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Front axle DW vs. Trailer DW

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Leadfoot, Apr 25, 2002.

  1. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Last night I had a poop in my pants experience. I was towing my trailer down the interstate and it (single axle 6 X 8 trailer) started to sway uncontrollably. I was towing it with my shortbed 78 K10 and the whole truck started to shake. I tried to load the trailer as far forward as I could with a 36" lawn dethatcher, a 54" commercial walk behind mower, and a 5 gal gas can pushed as far forward as I could. I noticed that it would start when I hit certain speeds, when I would hit a bump just right, and when I made sudden certain movements. The shakes produced by the trailer were similar to those I feel with my 80 that has DW.

    From what I have learned about trailer sway is that single axles are more likely to develop it as they are not as stable as multi-axle trailers, tail weight will add to it, and it is due to the laws of physics (not something "wrong" with the trailer or components) and the only way to help solve it is by using anti-sway controls (essentially dampening shocks.......similar to steering stabilizers).

    Now what if this is the case with steering DW. Something inherent that is non hydraulic induced (trailer DW is definitely not hydraulic and others have replaced all the hydraulic components and still have front axle DW) and the only cure is to help dampen it? I know that is not the answer everyone is looking for, but after all this back and forth of DW it has me thinking. I was hoping it may be hydraulic (as somebody hypothesized) but not I'm not so sure that will/can cure it.

    Also the design of the D60 is different from a 10 bolt or 44 and uses taller perches different tube diameters, MAYBE different caster/camber and I forget the other geometry terms for front end travel. Maybe the design has something inherent that puts similar forces on the front axle similar to the forces put on a single axle trailer (like a heavy tail load). Different mods to a 10 bolt or D44 may contribute in the same way (or as they wear), since people with those axles have said they have experienced DW (just not nearly as frequently or in the same numbers.....number of D44 and C10 equipped rigs vs. rigs equipped with D60's and the % of each that experience DW).

    Trailers sway side to side as the axle and wheels are fixed and the front axle steers steers side to side as it is easier to turn the tires than it is to move the axle side to side due to a front axle having steering knuckles and a trailer axle not??????

    Just a thought?
     
  2. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    i am not sure what DW is...
    but i know one thing for sure. ALWAYS LOAD YOUR TRAILER IN THE CENTER. try to get the weight as centered as possible. it is better on the truck and the trailer is meant for it. thats why they make little diagrams.
    grant
     
  3. Sparky

    Sparky 1/2 ton status

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    Actually, you dont want the weight exactly centered. Most trailer places will tell you want about 10 percent of the trailers weight on the tounge. So if you have a 3000lb trailer you want 300lb. of tounge weight. This will dramaticly reduce the amount of trailer sway. Another thing that must be done is to get the hitch very close to level with the trailer. I am guessing that your trailer was pointed way up hill behind a lifted truck. Get a big drop hitch so that the trailer sits as level as possilbe behind the truck. There is no way a 8x16 trailer should need some type of sway control. You shouldnt need anything like that untill you start pulling horse trailers or fifth wheel trailers.

    Sparky
     
  4. ChevBlazin

    ChevBlazin 1/2 ton status

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    I pull a 5x8 utility trailer (just one axle) quite a bit with my quad in it. It always trailers great behind my blazer. It is rated at 3500 lbs which maybe is a factor. maybe your springs are too soft. The leafs on my trailer are very stiff and the trailer needs quite a load for them even to compress. Also my tires are LT 215/75/15. Tires could probably affect it too. my $.02
     
  5. Sparky

    Sparky 1/2 ton status

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    One of the main reasons everyone with the D60s is experiencing the DW is because they are heavier than D44s and 10 bolts. That, and the fact that most people with D60s are usually running 37 inch + tires. The natural frequency will decrease as the mass of the axles and tires increase. The suspension is more likly to get excited at these lower natural frequencies causing the DW that everyone keeps talking about. Yes, there are many other contributions in the steering, shocks, springs, etc. that contribute to DW, but that is the primary reason the D60 people get more of the DW than the D44 and 10 bolt people. So, to make a long story short its becasue the have a higher unspung weight.

    Sparky
     
  6. m j

    m j 1/2 ton status

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    does the trailer have shocks?
     
  7. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    You can try, and I know this, but odd shaped items can only fit certain ways and/or in certain places sometimes.
     
  8. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    People with stock D60's and stock tires say they get it too.
     
  9. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Nope, and it doesn't hop per say, but the trailer is rated at 2000 lbs so are the axle/springs. It doesn't sag with the load and I would say the GVW loaded is 1500 lbs. With enough tongue weight I don't get the shakes but it does sit a little tongue high and because of the odd load I was carrying I had more rear-end weight than usual. It was not a 16x8 (which I think somebody else stated) it is a 6x8. I tow tandems and singles all the time and never have too much trouble or sway, but yesterday was different as I tried to make do with what I had (equipment and room.....a 6x8 trailer doesn't give you too many options when carrying this size/shape equipment).
    As soon as I had the first "DW" scare. I knew to watch my speed and avoid situations where trailer sway started to occur. A slight pause in the throttle, followed by a quick burst and leveling out speed stopped any sway as soon as it started.

    This was more of a post to invoke thoughts related to axle DW than it was supposed to be how to load a trailer, although trailer safety IS important as many of us on here do tow occasionally, and looking at some of the vehicles and items in tow on the roadways it is sometimes scary to see what people do.
     
  10. Sparky

    Sparky 1/2 ton status

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    Sorry, i was thinking 6X8, but 16x8 came out. 16x8 would be kinda different. But, like i was saying, unsprung weight is not the ONLY reason for the DW that everyone is getting, but its a large contribution. Yes, some people with stock tires and D60s do get a little bit of DW, but that axle is still alot heavier than a d44, and the number of people with stock tires and D60s that get DW is fairly minimal compared to the numbers that have it with large tires. Obviously unspring weight is not much of an issue with a trailer. With that being said, a trailer being pulled and a truck driving under its own power are two totaly different mechanical systems, and from what I know and have experienced, they experience "DW" for two toatly different reasons. IMO there isnt much relationship that i can see between the two.

    Sparky
     
  11. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    You are probably right, I just thought there might be some correllation. Unsprung weight may be a factor but since a trailer feels it (with a feather weight axle), I'm not so sure that is one of the Major contributing factors. Not saying your wrong just trying to pursue this a little more in depth and trying not to dismiss or put all eggs into one basket.

    Actually another thought came to me......Granted a trailer axle is being driven by the power of the truck, but so is the front axle (unless in 4WD). Granted the trailer is being pulled, but technically the front axle is too. The solid (non shackle) spring eye is connected to the front of the truck and the spring goes toward the rear (like a trailer tongue) and the axle connects behind it and is being pulled by the spring. I believe that is one of the reasons for putting the shackles toward the rear instead of in front (on both axles and that of a single axle trailer). The shackle is acted upon by the weight of the vehicle instead of the act of pushing and pulling (while going forward) as would not be the case if they shackles were put into the front. Again maybe reaching here, but the more I think of it, the more sense it makes.
     
  12. rlhenry

    rlhenry Registered Member

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    Here's another tid bit related to this topic. DW in my Blazer is worse when I tow a trailer. The heavier the tongue weight, the worse the DW. This leads me to believe the more 'unsprung' the front axle is, the more accentuated DW is. Following with that line of reasoning, it would seem the more weight on the front axle, the more DW is removed or hidden. I'm not entirely sure of the relationship, but it's something to think about. How about you guys with heavy front bumpers and winches, do you have DW too?

    Based on that logic, I'm going to tell my significant other that I need a Runel or Trail Ready front bumper and a Warn 15,000 lb. winch for more weight up front. Maybe this DW thing isn't so bad.
     
  13. jimmy88

    jimmy88 1/2 ton status

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    Like DW, trailer sway is the right combination of many different factors. Tow vehicle rear suspension stiffness, distance from the rear axle to the hitch ball, tire sidewall stiffness all have some effect. Trailer loading, tongue length, tire sidewall stiffness, attitude (tongue up or down), etc. all influence sway. Basically all trailers have a critical speed which they will sway. The ideal trailer has a critical speed so high you'll never hit it, like 100mph (well most of us won't hit it). Any time you load it wrong, too little tongue weight or have the tongue pointing upward your looking for trouble. Also the heavier the trailer is compaired to the tow vehicle the more effect it will have. I learned this after riding shotgun while watching the guardrail come and go as driver lost it going down a hill on route 80 in PA. Kept praying for the meadian, not over the rail and down the long steep slope. Wound up jacked knifed facing traffic on the left shoulder. We were towing about 5,000lbs on a tandem (rated 10,000lbs) with a 1/2 ton suburban. Next trip about 9,000lbs and same trailer with 1 ton van was like piece of cake. The van has stiff springs, stiff tires and a much shorter distance from the rear axle to the hitch ball. Turns out going down hill especially on a curve is the most likely time to get sway. Only solutions at that point are to apply only the trailer brakes or gas it (hard to do when all you want to do is slow down). I've seen 7% tongue load recommended, but I'd stick with 10%. Just like DW, trailer sway sucks but thats about all they have in common.
     
  14. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I'd sincerely hope no 5th wheel trailer would need sway control. I don't understand how a 5er could sway when the hitch point is at or forward of the rear axle.
     
  15. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Anybody with Big Blocks have DW? Only a few hundred pounds difference but.....?
     
  16. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    It's not so much where the trailer is hitched, although a fifth wheel setup is better as motions of the tow vehicle are not exagerated by the "lever" of a rear mounted hitch (i.e. the vehicle may sway a little but it gets exaggerated by a rear mount ball hitch). Its more of how much tongue weight versus how much weight is rearward of the trailer axles. Most 5th wheel trailers are designed not to have much weight to the rear of the axles.
     
  17. Blazer1970

    Blazer1970 1/2 ton status

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    <blockquote><font class="small">In reply to:</font><hr>

    This leads me to believe the more 'unsprung' the front axle is, the more accentuated DW is. Following with that line of reasoning, it would seem the more weight on the front axle, the more DW is removed or hidden.

    <hr></blockquote>

    I believe that this is a big part of the problem. The heavy axles were made to be used under heavy trucks. Try this analogy. You have a 235/75R15 tire mounted on a rim with a hub and a two foot long axle shaft attached. You hold on to the axle, and run along side the tire as it is rolling down a bumpy hill. With this small, light tire you would be able to keep the tire on the ground and under control as it encountered obstacles on the way down the hill. Your body is the vehicle chassis, and your arms are the suspension. Now imagine yourself doing the same thing with a 38 inch swamper attached to your axle shaft. If the swamper hit a big bump, you would be thrown into the air, and you would never be able to keep the tire under control. Once the unsprung weight (tires and axle assembly) gets to be too big a percentage of the weight of the truck on the front axle, there is no kind of suspension (springs and shocks) that will be able to control it. Everyone with the DW problem should get a big block, or better yet, install a Cummins diesel or even better yet, a Caterpillar from a medium duty application.
     
  18. 84_Chevy_K10

    84_Chevy_K10 Banned

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    My new 5er has +/- 1800 lb. pin weight empty. I doubt that thing's going to sway. (I definitely hope not)
     

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