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RE: Rumbling-Spitfire MK3

Subject: RE: Rumbling-Spitfire MK3
From: "Randall Young" <ryoung@navcomtech.com>
Date: Sat, 25 Jan 2003 07:19:06 -0800
Cc: <triumphs@autox.team.net>
Darrell, I don't know anything specific about Spits and GT6, but here's some
general comments.

> The main problem that has me stumped is that at speed, which
> isn't that fast with the 455, there is a
> real bad vibration.  One would think that the driveshaft is the
> problem so I
> switched to another last summer but the rumble did not improve. Both
> driveshafts seem to be running out of true about an 1/8" if you
> jack it up and watch them rotate.  Is it possible that both shafts
> are no good or am I barking up the wrong tree?

That's definitely too much runout for something that's turning 5000 rpm or
more.  Could be you found two bad shafts in a row, could also be that the
mounting flanges are bad or even that they don't match.  I'd start by
looking for a local shop that can true and balance your driveshaft.

> Are the u-joints supposed to lined up in any way?

Yes, the U-joint flanges on the driveshaft should lie in the same plane.

> The flanges on the diff side don't look like they are mating real well
> either.  I can see a little gap going around.  Is it possible
> that they are bent.

It's certainly possible, and since you see a gap I'd say it's likely that
this is the problem.

Enco sells a cheap dial indicator and magnetic mount that can help you check
the trueness of both the flange face, and the ring that locates the mating
flange (if your flanges use it); or you can just replace both flanges and
try again.  Of course, the problem could even be a bent pinion shaft ...

http://www.use-enco.com/
P/N BC625-1340 currently on sale for $20

HF probably has the same thing, but I refuse to buy precision tools from HF.

Randall

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