Re: alfa-digest V7 #506

[Joel Hailey <alfadoc@domain.elided>]

> Date: Fri, 26 Feb 1999 07:40:08 -0500
> From: "Brad Harris" <brad.harris@domain.elided>
> Subject: RE: Tunnel Slap
>
> I had this same problem in my 1986 Spider. I needed new u-joints anyway so I
> replaced all u-joints, driveline support bearing and flex donut with no
> improvement. I thought that would fix it because the support bearing had a
> huge rip in the rubber around the bearing. I replaced the motor mounts for
> the sagging engine problem and that did not help the driveline slap. I
> finally replaced the transmission mount. The old mount was not torn or
> cracked and it was positioned properly. This fixed the problem and it has
> not come back in over 50k miles.

In my experience, the most common cause for the dreaded driveshaft
thump is tired rear springs. When the springs are partially collapsed,
the driveshaft is working at an angle, with the bend in the middle, at
the first U-joint, just behind the center support. The torque reaction
on takeoff causes the driveshaft to want to push up where the bend is,
hence the "thump". Replace those springs, preferably with something that
makes the car handle a little bit better at the same time.

Joel Hailey
Centerline Products
Boulder CO
303-447-0239

------------------------------