Help please with a chassis question

Old 03-20-2008, 04:57 PM
  #1  
s10dragracer
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Default Help please with a chassis question

Ok at the track this past weekend I had what seemed to be tire shake but it didn't spin. It just vibrated on the launch and then cleared up. This has had me puzzled and can't figure it out. First I thought it may be the pinion angle but others on another site don't think that is the problem that most of the time improper pinion angle will cause problems on the upper end of the track. Right now I have +3 on the rearend and -4 on the transmission so this would make my pinion angle -1. What are your opinions on this? Just picture the first 100' feeling a vibration like a tire shake or something and then just clear up after the 100'.

This is a 1984 Chevy S10 stock suspension with Slide-A-Links, Calvert Racing Mono Leafs, Rancho 6000 rear adjustable shocks with 12 settings, front is QA1 "R" Series coil overs. BBC615 Big Chief engine with 3 stages of nitrous. This weekend was first pass out and was on motor only and NO spray.

All help will be greatly appreciated.
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Old 03-20-2008, 05:58 PM
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johnracer
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How bad was the vibration? The only time I've experienced tire shake was in my old FED. It rarely shook, but when it did, it wasn't at the hit. It was usually when the front end touched down and it hurt!! I'm talking about teeth rattling, vision blurring shake. It didn't last long (thankfully) but it wasn't just a vibration. Tire shake isn't spinning. It's the tires wadding up and trying to run over themselves. A little spin would be much better.


I'd think with that much torque and a leaf spring suspension, you really need more down angle on the pinion. Probably to the tune of 4-7 degrees down from the driveshaft at rest to be straight under power....
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Old 03-20-2008, 06:22 PM
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s10dragracer
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Default Vibration

The vibration wasn't teeth chattering but noticable enough that I could feel it good but approx. 100' out it went away everytime at about the same point and the truck would be smooth except for a steering issue that I had. It was a feeling I have never felt before and just didn't feel right. I may jus be overreacting to this whole new big block build but it just didn't feel safe on take off but after approx. the 100' out it felt real good.
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Old 03-20-2008, 06:24 PM
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s10dragracer
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Default Pinion angle

What is your theory as to what pinion angle will do whether it be too much or not enough? I am in a new ball game with this build so trying to learn everything I can. Thanks for the help.
Thanks
Travis
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Old 03-20-2008, 06:50 PM
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johnracer
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Without enough down angle, the pinion may be rotating far enough to cause the ujoint to bind, causing the vibration. Most leaf spring suspensions rotate a bunch. With a big tire/really good traction, and a bunch of torque, it'll be even worse...
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Old 03-23-2008, 06:40 PM
  #6  
earthquake
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Don't forget to check the easy stuff, too. If your tires aren't spinning, maybe your clutch assemblies in the trans are chattering. Is the fluid burnt? May not be this, but it couldn't hurt to check.
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Old 03-23-2008, 07:52 PM
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sp2816
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I would also make sure of the driveshaft length to verifyol that it isn't bottoming out when the truck squats. As stated earlier, with leaf springs you will want the pinion angle to be 4* or more especially with the mono leafs, since they will allow the rear end to twist more.

Bill M
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Old 03-23-2008, 08:05 PM
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sg5492
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Could it be tire pressure? You Might want to put a little more in and give it another shot.
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