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Old 12-22-2013, 04:55 PM
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Hopping under acceleration

Going to be a kinda of a long story so i can get all the details out in one post, sorry.

Truck specs:
Early 99 7.3, stacked lift blocks, factory driveshaft, stock gears, 35" tires, 6spd manual trans, 110k miles

I regularly tow my toyota pickup play truck to and from the desert. Not a heavy load, about 6k lbs with the trailer. Everything has been 100% fine until the last trip. The drive to the desert (100 miles) was a night mare due to traffic, constant stop and go traffic the entire drive made the trip take about 3.5 hrs but everything felt normal other then my sore leg from the clutch. Truck felt entirely normal when i parked it in the desert and didnt touch it for 3 days. Loaded up to head home and got directly on the freeway and set the cruise control at 60. About 30 miles later i decided to stop for lunch. I came to a stop at the top of a fairly steep uphill offramp. when i tryed to accelerate there was a VERY significant hopping, bad enough that i stalled the truck. restarted it and tried to go again and the hopping was still very bad but was ONLY there while i was slipping the clutch. Parked at a restaurant and noticed the u-joint at the pumpkin was pretty sloppy so i figured that was the problem. Drove the rest of the way home, hopping at every start up (0-2.5ish mph) but completely normal at speed.

Without the load behind the truck i could feel a slight hopping but not bad at all. Replaced the u joint and it made 0 difference. Also added traction bars which made the unloaded truck ALMOST impossible to hop but still possible. Again ONLY while slipping the clutch. It had the factory clutch so i figured it was about gone. Yesterday i installed a new southbend clutch and flywheel and towed today. Hopping is still THERE! Not nearly as bad as last time i towed but im guessing that is because of the traction bars.

Anyone else experience this? what the hell could it be? It feels like something in the drive train is loading up and releasing


thanks!
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Old 12-22-2013, 06:37 PM
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This is the whole reason I made this thread.

Before you run lift blocks!....Look HERE!

You are describing axle wrap. Take a good look at your springs, I wouldn't be surprised to hear you find a broken one. You absolutely never ever ever ever stack lift blocks
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Old 12-22-2013, 06:39 PM
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I have looked at them closely. Everything looks perfect. I'll take another look
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Old 12-22-2013, 06:40 PM
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Take the traction bars out, and get somebody else to accelerate in your truck, while you watch the rear pumpkin. See how much it pitches up? See how your leaf springs look like a "S" when accelerating? That's what's happening, traction bars have a purpose, but band-aiding an improper lift is not what they are for ( don't get rid of them I'm just saying they are going to mask your problem, not fix it)
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Old 12-22-2013, 06:43 PM
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I know exactly how much it used to move. I design and build offroad suspension for a living, I know how things work. Thanks for the info though
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Old 12-22-2013, 07:00 PM
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If you design and build suspension why do you have stacked blocks? No offense but that's dangerous as hell.

I've been there on my truck.... the kid I bought it from had stacked the blocks. I had wheel hop like hell, even in 2nd gear.

Last edited by schlutzer; 12-22-2013 at 07:22 PM.
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Old 12-22-2013, 08:02 PM
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The truck came with them, they work and I don't feel like spending money fixing something that isn't broke haha. Didn't mean to sound like a know it all if it came across like that.
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Old 12-23-2013, 12:50 AM
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Fair enough. I was in the same boat. I got rid of mine and kept my ~6" lift with what I said in that thread I linked.

IF it's not axle wrap (which I would still lean toward) check your mounts too, your description could also be a bit of clutch chatter. I doubt it since you've changed the clutch out. But a bad motor mount can cause chatter from loading up and releasing. Traction bars shouldn't fix that though. If you rev higher and slip into it more does it still do it? Like if you go to 1500 rpm or so and smoothly slip the clutch to take off does it happen still? If not I doubt it's mounts.

You should know this but I'll say it anyway for everybody reading. When you have lift blocks that high... You look like roughly 6" right? So that would mean 8-9" of lift block like mine was. All that distance acts like mechanical advantage, or a lever putting increased stress on the leaf springs, I don't know the mathematical formula but the bigger the block, the great the stress, many times over. It's not really about stacked blocks, but about the total amount of block.

If your springs aren't broken, they may just be getting weak. Since you have them roll with the bars for a while but I would make a point of doing the rear suspension properly. Shackle kit and springs like I did rides 10x better anyway
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Old 12-23-2013, 11:44 PM
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I didnt drive the truck today but i did take a very close look at the leaf springs and didnt find anything at all wrong. End of this week ill be towing a little over 100miles, guess we will see what breaks.
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Old 12-25-2013, 05:52 PM
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Got it all figured out. The original issue was the clutch and the slight hopping now is actually caused by the traction bars and leaf springs fighting eachother. I towed 8k pds with the bars, then came back and towed it without the bars. Hopping was entirely gone without the bars but i can feel the leaf springs twisting every time i accelerate. Thanks for the help!
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