I have 3.73 rear gear, balanced driveshaft and good u joints. The car vibrates at 75 MPH but when shift into neutral during that speed the vibration goes away. It's a resonating vibration (comes and goes at a steady pace). The RPM's at that speed are around 2600. What could this be? Is the engine (crank) itself out of balance? There is a brand new harmonic balancer on the engine too.

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1988 GTA 5.7L TPI Auto
355 ci. block,TPIS ZZ-9 Camshaft, SLP Headers, Borla Cat Back, B&M Holeshot 2400 Stall Converter, 3.73 Richmond Gears

"Why ride a stang when birds can fly?"

http://www.geocities.com/thegta

[This message has been edited by Joseph Andres (edited September 20, 2001).]

 

Vibrations at 75 MPH is the cause of a bad driveshaft, but you said you had yours balanced already. Sometimes taking the driveshaft out, rotating it 180 degrees, and putting it back in helps for some strange reason.

Edit: You could also have bad u-joints, if they werent replaced when you balanced the driveshaft.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

[This message has been edited by Kevin91Z (edited September 21, 2001).]

 

I had a vane collapse in a torque converter one time that caused a pretty steady vibration around 70mph and again at 110mph.
GM replaced the balancer under warranty.

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Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

Will replacing the u-joints solve this problem or should i look into a new driveshaft?

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1988 GTA 5.7L TPI Auto
355 ci. block,TPIS ZZ-9 Camshaft, SLP Headers, Borla Cat Back, B&M Holeshot 2400 Stall Converter, 3.73 Richmond Gears

"Why ride a stang when birds can fly?"

http://www.geocities.com/thegta

 

Sounds to me like it is in the engine or tranny if it goes away when the engine speed changes.

Dale

 

Yeah, but it is only when the car is at that speed and in OD. I tried the same RPM in D and there were no vibrations.

BTW, tried rotating the shaft 180.....still there.

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1988 GTA 5.7L TPI Auto
355 ci. block,TPIS ZZ-9 Camshaft, SLP Headers, Borla Cat Back, B&M Holeshot 2400 Stall Converter, 3.73 Richmond Gears

"Why ride a stang when birds can fly?"

http://www.geocities.com/thegta

[This message has been edited by Joseph Andres (edited September 24, 2001).]

 

sounds like either the transmison, drive shaft, or u joints. i would start with the cheapest and go up. It is possible it is the rear. i had a truck the rear was starting to go in and it vibrated bad over 120

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86 IROC-Z
305 TPI
th350
flowmaster exhaust
chip

 

Fixed the problem. It was bad U-joints.

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1988 GTA 5.7L TPI Auto
355 ci. block,TPIS ZZ-9 Camshaft, SLP Headers, Borla Cat Back, B&M Holeshot 2400 Stall Converter, 3.73 Richmond Gears

"Why ride a stang when birds can fly?"

http://www.geocities.com/thegta

 

I figured I'd brign this up since my problem is similar, vibration ~70+(worse under decceleration), sometimes goes away at very slight throttle(no load). This is a vibration (high freq), not like a wheel out of balance, more like sitting in a vibrating chair, comforting at first then annoying after say 10-12 hrs of driving. I tried replacing the driveshaft to an AL one. The car is a 5 speed w/ 3.73 gears. I can say that I believe it appeared after a clutch change and flywheel cutdown, but not sure if that caused it or if it could. The car sat for ~ 2 yrs, clutch had a mech. failure(wouldn't disengage) during that time of sitting.

Also can notice something wierd while shifting slowly at 3500+(cruising?) feels kinda like the clutch still grabbing, but the car shifts great so. This is not the car in sig.

 

I have kind of the same problem

I have a balanced Alu Driveshaft, Bought from JamesC, new U joins, changed transmissions (TC was different also). Other than that, everythign else is stock. Vibration starts around 65-70 and gets worse as I go faster. Tires new, balanced many times, by many different people. Rims are perfectly fine, they were polished on high rpm polishing machines and if they were even a gram out they woulda vibrated right off of the machine. Or so the people who did them told me.

I have no idea. I am lost. Scott_92RS had even worse problems, I am sure I can dig up the post somewhere.

 

found the post

https://www.thirdgen.org/techbb2/sho...ight=vibration

 

Excessive driveline angle can cause vibration. More than 3 degs at the trans or rear will cause vibes. Installing higher or lower trans or engine mounts, aftermarket torque arm, LCA's all can change this angle. Keep in mind, 3.73 or higher gears makes the driveshaft spin faster, increasing vibration, mods a lot of us have, requiring a more precise driveline.

 

I had a bad vibration at that speed due to a slightly bent axle hub. I don't know how it got bent, but it did.