hgh speed vibration, part arrghh!!! - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 7 (permalink) Old Apr 14th, 01, 04:24 PM Thread Starter
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A follow up to previous high speed vibration:
Vibration experienced at high speed (>70mph) and worsens as increased. Recent history from response to original post; found and replaced bad tranny mount: vibration remained. Repositioned angle of rear pinion (added +4degrees of upward tilt to match drive line): vibration remained. Took drive shaft to drive line shop; rebalance (added 6gms) to foreward portion of shaft: vibration remained.

Replaced the flex fan w/ a clutch type fan from an s-10 p/u (salvaged from a junk yard and clutch probably bad : THe vibration would come and go in a harmonic type fashion., Although the new type of vibration would start at lower speeds and would come and go at all speeds ( as opposed to constant at high speeds).

Some thoughts: the original (307) crank pully is quite large and may be turuning the waterpump and fan extremely fast. (a 350 harmonic balancer replaced the 307 at rebuild, but not the pulleys) Could the fan/waterpump cause vibration if RPM 's are excessive.
Should i consider a good fixed non flex fan. Any suggestion or experiences???
THx Joe.c
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post #2 of 7 (permalink) Old Apr 14th, 01, 04:56 PM
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Joe,
The first thing you have to determine is if the vibration is speed related, or engine rpm related ?? You say that the problem happens at speeds over 70 mph. If you have a tach, check the rpm when it starts. Then leave the car in 2nd gear and run it up to the same rpm. If the problem does not occur, then it probably is not anything attached to the engine.
If it is engine speed related, the first thing you need to do is get a NEW fan clutch, not a junk one. I have seen them cause the exact type of vibration that you describe. I would stick with the clutch type fan as it uses a lot less power at high speeds than a fixed fan. The clutch fan only drives the fan when it gets hot, usually at low speeds in traffic. Once you get up to highway speeds, there is enough air flowing through the radiator that the fan really is not needed.
Hope this helps,

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post #3 of 7 (permalink) Old Apr 15th, 01, 07:19 AM Thread Starter
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<BLOCKQUOTE>quote:</font><HR>Originally posted by BillK:
Joe,
The first thing you have to determine is if the vibration is speed related, or engine rpm related ?? If it is engine speed related, the first thing you need to do is get a NEW fan clutch, not a junk one. I have seen them cause the exact type of vibration that you describe. I would stick with the clutch type fan as it uses a lot less power at high speeds than a fixed fan. The clutch fan only drives the fan when it gets hot, usually at low speeds in traffic. Once you get up to highway speeds, there is enough air flowing through the radiator that the fan really is not needed.
Hope this helps,

<HR></BLOCKQUOTE>bill, performmed your test and i fell that it is engine or engine attachment related. Nuetral: engine vibration noticable but not bad @4Krpm.
1st gear: noticable but not bad @4Krpm,
2nd gear: increasing in vibration noticability ( more pronounced feel
on shifter) @ 4K rpm.
Third Gear: more noticable on shifter @ 4Krpm
This test was performmed w/ the flex fan as this is when the vibration is constant, Wasn't constant w/ junk clutch fan ( but was present). Test proves that at a high RPM the vibration is amplified as the car speed increases. Could this be the flex fan reacting to wind forces created by vehicle speed (assumming fan is vibrating at high rpms). THe faster the engine turns, the more vibration is felt. Plan to purchace new clutch and fan assy: any suggestions on brand, style , diameter? Need both fan and clutch.
thanksjoe c


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post #4 of 7 (permalink) Old Apr 15th, 01, 09:36 AM
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I think it's drivline not fan.If you take it above the speed where it's the worst than put tranny in nuetral and coast back threw the speed range where it was bad, if the the vibration goes away it's not the driveline if it's still there it's not the motor.

You mentioned moving the pinion angle,you don't want the angle the same as d/s all ujoints need angle to work poperly.You may need to go back and check the tranny yoke angle along with the d/s and diff I can't remember the specs but if you post them I can find out for you.
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post #5 of 7 (permalink) Old Apr 15th, 01, 04:12 PM
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It's probably not the problem, but here is what cured my driveline vibration which occured about 65 MPH. If you have wheels which require balancing on the inside of the wheel, go to your tire shop and have the tires balance checked. I found that one of the rears on my car had a defective tire with 4oz imbalance and the weights had fallen off the inside of my Cragar SS wheels. Got new tires and balanced ---vibration gone.

Good Luck,

Lance
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post #6 of 7 (permalink) Old Apr 16th, 01, 11:24 AM
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Assuming your rear tire balance isn't the problem, I'd go back to your rear pinion angle; a single prop shaft with two "U"-joints is designed so the angle is supposed to be the same at both joints. You should have exactly the same operating angle at the diff that you have at the tranny; by having no angle at the diff (by shimming as you mentioned to match the driveline), you will introduce a speed-related vibration at the front "U"-joint, as its harmonics will not be canceled by the opposite effect at the rear "U"-joint. Try it.

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post #7 of 7 (permalink) Old Apr 16th, 01, 03:51 PM
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Joe,
It sounds to me from your response that the problem is in something connected to the motor, especially if you can feel it in neutral at 4000rpm. One thing you could do is to warm the motor up somewhat, then take the belps off and try it. You can run a motor like this for a few minutes without harming anything. Just start it up and take it up to 4000rpm and see if the vibration is still there, then let it idle for about 15 seconds and shut it off and hook the belts back up. This will absolutely tell you if it is internal or something like the fan, alternator etc. If you feel that it is the fan assembly, which it could be, I think any of the good, name brand, clutches should be fine. The fan itself could be out of balance but the only place you are going to get one of those is the dealer. I would not go back to aflex fan, they are not as efficient on a street driven car, and they are dangerous...I have seen and heard of too many of them coming apart, including one mechanic that was killed by one because he was leaning over the front of the car when it decided to come apart...not a pretty picture.
Hope this helps,

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