As the vibration is described as being RPM related, it seem to me that it is
probably something out of balance that turns at engine speed. If the
engine has never been apart, the most likely culprit would be a clutch,
probably a "rebuilt" unit that was not rebalanced after being "rebuilt." We
have found that any imbalance in the engine rotating masses first
manifestes itself as a vibration between 2700 and 3200 RPM.
On race engines that I have built that were in very good balance and that
were perfectly smooth when first assembled, a vibration around the 3000 RPM
engine speed always meant that the crankshaft had cracked!
This crack always began as a very small crack in the rear radius of the #4
rod journal. This would occure after 7,000 miles of hard street driving,
drag racing and autocrossing and happened 4 times in a row until we started
nitriding the cranks. If the vibration that was an indication of a crack
was neglected, the engine would go about another 5,000 miles until the crank
would actually break in two pieces between the #4 rod journal and the front
of the rear main. As the crack got worse, the vibration got worse and the
2'nd order of the vibration which first occured at around 6,000 RPM would
move lower in the rev range. The crank broke in two just after that 2'nd
order vibration had moved down to 4,000 RPM.
I would check into the clutch being out of balance.
Regards,
Greg Solow
----- Original Message -----
From: <N197TR4@cs.com>
To: <jwheeler@seidata.com>
Cc: <fot@autox.team.net>
Sent: Thursday, April 06, 2000 7:26 PM
Subject: Pile-o-Parts...Plus driveline vibration inquiry
> Pile -O-Parts Collection of TR Parts...I resemble your remarks, Jack
> Wheeler.
>
> On to a diagnosis of drive line vibration in IRS TR4A w/OD, if I may
solicit
> some help from the FOT. Important!!!!
>
> Subject Car: TR4A 1965 IRS with OD.
>
> Operating Conditions: Long distance high speed driving for extended
periods.
>
> Symptoms: Vibration (which seems to be RPM related) at about 3000 RPM at
each
> shift point and during cruise.
>
> Discussion: Seems to be a long term problem...before I became familiar
with
> the car.
>
> *Overdrive unit replaced in recent years with rebuilt unit. Not known if
> condition was there before.
>
> *U-Joints replaced on 'regular basis'...this car is accumulating
substantial
> miles.
>
> *Not known if driveshaft is "out of phase" or even if TR is sensitive to
same.
>
> *Condition of engine and driveline mounts unknown.
>
> *Total restoration in recent years...Nut & Bolt frame off.
>
> Effect: Driveline is fairly smooth, but not necessarily 'good' at below
3,000
> RPM (indicated). Smooths out again at 3400 RPM (indicated) or better. A
bit
> too fast for most roads in overdrive.
>
> This car will continue to be driven for long distances...likely another
> 10,000 miles yet this year. And more in years to come....knowing the
owner.
> He deserves better.
>
> FOT? Jack Wheeler?....of course you know this driveline. Have any
> suggestions? Anyone else?
>
> (I had a 1966 TR4A IRS that I remember running to 108 MPH (non-OD) without
> this vibration and it spent most of it's life with a bit of squat to rear
due
> to sagging springs)
>
> There is a 4,000 to 5,000 mile trip planned this Fall in this car. Enuff
said
> here.
>
> Regards & Thanks,
>
> Joe Alexander
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