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 Post subject: Re: Mid Track Vibration.
 Post Posted: Sun Nov 08, 2009 7:26 am 
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Tuner wrote:
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


thanks for the link. I'm running 5/8th studs, so the wheels center on the flange center boss. The eccentricity was measured at the outer edge of the flange. We measured it here as we couldn't get a reading off the center boss. The thinking was the shaft was machined round and any eccentricity at the outer edge now would be consistant with the center boss. The shaft was held in the lathe by the splines and turned, there was some very slight wear in the chuck but the shorter shaft had approx 0.8mm eccentric movement and the longer virtually zero. Anybody got any thoughts on this ?

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Sun Nov 08, 2009 8:08 am 
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Location: Benton, KY
Was the shaft in a 4 jaw chuck in the lathe or a 3 jaw ? A 3 jaw normally has some run out.


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 Post subject: Re: Mid Track Vibration.
 Post Posted: Sun Nov 08, 2009 4:12 pm 
 
Measure it installed in the axle housing so it is turning in the bearing as it will in service.


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 Post subject: Re: Mid Track Vibration.
 Post Posted: Sun Nov 08, 2009 9:15 pm 
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After all your double checks, I can only think of a couple things that might do this. Sidewall damage that could be hidden. Or areo thing. You could try tipping that wing a couple degrees and see if it still does it. You may put it on stands, chain it down and run it up a bit.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Nov 27, 2009 9:41 am 
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thought I'd update you guys. Tried to measure the eccentricity with the shaft installed in the housing but the dial gauge was too sensitive and all over the place. I'm gonna chuck the shaft up in another friends lathe to try and repeat the results. I'm also gonna pull the rear end out to check the spool and bearings for any damage.

I've priced up just replacing the shaft and it's gonna work out about $300 shipped. I'm probably going down this route regardless but I just wanna repeat the results one more time to convince myself to spend some cash and see if I need to order anything for the spool.

Aside from this issue, we've got some far fetched plans of going to race over at Hockenheim in Germany for the Nitrolympix in Aug. They've added S'Pro to the bill and it would be great to make it over there. It's gonna take a ferry crossing the English channel and a 500 mile drive through Northern France then down through Germany but it should be a good trip. We're struggling to get the cost of the travel down through. At the moment the travel is working out the equivilent of aboout $700 so we're trying to raise some sponsorship to cover this.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Fri Dec 04, 2009 5:15 pm 
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That sounds like a nice road trip. I'll be envious when you go.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Mon Feb 01, 2010 4:20 pm 
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My first altered was a hardtail. It had a driveshaft. It was out of balance. Made for a blurry ride until I found it. However, I dont think it would make it unload, but I just wanted to mention it because that was one of the things that was in there during the mishap. I had mine balanced - found out someone had also welded the end on it crooked. Fixed all that and it drove like a champ. Keep us posted.

BTW: I've always bubble balanced mine. Who cares how you balance them, just do it. I think you will notcie a big difference.

Good luck.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Wed Feb 03, 2010 8:24 am 
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thanks for the advice. My driveshaft is a solid set up with couplers, I'll pull it and check it's true. I reasinably confident that the vibration was the halfshaft and balance of the wheels.I've got a replacement shaft on order to replace the one with excessive eccentric run out. It's worked out at just over $280 delivered so not too bad.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Mon Apr 19, 2010 8:29 am 
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just an update, new Moser shaft is here and in. My findings of eccentricity in the shaft we're confirmed when I felt significant play in the axle bearing of the offending side. The bearing was 2 meetings and about 12 passes on it . So clearly it had been wearing the bearing in the short time it was installed.

Wheels we're spin balanced and needed approx 7oz on each wheel to get them to balance properly, this was after having turned and rotated the tires to get as close to naturally balanced as possible. Now the guy in the tire shop seemed a little clueless but their machine was good, took the rim width, backspacing etc, calculated it for weights inside only and on the inside/outside of the rim. To satisfy my own curiosity, I bought a bubble balancer and it looks like the old technology agrees with the new, so the wheels are now balanced. ](*,) Stil a lot of weight and I may have got closer by moving the tyre on the rim but the bubble balancer say yes, and that what MT suggest. This is the second set of MT tires and I have to say, not impressed, they leak air, have differing roll outs and clearly have a heavy spot. I've always had good results with Goodyear, when these are done, I'm going with them again.

Having read the Mickey Thompson bulletin about checking rollout, it appears my tires have approx 1/4in difference in rollout. I've tried stretching the smaller and it doesn't seem to have much affect on it once down to normal racing pressure.

Question for you guys, would you run greater pressure in one tire to even up the rollout ? I run 33x14.5x15 in softwall tires, anywhere between 5psi and 6.5psi. Car is a hardtail altered, I have no problems hooking, so I'm tempted to give it a try ?.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Mon Apr 19, 2010 10:12 am 
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I've run'em all, Hoosier, Goodyear, MT and Firestone/Phoenix and the MT tire seems as good or better performance wise as anything else I've ever run before. That and they seem to last longer than the others too.

I coat mine inside with Joy liquid soap before I mount them and they hold air pretty good then. Barry uses some stuff called "Slime" in his that he says works well too. My Camaro was last run Sunday a week ago and those MTs are still up and will stay up for weeks on end. Yes, they do leak down some if not pumped up over the winter but hey, that's about a 3 or 4 month period. For what tubes cost I can put air in'em a lot cheaper.

As far as roll out is concerned, if memory serves anything under 3/8" is "acceptable"? Look at it another way, how much impact does that have on the car now? If it hooks good and runs straight.......?

On the unequal tire pressure thingie, don't forget that tire pressure IS the spring on your car so if you change that, then you change the spring rate side to side.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Mon Apr 19, 2010 12:05 pm 
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You have to correct the rollout before you run the tires. Once they have a burnout on them the tire pressure trick will not change the rollout. 1/4 inch is so close that it won't make any difference and the amount of air it will take to match the tire size will cause a problem. I agree with Ken on the M/t tires. I ran firestone, goodyear and as far as I'm concerned the M/Ts performed way better and last way longer than the others.

7 oz on a tire that size isn't bad at all. I have balanced different brands of slicks and have similar results with all. Sometimes they only take a couple of ounces and other times with the same brand tire they will take 9 +.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Tue Apr 20, 2010 4:00 am 
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problem was it was hooking fine, but bouncing and breaking loose at 1000ft at about 130mph, something I wasn't used to and if I' m honest really knocked my confidence in driving it flat out. Having nearly crashed it and done all the damage bouncing hard in the shutdown, (rame and engine mount repairs, new belly pan, one halfshaft, 2 rear wheels and tires, I'm kind of over cautious and exploring everything !. We'll see how the MT's do, I think they may need more pressure than the Goodyears I ran previously, so I'll maybe start at about 6psi and see what it does.

I'm reasonably comfortable with 1/4in rollout, I think it'd need about 3-4 psi to even it up and like you say Ken, I'll probably create another problem of contact patch and uneven rebound in the tires, so I'think we'll leave it where it is and run it

I'm glad the wheel weight doesn't sound overly excessive.

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Tue Apr 20, 2010 4:52 am 
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Is it still doing the bouncing?
If it broke stuff in the frame when it did its original bounce then its important that it has a relaxed frame now. Stress in members will cause the frame to unload one side etc. Ive seen the problem many times in sprintcars. Of course you have to address the balancing issues etc but from what Ive been reading your saying that a nasty incident broke the car and now its not the same anymore.


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 Post subject: Re: Mid Track Vibration.
 Post Posted: Tue Apr 20, 2010 8:03 am 
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It's been my experience that MTs do require a little more air than other tires. We run 10.5lbs HOT in the Camaro now.

Bouncing under power is odd? I've had that happen in the shut down area with the hard tail diggers I had but never under power? In fact, applying power will stop the bounce at shut down. if you have the room to use it.

Had a car builder tell me that I should always use the chute before the brakes but I never did since I've never had one out and don't even know how to repack one. ;-)

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 Post subject: Re: Mid Track Vibration.
 Post Posted: Tue Apr 20, 2010 9:36 am 
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Wow Ken that's a lot of air. I run 5 in mine. M/T told me that the lighter the car the less air it will require. For my car they they said I should be around 4-6 lbs.

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