Mercedes-Benz Ponton Heater Box Repair

by Tom Miller / / January 6, 1999

A few hours ago, I finished the refit of the new fiberglass heater shell. If you've never pulled the heater unit before, I would recommend checking the "Heater Box Removal and Installation" page.

View the Heater Box Removal and Installation page

Forgive me if I get a bit long-winded.... As far as the fiberglass unit goes, I'll admit it's nice to know that someone is at least willing to make these in repro form. The unit is dimensionally accurate and sturdy. I question the high price ($90) for what is essentially a bare shell.. no mounting holes, brackets, etc..

As shipped, it has a grey gel coat with a quick shot of black enamel. The paint comes off with your fingernail..

1) So first off, take some steel wool and 180 grit to it and remove all the paint and rough up the surface for something more substantial. I intend to paint this with rubberized undercoating which leaves a tough black matt finish which looks close to original.

2) You'll need to disassemble the original heater box.. down to the last bracket. This includes the front mounting plate, defroster tube, the air "paddle", cable holders. I even took the two brackets which receive the four screws holding the heater core. Oh, and don't forget to save the fiber mat at the bottom of the core. In some ways this destruction was therapeutic.... It's amazing how that old cardboard crumbles. Take particular care with the "air control paddle.". To remove it you must remove the steel axle shaft. Loosen and remove the nut and jam nut. Don't bother removing the control lever on the other side. Squirt some WD 40 liberally on the shaft to loosen things, then tap the shaft on the threaded side with a plastic mallet. It should slide out. Save the nuts, washers and bushing.

3) Assembling the fiberglass unit will require some trial and error fit up, especially with the paddle, then some careful drilling. I used a pair of home-made wire calipers to locate where to drill the shaft holes while the paddle was laying in place. The hole on the control lever side is larger.. to fit the larger diameter bushing.

4) The other brackets were laid in place, then drilled and pop-riveted. I used washers on the inside to keep the fiberglass from shattering. Don't feel ashamed if you have to drill out and redo an number of them.

5) I found the main mounting plate ( where the unit attaches to the firewall ) a bit touchy.. I had to recheck alignment several times as I secured it with the pop rivets. Gaskets were made out of some old 3/16 closed cell rubber mat I had laying around, applied with RTV. Same stuff was used inside for the air paddle gasket.

This was a Saturday morning job.. the results look surprisingly stock.. and the fiberglass should last considerably longer than the cardboard. Hope this helps.

Tom Miller
Charlotte, North Carolina USA
1959 190
1964 190c
1972 220D

Created January 26, 1999

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