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Old 06-21-2004, 01:58 AM   #15
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watch that tranny

Do not run that rig in OD or you will ruin your transmission. Guaranteed. The 4L60E is not long-lasting to begin with. Instead, run in 3rd (Drive). You will spin higher rpms, probably about 2500-2600 at 60mph, but it will live a lot longer because increased coolant and fluid are pumped through at higher rpm. It will not harm your engine in any way or hurt your economy significantly. In addition, the torque converter and OD clutch packs on the 4L60 are not very strong, another reason to stay out of OD and try to ensure your torque converter stays locked up by not trying to run in too high a gear. A 3/4 ton uses the 4L80E tranny which is a lot stronger, and has an OD of .75 instead of .70, so there is less rpm reduction.

A good technique to learn is to not let the tranny unlock the torque converter for long periods of time, or lock/unlock frequently - this is very hard on it and overheat the trans fluid. You can tell when it unlocks by a rise of 300 rpm or so when in OD, 3rd or even 2nd, which indicates that the torque converter has unlocked and is slipping to help multiply torque, which unfortunately generates a lot of heat. Sometimes the TC lock/unlock feels like another gear change, although it is a smaller rpm difference than a full gear. When this happens it is better to force a full downshift, either through throttle pressure or manually pulling the lever back, and run in the lower gear at higher rpm with the TC locked up. Over short grades it isn't so critical.

The other weak spot is the small 10 bolt rear-end in the 1/2 ton. They are not designed for heavy towing and often fail by 80-100k even without towing. If you did not have the diff fluid changed before you left, get it done along the way and put synthetic in it. Keep your speed at 60-65 and it should be fine.

Fortunately, the run up to Alaska and back does not involve a lot of high mountain passes - mostly the highways run between the mountain ranges so if you get through the Rockies you will be Ok.

Have fun up there - it is gorgeous!

john
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Old 06-21-2004, 11:52 AM   #16
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Thank you for the comments. I did have the differential fluid repaced before I left Nashville but I'll have it changed again with synthetic before leaving Denver.

Referring to the above post by hohne, there is a "Tow/Haul" enable button at the end of the shifter on the steering column. I believe enabling this disallows the transmission from going into overdrive, amongst other things.

On your comments on locking/unlocking the torque converter, I don't know what effect the "Tow/Haul" has on this..does anyone know? Do you think enabling this function will get rid of this "problem"

Thanks,Gerry
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Old 06-21-2004, 01:03 PM   #17
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try it

I believe that it will still use OD even in tow-haul mode, it just raises the shift points and may do a better job of locking up the TC. Try it and see what difference it makes. I still would not tow in OD with a trailer that heavy unless you are really able to discern when the TC unlocks and immediately take it out of OD and go into Drive.
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Old 06-21-2004, 03:30 PM   #18
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John,

I just checked my car's manual and I see that it standardly uses synthetic lube in its differential, as well as in some other places. What made you think the differential used standard lubricant?

I will go ahead and engage the "tow/haul" function when trailering the trailer, but I don't think I am able to discern when the trans falls in and out of lock up.

I will reread your post several times and look for a change of engine rpm, I guess I have a hard time with pouring on more power to get it to lock up. Seems when I do this it shifts to a lower gear and the engine spins at 4000 rpm or so.

Gerry
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Old 06-21-2004, 03:31 PM   #19
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My advice would also say stay out of OD. That engine combo and rear end spells potential transmission problems unless you hold 3rd gear. I had a 5.7 liter 3.73 rear axle on my half ton van and I pulled in 3rd all the time.

My current 3/4 ton van sports a 6.0 liter 4.10 rear axle and 4L80E transmission which is up to using OD. Tow haul as noted by others will raise your shift points but will not lock out OD. With tow/haul engaged I don't hit OD in the current van on flat roads until slightly over 50 mph.

Even with Tow/Haul I can hear the torque converter unlock when I'm in OD and start pulling a decent sized hill. In my case it just unlocks earlier. I won't let it do this much though and I'll pull it down to 3rd to get the extra torque I need.

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Old 06-21-2004, 03:44 PM   #20
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Hi Gerry,

Yes, my point was to "pour on more power" and force the downshift, then hold it there by pulling the lever back, at which point you can ease up on the throttle to hold a reasonable speed and rpm. Jcanavera also explained it well I believe. Better to be in the lower gear with it all locked up than in a higher gear and slipping.

If you are turning 4000 rpm you have downshifted to 2nd gear out of 3rd, which is ok on steeper climbs - my F250 with 5.4L does the same, and so did my Chev K2500 with 5.7L (and it had 4.10's). If you want, slow it down a bit to about 3500-3600 if it sounds too noisy, that should still give you 50-55 mph, which is fine for climbing over mountain passes. The small block Chevy can run all day long at 4000rpm as long as it is cooling adequately - watch your gauges. The GM marine engines are tested at full throttle for 300 HOURS!

On the rear end I just meant to ensure it had synthetic in it, if they put it in when it was changed you will be fine - no need to change again.

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Old 06-21-2004, 04:13 PM   #21
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OK, thanks to all for the replies. Will study them all; looks like drive in 3rd all the time except when on level ground then enable "tow/haul". Really difficult this towing business. I wonder what "tow/haul" does when you put and leave the shift lever in 3rd gear. So much to learn and so little time! (I think Jack Nicholson as the joker said it first in a Batman movie).

GG
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Old 06-22-2004, 12:03 AM   #22
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Quote:
Originally Posted by nangoff
OK, thanks to all for the replies. Will study them all; looks like drive in 3rd all the time except when on level ground then enable "tow/haul". Really difficult this towing business. I wonder what "tow/haul" does when you put and leave the shift lever in 3rd gear.GG
Tow/haul still controls your shift points, even if you are in 3rd gear. You will notice it the most when starting from a dead stop. Each upshift will come at much higher RPM's. So its not a matter of coming up to speed and pushing tow/haul. Just hitch up push the button and drive....just in your case, keep your tranny cool and keep the shift lever in 3rd.

Jack
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Old 06-22-2004, 12:44 AM   #23
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Gentlemen,

Indulge me one more time.

My 2001 Suburban owners manual says with my car (5300, V8, 4wd, 3.73) I can pull a maximum of 7,700 lbs with a hitch weight not to exceed 1,200 lbs.

That's all they say (period).

My total trailer weight (measured and loaded) is 6,600 lbs and my hitch load (measured) when placed on the ball is 1,000 lbs of that. Only my wife and I are riding in the car (400 lbs max) and we have no more than 150 lbs of additional stuff in the car, plus the rear seats have been removed. I should be well within the GVWR, GAWR (front and rear) of the car but I have not measured these items.

We are well within the limits defined by GM for pulling and loading on their car. Why do you all say I am borderline and need to take special care of what gears and speeds and etcetra I use?

GM's manual does not give any other considerations, all they say is that these numbers should not be exceeded.

Implied is that if they are not exceeded the rig is within their design limits and may be run normally; that is, without "special handling".

What am I missing?

Thanks,

Gerry
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Old 06-22-2004, 07:08 AM   #24
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Quote:
Originally Posted by nangoff
...Indulge me one more time. ....My total trailer weight (measured and loaded) is 6,600 lbs and my hitch load (measured) when placed on the ball is 1,000 lbs of that...... I should be well within the GVWR, GAWR (front and rear) of the car but I have not measured these items.
What am I missing?
Gerry:

What's missing is an actual weight measurement of the total tow hookup.

I think it's great that you have an actual weight measurement on the CCD. I would recommend, for only 10 bucks, get a weight of the whole tow, hooked up and on the road. Just fuel up at a truck stop with a "Cat" scale, position your front 'burb wheels on the front pad, rear 'burb axel on the middle pad, and the trailer on the rear weight pad - it doesn't make any difference if all (or any) of the axels are "centered" on the pads or not, as long as the wheels are totally on the pad you will get an accurate weight.

Without an accurate weight, all talk of being over or under the GVWR is pure speculation. - While bringing in the total weight under the GVWR is all well and good, many Forum members advocate a "safety factor" of 20 % or so. An accurate assessment of your driving skills and habits is necessary for a "warm and comfy" with this number. Age ? - as the years pass all of our reflexes slow down - need more Safety Factor. Normal Driving Speed ? If you tend to drive faster (>55mph), dial in a BUNCH of safety factor in order to control the trailer and not have it control you and the 'burb.

As you probably know, the 3/4 ton chassis is in many ways superior to the 1/2 ton for towing purposes - practically everything is "heavy duty". Suspension, brakes, rims, tires, frame, cooling and steering are some of the items that you will find have more beef in the 3/4 ton as compared to the 1/2 ton. Add a bit more to the "warm and comfy" Safety Factor.

As an example, I purchased a new “bottom end” Chevy 1500 short bed a few years back to use as a commuter vehicle - it barely had a tow rating of (I think) 2000 lbs or so, while the "Edmunds" website rated the tow capacity substantially higher - it was a "special edition" low end model - really lightweight. I think it was the tranny or clutch that brought the rating down so low - it is so necessary to check the actual ratings of your own vehicle, and not rely on "posted" numbers. Your numbers should be on the pillar post.

You get what you pay for.


Good luck on your upcoming trip.
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Old 06-22-2004, 07:44 AM   #25
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...this has helped me a lot!

I tow The 28W about 55, and have kept a close eye on the RPM's -- it seems to favor a full downshift instead of unlocking while the trailering mode switch is set. It seems to unlock a lot more at 60 -- the wind resistance is proportional to either a square or cubed term of velocity -- I forget...so I have reduced that a great deal by just slowing down to 55.

I can forsee, even in the flater part of the midwest, headwinds that would cause the set-up to favor that fine line between OD and third, when the TC unlocks. I would not have been looking out for that in such a way as to alter throttle to force the downshift. I would notice it, and go on...

To be clear, I have the smaller engine (5.3) and the 3.73 rear end. The trailer is towed less than 2000 miles per year, if I would estimate it...most of our camping is around the house, in the huge number of good state partks available...

I still have to get the tranny temp gauge installed -- want to do that before we go to the Smokies...

-R
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Old 06-22-2004, 08:03 AM   #26
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Just for reference. I have been towing for about 10k with both a 2003 19' Bambi and now a 25' 2004 Safari. Before that and to this day, I tow a 2500lb boat all summer long (this being the first summer that I haven't).

I tow in overdrive, I have the 10 bolt rear end and I use fully synthetic oils all along the drivetrain.

I have had my PCM modified to lock the TC sooner than later and the only time I shift out of OD is when the car starts to hunt a bit and when towing up a hill.

Now I've driven a 5.3L 2000 Silverado with a trans temp gauge as well as my car--- it also has a self installed trans temp gauge. What I found interesting is that my trans temps are identical to that of the 2000 Silverado. My trans sits right at 175-180 degrees when towing. It peaks at times at about 195-200, but comes right back down when I hit crusing speed.

Bottom line is that there are strong opinions on both sides of the fence on this issue. I will say that if you know what you are doing, take all the necc precautions, you can do it.

Perhaps I will need a trans sooner than later, then again, maybe not...who knows....
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Old 06-22-2004, 08:31 AM   #27
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Quote:
Originally Posted by Silvertwinkie
I tow in overdrive, I have the 10 bolt rear end and I use fully synthetic oils all along the drivetrain.
Now I've driven a 5.3L 2000 Silverado with a trans temp gauge as well as my car--- it also has a self installed trans temp gauge.

Bottom line is that there are strong opinions on both sides of the fence on this issue. I will say that if you know what you are doing, take all the necc precautions, you can do it.

Perhaps I will need a trans sooner than later, then again, maybe not...who knows....
Eric, the difference between you and most people towing is that you know the temps of your fluid. You've made some significiant changes in your tow vehicle to eliminate excess trans. fluid heat. I've seen too many posts from Suburban half ton owners who prematurely lose transmissions due to towing in OD and not knowing the fluid temps. Once that fluid exceeds 200 degrees, deterioration of the fluid begins. The best indicator of that will be the change of color of the fluid. It will change from its pink color to a brownish tinge.

Gerry go back and look at your owners manual. Does is say OD towing is permitted? My '99 Chevy van said 3rd gear. My '03 GMC van says OD is ok, but use 3rd when hunting starts. The difference? A 5.7 liter 3.73 rear axle, no auxillary transmission cooler on the Chevy. A 6.0 liter 4.10 rear axle, and auxillary transmission cooler on the GMC. Based on your towing combo you are right at the edge.

Unless you add a temp. gauge you are guessing what's going on under that hood. If I'm guessing then I'll error towards towing in 3rd rather than in OD. If you can get a gauge then OD may be entirely permissible if temps stay reasonable.

I think we are all attempting to keep you from a very expensive future repair and potential breakdown on the road. The school of hard knocks teaches some nasty lessons.

Regards,

Jack
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Old 06-22-2004, 10:17 AM   #28
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I agree Jack. My point is that Gerry can do the same thing to his Suburban. The easiest of which is adding an additional or larger trans cooler and a trans temp gauge. Both took me about 3 hours (mostly due to the fact I fabricated most of my own brackets, mounting plates, etc).

Additionally, if you use fully synthetic oils, they take more abuse...check out the Amsoil site:

http://www.amsoil.com/products/atf.html


Now a word about the graphs...although they clearly indicate that Amsoil trans fluid (what I use) can take upwards of 260 degrees, the reality is that past 215-220 degrees, your bands and internals will start to cook and self destruct. Anything IMHO at 200 or higher starts to reduce trans life. Your goal is to keep it as far below 200 degrees as possible. Standard ATF, Jack is right on the money....about 200 degrees it starts to break down.

BTW, another cheap mod is getting the GM or eqiv deep trans pan (and deep pan filter kit). It adds about 2 extra quarts. Now I am no physics major, heck I need a calculator to add 1+1! However, I believe it make sense to add the deep pan since adding fluid increases the volume of fluid taking it longer to heat up when flash heat happens.

Everything I've talked about cost me less than $200 and a half of a Saturday installing.
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