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Old 11-19-2002, 07:01 PM
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Post drive line vibrationsssssssssss

My toy is a 34 ford with a 468ci chevy,350 turbo,3500 stull,and ford 9"rear. I am pro street with 33x19.5 with 15"wheels and a 6'back spacing
With in the last year I have replaced the converter,new mickey's, and had a new rear housing built going with the 11" breaks. still vibrates. I now noticed that the housing is centered in the frame,and being the 9" has an off set pinion, means my drive shaft not only has an angle from top to bottom, but also from side to side. Is this my problem? has anyone else encountered this problem, and what can i check or do. thanks pete

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Old 11-19-2002, 07:11 PM
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If I understand you right you have at least found a problem. Your rear axle needs to be on an even plane with your trans. The 2 snould add to 180 degrees. That puts them on the same plane up and down if you will. Side to side needs to be exactly on the same plane as the output of your trans. You need to take your car to a shop that does custom rear axle work. They can save most of your rear instead of starting over. Ryan
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Old 11-19-2002, 09:34 PM
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As long as it's a small angle there should be no harm, remember u-joints are meant to work at an angle...compound or not. Have you tried coasting with the engine off to see if you can isolate the vibration? Is it worse in different gears? Does the vibration vary with rpm or speed? Ideally you have your pinion and trans output shaft as close to aligned as possible but there is a total working angle of about 15 degrees up and down and side to side. Add more power and it becomes more and more important the angle is less. Don't overlook the trans either I have seen many trannies cause vibration if the front bearing or main shaft is cooked. Pilot bearings too. Are the u-joints new and have no play?
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Old 11-20-2002, 08:21 AM
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got a carrier bearing?
loose/frozen u-joint?
dents in the tube?
missing weights?
trans. mount good?
broken leaf springs? <img src="confused.gif" border="0">
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Old 11-20-2002, 01:29 PM
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4 jaw, Are you saying that 15 degrees off set to the side is ok? Are you also saying that you want to match the rear axle fange angle to the output shaft of the trans? Just for kicks how many custom installs have you done? Do you find that those owners have to make regular dental vists to refill teeth ? The internet is a great thing and good source of info but sometimes a guy needs to remeber a 12 yr old or a guy that knows nothing of what he is talking about is the "web expert". 4 jaw, don't take my comment as a slap in the face just hate to have the guy misinformed.
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Old 11-20-2002, 10:52 PM
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-Pinion Angle Theory-
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Old 11-21-2002, 01:47 PM
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Thank you Kultulz. You are the link master!
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Old 11-21-2002, 02:12 PM
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Pete, Let us know what you find. I looked at the link that was posted. Some good info. They take a very simple process and try and make it rocket sience though. As to far far off is acceptable is guess I will say this. Some carpenters feel 1/4" here or there is great but I feel a board cut to exact size is the only way to go. Heck I've seen guys putting small blocks in old rods that never measure a thing. That don't make it right.
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Old 11-21-2002, 04:00 PM
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Hey! don't get all bent out of shape! All I said was that there is many different types of u-joint installations and the rules of installation are that off axis axle location is not unusual or even undesirable. RPM and load dictate how it should be aligned, meaning that closer to perfectly aligned is better than not for heavy duty use.

But...an off axis installation by itself will not cause vibration, if it did the u-joint would have destroyed itself already. Thousands of stationary engines and even automotive engines are installed in the off axis manner and work just fine. What else do you think a universal was designed to do?

The more power/RPM and the more off axis you go the less power/rpm that can be transmitted safely without overloading the joint and causing catastrophic failure. The 15 degree number is one that is mentioned in most engineering manuals as a maximum angle any standard universal type joint can operate at before excessive angular velocity and acceleration will cause the output rpm to vary up and down. This number is only good for low rpm. What isn't mentioned at that site is the various alternatives to standard u-joints that are out there, CV joints, double cardin joints, rubber donut types etc. etc. etc. All of these have specs where they run best also.

Just remember that there are a million ways to skin a cat. :p
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Old 11-21-2002, 04:50 PM
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I'm not bent out of shape if your refering to me. I just felt that was very poor advice to give to someone having that kind of trouble. As you stated yourself 15 would only work with very low rpm for any length of time. When the guy has a 468 in a 34 coupe I'm guessing he isn't taking grandma to the store! With the output of a well built 468 I would say if your having vibration problems and can notice just by looking that you have a angle side to side in the driveshaft, then I would bet that has something to do with it. I've been building cars since I was a kid and have built cars that run into the 6's so I think I know abit about drive line dynamics. Remember just cause you saw it in print doesn't mean it's so. I speak from hands on exp. not a book.
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Old 11-22-2002, 02:24 AM
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[quote]Originally posted by 4 Jaw Chuck:


<strong>Thank you Kultulz. You are the link master!</strong><hr></blockquote>

That's me....The Duke of URL...
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Old 11-22-2002, 12:23 PM
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I think we need more info to help 34 with his problem, are you out there 34?

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Old 11-22-2002, 01:24 PM
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34, I went back and looked at the original post. I noticed you said still vibrates. How long has it done this? Did it start with the new rear or before? At what rpm or road speed does it shake? This should give us some more insite to the problem. You could always bring it by here in SW Missouri and we could kill some tires finding the problem . Ryan
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Old 11-22-2002, 01:45 PM
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i would check the obvious stuff first.
like i said, u-joints, dents in the tube, trans mount, broken springs.
any and all of those things can and will make your ride shake your teeth loose.
missing weights, shaft could be bent.
was tthe shaft lengthened or shortened to fit your application?
1 or 2 piece shaft?
i work on this stuff for a living, and these are the most common causes of drive line vibration. if you check angles, take your findings to dana.com and use the expert.

on another note, my kid realy wants to type something and she bugs me every time i'm on here. please bear with me.
uzplt my name izzz pandora,
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Old 11-23-2002, 04:38 AM
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not an expert, but been down this road and wrestled with this issue myself. It about drove me crazy as everywhere I went, got different answers. Been to the websites mentioned as well, and it got too deep for me. I decided to research with others on cruise nights. Found many many with 9" narrowed fords and almost all had centered their rear end housing, thus ending up offset. What I found was a couple things. The lateral angle on the front needs to be as close to the lateral angle on the rear as possible. Same is true on vertical angle, but you MUST be within 3-5 degrees. Vertical seems to be more important than lateral. In my particular case, i made a bunch of shims and kept adding them between the transmission crossmember and the mount until the vertical was right on. Different cars however may react differently. Remember, these cars didn't come from detroit this way and we're chopping, modifying and changing weight distribution etc. , so your car may not react the same as mine or anyone else's.
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