factory
new specs and the duds are replaced.
In the case of a new trans, is there any guarantee
they inspected all the parts? Perhaps they
just pulled them out of the parts bin and tossed
it together. In adc100's case, that's probably
exactly what they did!
OTOH, some rebuilds are sloppy and sometimes the
new ones may get a good looking over. Like so
many things automotive, we just don't know.
Maybe the manufacturer knows, but they never want
to tell you things like this.
I'd probably twitch a bit if they wanted to put
a rebuild in my brand new car. (if I had a brand
new car that is!) A factory rebuild for my '98
wouldn't bother me a bit.
Mike
Al
A rebuilt is disassembled, inspected, and defective parts replaced as required. When a unit is remanufactured, all components are inspected, measured for tolerances re original engineering specs, and replaced as required, all wear items are replaced, and any components or sub-assemblies which have had an update or modification partway through a production run (based on field reports of failures) will be changed. So you can actually end up with a superior, more reliable assembly. Hope this helps soothe the sting.
Btw, check out this site for typical remanufacturing info:
http://www.acdelco.com/parts/1350_set.htm
P.S. I can feel the hot breath of our hosts coming to shoo us outta here and into the Transmission Trauma forum again :-)
Al
As you are the expert, I want to get your opinion on the same question: Is it good or bad to shift to N while stopped at a light and shift to D before you go? Since you mentioned when car is stopped, it is slip instead of cut the engine off the wheel, does it mean it will have wear if you leave it in gear? or maybe D-> N ->D will make more wear/damage to the trans?
Thanks
I have read, but do not have first hand knowledge, that some transmission's pumps do not engage if the trans is in Park or Neutral. If this were the case, I would feel better leaving the car in gear, when stopped.
Drive or Overdrive = 50-70 psi @ closed throttle
150 - 200 psi @ wide open throttle
Reverse = 200 psi @ c.t.
300 psi @ w.o.t.
Fluid out from the converter goes directly to the cooler circuit, then back in to the trans to feed the gearset and bushing lube system. If the pump stopped working in Park or Neutral there'd be no pressure feed to the converter, cooler, or lube system.
Seems like every time I turn around there's changes in technology but I can't see how an automatic could live very long without adequate cooling or lubrication.
We have access to all the latest domestic product training (Chrysler and GM sublet their dealer tech training to us) but our info on imports is a bit sketchy. I pick up some things such as the dedicated cooler portion of the rad you pointed out from forums such as this one. Thanks for that info.
A method of doing the fluid filter change was recommended to and tested on my F-250 E4OD by me recently.
Unload drive wheels by placing axle on stands. disconnect supply hose from radiator and place in suitable container. Start engine, engage transmission and shift through all ranges observing when drive wheel stops turning. Stop engine and proceed dropping pan and filter. (Very little fluid remains in the pan.)
My question: does this method cause any undue wear if done discreetly in a safe manner?
Thanks for your help.