[tech] installing a rabbit rear axle beam on a 16v scirocco

[treed2@u.washington.edu (T. Reed)]

Here's the what, why and how..

My rear axle beam has been bent for a looong time.. the right rear wheel
is visibly toe out. This is bad for my tires, and makes the car unsafe
especially in the rain and at high speeds.

Normally, the course of action here is to go to a junkyard and buy a 16v
Scirocco rear axle beam for $150-ish. Being that I have no money, I opted
for a cheaper alternative. My brother was junking an otherwise
straight rabbit shell with a rusted-through floorpan and he gave me the
rear axle beam out of it.. Since the rabbit and 16v Scirocco are both from
the A1 chassis, I thought swapping the rabbit axle in was worth a shot.

Differences I observed immediately were that the 16v came with a rear sway
bar while the rabbit did not. The 16v also has rear disc brakes.

I suspected that one or both stub axles might be bent as well but they
turned out to be straight when I removed and checked them. I determined
that the rear beam was bent by measuring the distance between the trailing
arms on the open end of the beam. It was 1/4" less on the bent beam than
the straight one, indicating that one or both wheels were toed outwards
(in truth it was only the right wheel).

When I got my rear beam out and put it side by side with the rabbit
beam, I found another difference. The Scirocco has a bracket right beneath
the stub axle where the brake line switches from soft to hard. On the
Scirocco beam there are two holes drilled and tapped for 6mm hex head
sheet metal screws. There are no such holes on the rabbit beam. Also,
there are two "nail heads" welded on the Scirocco beam where a parking
brake cable clip attaches and these are missing on the rabbit axle.

I drove the outer sway bar clips off and unbolted the inner clamps.
I drilled holes for the sway bar on the new beam and transferred it over
without issue. I also drilled the four holes for the two brake line
brackets.

I had one hell of a time trying to find a tap that was the same thread
as the 6mm bolts, so I resorted to buying a self tapping SAE screw of
very similar thread and using it to tap the holes. The thread was so
close that the metric screws went back in the holes with hardly any force
at all. Problem solved.

I chose to ignore the parking brake cable bracket that attached to the
nail heads and left it off of the new axle.. since I couldn't figure out
any good way to add the nail heads to the rabbit axle.

So, at this point I was ready to re-install the beam. I attached it to the
rear shocks and reconnected the brake lines, and the rear axle mounting
brackets. I put the wheel bearings and brake rotors back on (also repacked
the bearings with grease and adjusted them). Then I tried to re-install
the brake pad carriers and discovered another difference between the axle
beams.. the Scirocco beam had about 1/8" less "round tube" protruding from
its "square tube". This allowed the upper allen head bolt for the pad
carriers to be installed. I had to resort to grinding a small amount of
metal away so I could get the allen bolt in. No biggie.

When I went to put on the calipers I discovered the last difference.. the
curve at metal on the rear edge of the top of the trailing arms was
clearanced on the scirocco axle to keep the caliper from hitting the beam.
I once again had to break out the dremel to make room for the caliper's
integral parking brake cable bracket.

As it turns out, I didn't have to grind for the allen bolt to clear on the
rear passenger side, just on the rear driver side. I had to grind for the
caliper on both sides, though.

Last step was to bleed the brakes and flush them with new castrol gtlma
(got rid of my 2 year old super blue)..

Anyway, the axle is in and the car rolls and seems to drive fine in the
driveway, although I haven't taken it on a "real" test drive yet.

I can tell just by looking that the toe problem on the right rear wheel is
corrected.

Just wanted to share this information with the list since rabbit rear
axle beams are much easier to find than 16v scirocco rear axles..

-Toby