[DeTomaso] Oscillating vibration

Charles Engles cengles at cox.net
Sun Aug 26 15:48:31 EDT 2007


Dear Tomas,


              "Half-shafts in phase"......?     I recall hearing of this in 
the past, but I can't remember what the heck it is.   Could you refresh my 
failing memory?


                        Warmest regards, Chuck Engles



----- Original Message ----- 
From: "Tomas Gunnarsson" <guson at home.se>
To: <Detomaso at realbig.com>
Sent: Sunday, August 26, 2007 12:42 PM
Subject: Re: [DeTomaso] Oscillating vibration


> Mike,
>
> Are your half-shaft-halves installed in phase?
>
> Tomas
>
> ----- Original Message ----- 
> From: "Mike Thomas" <mbefthomas at comcast.net>
> To: <Detomaso at realbig.com>
> Sent: Sunday, August 26, 2007 6:30 PM
> Subject: [DeTomaso] Oscillating vibration
>
>
>>I have about 200 miles on my new motor, and am in the debug phase of the
>> project.  I've had an interesting issue pop up and wanted to post it to 
>> see
>> if there is anything I am not considering as a potential solution.
>>
>> When I get up to about 75-80 in fifth gear (2500-3000 rpms), I get an
>> unusual oscillating vibration.  I've certainly felt alignment or wheel
>> balance vibrations before in other cars, but never of an oscillating 
>> nature
>> that rose and fell at a constant speed/rpm.  I am pretty sure it is 
>> chassis
>> related as hanging in the same rev band in lower gears does not induce 
>> it.
>> I checked the tightness on all 16 half-shaft bolts, and they are snug.
>> Next, I am going to have the wheels balanced tomorrow.  If that does not
>> cure it, I am going to have the balance checked on my new half-shafts.
>> Other than that, I know both rear rotors are slightly out of true, 
>> dragging
>> a bit at one point when I spin the wheel while it's off the ground, so 
>> I'm
>> wondering if the drag on the brakes at that particular speed sets up a
>> harmonic between the two rear wheels to create the oscillating effect, 
>> but
>> that would suggest the wheels were of a different diameter and rotating
>> different speeds.  I had the alignment recently done and no changes to 
>> the
>> suspension or bumps hit to knock it out, but I guess that could be 
>> something
>> else to check.
>>
>> Any thoughts from you guys would be appreciated.
>> Thanks
>> Mike Thomas
>> Panteras Northwest.
>>
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