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Old 03-22-2004, 08:11 PM
WCF WCF is offline
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Join Date: Jan 2004
Location: Columbus, GA
Posts: 6
Post Instrument Cluster Removal & Service, '74SL

Preface:

Observations and comments made here apply to the ‘74 SL but servicing techniques may be applicable to companion MB models. For sure, it does not apply to models with air bags. Don’t even think about it. Seek dealer advise for vehicles so equipped.

Preparation:

In that some electrical components must be worked with or removed, it is advisable to disconnect the battery for safety reasons.

The instrument cluster is made of plastic and may become brittle when cold and are subject to breakage. To be safe, select a suitably warm day to do the removal.

Tools needed:
Small bladed screw driver.
7/8 in socket, 6 inch extension and ratchet.
Pliers
2 special (U make em) removal hook tools. (Instruction below.)
13 mm open end wrench.
6 mm nut driver or socket wrench.

Removal of the STEERING WHEEL:

1. Verify the alignment of the steering wheel before you begin -for more accurate reassembly.

2. To the side of the plastic horn button (center star medallion), insert a small screwdriver and pry up the edge of the medallion. Then remove the button.

3. Insert the 7/8 inch socket and extension into the open hole and down on to the retaining wheel nut on the column shaft. Prevent the steering wheel from turning and remove the locking nut and washer. Pull the wheel off the column shaft. If restrictive, spray with PB Blaster penetrating oil to help free it up.

4. With mineral spirits, clean the old grease and debris from the back of the wheel hub as well as the 2 brass horn contact rings and the 2 contact pins on the column shaft. Further polish the brass contact surfaces with a rubber pencil eraser. Apply a thin coat of Vaseline to lubricate these surfaces before reassembly.

Making of the special instrument cluster REMOVAL TOOL:

In essence you are making a modified “meathook”. Rather than making one with a “J” for the hook configuration you simply make a straight right angle “L”type hook.

1. Take a good grade metal coat hanger (or steel welding rod). Find the center of the horizontal hanger piece and cut it in half. Remove any burs or sharp edges from the cut site.

2. With a pair of pliers, fold down a 1/4 inch of the rod ends with a full crisp 90 degree bend. This becomes the “L of the hook”.

3. Next make a cut about 2 inches above the shoulder end of the coat hanger. This will become the handle end of the tool. You can make a loop out of this end or fabricate a “T” handle if you feel a bit more creative.

Removing the INSTRUMENT CLUSTER from the dash:

The instrument cluster is held in place by the friction of a flat rubber gripper belt against the dash framework that surrounds and houses the cluster. Much as a cork is held secure in a bottle of white Zinfadel.

1. Take the “L” portion of the tool. Lay it on it’s side and slip it in between the cluster frame and the vinyl dash. The best places for the insertions are on the top of the cluster near the left and
right ends. Insert the hooks in about 1 to 1 ½ inches.

2. With the tool handle, rotate the hook tip down against the cluster body until you feel resistance. Slowly and gently begin to pull both hooks straight towards you. As they begin to slide, you
should feel them eventually catch or snag against the ridges that are made for them to latch on to.

3. Alternately pull one tool and then the other in a sea-saw fashion. The cluster should begin to progressively work itself free after a few tugs. If not, try other cluster locations to tug on.

4. Once the cluster is loose from the dash you must unscrew the speedometer cable from the back of the speedometer. This will give a little more slack for you to then unscrew the 13mm brass
OIL PRESSURE line.

5. There are two electrical cables. One for the left instruments and one for the right.. Unplug and label them. Their plugs have a center guide pin that is “keyed” to their respective sockets. They
will not go on but one way. It is just difficult to see this “key” feature until the cluster is fully removed from the dash.

6. This should free the cluster from the dash for what ever service you may choose to do to it. There are 6 various “idiot light” indicator bulbs (Sylvania #2821) and 2 general illumination bulbs
(# 2721). Considering the effort involved in removing the cluster, I would suggest replacing all of the bulbs at this time.

Servicing the CLUSTER:

1. The speedometer is secured to the center rear of the unit by 4, 6mm screws. Remove them as well as the dimmer (rheostat) near it’s base. Note: some screws may be of slightly different size,
replace them accordingly. A light wire from the rheostat partially encircles the speedometer. It is held there by a couple of black plastic clips. Just pull them out of their mounting holes and free
the wire.

2. Remove the left and right instrument (printed circuit) boards by again removing the 4 to 5 surrounding screws. There are 2 NUTS at the top edge of these boards mixed in with the screws that also need to be removed so that the boards can be fully removed. These nuts help to clamp much of the plastic cluster sections together.

3. Clean and polish the instrument faces as you choose. If the needle pointers have become faded, repaint them with a little fresh coat of flourescent paint from the hobby shop.

4. The balance of the plastic cluster will separate in to different sections. Clean and polish them and the instrument lens as you see fit.

5. You may wish to clean and lubricate the speedometer gears at this time.

6. While the dash is open, you may also wish to lubricate the windshield wiper arm bearings.

7. Before reinstalling the cluster, clean and lubricate the rubber gripper band on the cluster housing. A little Vaseline (or Preparation H if you so choose) will make for better R&R.

8. Reverse this sequence for reinstallation of the cluster and steering wheel. Do not forget to connect the oil pressure line or you will not be a happy camper.


This posting was submitted in behalf of all those forum “Searchers”. -----“Been searchin, ever whitch
a way-Yeah-Yeah”!

Happy restorations!
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  #2  
Old 03-22-2004, 09:51 PM
Registered User
 
Join Date: Jul 2002
Location: S. Texas
Posts: 1,237
WCF,
A note on your very well done proceedure. You don't need to remove the "star" button to get to the wheel nut. If you run your fingers around the outside edge of the horn pad and lift up the entire rubber pad comes off. This makes it much easier to get to the nut and much, much easier when replacing it.

The first time I took out the cluster on my 1977 450 slc was because a small screw in the inside of the speedometer had come out jamming it. The screw is located inside the housing where the cable comes in. Inside this housing is the cup that rotates and drives the magnetic pick up that drives the speedometer neddle. As with replacing all the bulbs, it is worth checking this since you are already in there.

When you are inside the speedometer be VERY careful not to dislodge the little bar that runs across the top of the odometer numbers. It is swedged on one end but not the other. Mine slipped out and I spend an interesting but very tiresome 2 hrs. geting it back in. You need at least 4 and better 6 hands to get it back together.

Another thing I noticed about these speedos is that the little aluminum cone that is on the center of the needles comes off very easily. I had mine completely back together when I noticed that it had fallen off. A little dap of hot glue or something similar will hold it in place.
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