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 Towing in Overdrive?

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Deadmanonduty



Posts : 539
Join date : 2011-08-30
Location : Green Bay, WI

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PostSubject: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 12:25 am

I'm wondering about towing with my 95 RMW in OD. It has 2.93 gears with the tow package.

The reason I'm asking is because when I had my PCM tuned by PCM4less (or whatever there exact name is), THEY TOLD ME to tow in OD and let the tranny do whatever shifting it needs to do. I thought that was crazy, but figured they knew what was best since they programed the trans to shift firmer and more aggressively. The engine is stock internally and the trans is too.

So my question is, tow in OD or not? I towed 4,000 Lbs today on an open trailer 75 MPH and it stayed in OD most all the time unless I climbed a steep hill. Is this good for the tranny or am I harming it? It held it in OD and turned about 1,800 rpm most all the time. Sometimes it jumped 3-400rpm which I assume is the torque converter unlocking. It only shifted down into 3rd gear twice on the 100 mile trip.

So, OD, or no OD?

I always grew up towing with OD OFF...........

Thanks Guys! Smile
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sherlock9c1



Posts : 2144
Join date : 2009-05-28
Location : Huntsville, AL

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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 6:39 am

In the old days of the 700R4 and mechanical control of shift points, you'd get nasty 3-4-3-4-3-4-3-4 shifting if you did this. Not any more.

  • With electronic control of the 4L60E, you can program it to behave just about any way you want it to. No more crazy shifting. So that solves that problem.

  • As long as the torque converter is locked, you aren't pumping heat into the transmission by churning the fluid in the converter; again, this can be done via programming.

  • It is a proven fact that there is more line pressure available for the 2-3 shift when the 4L60E is in OD than in D due to the internal hydraulic design. Try it yourself if you want.


Bottom line: yes, do what the programmer says.
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Deadmanonduty



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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 9:04 am

It is a proven fact that there is more line pressure available for the 2-3 shift when the 4L60E is in OD than in D due to the internal hydraulic design. Try it yourself if you want.



That one I know, because my old 96 RMW shifted totally different if the gear selector was in D instead of OD. It even upshifted into 2nd gear early in D, so I always ran it up to speed in OD and then dropped it down into D after if shifted unto 3rd.

So, are you saying to run it in OD? I'm all ears! Smile
Thanks for the info!
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COL

COL

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Age : 72
Location : Lincoln City Oregon

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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 10:47 am

I am a little confused so far on this OD question even after reading the above. Last year I towed (1992 OCC with 3.23) my 22' Airstream from Oregon to California, Nevada, Colorado, Utah, Idaho and back.
Much of the trip was on curvy mountain roads and and a few times on freeway and flat roads.

I towed in Drive, not OD. The RPM runs consistantly above 2100. In OverDrive it runs below 2000.
My gas milage was around 15.5 average.

Is it okay to tow sometimes in OD? Picture Nevada, Kansas, or Texas flat country. Next year I am taking a year long trip in the OCC/AS combo. I want to be in the right gear and save the tranny.
Thanks
Dick
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jayoldschool

jayoldschool

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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 10:55 am

Your 92 has the old 700R4/4L60 non"E". See sherlock's info above (but I would say "D").
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sherlock9c1



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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 11:14 am

Deadmanonduty wrote:
So, are you saying to run it in OD? I'm all ears! Smile
Hmm. Let me see if I can figure out a way to be less subtle. How's this:

"Do what your programmer says."

jayoldschool wrote:
Your 92 has the old 700R4/4L60 non"E". See sherlock's info above (but I would say "D").
Yep. What I wrote only applies to 4L60Es which were used in the B-car platform 1994 and newer. 1993 and older with the 4L60 or 700R4 should run in D when towing.
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Deadmanonduty



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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 1:21 pm

sherlock9c1 wrote:
Deadmanonduty wrote:
So, are you saying to run it in OD? I'm all ears! Smile
Hmm. Let me see if I can figure out a way to be less subtle. How's this:

"Do what your programmer says."

jayoldschool wrote:
Your 92 has the old 700R4/4L60 non"E". See sherlock's info above (but I would say "D").
Yep. What I wrote only applies to 4L60Es which were used in the B-car platform 1994 and newer. 1993 and older with the 4L60 or 700R4 should run in D when towing.


Cool Thanks. I questioned him because he was in a huge hurrry and didn't have time to explain why...
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s1l1sc



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Location : Rock Hill, SC

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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 7:14 pm

Last time i towed in OD I tore up the differential... But mine is a 91...
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buickwagon

buickwagon

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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 8:10 pm

OD or not won't affect the differential -- the diff will see the same load no matter what gear you are in. Dropping into a lower gear has an effect on the input side, not the output.

Hauling 4,000lbs probably isn't a problem with the tow package. The final ratio is somewhat akin to dropping into a lower gear with a non-tow pack car anyway. I would watch the temperature gauge -- if the temps are climbing above normal then the engine is working harder and a lower gear should help ease the burden. Gas mileage may be another good guide -- if a lower gear produces better mileage, it's a sign that the engine is working outside it's optimum power band in the higher gear.

Personally, I've towed 6,000lbs with a 92 tow pack car. It was fine in OD but better in 3rd once I hit hill country. I haven't towed that much with the 95 yet, but I imagine the extra power would keep the engine from lugging up most hills.
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convert2diesel



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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeThu Apr 04, 2013 10:29 pm

The trick to using OD while towing is to keep your eye on the RPMs. If the convertor is constantly hunting between locked and unlocked then your driving on the edge of the trans wanting to be in third. You'll get the better mileage in third, locked up, than in forth unlocked and your trans will thank you for it.

If your going to be towing heavy alot, I would consider getting into a new set of gears. Put the factory spec towpack gears (V4P) in the Caddy and it made a world of difference when towing the RV (5,500 lbs). Except on the hills, it happily stays in OD locked up. Took a 2 MPG shot in the arm when not towing but the powertrain is much happier with the new gears.

By comparison, am now sitting on a campsite in central Florida (near Sebring) having pulled the RV some 1,500 miles with a friends 06 Silverado. 6.0 LS, 4L80 and 4:11 gears. Best combination yet. In the hills have been averaging 8.5 to 10 MPG and down on the flats 10 to 12.5 MPG. This is bang on the same performance as the Caddy but this one has some real bottom end umph that the Caddy lacked.

Only issue is if there is any headwinds at all, the programming for the convertor, and the 4/3 shifts are a little wonky. In tow/haul mode, the upshifts are really elongated but with it off, the tranny does weird 4/3/2 shifts even on slight grades. All could be corrrected with programming.

Now if I could only get my trailer brakes to work properly affraid

Bill
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buickwagon

buickwagon

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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeFri Apr 05, 2013 6:02 am

He has the tow pack gears already:

Deadmanonduty wrote:
I'm wondering about towing with my 95 RMW in OD. It has 2.93 gears with the tow package.
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convert2diesel



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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeFri Apr 05, 2013 10:43 am

buickwagon wrote:
He has the tow pack gears already:

Deadmanonduty wrote:
I'm wondering about towing with my 95 RMW in OD. It has 2.93 gears with the tow package.

The Caddy has 3:63 (if I remember right) gears specs for the tow pack. Works better than the 2:93s.

Bill
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buickwagon

buickwagon

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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeFri Apr 05, 2013 10:59 am

The older Roadmaster (L05) towpacks had 3:23s. I don't know if the gears themselves would fit, but a rear-end swap should be possible.

Of course, it's cheaper and easier to just tow in 3 instead of 4, with much the same -- but less permanent -- effect.

I do like the suggestion about watching the tach to see if the converter is unlocking. Another good sign of what's going on.
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81X11

81X11

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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeFri Apr 05, 2013 1:01 pm

I always tow in Drive, never Overdrive. Goes for my Roadmaster and our past Suburbans, and will with the Denali.
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Guest
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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeFri Apr 05, 2013 10:45 pm

The Denali should be just fine in OD with such a light car as the camaro in tow.Now whenever you hit any long hills hit the O/D button but just when climbing,no sense in burning more gas than necessary!
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s1l1sc



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PostSubject: Re: Towing in Overdrive?   Towing in Overdrive? Icon_minitimeSat Apr 06, 2013 11:19 am

buickwagon wrote:
OD or not won't affect the differential -- the diff will see the same load no matter what gear you are in. Dropping into a lower gear has an effect on the input side, not the output.

Might have had something to do with 200,000+ miles on the drivetrain... And mine not being a towpack car. No telling what really happened, but it does have me a bit paranoid at this point ;-)
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