I have a stock 2004 S10. I know that shifting in and out of overdrive too
much is a bad thing, so when going uphill, or when travelling in hilly
country you need to shift out of overdrive.
What is it exactly that is hard on the transmission?
- selecting overdrive but not going in
- the actual shifting from drive to overdrive
- driving with the torque converter unlocked
- none of the above
I've read numerous posts, but I haven't been able to put a finger on what
exactly causes the overheating problems in a transmission or premature wear
on the parts.
I guess my torque converter locks in both Overdrive and '3', is this
correct? and if so is it relevant to driving in a way so as to protect the
Any help or a link to a source would be appreciated. Thanks.
Heat in a transmission is caused primarily by two things:
1) Torque convertor slippage
2) Shifting gears.
For #1, the TC produces heat as a by-product when it is in replication mode
(NOT locked), the more it's replicating torque, the more heat it creates.
So, an AT will produce more heat in 4th gear, unlocked, than it will in 3rd
gear, unlocked, becuase the engine RPMS's are higher in 3rd gear hence to
engine is producing more torque that the TC doesn't have to "make."
Shifting gears causes hear as the frictions apply the selected gear. The
longer the shift, the more heat is produced.
Just my personal feelings, but when I'm towing, I lock out OD...
More of a peace of mind thing, really.. I figure that you can run
forever without OD and not hurt anything, but might add heat or strain
on the tranny if in OD at the wrong time..
With our setup, (99 ram/360/3:55 6,000# TT), even running on flat
ground it seems to pull better and use less fuel if OD is locked out..
In OD, it takes more pedal to do the same speed, so I'm guessing that
it's more efficient for us to just not use OD.... YMMV
Like Doc said, shifting produces heat, especially downshifting on a
grade... I know my truck is going to downshift going up the hill, but
it seems like starting with OD locked out is easier on the tranny..
yp that's what I've been hearing from Gary and others for quite some time on
this group, so I made sure to lock out OD.
Still-- seemed like it was revving awful high. Probably just my not being
used to the tranny not using it's OD.
Think back a few years back before OD trannys werre the norm.
I had a '64 Chevy pickup with 3.73 gears and no OD. It would run about
3000RPM at 65. It would run like that all day long if you wanted it to. I
had a '73 GMC that was the same.
Enter OD transmissions and now it is a sin to run much over 2000 RPM at 65
MPH. You have to be crazy to run that engine at 3000 RPM!! (or so many
I run my '93 Caprice, pulling my boat, all day long at 70 in drive. It is
still turning less RPM that the old pickups were.
Greg... I use a similar guide when I'm towing....
I think of a 5 speed stick... you can run full out all day in 4th
without hurting it...
When we took a trip from Ca. to Wa. and back last month, we were
pulling grades at 40 or 45 mph and turning about 3,300 to 3,500 rpm...
Once we got used to hearing the truck stay in "passing gear" all the
way up the grade, everything was fine.. flat land, we held about 60 or
so at about 2,500 rpm..
(not towing, we turn about 2,200 at 65 mph in OD)
probably what you're hearing is the engine being in the "sweet spot"
of the power band... not usually heard unless you're towing or have a
BIG foot.. lol
In my limited experience, engines seem to do better at a little higher
rpm when towing... unless, of course, you can afford a turbo diesel..
He needs to try and drive a old 'Benz with 4 on the tree. The mech. at the
station I worked at in the '70's got a laugh when it took me 10 min. to
figure out how to get it in reverse to bring it into the bay. I figured it
out. Damn furrin cars.........LOL
"anything you say can & will be misquoted & used against you"
I don't think you NEED to shift out of OD, but I and I'm sure many others do.
I personally do it because all of the shifting irritates me.
I've found that my tranny temp rises when I'm driving around in 3rd under the
rated stall speed for my converter. IE: in traffic never going much above
35-40mph. For my full sized truck running the
4L65 tranny, it's around 1800rpm brake stall.
I can basically drive around all day at 2,000rpm in 3rd, and not generate much
more heat than if I was locked up in OD.
My computer is set to apply lockup in third as early as 43mph... lockup in
fourth as early as 36mph. The thing is, if I manually select 3rd gear, I never
once feel the lockup take place. "Torque
converter clutch lock during shift" is not turned on, so I know that's not
One thing I hear that takes place, is a "partial apply" of the lockup clutch in
fourth when you go up a moderate grade or feed on moderate throttle. I haven't
logged any data about this yet, or felt
it myself, but the TransGo kit for the 4L60's are supposed to delete this
TCC lockup will be more of a kickdown of a gear, rather than a smooth (partial)
release. That might be where the "don't tow in OD" thing comes from. It's
probably pretty easy to cook a TCC if you
drive around in this mode for too long.
With that said though, I have no problems pulling 5,000lb loads at 65-75 on the
highway, in OD. Around town, I use 3rd.
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