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Towing with 700r4 question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by shum1, Apr 10, 2001.

  1. shum1

    shum1 1/2 ton status

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    I have a beefed up bowtie overdrive 700r4. If I go to 4.56's to compensate for my 33" tires at my higher altitude will I be able to tow in 4th gear? If I have to stay in 3rd Ill be reviving way to high at 70mph. is the reason you are not supposed to tow in 4th because of the very high final gear ratio or is there some other fundemental weaknes? Thanks

    <P ID="edit"><FONT SIZE=-1>Edited by shum1 on 04/10/01 06:45 PM (server time).</FONT></P>
     
  2. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    The 4th gear isnt designed for a load. Its meant to save on gas. Towing at 70 mph seems a little extreme, just gonna have to kick back, enjoy the ride and go slow.

    [​IMG]
     
  3. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Two comments:

    1. NEVER tow in OD with a 700r4. In overdrive, the fluid(which also acts as a coolant) flows through the system 40% slower. This means that you're basically losing 40% of the internal cooling ability. I read somewhere that as little as a 20' increase in average operating temperature can cut the life of your ATF by 50%.

    2. 70mph while towing? Keep in mind that your stopping distance is greatly increased with the weight of a trailer behind your rig. Also remember that a short wheelbase K5 is already at a disadvange as far as emergency maneuvers go- add the weight of a trailer and 70mph to the equation and it's a recipe for disaster. My average towing speed is around 60 MPH and if i could get away with going around 50 I would............I would use a lot less gas!!!!!!!!![​IMG]

    I'm not trying to hack on you, BTW.


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  4. shum1

    shum1 1/2 ton status

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    Does GM still say you shouldnt tow in OD in their 2001 1/2 ton trucks? Just curious. I tow a light alum (350lb total) boat, usually I keep it under 65mph but on desolate wetern interstates I'll kick it up a little. I should have told you that I have a burban not a blazer, I guess the wheelbase thing is a little less of an issue for me. Thanks.
     
  5. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Apparently the tranny cooling systems are much improved in the new trucks. I have a buddy with a 98 GMC who tows a 4000lb trailer and regularly uses OD on flat areas with no heat issues- he's got a tranny temp gauge and says there's not much of a difference between OD and D.

    I was under the impression you were towing heavier loads. I can't imagine that 350lbs would put too much strain on the tranny, though. It might be worth it to install a sender and a gauge and see how/if things heat up. The money you spend on monitoring equipment could save you TONS of cash in fuel if you can get away with driving in OD.........

    Just a thought........



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  6. ken

    ken 1/2 ton status

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    "I love the smell of a burning 700r4 in the morning...it smells like...victory".

    Good frigging luck with your 700-junk-4!! I couldn't get SIX of them to last in my '90 Suburban. Finally did the smart thing and swapped it out for a TH400. Boo hoo, I lost my overdrive!! But I sure like knowing that I'll make it where ever I go, and not have to break the bank every year for a new 700! But hey, that's just my experiences...SIX 700s!!!!

    ken
     
  7. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    OH GOODY!!!!!!!!!!! Here we go again.............[​IMG]

    My half-ton diesel, which tows thousands of miles through the Canadian Rockies every year, has a 700r4- THE SAME 700r4 THAT WAS INSTALLED IN THE FACTORY IN 1983!!!!!!!!!!!!!!!!!!!!

    I guess I'm just lucky.............OH, BUT WAIT..........My K5 has a 700r4, too. Rebuilt 7 years ago(due to poor driving and maintenance habits) but no trouble since.

    Let it go, Ken. Let it go..............





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  8. Wheels

    Wheels 1/2 ton status

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    The 2001 Chevy's have a "TOW" selection switch on the end of the shifter that reprogram's the shift points in the tranny for towing when the TOW switch is depressed. They recommend using D or 3 for towing heavy loads (heavy loads not defined) or when towing through hills/mountains and only use "OD" for flat roads with light loads only (again light loads not defined). Depending on the weight of the load and the region that you're towing in and the regular maintenance schedule that you perform on your tranny will depend on how long it will last. GM came up with "generalize all towing and cover all aspects with one statement" to cover their butts. Dirving I-95 south in Fla with a 4000 pound load and driving I-25 north of Raton NM with the same load are have two totally different effects on the life of any given transmission.
     
  9. 89Blazin

    89Blazin 1/2 ton status

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    Wait a minute.....you are saying that the ECM chip comes into play with the tranny shift points? I was told that your "chip" has nothing to do with the 700R tranny. I was wanting to change my shift points and posted a "Chip and Tranny" posting which we are still tossing back and forth. Can you please clarify ? I understand the new L series (modified 700R) trannies are tied to the chip, but not the 700R.

    85 Burb and an 89 Blazer
    One just for fun, one simply for pleazer<P ID="edit"><FONT SIZE=-1>Edited by 89blazin on 04/11/01 08:42 AM (server time).</FONT></P>
     
  10. 6.2Blazer

    6.2Blazer 1/2 ton status

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    I believe that both a combination of heat buildup and a fundamental weakness in the design of the overdrive gear are why you shouldn't tow heavier loads with the trans in OD. Drive (or 3rd gear in the 700r4) is considered a direct drive (1.00:1 ratio) which basically means the power goes straight through the tranny. Overdrive on the other hand has to be routed through a combination of gears in order to achieve it's purpose (0.70:1 ratio), and is therefore weaker mechanically than when in drive. The only mechanical breakage (versus the more common failure due to heat buildup) I have personally seen on a 700r4 was when my cousin attempted to pull a 15,000 lb. livestock trailer.

    Heat buildup is the next biggest concern, especially with all of the 3-4 up and down-shifting you would probably experience when pulling a heavy load.....not to mention the strain on the engine. Remember, when in overdrive those 4.56 gears effectively become 3.20 gears (4.56 x 0.70 = 3.20), not exactly the idea towing setup when running 33" tires. Both my dad and myself have trucks with 4.10 gears and stock size tires (about 31" tall), which would be pretty close to giving the same rpm as 4.56 gears and 33's, and neither has a problem driving 70 mph with the overdrive off. Just remember, before overdrive tranny's became popular you could get a 1-ton Chevy with 4.56 gears, little dinky tires, and no overdrive. My friend had a late 80's model dually with a 454, 4-speed manual (non-overdrive), 235/85r16 tires, and 4.56 gears and towed a fifth wheel trailer down the freeway for years....and he usually was breaking the speed limit when he did it.

    Concerning the optional Tow/Haul mode on the newer Silverados, when this function is engaged the transmission will NOT shift into overdrive.

    And finally this is for Ken...............I thought you promised to stop hacking on 700r4's after the post a while back??????????
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    They are talking about the 4L60E, younger brother of the 700R4, and used well after our body style was gone. E=Electronics.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  12. ken

    ken 1/2 ton status

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    OK, OK, OK...I promise now!! I just had lotsa pent up 700r4 frustrations between now and the last time I said I'd refrain!! Enough already!!!!! I am finished!!!

    ken
     
  13. kpanza

    kpanza 1/2 ton status

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    Shum1,

    I also have a Bowtie Overdrives beefed 700R4. Do you have the tranny temp gauge on your truck? I regularly tow my Jeep CJ5 behind my Blazer, and on the long flat desert stretches of highway, I can tow it in OD. I just keep an eye on the temp gauge. Also, I have the lockup torque converter switch, so I can control it from the cab...I am running 35" BFGs with 4.56 gears...there is kind of a zone between 55 and 65 that is hard to tow in, meaning that Drive is perfect up to about the 55mph mark, over that it gets a little buzzy with the motor around 2800-3000 rpm, then when I hit about 65 mph I can usually throw it in Overdrive and just cruise if it is nice and flat. But with a light trailer like you have, I wouldn't worry about the tranny in OD...just get a trans temp gauge to put your mind at ease!
     

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