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 Post subject: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 10:59 am 
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hi all, got an issue with my altered I'm hoping to pick up some advice on. This spans about 18 months so pls bear with the story so fair

Last year I got heavilly out of shape in the traps slowing from 150mph, I put this down to poor braking on my part and also only having rear brakes at the time. Anyhoo, I bounced about, getting about 3ft of air under the rear tires and landed pretty hard. I flattened the bottom rails, took out the belly pan, trans pan hit the floor and it bust the mid motor mounts. I then had it all repaired and re-fitted my front brakes. I ran the car, ran perfectly straight, hooked up, was running 6lb in the rears and on each run in was it starting to bounce at 1000ft, when I lifted it was ok but stay on it and it was all four wheels off the gorund in the shutdown which can get ugly. Actually won a meeting lifting at the 1000ft, how I don't know...

Anyway fast forward this season, I bought new rear wheels and tyres. The wheels we're spin balanced without tyres to withing 5grams of each other. I then fited the slicks with screws and have put probably 20 run on the car. It still hooks up, goes arrow straight and then bouces about 1000ft where I come off it.

I've been running the car throttled down by to half throttle which generallt runs 9.2's flat out. Whilst it's still vibrating and bouncing like it I can't run it flat out or be competative (despite winning a meeting and reaching the quarters...thinking about it I've had more luck with it.....)

The bouncing starts off as a vibration and then bouncing. The tires are softwall tires 15 x 14.5. I've run then everywhere from 6.5lb down to 4.75lb. I haven't balanced the wheels with the tires because I've been told not to spin balance slicks. I've chucked up my halfshafts in a friends lathe and the sorter shaft had approx 0.031in run out / eccentricity at the flange, some of which I put down to slight play in the lathe chuck. Would this amount of run out cause this sort of action, given that theres a big soft slick tire at an average of 5.5lb to take up vibration ? Also I'm guessing this would drastically shorten the life of the bearing ?

Aside from measuring the roll out and bubble balancing the slicks, what else can I do to try and diangnose this problem ?

any ideas greatly appreciated.

Phil

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Last edited by PSweeney on Fri Nov 06, 2009 11:58 am, edited 1 time in total.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 11:10 am 
 
Phil i would definitely balance the tires for sure i have always had my tires spin balanced at that speed a tire out of balance can and will cause you some serious vibration i haven't seen one get the tires off the ground from it but it is possible i would think but that's were i would start


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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 12:04 pm 
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I read up a bit and there was so many differing opinions on spin balancing, but I'm definatly gonna do it. Where and how tdo you guys mount your weights ? I'm using stick on weights but the guy who did it reckoned he needed to put weight on the shiney side of the rim, hence they're within 5gms of each other. Are clip on weight acceptable ?

I should add the car is a hardtail and I don't get the vibration in the burnout. I static burnout to the limiter in high gear. On the run the vibrations enough for me to get blured vision slightly.....tire shake running 9's. ...

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 12:11 pm 
 
Phil the guy that does my tires for me always puts the weights on the inside of the rim and we use the stick on weights also and then put some duck tape over them the clip on weights we tried those once and they came off .


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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 1:12 pm 
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You definitely want to balance the wheels with tires mounted. I have used both clip on and stick on weights. Depending on the type of lip the wheel has on it the clip ons may not work. With the stick ons just make sure the wheel is clean. I use a little brake parts or carb cleaner where I put the weights on and have never used duct tape. The only time I've had a stick on come off is when I broke a ring & pinion and the vibration shook them off.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 2:31 pm 
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When we had tubes put in at BG buy the M/T trailer they swore by the bubble balance. They also used stick on weights side by side from the out side to the center at the same lenght. then duct tape. When Jake does it at work he spin balances it and then duct tape. We haven't lost any yet. If you still have the vibration get the drive shaft balanced. Cheap insurance. Speaking from experience. ;-)

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 5:20 pm 
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Steve, a hard tail likely doesn't have a drive shaft. I think it's just a coupler from the rear of the tranny to the pinion flange on the rear end.

I bubble balance mine because that's what I have. I also reuse the stick on weights and glue them on with RTV then use tape to hold them in place so the RTV can cure. Only problem is it's a bitch to get'em off again.

I really don't think it matters whether you bubble or spin balance'em, just that you do one or the other.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 7:53 pm 
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#-o :-k Is the coupler balanced ;-) =; What about tail shaft or pinion bearings? I hope it is just the tires.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 8:22 pm 
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PSweeney wrote:
I haven't balanced the wheels with the tires because I've been told not to spin balance slicks.
Phil


I'm kind of curious as to who told you this and what the reasoning is?

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 06, 2009 9:52 pm 
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I'm with the others on the balancing. Most tires need it new. Some need it again later. I've had mine spin balanced in the past, but I have a bubble balancer now so I can do them myself.

I do the weights just like ken ... silicone the stick on weights on the back side of the wheel and duct tape over them. Some have needed over a pound (>454gms to you =; ) of balance weight.

Rick


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 Post subject: Re: Mid Track Vibration.
 Post Posted: Sat Nov 07, 2009 1:02 am 
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Yup, bubble balanced tires on both dragsters too and they never did give me any hint that they was a problem with'em. The BBC Boulton car went 7.96 @ 168 and change on bubble balanced tires. \:D/

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Sat Nov 07, 2009 6:06 am 
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gearhead1011 wrote:
PSweeney wrote:
I haven't balanced the wheels with the tires because I've been told not to spin balance slicks.
Phil


I'm kind of curious as to who told you this and what the reasoning is?



All the big tire companies say bubble is the way .. I spin mine because I have it, but have had harlow bubble and they are the same. I've been 7.4's on both and never really noticed a difference.

You for sure need to get the fronts done .. stick on weights inside of rim your problem will be gone

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Sat Nov 07, 2009 12:28 pm 
 
PSweeney wrote:
hi all, I've chucked up my halfshafts in a friends lathe and the sorter shaft had approx 0.031in run out / eccentricity at the flange, some of which I put down to slight play in the lathe chuck. Would this amount of run out cause this sort of action, given that theres a big soft slick tire at an average of 5.5lb to take up vibration ? Also I'm guessing this would drastically shorten the life of the bearing ?

Aside from measuring the roll out and bubble balancing the slicks, what else can I do to try and diangnose this problem ?

any ideas greatly appreciated.

Phil


Unless you missed a keystroke .031"????!!!!!! O:)

http://www.vibratesoftware.com/html_hel ... cification


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 Post subject: Re: Mid Track Vibration.
 Post Posted: Sun Nov 08, 2009 7:10 am 
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gearhead1011 wrote:
PSweeney wrote:
I haven't balanced the wheels with the tires because I've been told not to spin balance slicks.
Phil


I'm kind of curious as to who told you this and what the reasoning is?


I can't recall who but it's supposed to be down to the cords stretching in the tire.Many other racers I know don't even balance them at all. I guess they're just lucky with it. anyway it looks as though I'll get these spin balanced and then check it with a bubble balancer. We're pretty limited on who can balance a 14.5in wheel. My local place had the wheel fit on their balancer, but i'm not confident their machine or the operator was 100% on where to place the of weight weights with a 7.5in backspacing. At the moment they're just off center on the back face.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Sun Nov 08, 2009 7:13 am 
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WR169 wrote:
#-o :-k Is the coupler balanced ;-) =; What about tail shaft or pinion bearings? I hope it is just the tires.


never though about the couplers but given its a hardtail, I can't see anything amiss in the coupler being transmitted to the wheel without ruining the pinion or diff bearings. Which is another avenue I'm exploring.

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