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Towing and rear diff ratios

Discussion in 'Differential & Driveline' started by SirRobyn0, Jun 25, 2020.

  1. Grit dog

    Grit dog Full Access Member

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    ^ In 1984, cars barely had enough power to pull their own @ss in Overdrive, much less a trailer.
    This like other subjects is, well, very subjective. There's nothing magical about overdriven vs direct vs under driven save for the fact that the taller the overall ratio, the harder it is to pull it.
    It is not "so simple". There are many variables that someone who thinks it's so simple are likely not aware of. I'm not just speaking about 700R4s in clapped out 30 year old trucks either.
     
  2. AuroraGirl

    AuroraGirl Supporting Member Supporting Member

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    My ford 300 with california emissions in my 96 f150 and e40d transmission see the overdrive really put it to its match. THe engine makes its power low, the engine is great. Glad to have it for a ford(would only ever want another 400 or an IH diesel NA) but the taper of power below that and above that 2k rpm or so is distinct. So a small hill in OD Is hell, but flat ground OD makes it SO much less-labored. Even without a load. The tractor engine makes it unique, but a good example where OD may benefit from disabled OR a good driver to know when to not use it. I use it for half my trip on garbage runs, half is up and down constant, other half is flat. BUt the transmission otherwise is really good at shifting especially to keep that engine in its power curve, despite the 3.88 gears
     
  3. Bextreme04

    Bextreme04 Full Access Member

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    My transmission just gave up on a family vacation last week. 2011 Suburban K1500. We towed our smallish pop-up tent trailer from Oregon out to Henry's lake in Idaho and spent the week in Yellowstone and Grand Tetons. On the way back, we went the northern route through eastern Montana and northern Idaho(very hilly). It's a 5.3L with the 6L80e. It doesn't have an external trans cooler, has 3.08 gears, and 180,000 miles. It has always pulled great, and with the tow/haul mode it has always dropped down to 4th on almost all hills(both 5th and 6th gear are OD). I was pulling lightly up a slight hill, in 4th gear, maybe 65% engine load, and the trans temp suddenly shot from ~208 deg to 265 deg. I immediately let off the gas and started to pull over but by the time I had come to a stop on the side of the road the trans temp had shot to ~350 deg and was smelling burnt.

    Its a fully electronically controlled engine/trans so it doesn't do the high revving while not moving that lets you fell it slipping. The torque management will actually pull timing as it detects slippage, but something must have stuck and it just smoked a clutch pack. I had the dealer in Missoula, Mt flush the trans fluid and reset the TCM and we managed to limp it the remaining 400 miles back to Oregon. It still drives around fine without a load on it, but it is getting hot faster than it should and we have a few more camping trips planned for later in the summer so I have the parts on order for a rebuild and a nice external engine/trans cooler. Eventually it will get a small lift, bigger tires, and MUCH taller gears. Those 3.08's with 30" tires and crazy tall OD gears is stupid. It cruises at 80mph at around 1400rpm right now, which the 5.3 hates. I'm sure if I had better gears the AFM would be engaged more often and it would actually get better mileage at a higher RPM. Not to mention less strain on the trans and drivetrain.
     
  4. SirRobyn0

    SirRobyn0 Full Access Member

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    FYI not all 30 year old trucks are clapped out. While mine certainly isn't restored I'd hardly call it clapped out and if I broke a major component I'd fix it, because the truck is worth it to me. I know I could drive a modern truck, but as someone that fixes cars I just don't see the value in buying a newer truck that's going to cost 10K plus for a used one, with potentials for a lot more in repair. I know my 84 isn't going to pull a trailer as well as a modern truck, but seeing some of the computer problems I see at the shop..... No thanks, I'll stick to my old rig.

    Sorry to hear of your issues, glad you'll be fixing it. Like you that's my problem to high of a gear ratio.
     
  5. Bextreme04

    Bextreme04 Full Access Member

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    Yeah, it sucked.. ended up delaying our arrival home to about 5am on the 4th. At least it was able to limp all the way back home. I just ordered all the rebuild parts, its had a leaking rear main seal for a while now and this is a good excuse to fix that too. Looks like I won't have all the parts in until middle of next week, so it looks like i'll be spending the weekend putting parts on the square to clear out some room in the shop for the transmission repair. Unfortunately no lift, so I need to lift the truck up onto my normal jack stands with some cribbing under them to get the truck high enough to pull the trans out from underneath.
     
  6. SirRobyn0

    SirRobyn0 Full Access Member

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    I have to admit one of my biggest fears about road travel is to have a transmission or major engine failure. I can pretty much fix anything else on the side of the road but a major tranny failure, no. And imagine the tow bill to get the truck and trailer back home. You were very lucky to be able to limp it back home.
     
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  7. Bextreme04

    Bextreme04 Full Access Member

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    Mine too. The only reason I stopped at a dealership was because it threw a TCM communication fault at the same time it overheated. I was hoping it was a connector or other issue that caused the TCM to take a nap and that was what overheated the trans. Turns out that the overheating had shut off the TCM and put it into limp mode. I had them flush the trans and test the cooler to see if it was plugged, but everything tested out fine. So it was either see how far we can make it as-is, or rent a U-haul one-way to tow my trailer and take the load off the suburban. The long, steep pulls had it running about 35mph with the temp spiking up to 265 deg, but everywhere else it stayed down around 210 degrees and it is still limping around town while I wait for parts to come in.

    Next weekend will be pulling the trans and rebuilding it with some upgraded parts so it hopefully lasts a lot longer. Going up to portland next week to get a rebuilt converter for the Burb and for my 4L80e that i'll be rebuilding for my Vortec 454 swap into the K25 at the same time. It going to be a busy couple weeks, as I need to clean out the shop and put some other parts on the K25 to clear out space and also taking my Private Fixed wing check ride on the 16th as well.
     
  8. Grit dog

    Grit dog Full Access Member

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    Was not a personal affront to you or your vehicle.
    And a person’s preference (or necessity) to drive old vehicles is based on many factors.
    In general though, I’m betting there’s more “clapped out” old vehicles on the road than those that are reliable, rebuilt, owned by someone such as yourself who knows what it takes to keep them on the road, etc.
    For those folks I wouldn’t even consider towing my garbage can up to the culdesac on garbage day in OD.

    Take the 86 we just bought. Drive it anywhere? Sure, looks like it would make it. Also had enough nuances that I wouldn’t consider it until I’ve taken care of several more issues. And then, unless out of necessity, it would be the last vehicle I’d take on a road trip save for the 74 Jeep.
    But in my case, 4.10s and whatever horrid mileage the carbed 454 is getting also do not make it cost effective.

    But in our case, it is/was not meant to be a DD vehicle. It is/will be a fun project/resto.

    Cheers.
     
  9. SirRobyn0

    SirRobyn0 Full Access Member

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    Actually I'm the one on the wrong on this. I had a particularly crappy day at work and I think I could have taken just about anything the wrong way at that time. So no worries here from me.
     
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  10. Grit dog

    Grit dog Full Access Member

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    It’s all good!
     
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  11. idahovette

    idahovette Full Access Member

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    Aw, you guys kissed and made up!!!....LOL... good for you, had a few of those days myself!!
     
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  12. SirRobyn0

    SirRobyn0 Full Access Member

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    Ok slightly off topic story that you might enjoy. I live outside Seattle, far enough to be in the foot hills of the cascades. In the late 90's into the early 2000's I did some work for band based out of San Francisco, it's an old 70's bay area band called the Sons of Champlin, unlikely that you have heard of them but they had some luck in that area and still get together a few times a year to play. So back then I did videography work for them. They wanted all of their concerts video recorded, to be used later for PR purposes or to practice with. I don't fly, so 6 - 8 times a year I would drive down there. Often leaving after a full day of work up hear, sleeping in a rest stop and getting in down there a few hours before the show. The best part of this is when they had a show on the coast I'd take some extra time off to spend down there. But back to the story. Sometime in the late 90's I was down there in my 1988 Olds 88, they did a show in Petaluma, and the next night was in Chico, a cool 2 1/2 hour drive. So we started out with plenty of time, but only about 1/2 an hour after leaving I ran over a big metal rod in the road which tore foot long by 6 inch wide whole in the gas tank. This is on Easter Sunday, and I could not find a rental car to get to the next show. Eventually I ended up in a 26 foot u-haul truck with car trailer. Good thing I know how to drive a manual, big trucks and trailers. I arrived about a 10 minutes before the show in Chico, and drove that rig home the next day. Cost me $1,400 dollars for the rental including mileage. And who knows how much in fuel, I didn't keep track. While the road travel was typically very predictable, I've sure got a lot of stories from those days.
     
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