8558 Restoration & Repairs

This Section is to help - aid in the repair and restoration of the 8558 autotune antenna.

Illustration is given as a guide only.  If you run into difficulties SEEK HELP.....!

The owner of this site takes NO responsibility in how you use this information or the end result in your repairs.

If you are in doubt about your ability in repairing the autotune, return it to the closest Codan Agent for service.



Frequency Range:-      Tx Rx Operation 2 - 24MHz

                                   Rx Only Scan Mode 250KHz - 30MHz

Channel Capacity:-      None Continuous

Power Rating:-            130 Watts PEP

Power Consumption:- 200mA static

                                  2A Tuning Typical

                                  12Vdc Nominal supplied from radio

Impedance:-               50 Ohms VSWR 1.5:1 typical

Control cable:-           multicore 6mtrs, 8551 2mtrs

Tuning Time:-             8 seconds typically from one channel to another.

Mounting Stud:-         16mm


Mounting precautions:-

With all antenna's regardless of auto tune or otherwise the best possible earth 

is required between the base of the antenna and the vehicle. Relying on a

mechanical connection sometimes isn't enough. You need an electrical 

connection aswell, sometime several. ie between antenna and body, then 

body to chassis. Replacing certain straps within the vehicle is sometimes a 

good idea as this stops earth loops and voltage and current drops.

ie battery to chassis and engine to firewall, bumper bar to chassis.

The antenna should always be mount up and clear of any body structure

with at least the top 2/3rd's of the radome clear. The more the better...!


External cleaning and maintenance:-

General external cleaning is pretty straight forward. The use of shellite

is preferable as unlike thinners doesn't remove paint as coarsely, but

does remove grease and stains well. Avoid using paint stripers of caustic

based chemicals. For those who wise to repaint the aluminum areas the use

of a "Hot Engine" matt paint from your favorite auto store works fine.

Precaution needs to be taken when repainting the fiberglass radome section.

Some paints contain lead and this alone will cause the antenna NOT to tune correctly.

If its not to bad, personally I use Lanotec also from your favorite auto store,

Super Cheap for $10.95 approx.

yes its lanolin based and may cause some really bad jokes...hahaha

some people have been known to use boot polish...?


Tools required:-

Allen keys 4mm & 5mm or 3/16

#2 pozi drive screwdriver

Pliers - small shifter

Soldering Iron - solder


1ltr bottle shellite

Oring grease

PVC glue, fiberglass repair kit, 5min Araldite

Small tube of Silicon (neutral cure) NOT the acid smelling one.

A good helping of patience




Base Mounting Plate Removal

Through the 4 wholes loosen then remove the 5mm hex bolts,

removing the base mounting Assembly.


Connector removal

Remove all 8 Stainless Steel screw from the antenna socket

and the control cable socket. Caution as both are sealed with a thin

film of silicon sealant and maybe difficult to remove. On reassembly

do NOT get silicon in screw holes, More is not always better....!


Dismantling Mounting Plate & Rubbers

Using your 4mm allen key and a small shifter, unscrew remove all 4 bolts.

On closer inspection if the earth strap cant be cleaned up or has to many

broken  fibres in the weave it will need to be replaced with something

equivalent. With out the earth strap the antenna will fail to tune. "balk balk"

Separate the rubbers for cleaning, its always a good idea to replace the 

nylock nuts. For the lucky few with a sand blaster all pieces need to be 

spotless. Use a wire brush, shellite and lots of elbows grease to clean

the mounting plates. The rubbers should only need a soft cloth and a squirt

of Lanotec to clean them.


Rattle plate

Now remove the 4 corner screws from the rattle plate.

Be careful that the hex studs don't come out with the rattle plate,

if this happens some reassembly later maybe required.

A thin film of rubber grease on the Oring is required on reassembly,

DON'T fill the groove with grease, it only causes more problems.


       yep it happens to everyone......!   even me.


Check leveling screw

Check to see that the center screw is level with the body otherwise

the tuning section move causing poor earth and intermittent connection

on the 4mm banana plug inside the radome. Adjust with caution......

remove Oring and store safely for reassembly later.


Earthing wire removal

Using #2 pozi drive screwdriver through the data socket hole unscrew

the earth lug. You can see the antenna wire has already been removed

from the solder lug, it will be a plug or soldered.


Tuning section removal

Now you have everything disconnected, invert the antenna and tap it on

a block of wood or carpet until it slides loose. Be careful not to put to

much side pressure on the hex studs, they are hard to repair and replace

if broken.


Separating motor from tuning section

Unscrew remove the 2 brass hex bolts, be careful not to round the heads.

gently pull the red antenna wire through the hole in the circuit board and

aluminum housing, you may not need to cut the cable tie if present.


Removing Antenna wire & tuning slug

Unscrew and remove the brass spacer.

Here is the later version of the tuning slug, earlier models used a PVC plastic which with 

time becames brittle.


Maintenance and repair of tuning slug   (The jigsaw puzzle)

The disastrous happenings of an early model slug where either severe vibration and shock

has fractured to PVC tube in many places. Another cause is where the slug jams inside

the coil section and when tuning drives the brass worm drive into the slug pushing its way

internally destroying the tube as it goes. It is possible for the brass slug to come out 

completely and jam pushing the tuning slug to the top inside.

Another 2 tubes under reconstruction repair. Having found a mandrel or wooden dowel

that fits snugly, each piece is glued until complete. Then cotton thread is wound over the 

cracked area just like replacing a runner on a fishing rod. A thin film of glue is used over

the thread to hold it permanently. Once all glues are cured and mandrel is removed you 

may find lumps of glue stopping the brass tuning piece from going back into it correct 

position. Use a round file to remove any lumps, the glue brass tuning piece in.


Cleaning tuning section

The 3 spring coils are phosphor bronze and need to be kept very clean. The connecting

wire may break at any solder joint requiring repair or replacement. Over time the glue

holding it all together may weaken requiring a full rebuild of the tube section. If the tube 

can be replaced with the later fiberglass tube type please do so. Keep note of parts

locations and positions otherwise it may not tune as before.

See fiberglass suppliers ( pacific composites Brisbane Qld ).


Worm Drive coupling

Worm drive coupling consists of a rubber tube push fitted onto the motor. It has been known

for this to become disconnected through vibration and lubricants being used on the motors

shafts. A roll pin is used on the worm side, DON'T PULL IT as it may rip through the hole.

Use a flat blade screw driver under the rubber coupling and ease it up off the motors shaft.

The worm drive itself should dirt free for smooth operation. Use little or no grease.


Coil Tube Variations

3 different variations of tuning coil tubes. The top one is slightly longer then the bottom 2...?



Top Connector Care

The tip connector is a standard 4mm banana plug. DO NOT lubricate...! If damaged in any

way replace it. using your multimeter from the tip to bottom slide terminals you should have 

continuity, check all solder connections. If you put a piece of steel wool on the end of a

stick with your multimeter lead and push it up the inside of the tube, if you get continuity or a

beep sound, the inside of the coil tube is worn out. The enamel winding has worn through

making direct contact with the tuning slug as it moves.....  The tuning slug is what they call

"capacitively coupled" and shouldn't make direct or electrical connection.


Radome Top to Whip or Spring

The internal thread in the top section is a helicoil in the aluminum housing, (toughened steel)

If your adaptor is as bad as this one replace it and clean out the thread carefully.

   Rusted in Spring adaptor threaded section.                  A clean free thread gives the best results


Connector Pinouts:-

8551C to Transceiver connection           DB15

Pin1  0V  Ground                                       14,15

Pin2  12Vdc                                               12,13

Pin3  Indicator                                            11

Pin4  PTT Tune                                          4

Pin5  Scan Select                                        5



Reassemble in reverse order......

All this adds up to whether your autotune will or wont tune properly.

the most common sound heard is "balk balk" after you have tuned and try to talk.

there are still other reasons for this discussed elsewhere.