SORT of towing subject

Discussion in 'Towing' started by LVJJJ, Jun 9, 2020.

  1. LVJJJ

    LVJJJ Newbie

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    Just got done with our first mountain pass tow with the new 383 stroker. It's amazing, huge power increase over the 350, charged up the hills and pass mostly in 3rd, 2nd gear on the last climb over Stevens Pass. Had a fully loaded 28' Trail Cruiser and the Suburban weighs 6,000 lbs just sitting there. Cruises in 4th on I-5. Trans stayed cool, have a guage.

    anyway, the purpose of this post is a dumb question. The '94 GMC is a 4 wheel drive (K1500), I've never had a 4 wheel drive in my 74 years. Does that mean it has positraction? I was backing the trailer onto some leveling blocks in gravel and the rear wheels spun and dug in. I was surprised to see that both rear wheels had dug in. I did put it in 4 wheel to get the trailer on the blocks.
     
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  2. TechNova

    TechNova I'm Awesome

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    The RPO codes on the glove box will tell you if it's a posi. HAving 4x4 is no guarantee of a posi, my 89 K1500 did not (does now).
    If you haven't done it yet, a fluid change on the differentials would be a good idea, you can see if it's a posi when the rear cover is off.
     
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  3. Curt

    Curt I'm Awesome

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    First check your glovebox for the RPO codes, then make sure the VIN matches your truck (some trucks get the glovebox replaced and the VIN wont match). If it does match, look for the G80 code to find out if you have posi... or you could verify posi the old fashioned way ;)
     
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  4. Supercharged111

    Supercharged111 I'm Awesome

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    If you're going to tow in OD, consider raising line pressure in the transmission. This is most easily done with a tune, which you really need anyway if you don't already have one.
     
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  5. LVJJJ

    LVJJJ Newbie

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    Thanks all. The only "G" on the RPO list is GT4. I've had the bearings and seals replaced on both diffs and recently had fluid changed in both and transfer case. I keep up with maintenance to be safe when towing. Had fluid and filter changed in trans (4L60e) and added a temp gage bung. Old School EFi recently tuned my chip to mate up with the new 383. I'll have to ask him if there was a way to increase the line pressure, probably has as it runs real strong in 4th and trans temp stays less than 180 all the time except went to 190 on the mountain pass.

    So unless you have posi, essentially you have a 3 wheel drive system when using 4 wd?

    Is there an index somewhere that explains the 1994 RPO codes?
     
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  6. 92_Bahama

    92_Bahama Newbie

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    If it does not have the G80 code in the glove box and the rear axle is all original then you have an open diff. To double check this jack the rear tires up off the ground and spin them. If they both spin in the same direction you have a limited slip, posi, Gov-Bomb, etc. However if they spin in the opposite direction then you have an open differential as the torque is allowed to go through the path of least resistance!
     
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  7. Supercharged111

    Supercharged111 I'm Awesome

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    If you spin a rear tire quick enough by hand it should lock with the G80. My 1500 will do this. Old School can definitely bump your line pressure, they can shorten shift times as well. Keeping it cool is a good start, but that 3-4 clutch pack doesn't like getting leaned on in OD. If both diffs are open, you'll have 1 front and 1 rear digging worst case. With a rear locker it bumps to a 3wd and with lockers on both ends of a 1500 you'll blow the case up on the front diff.
     
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  8. stutaeng

    stutaeng I'm Awesome

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    Lift one side of the truck and locate a jackstand under it. Get in truck and carefully try to drive away....

    Or just remove diff. cover. I suppose you could have the G80 and it's not working?

    If you know the "slight jolt" and feel truck immediately gain extra traction, you'll know it is working.
     
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  9. Wheeler

    Wheeler OBS Enthusiast

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    Any idea of how much weight u r towing? What rpm r u at in 4th at what speed?
     
  10. LVJJJ

    LVJJJ Newbie

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    Wheeler, just saw your question. the Burb weighs 6,000 lbs and the 28' Trail Cruiser only weighs 5,000 lbs loaded so that's a total of 11,000 lbs, I think its rated to tow 13,000 GVWR. I try to keep it at 65 mph which isn't easy cause the speedo is off by 3-4 mph, reads slow. I'll have to pay more attention next time but I think that 65 mph in 4th is about 2100 rpm.
     
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